Johns new Gen 4


Jay Scheevel
 

Hi John,

 

Please share the relevant oil analysis numbers with the group. I just got an oil analysis back and iron jumped from ~40 to 100 ppm. I think it may be just from not flying much since the fall, but it would be interesting to compare your new Gen4 results. Thanks.

 

Jay

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of John Miller via groups.io
Sent: Thursday, February 04, 2021 7:58 AM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] EarthX Battery

 

BobP

I have never hoked  up the sense wire on the regulator. Hasn't been an issue, but I'll check into it.

Glad to see someone giving Jabiru some kudos. Thanks for that. Someone on this forum said, "If Jabiru could get their design all worked out this engine could be one of the best for small planes."

I have been on this forum for many moons and remember when all the bad mouthing happened when CAMIT came out with their engine touted to be far superior to Jabiru. Then, sadly, CAMIT went bust and we all had to suck it up with Jabiru.

As you may know, I have had relatively good luck with my earlier engines and I'll take responsibility for running them beyond top TBO and then experiencing sucked valves.

During the time when I was waiting to see if Jabiru would honor the warranty I had many suggest this was a good time to change over to the 100 HP Rotax. I didn't want the  extra weight, gear box, high revs, complexity with water, hoses, radiator and water pump which all made it a crowded fit in my Avid MK4 cowl. Parts are 2-3 times as expensive.

I told them I would stop flying if Rotax was the only option for my plane. Fortunately Jabiru came through and I am hoping this engine will give a solid 1000 hours which will take me to the end of my flying days which began in 1963.

I just did an oil change at 25 hours and added no oil during that time. I sent a sample to Blackstone Labs for analysis. The 1st Gen 4 showed a lot of metal and slowly became less on subsequent test. The oil looked brown, not black so I think this sample will be better.

John M


John Miller
 

Roger WILCO.

As soon as I get the report.

John M



Sent from my Verizon, Samsung Galaxy smartphone


-------- Original message --------
From: Jay Scheevel <jay@...>
Date: 2/4/21 8:22 AM (GMT-08:00)
To: main@JabCamit.groups.io
Subject: [JabCamit] Johns new Gen 4

Hi John,

 

Please share the relevant oil analysis numbers with the group. I just got an oil analysis back and iron jumped from ~40 to 100 ppm. I think it may be just from not flying much since the fall, but it would be interesting to compare your new Gen4 results. Thanks.

 

Jay

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of John Miller via groups.io
Sent: Thursday, February 04, 2021 7:58 AM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] EarthX Battery

 

BobP

I have never hoked  up the sense wire on the regulator. Hasn't been an issue, but I'll check into it.

Glad to see someone giving Jabiru some kudos. Thanks for that. Someone on this forum said, "If Jabiru could get their design all worked out this engine could be one of the best for small planes."

I have been on this forum for many moons and remember when all the bad mouthing happened when CAMIT came out with their engine touted to be far superior to Jabiru. Then, sadly, CAMIT went bust and we all had to suck it up with Jabiru.

As you may know, I have had relatively good luck with my earlier engines and I'll take responsibility for running them beyond top TBO and then experiencing sucked valves.

During the time when I was waiting to see if Jabiru would honor the warranty I had many suggest this was a good time to change over to the 100 HP Rotax. I didn't want the  extra weight, gear box, high revs, complexity with water, hoses, radiator and water pump which all made it a crowded fit in my Avid MK4 cowl. Parts are 2-3 times as expensive.

I told them I would stop flying if Rotax was the only option for my plane. Fortunately Jabiru came through and I am hoping this engine will give a solid 1000 hours which will take me to the end of my flying days which began in 1963.

I just did an oil change at 25 hours and added no oil during that time. I sent a sample to Blackstone Labs for analysis. The 1st Gen 4 showed a lot of metal and slowly became less on subsequent test. The oil looked brown, not black so I think this sample will be better.

John M


Jay Scheevel
 

Hi Marc,

 

I think you may have had an attachment, but it did not come through.

 

Jay

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Marc Halcomb
Sent: Friday, February 05, 2021 3:11 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

 

Here are the Samples from my new Gen4 3300 for the first 125hrs.  FE and AL all increased steadily from the test flight phase/break in period.   My engine has received new pistons/rings as part of a Jabiru recall and during that service, excessive wear on the rocker shaft’s were discovered and all 6 were replaced.  (All warranty work, in Shelbyville TN).


glen english LIST
 

Lubrication issue to the rocker shafts on Gen4 ???

I'm always amazed the rocker compartment gets oil to the right level inside it.
Crankcase pressure issue? Those vids with the clear polycarb rocker covers versus CC pressure are interesting.

On 2/6/2021 9:11 AM, Marc Halcomb wrote:
Here are the Samples from my new Gen4 3300 for the first 125hrs.  FE and AL all increased steadily from the test flight phase/break in period. My engine has received new pistons/rings as part of a Jabiru recall and during that service, excessive wear on the rocker shaft’s were discovered and all 6 were replaced.  (All warranty work, in Shelbyville TN).


Jay Scheevel
 

I think that two things play havoc with the rocker shaft wear: 1. The double springs mean much higher loads, 2. The line between the valve stem contact point and the push rod contact point is not perpendicular to the rocker shaft. This puts an off axis load on the rocker bushing. This means more wear and uneven wear. Don’t know if this was fixed in the Gen4, but it looks like it was not.

Jay

-----Original Message-----
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
Sent: Friday, February 05, 2021 3:57 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

Lubrication issue to the rocker shafts on Gen4 ???

I'm always amazed the rocker compartment gets oil to the right level inside it.
Crankcase pressure issue? Those vids with the clear polycarb rocker covers versus CC pressure are interesting.

On 2/6/2021 9:11 AM, Marc Halcomb wrote:
Here are the Samples from my new Gen4 3300 for the first 125hrs. FE and
AL all increased steadily from the test flight phase/break in period.
My engine has received new pistons/rings as part of a Jabiru recall
and during that service, excessive wear on the rocker shaft’s were
discovered and all 6 were replaced. (All warranty work, in Shelbyville TN).


glen english LIST
 

mmm
or some problem with getting the oil into the rocker galleries. mismatch or something going on the with pushrod alignment to the rocker sockets. That is a particularly important alignment...

IE manufacturing/ parts issues ...

On 2/6/2021 10:29 AM, Jay Scheevel wrote:
I think that two things play havoc with the rocker shaft wear: 1. The double springs mean much higher loads, 2. The line between the valve stem contact point and the push rod contact point is not perpendicular to the rocker shaft. This puts an off axis load on the rocker bushing. This means more wear and uneven wear. Don’t know if this was fixed in the Gen4, but it looks like it was not.
Jay


Easy rider
 

What serial numbers on Gen 4 being recalled?

On Feb 5, 2021, at 5:30 PM, Jay Scheevel <jay@scheevel.com> wrote:

I think that two things play havoc with the rocker shaft wear: 1. The double springs mean much higher loads, 2. The line between the valve stem contact point and the push rod contact point is not perpendicular to the rocker shaft. This puts an off axis load on the rocker bushing. This means more wear and uneven wear. Don’t know if this was fixed in the Gen4, but it looks like it was not.

Jay

-----Original Message-----
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
Sent: Friday, February 05, 2021 3:57 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

Lubrication issue to the rocker shafts on Gen4 ???

I'm always amazed the rocker compartment gets oil to the right level inside it.
Crankcase pressure issue? Those vids with the clear polycarb rocker covers versus CC pressure are interesting.

On 2/6/2021 9:11 AM, Marc Halcomb wrote:
Here are the Samples from my new Gen4 3300 for the first 125hrs. FE and
AL all increased steadily from the test flight phase/break in period.
My engine has received new pistons/rings as part of a Jabiru recall
and during that service, excessive wear on the rocker shaft’s were
discovered and all 6 were replaced. (All warranty work, in Shelbyville TN).











Ron Milan
 

Jay: Just a thought---"The double springs mean much higher loads"--is NOT necessarily the case. I agree that excessive valve spring pressure can cause more/excessive valve guide/valve stem and rocker arm bushing/rocker arm shaft wear.   However, double valve springs do NOT necessarily equate to more or excessive valve spring pressure.  The springs can be designed with different K constants and pressures such that the sum loading of the two springs (at installed height and full compression of maximum valve opening) is the same or even less than a single spring.  The JABIRU 3300 maximum RPM "red-line" and the light valve mass (7 mm stem diameter) does not require a lot of spring pressure..   I feel that double valve springs can be a good thing.  Two advantages to consider:  If one brakes the other can keep the valve in operation---at lease at lower engine RPM, The two can be designed to have different frequency so one can dampen the other.  Both of these advantages come with very little mass penalty.  I am NOT sure that double valve springs are a bad design---an increase in spring pressure beyond what is required would be my only concern.

As always, there are other points to consider!

Ron M


-----Original Message-----
From: Jay Scheevel <jay@...>
To: main@JabCamit.groups.io
Sent: Fri, Feb 5, 2021 6:29 pm
Subject: Re: [JabCamit] Johns new Gen 4

I think that two things play havoc with the rocker shaft wear: 1. The double springs mean much higher loads, 2. The line between the valve stem contact point and the push rod contact point is not perpendicular to the rocker shaft. This puts an off axis load on the rocker bushing. This means more wear and uneven wear. Don’t know if this was fixed in the Gen4, but it looks like it was not.

Jay

-----Original Message-----
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
Sent: Friday, February 05, 2021 3:57 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

Lubrication issue to the rocker shafts on Gen4  ???

I'm always amazed the rocker compartment gets oil to the right level inside it.
Crankcase pressure issue? Those vids with the clear polycarb rocker covers versus CC pressure are interesting.

On 2/6/2021 9:11 AM, Marc Halcomb wrote:
> Here are the Samples from my new Gen4 3300 for the first 125hrs.  FE and
> AL all increased steadily from the test flight phase/break in period. 
> My engine has received new pistons/rings as part of a Jabiru recall
> and during that service, excessive wear on the rocker shaft’s were
> discovered and all 6 were replaced.  (All warranty work, in Shelbyville TN).













glen english LIST
 

about 1.3x more according to the spring data. certainly not 2x.
yes dampening resonances.

On 2/6/2021 1:24 PM, Ron Milan via groups.io wrote:
Jay: Just a thought---"The double springs mean much higher loads"--is NOT necessarily the case. I agree that excessive valve spring pressure can cause more/excessive valve guide/valve stem and rocker arm bushing/rocker arm shaft wear.   However, double valve springs do NOT necessarily equate to more or excessive valve spring pressure.  The springs can be designed with different K constants and pressures such that the sum loading of the two


Jay Scheevel
 

All good points, Ron.

 

It would be nice to think that Jabiru did all of the extensive modeling to know that their choice of two springs was optimal to take advantage of everything you mention, but I have this sneaking suspicion….

 

I believe my number 2 item is the real problem, because it plagues both single or double spring models. Jabiru moved their valves farther apart at some point in distant history, but they did not want to mess with the cam lobe spacing and different push rod tube hole positions in the block. So the “asymmetric” rocker was born.

 

I think that Ian Bent gave some serious thought to this issue in his reworked design on the CAMIT rockers. The photo below shows my original Gen2/3 rocker (left) next to the Camit one that went into my engine. Note first that the valve stem contact point (projected perpendicular to the rocker axis center) is offset from the center. For the push rod end, the projected center is offset in the opposite direction. On the Camit rocker, these offsets are as equal as possible, whereas on the Jabiru not so. As a result, the Jabiru design always will have an unbalanced torque on the rocker that must be borne by the bushing and the rocker shaft. At least Camit appeared to try to balance/cancel this torque.

 

The best design would be to have the shaft perpendicular to a line that connects the center of the pushrod tube to center of the valve stem (ie. the shaft should be perpendicular to the blue line below), and all rockers would be the same and symetrical.

 

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Ron Milan via groups.io
Sent: Friday, February 05, 2021 7:24 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

 

Jay: Just a thought---"The double springs mean much higher loads"--is NOT necessarily the case. I agree that excessive valve spring pressure can cause more/excessive valve guide/valve stem and rocker arm bushing/rocker arm shaft wear.   However, double valve springs do NOT necessarily equate to more or excessive valve spring pressure.  The springs can be designed with different K constants and pressures such that the sum loading of the two springs (at installed height and full compression of maximum valve opening) is the same or even less than a single spring.  The JABIRU 3300 maximum RPM "red-line" and the light valve mass (7 mm stem diameter) does not require a lot of spring pressure..   I feel that double valve springs can be a good thing.  Two advantages to consider:  If one brakes the other can keep the valve in operation---at lease at lower engine RPM, The two can be designed to have different frequency so one can dampen the other.  Both of these advantages come with very little mass penalty.  I am NOT sure that double valve springs are a bad design---an increase in spring pressure beyond what is required would be my only concern.

 

As always, there are other points to consider!

 

Ron M

 

-----Original Message-----
From: Jay Scheevel <jay@...>
To: main@JabCamit.groups.io
Sent: Fri, Feb 5, 2021 6:29 pm
Subject: Re: [JabCamit] Johns new Gen 4

I think that two things play havoc with the rocker shaft wear: 1. The double springs mean much higher loads, 2. The line between the valve stem contact point and the push rod contact point is not perpendicular to the rocker shaft. This puts an off axis load on the rocker bushing. This means more wear and uneven wear. Don’t know if this was fixed in the Gen4, but it looks like it was not.

Jay

-----Original Message-----
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
Sent: Friday, February 05, 2021 3:57 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

Lubrication issue to the rocker shafts on Gen4  ???

I'm always amazed the rocker compartment gets oil to the right level inside it.
Crankcase pressure issue? Those vids with the clear polycarb rocker covers versus CC pressure are interesting.

On 2/6/2021 9:11 AM, Marc Halcomb wrote:
> Here are the Samples from my new Gen4 3300 for the first 125hrs.  FE and
> AL all increased steadily from the test flight phase/break in period. 
> My engine has received new pistons/rings as part of a Jabiru recall
> and during that service, excessive wear on the rocker shaft’s were
> discovered and all 6 were replaced.  (All warranty work, in Shelbyville TN).












glen english LIST
 

Nice work Jay.
A bit pot of agitated oil in the rocker housing can remove a fair bit of heat from the heads. Oil is regularly used in inductrial electronics for cooling.
I've seen a few video of jab engines running with clear rocker covers with various heights of oil CC pressure dependent.
In the 'typical user case' I wonder just what height we end up with.
In looking to remove alot of extra heat from the heats, I would have thought ramping up the level in the rocker housings would have been very useful. Does anyone know what sort of flow to expect up the pushrods ? A maximum could be determined from dia, pipe size, surface, viscosity, pressure etc.
?

On 2/6/2021 2:32 PM, Jay Scheevel wrote:
All good points, Ron.
It would be nice to think that Jabiru did all of the extensive modeling to know that their choice of two springs was optimal to take advantage of everything you mention, but I have this sneaking suspicion….
I believe my number 2 item is the real problem, because it plagues both single or double spring models. Jabiru moved their valves farther apart at some point in distant history, but they did not want to mess with the cam lobe spacing and different push rod tube hole positions in the block. So the “asymmetric” rocker was born.
I think that Ian Bent gave some serious thought to this issue in his reworked design on the CAMIT rockers. The photo below shows my original Gen2/3 rocker (left) next to the Camit one that went into my engine. Note first that the valve stem contact point (projected perpendicular to the rocker axis center) is offset from the center. For the push rod end, the projected center is offset in the opposite direction. On the Camit rocker, these offsets are as equal as possible, whereas on the Jabiru not so. As a result, the Jabiru design always will have an unbalanced torque on the rocker that must be borne by the bushing and the rocker shaft. At least Camit appeared to try to balance/cancel this torque.
The best design would be to have the shaft perpendicular to a line that connects the center of the pushrod tube to center of the valve stem (ie. the shaft should be perpendicular to the blue line below), and all rockers would be the same and symetrical.
*From:* main@JabCamit.groups.io <main@JabCamit.groups.io> *On Behalf Of *Ron Milan via groups.io
*Sent:* Friday, February 05, 2021 7:24 PM
*To:* main@JabCamit.groups.io
*Subject:* Re: [JabCamit] Johns new Gen 4
Jay: Just a thought---"The double springs mean much higher loads"--is NOT necessarily the case. I agree that excessive valve spring pressure can cause more/excessive valve guide/valve stem and rocker arm bushing/rocker arm shaft wear.   However, double valve springs do NOT necessarily equate to more or excessive valve spring pressure.  The springs can be designed with different K constants and pressures such that the sum loading of the two springs (at installed height and full compression of maximum valve opening) is the same or even less than a single spring.  The JABIRU 3300 maximum RPM "red-line" and the light valve mass (7 mm stem diameter) does not require a lot of spring pressure..   I feel that double valve springs can be a good thing.  Two advantages to consider:  If one brakes the other can keep the valve in operation---at lease at lower engine RPM, The two can be designed to have different frequency so one can dampen the other.  Both of these advantages come with very little mass penalty.  I am NOT sure that double valve springs are a bad design---an increase in spring pressure beyond what is required would be my only concern.
As always, there are other points to consider!
Ron M
-----Original Message-----
From: Jay Scheevel <jay@scheevel.com <mailto:jay@scheevel.com>>
To: main@JabCamit.groups.io <mailto:main@JabCamit.groups.io>
Sent: Fri, Feb 5, 2021 6:29 pm
Subject: Re: [JabCamit] Johns new Gen 4
I think that two things play havoc with the rocker shaft wear: 1. The double springs mean much higher loads, 2. The line between the valve stem contact point and the push rod contact point is not perpendicular to the rocker shaft. This puts an off axis load on the rocker bushing. This means more wear and uneven wear. Don’t know if this was fixed in the Gen4, but it looks like it was not.
Jay
-----Original Message-----
From: main@JabCamit.groups.io <mailto:main@JabCamit.groups.io> <main@JabCamit.groups.io <mailto:main@JabCamit.groups.io>> On Behalf Of glen english LIST
Sent: Friday, February 05, 2021 3:57 PM
To: main@JabCamit.groups.io <mailto:main@JabCamit.groups.io>
Subject: Re: [JabCamit] Johns new Gen 4
Lubrication issue to the rocker shafts on Gen4  ???
I'm always amazed the rocker compartment gets oil to the right level inside it.
Crankcase pressure issue? Those vids with the clear polycarb rocker covers versus CC pressure are interesting.
On 2/6/2021 9:11 AM, Marc Halcomb wrote:
Here are the Samples from my new Gen4 3300 for the first 125hrs.  FE and AL all increased steadily from the test flight phase/break in period.
My engine has received new pistons/rings as part of a Jabiru recall and during that service, excessive wear on the rocker shaft’s were discovered and all 6 were replaced.  (All warranty work, in Shelbyville TN).


Mick O'Connor
 

Ron,
The next question is, did Jabiru design the double springs to offer the advantages you refer to ?

Mick

On 6 Feb 2021, at 02:44, glen english LIST <glenlist@cortexrf.com.au> wrote:

about 1.3x more according to the spring data. certainly not 2x.
yes dampening resonances.

On 2/6/2021 1:24 PM, Ron Milan via groups.io wrote:
Jay: Just a thought---"The double springs mean much higher loads"--is NOT necessarily the case. I agree that excessive valve spring pressure can cause more/excessive valve guide/valve stem and rocker arm bushing/rocker arm shaft wear. However, double valve springs do NOT necessarily equate to more or excessive valve spring pressure. The springs can be designed with different K constants and pressures such that the sum loading of the two




Mick O'Connor
 

Kevin Hyams strongly advised me not to use the double springs I received with my Jab head overhaul kit. He said they are not suitable for solid lifter engines, they may cause premature cam lobe wear. When I remove my springs, I’ll see if I can compare overall strength between the two types 
Mick

On 6 Feb 2021, at 03:32, Jay Scheevel <jay@...> wrote:

All good points, Ron.

 

It would be nice to think that Jabiru did all of the extensive modeling to know that their choice of two springs was optimal to take advantage of everything you mention, but I have this sneaking suspicion….

 

I believe my number 2 item is the real problem, because it plagues both single or double spring models. Jabiru moved their valves farther apart at some point in distant history, but they did not want to mess with the cam lobe spacing and different push rod tube hole positions in the block. So the “asymmetric” rocker was born.

 

I think that Ian Bent gave some serious thought to this issue in his reworked design on the CAMIT rockers. The photo below shows my original Gen2/3 rocker (left) next to the Camit one that went into my engine. Note first that the valve stem contact point (projected perpendicular to the rocker axis center) is offset from the center. For the push rod end, the projected center is offset in the opposite direction. On the Camit rocker, these offsets are as equal as possible, whereas on the Jabiru not so. As a result, the Jabiru design always will have an unbalanced torque on the rocker that must be borne by the bushing and the rocker shaft. At least Camit appeared to try to balance/cancel this torque.

 

The best design would be to have the shaft perpendicular to a line that connects the center of the pushrod tube to center of the valve stem (ie. the shaft should be perpendicular to the blue line below), and all rockers would be the same and symetrical.

 

<image002.png>

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Ron Milan via groups.io
Sent: Friday, February 05, 2021 7:24 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

 

Jay: Just a thought---"The double springs mean much higher loads"--is NOT necessarily the case. I agree that excessive valve spring pressure can cause more/excessive valve guide/valve stem and rocker arm bushing/rocker arm shaft wear.   However, double valve springs do NOT necessarily equate to more or excessive valve spring pressure.  The springs can be designed with different K constants and pressures such that the sum loading of the two springs (at installed height and full compression of maximum valve opening) is the same or even less than a single spring.  The JABIRU 3300 maximum RPM "red-line" and the light valve mass (7 mm stem diameter) does not require a lot of spring pressure..   I feel that double valve springs can be a good thing.  Two advantages to consider:  If one brakes the other can keep the valve in operation---at lease at lower engine RPM, The two can be designed to have different frequency so one can dampen the other.  Both of these advantages come with very little mass penalty.  I am NOT sure that double valve springs are a bad design---an increase in spring pressure beyond what is required would be my only concern.

 

As always, there are other points to consider!

 

Ron M

 

-----Original Message-----
From: Jay Scheevel <jay@...>
To: main@JabCamit.groups.io
Sent: Fri, Feb 5, 2021 6:29 pm
Subject: Re: [JabCamit] Johns new Gen 4

I think that two things play havoc with the rocker shaft wear: 1. The double springs mean much higher loads, 2. The line between the valve stem contact point and the push rod contact point is not perpendicular to the rocker shaft. This puts an off axis load on the rocker bushing. This means more wear and uneven wear. Don’t know if this was fixed in the Gen4, but it looks like it was not.

Jay

-----Original Message-----
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
Sent: Friday, February 05, 2021 3:57 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

Lubrication issue to the rocker shafts on Gen4  ???

I'm always amazed the rocker compartment gets oil to the right level inside it.
Crankcase pressure issue? Those vids with the clear polycarb rocker covers versus CC pressure are interesting.

On 2/6/2021 9:11 AM, Marc Halcomb wrote:
> Here are the Samples from my new Gen4 3300 for the first 125hrs.  FE and
> AL all increased steadily from the test flight phase/break in period. 
> My engine has received new pistons/rings as part of a Jabiru recall
> and during that service, excessive wear on the rocker shaft’s were
> discovered and all 6 were replaced.  (All warranty work, in Shelbyville TN).












Ron Milan
 

Jay: I agree  from an engineering perspective, the an alignment of push rod center line to the head of the valve stem center line would be BY far the best design.  A symmetric rocker arm would not only minimize side loading on ALL parts involved it would also facilitate the switching of the arms from left to right---thus requiring the manufacturing of ONLY one rocker arm (ONE SIZE FITS ALL)!

Maybe we should go into engine design?  There is a tremendous amount to consider when designing a new engine from scratch. It is much easier to visualize the deficiencies of an engine and theorize the corrections to said engine when empirical reality highlights these deficiencies and failure points.  Also remember that these push-rods and there housings (push-rod tubes) must fit in-between the tubing of the intake and exhaust ports of the cylinder head.   

Lycoming went a different route and placed the camshaft above the crankshaft which eliminated the "plumbing' issue of the interference between the parts mentioned above.  This created another set of issues and Lycoming engines have an issue with eating camshaft lobes; they tend to run dry if they sit too long.  This also necessarily lowers the vertical center-line of the crankshaft thus requiring a shorter (smaller diameter) propeller at given engine height to provide proper ground clearance.  I prefer the camshaft be below the crank for many reasons.  

If the design incorporates a cross flow cylinder head (analogous to UL engines & the Continental I0240) only one port (hopefully the exhaust) is required to exit the bottom of the cylinder head.  This actually may be the best design of all, minimizing the plumbing interference issues and potentially maximizing flow through the cylinder head itself.  As a bonus, the camshaft can still be located below the crankshaft as well.

Again, easy to be a back seat driver or find fault in a manufactured product not so easy to correctly address all the issues involved!  All in all, so far my JABIRU 3300 has served me well, what lies ahead may change my mind but ONLY time will tell.

Ron M



-----Original Message-----
From: Jay Scheevel <jay@...>
To: main@JabCamit.groups.io
Sent: Fri, Feb 5, 2021 10:32 pm
Subject: Re: [JabCamit] Johns new Gen 4

All good points, Ron.
 
It would be nice to think that Jabiru did all of the extensive modeling to know that their choice of two springs was optimal to take advantage of everything you mention, but I have this sneaking suspicion….
 
I believe my number 2 item is the real problem, because it plagues both single or double spring models. Jabiru moved their valves farther apart at some point in distant history, but they did not want to mess with the cam lobe spacing and different push rod tube hole positions in the block. So the “asymmetric” rocker was born.
 
I think that Ian Bent gave some serious thought to this issue in his reworked design on the CAMIT rockers. The photo below shows my original Gen2/3 rocker (left) next to the Camit one that went into my engine. Note first that the valve stem contact point (projected perpendicular to the rocker axis center) is offset from the center. For the push rod end, the projected center is offset in the opposite direction. On the Camit rocker, these offsets are as equal as possible, whereas on the Jabiru not so. As a result, the Jabiru design always will have an unbalanced torque on the rocker that must be borne by the bushing and the rocker shaft. At least Camit appeared to try to balance/cancel this torque.
 
The best design would be to have the shaft perpendicular to a line that connects the center of the pushrod tube to center of the valve stem (ie. the shaft should be perpendicular to the blue line below), and all rockers would be the same and symetrical.
 
 
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Ron Milan via groups.io
Sent: Friday, February 05, 2021 7:24 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4
 
Jay: Just a thought---"The double springs mean much higher loads"--is NOT necessarily the case. I agree that excessive valve spring pressure can cause more/excessive valve guide/valve stem and rocker arm bushing/rocker arm shaft wear.   However, double valve springs do NOT necessarily equate to more or excessive valve spring pressure.  The springs can be designed with different K constants and pressures such that the sum loading of the two springs (at installed height and full compression of maximum valve opening) is the same or even less than a single spring.  The JABIRU 3300 maximum RPM "red-line" and the light valve mass (7 mm stem diameter) does not require a lot of spring pressure..   I feel that double valve springs can be a good thing.  Two advantages to consider:  If one brakes the other can keep the valve in operation---at lease at lower engine RPM, The two can be designed to have different frequency so one can dampen the other.  Both of these advantages come with very little mass penalty.  I am NOT sure that double valve springs are a bad design---an increase in spring pressure beyond what is required would be my only concern.
 
As always, there are other points to consider!
 
Ron M
 
-----Original Message-----
From: Jay Scheevel <jay@...>
To: main@JabCamit.groups.io
Sent: Fri, Feb 5, 2021 6:29 pm
Subject: Re: [JabCamit] Johns new Gen 4
I think that two things play havoc with the rocker shaft wear: 1. The double springs mean much higher loads, 2. The line between the valve stem contact point and the push rod contact point is not perpendicular to the rocker shaft. This puts an off axis load on the rocker bushing. This means more wear and uneven wear. Don’t know if this was fixed in the Gen4, but it looks like it was not.

Jay

-----Original Message-----
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
Sent: Friday, February 05, 2021 3:57 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

Lubrication issue to the rocker shafts on Gen4  ???

I'm always amazed the rocker compartment gets oil to the right level inside it.
Crankcase pressure issue? Those vids with the clear polycarb rocker covers versus CC pressure are interesting.

On 2/6/2021 9:11 AM, Marc Halcomb wrote:
> Here are the Samples from my new Gen4 3300 for the first 125hrs.  FE and
> AL all increased steadily from the test flight phase/break in period. 
> My engine has received new pistons/rings as part of a Jabiru recall
> and during that service, excessive wear on the rocker shaft’s were
> discovered and all 6 were replaced.  (All warranty work, in Shelbyville TN).












Pete Twissell
 

Continuing in the "armchair engineering" vein...
Although the crossflow design has some advantages, in this case with packaging the plumbing, it would also have the effect of making the engine taller above the crank centerline, as the intake plenum and presumably the carb would need to sit on top of the cases.
One of the (many) back burner projects I have is a very early 2200 bottom end, for which I would like to make a set of side valve cylinders and heads, assisted if necessary by a turbocharger.
My intention is to make all the new parts to fit the unmodified Jab cases.
If successful, the engine would power a Clutton Fred, so I only need to get 60HP out of it.
My design concept has each valve seat and guide made as a one piece insert, allowing for an oil cooling channel around the exhaust valve seat.
Don't hold your breath, I don't expect to start making parts for some time yet!

On Sat, 6 Feb 2021, 11:30 Ron Milan via groups.io, <ronmilan=verizon.net@groups.io> wrote:
Jay: I agree  from an engineering perspective, the an alignment of push rod center line to the head of the valve stem center line would be BY far the best design.  A symmetric rocker arm would not only minimize side loading on ALL parts involved it would also facilitate the switching of the arms from left to right---thus requiring the manufacturing of ONLY one rocker arm (ONE SIZE FITS ALL)!

Maybe we should go into engine design?  There is a tremendous amount to consider when designing a new engine from scratch. It is much easier to visualize the deficiencies of an engine and theorize the corrections to said engine when empirical reality highlights these deficiencies and failure points.  Also remember that these push-rods and there housings (push-rod tubes) must fit in-between the tubing of the intake and exhaust ports of the cylinder head.   

Lycoming went a different route and placed the camshaft above the crankshaft which eliminated the "plumbing' issue of the interference between the parts mentioned above.  This created another set of issues and Lycoming engines have an issue with eating camshaft lobes; they tend to run dry if they sit too long.  This also necessarily lowers the vertical center-line of the crankshaft thus requiring a shorter (smaller diameter) propeller at given engine height to provide proper ground clearance.  I prefer the camshaft be below the crank for many reasons.  

If the design incorporates a cross flow cylinder head (analogous to UL engines & the Continental I0240) only one port (hopefully the exhaust) is required to exit the bottom of the cylinder head.  This actually may be the best design of all, minimizing the plumbing interference issues and potentially maximizing flow through the cylinder head itself.  As a bonus, the camshaft can still be located below the crankshaft as well.

Again, easy to be a back seat driver or find fault in a manufactured product not so easy to correctly address all the issues involved!  All in all, so far my JABIRU 3300 has served me well, what lies ahead may change my mind but ONLY time will tell.

Ron M



-----Original Message-----
From: Jay Scheevel <jay@...>
To: main@JabCamit.groups.io
Sent: Fri, Feb 5, 2021 10:32 pm
Subject: Re: [JabCamit] Johns new Gen 4

All good points, Ron.
 
It would be nice to think that Jabiru did all of the extensive modeling to know that their choice of two springs was optimal to take advantage of everything you mention, but I have this sneaking suspicion….
 
I believe my number 2 item is the real problem, because it plagues both single or double spring models. Jabiru moved their valves farther apart at some point in distant history, but they did not want to mess with the cam lobe spacing and different push rod tube hole positions in the block. So the “asymmetric” rocker was born.
 
I think that Ian Bent gave some serious thought to this issue in his reworked design on the CAMIT rockers. The photo below shows my original Gen2/3 rocker (left) next to the Camit one that went into my engine. Note first that the valve stem contact point (projected perpendicular to the rocker axis center) is offset from the center. For the push rod end, the projected center is offset in the opposite direction. On the Camit rocker, these offsets are as equal as possible, whereas on the Jabiru not so. As a result, the Jabiru design always will have an unbalanced torque on the rocker that must be borne by the bushing and the rocker shaft. At least Camit appeared to try to balance/cancel this torque.
 
The best design would be to have the shaft perpendicular to a line that connects the center of the pushrod tube to center of the valve stem (ie. the shaft should be perpendicular to the blue line below), and all rockers would be the same and symetrical.
 
 
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Ron Milan via groups.io
Sent: Friday, February 05, 2021 7:24 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4
 
Jay: Just a thought---"The double springs mean much higher loads"--is NOT necessarily the case. I agree that excessive valve spring pressure can cause more/excessive valve guide/valve stem and rocker arm bushing/rocker arm shaft wear.   However, double valve springs do NOT necessarily equate to more or excessive valve spring pressure.  The springs can be designed with different K constants and pressures such that the sum loading of the two springs (at installed height and full compression of maximum valve opening) is the same or even less than a single spring.  The JABIRU 3300 maximum RPM "red-line" and the light valve mass (7 mm stem diameter) does not require a lot of spring pressure..   I feel that double valve springs can be a good thing.  Two advantages to consider:  If one brakes the other can keep the valve in operation---at lease at lower engine RPM, The two can be designed to have different frequency so one can dampen the other.  Both of these advantages come with very little mass penalty.  I am NOT sure that double valve springs are a bad design---an increase in spring pressure beyond what is required would be my only concern.
 
As always, there are other points to consider!
 
Ron M
 
-----Original Message-----
From: Jay Scheevel <jay@...>
To: main@JabCamit.groups.io
Sent: Fri, Feb 5, 2021 6:29 pm
Subject: Re: [JabCamit] Johns new Gen 4
I think that two things play havoc with the rocker shaft wear: 1. The double springs mean much higher loads, 2. The line between the valve stem contact point and the push rod contact point is not perpendicular to the rocker shaft. This puts an off axis load on the rocker bushing. This means more wear and uneven wear. Don’t know if this was fixed in the Gen4, but it looks like it was not.

Jay

-----Original Message-----
From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of glen english LIST
Sent: Friday, February 05, 2021 3:57 PM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Johns new Gen 4

Lubrication issue to the rocker shafts on Gen4  ???

I'm always amazed the rocker compartment gets oil to the right level inside it.
Crankcase pressure issue? Those vids with the clear polycarb rocker covers versus CC pressure are interesting.

On 2/6/2021 9:11 AM, Marc Halcomb wrote:
> Here are the Samples from my new Gen4 3300 for the first 125hrs.  FE and
> AL all increased steadily from the test flight phase/break in period. 
> My engine has received new pistons/rings as part of a Jabiru recall
> and during that service, excessive wear on the rocker shaft’s were
> discovered and all 6 were replaced.  (All warranty work, in Shelbyville TN).












Ron Milan
 

Mick:  I am in the United  States and have NEVER had any communication with JABIRU manufacturing.  I am sorry to say that I cannot provide a factual answer to why JABIRU decided to initiate their "double valve spring" design.

Ron





-----Original Message-----
From: Mick O'Connor via groups.io <mickoconnor909@...>
To: main@jabcamit.groups.io
Sent: Sat, Feb 6, 2021 4:06 am
Subject: Re: [JabCamit] Johns new Gen 4

Ron,
The next question is, did Jabiru design the double springs to offer the advantages you refer to ?

Mick

> On 6 Feb 2021, at 02:44, glen english LIST <glenlist@...> wrote:
>
> about 1.3x  more according to the spring data. certainly not 2x.
> yes dampening resonances.
>
>> On 2/6/2021 1:24 PM, Ron Milan via groups.io wrote:
>> Jay: Just a thought---"The double springs mean much higher loads"--is NOT necessarily the case. I agree that excessive valve spring pressure can cause more/excessive valve guide/valve stem and rocker arm bushing/rocker arm shaft wear.  However, double valve springs do NOT necessarily equate to more or excessive valve spring pressure.  The springs can be designed with different K constants and pressures such that the sum loading of the two
>
>
>
>
>







jabcamit@...
 

The rocker arms should ideally also apply a rotating force to the valve. This has the effect of helping to maintain a good seal between valve and seat.  I have no idea whether the Jabiru  and/or Camit engines do this  (perhaps David A knows?).  I read somewhere that one of the BMW motorcycle engines had a problem with valve seating, and that it was and they corrected using this technique.  Other things that might resist valve rotation include  having overly strong valve springs.

BobP


Marc Halcomb
 

Attached is a picture of one of the replaced rocker shafts.  This was discovered while the pistons/rings were being replaced as part of a voluntary recall for some Gen4 3300’s.  I was contacted by the North American Jabiru dealer in Shelbyville about this recall.  The engine had 125 hours at the time of the piston/ring and rocker shaft replacements.  I am doing oil samples every oil change (25hrs) and have had a steady increase in FE & AL.  I am looking forward to the next few to see if the trend continues after the new pistons, rings, and rocker shafts.


Marc Halcomb
 

Here are the oil samples from my Gen4 3300 for the first 125 hours.


jabcamit@...
 

Great idea Pete (oil cooling around side valve exhaust valve). I liked the original D motor concept (before clever fuel injection etc). As aircraft engines are slow revving  the side valve's "performance falls off at high rpm" should be less of an issue. And it has the advantages of a narrower engine profile (valves not mounted above the cylinders). And if it does drop a valve it doesn't fall into the piston (unless just the head falls off).

I guess a slight turbo effect could be achieved by the RAM air effect (but perhaps not much at Fred WOT speeds).  Perhaps RAM air turbo effect could also be applied to the Jabiru engine?


BobP