Excessive blow-by in 175hr 2200


Mark Dunstone
 

My 2200 engine started misbehaving in the past week.  First indication of a problem was rapidly rising EGT (plus 740C) on #4 on climb out at full throttle with corresponding CHT increase to 160C (normal max CHT is 145C).  Also a bit of smoke in cockpit that cleared quickly.  High EGT brought back easily to under 700C with reduced throttle and carb heat.  #3 EGT a bit lower than usual, but CHT normal.  At cruise everything normal...#4 egt came down to coldest at 650C (others 700-730) and CHT matched the others at around 125C; oil temp maybe 5C warmer than I’d expect given the OAT. On landing, oil catch bottle was full and oil smeared under plane...oil level started at mid level on dipstick, and just at bottom of dipstick after 40minute flight.   Pull throughs showed even compressions.  I’ve done several more flights...and the same thing happens.  I did a leakdown yesterday late afternoon on #4 and it was 70/80.  Spark plugs looked on OK on #4.....black except for centre electrode but that’s because I use 98RON unleaded fuel.  Too dark to check on #3.  Everything external on the engine looks great.

I’m thinking stuck or broken rings in either #4 or #3, though no loss of compression seems weird.  My initial thoughts  are on #4 with high EGT and CHT, but could it be #3 with a lower EGT?   Grateful for any ideas before I start pulling heads and cylinders off.  Cheers, Mark


glen english LIST
 

for a ring, maybe look at the leak down characteristic either side of TDC. that's what showed it up in mine. At TDC leakdown was OK, probably sealing the piston crown against the rim of crud at the top of the pot. but you have mogas fuel, so perhaps buildup wont be as much. maybe compare leakdown cold and hot. maybe use stethoscope to figure out where it is leaking ? bottom of cylinder interface ? maybe some soapy water for bubbles ? check inlet manifold/plumbing for sealing on #4 ?
g

On 30/04/2021 10:12 am, Mark Dunstone wrote:
My 2200 engine started misbehaving in the past week.  First indication of a problem was rapidly rising EGT (plus 740C) on #4 on climb out at full throttle with corresponding CHT increase to 160C (normal max CHT is 145C).  Also a bit of smoke in cockpit that cleared quickly.  High EGT brought back easily to under 700C with reduced throttle and carb heat.  #3 EGT a bit lower than usual, but CHT normal.  At cruise everything normal...#4 egt came down to coldest at 650C (others 700-730) and CHT matched the others at around 125C; oil temp maybe 5C warmer than I’d expect given the OAT. On landing, oil catch bottle was full and oil smeared under plane...oil level started at mid level on dipstick, and just at bottom of dipstick after 40minute flight.   Pull throughs showed even compressions.  I’ve done several more flights...and the same thing happens.  I did a leakdown yesterday late afternoon on #4 and it was 70/80.  Spark plugs looked on OK on #4.....black except for centre electrode but that’s because I use 98RON unleaded fuel.  Too dark to check on #3.  Everything external on the engine looks great.
I’m thinking stuck or broken rings in either #4 or #3, though no loss of compression seems weird.  My initial thoughts  are on #4 with high EGT and CHT, but could it be #3 with a lower EGT?   Grateful for any ideas before I start pulling heads and cylinders off.  Cheers, Mark


Jay Scheevel
 

Agree with the blowby probably being a ring issue, but check to see where the air is leaking by removing the dipstick and listening through the filler while pressure on each cylinder for comparison. See if there is any oil on the engine besides in the catch bottle in order to rule out other broken things, before you start pulling cylinders. My first guess would be that both compression rings are stuck in the groove with the splits lined up.  My 2 cents. Keep us posted.

 

Jay

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Mark Dunstone
Sent: Thursday, April 29, 2021 6:13 PM
To: main@JabCamit.groups.io
Subject: [JabCamit] Excessive blow-by in 175hr 2200

 

My 2200 engine started misbehaving in the past week.  First indication of a problem was rapidly rising EGT (plus 740C) on #4 on climb out at full throttle with corresponding CHT increase to 160C (normal max CHT is 145C).  Also a bit of smoke in cockpit that cleared quickly.  High EGT brought back easily to under 700C with reduced throttle and carb heat.  #3 EGT a bit lower than usual, but CHT normal.  At cruise everything normal...#4 egt came down to coldest at 650C (others 700-730) and CHT matched the others at around 125C; oil temp maybe 5C warmer than I’d expect given the OAT. On landing, oil catch bottle was full and oil smeared under plane...oil level started at mid level on dipstick, and just at bottom of dipstick after 40minute flight.   Pull throughs showed even compressions.  I’ve done several more flights...and the same thing happens.  I did a leakdown yesterday late afternoon on #4 and it was 70/80.  Spark plugs looked on OK on #4.....black except for centre electrode but that’s because I use 98RON unleaded fuel.  Too dark to check on #3.  Everything external on the engine looks great.

I’m thinking stuck or broken rings in either #4 or #3, though no loss of compression seems weird.  My initial thoughts  are on #4 with high EGT and CHT, but could it be #3 with a lower EGT?   Grateful for any ideas before I start pulling heads and cylinders off.  Cheers, Mark


jabcamit@...
 

I just wonder if you have 2 unrelated issues.  Especially if your engine has been gathering cobwebs for a bit.

1) PRV pulsing  might have started on your engine but it had previously been stable. If the PRV does pulse it  will cause much foaming and aeration of the oil in the sump -  resulting in oil getting thrown out of the breather. Also the oil tends to run hotter when this happens (I think the increased  oil mist/foam  in the sump results in more heat being extracted from the cylinder walls. 

2) you might have an induction path air leak   on the misbehaving cylinder connector  - eg split/leaking rubber connector. The resulting  weak mixture would cause that cylinder to run a hotter EGT when mixture should be WOT rich,  and well lean of peak in cruise and so  EGT reads low).

I would have thought that  badly leaking rings  (or scored cylinder walls)  would be  detected by a "soft" cylinder on manual pull through.   

Just guesses  - happy for my ideas to be shot down.

BobP


Mark Dunstone
 

Thanks for suggestions.  Engine is clean.....no oil leaks.  No leaks in the induction system.  Yes, I’ve been getting some momentary peaks in oil pressure....up to 80psi (sorry for cubit medieval units) in early stages of flight...I blame dark ages resistive Bosch oil pressure sensor.   But oil pressure otherwise sits at around 45psi.   Engine producing heaps of power.

But for the oil loss; the high EGT & CHT on #4 (yes I’m a worse....I don’t like my CHTs going above 150C despite the 180C Jab limit), I’d be content.  Oh, and the smoke in the cabin would scare the shit out of my kids’ partners, not to mention my daughter....whose ‘sperm dad’ was killed in a Morgan home built doing aeros (unlawful) with a CFI in the right seat.

The Gremlin on my shoulder is whispering piston melting and out of round cylinders. I’ve told him to bugger off back to Eyre.


Mark Dunstone
 

#4 had compression ring gaps lined up....see photo.  Head and valves ok.  #3 second compression ring stuck at point next to gudgeon pin, but I was able to remove it and clean the lands.  All back together, but not run due to fading light as we approach winter.


glen english LIST
 

Good fix Mark, at least not too much work to remedy.

just like mine- gaps lined up and stuck #2 rings.  (on 3 out of 6 cylinders).

On 6/05/2021 6:33 pm, Mark Dunstone wrote:
#4 had compression ring gaps lined up....see photo.  Head and valves ok.  #3 second compression ring stuck at point next to gudgeon pin, but I was able to remove it and clean the lands.  All back together, but not run due to fading light as we approach winter.
_._,_._,_
------------------------------------------------------------------------


Marc Bourget
 

Do you have success with removing the piston and replacing (same) rings without honing?

My recollection was honing was required anytime one removed a piston from a cylinder.

mjb


From: main@JabCamit.groups.io <main@JabCamit.groups.io> on behalf of Mark Dunstone <mark.dunstone@...>
Sent: Thursday, May 6, 2021 1:33 AM
To: main@JabCamit.groups.io <main@JabCamit.groups.io>
Subject: Re: [JabCamit] Excessive blow-by in 175hr 2200
 
#4 had compression ring gaps lined up....see photo.  Head and valves ok.  #3 second compression ring stuck at point next to gudgeon pin, but I was able to remove it and clean the lands.  All back together, but not run due to fading light as we approach winter.


jabcamit@...
 

Hi Mark,  For the stuck ring  was there evidence of the piston deforming/smearing to trap the ring in its groove? or was it  just a case of carbon etc build up  in the groove that caused sticking?  If the later I wonder if one of the  chemical cleaning compounds might  have avoided the need to remove the cylinder?   

My  ancient tuning motorcycle engines book  advocates adding just a smidgen of chamfer to the  top ring grooves so that if  the piston  does run a bit tight in the cylinder  its less lightly to smear and trap the rings.

Just curious

BobP


Mark Dunstone
 

Bob, difficult to tell.  But as the pinch point was at the gudgeon pin my feeling was it was deformed piston, not crud.  And contrary to that, was my observation that there was some very fine black carbon deposits that flaked off...suggestion crud, not piston deformation.  I’m taking the Sgt Schultz conclusion....ie. I saw nothing!   Still an inkling it’s deformation as the crud goes all 360 degrees around. I am, however, gunna remove the oil PRV tomorrow to have a look at it too.
Honing marks still very visible on the cylinder walls. Can’t see the point of doing more honing.

On Thu, 6 May 2021 at 22:23, <jabcamit@...> wrote:
Hi Mark,  For the stuck ring  was there evidence of the piston deforming/smearing to trap the ring in its groove? or was it  just a case of carbon etc build up  in the groove that caused sticking?  If the later I wonder if one of the  chemical cleaning compounds might  have avoided the need to remove the cylinder?   

My  ancient tuning motorcycle engines book  advocates adding just a smidgen of chamfer to the  top ring grooves so that if  the piston  does run a bit tight in the cylinder  its less lightly to smear and trap the rings.

Just curious

BobP


Jay Scheevel
 

Thanks for posting these, Mark. I am assuming you are running auto gas, right?

 

Jay

 

From: main@JabCamit.groups.io <main@JabCamit.groups.io> On Behalf Of Mark Dunstone
Sent: Thursday, May 06, 2021 2:34 AM
To: main@JabCamit.groups.io
Subject: Re: [JabCamit] Excessive blow-by in 175hr 2200

 

#4 had compression ring gaps lined up....see photo.  Head and valves ok.  #3 second compression ring stuck at point next to gudgeon pin, but I was able to remove it and clean the lands.  All back together, but not run due to fading light as we approach winter.


jabcamit@...
 

A good check to see if the PRV is oscillating is to  closely monitor oil pressure whist slowly increasing and decreasing rpms.  If/when the PRV goes unstable you will see a sudden slight dip in pressure as rpms increase and  (at a slightly lower rpm value)  a step increase in oil pressure when the PRV closes with slowly decreasing rpms. Monitoring the voltage across the pressure transducer  (meter on ac millivolts range)  is an even better test.



My BSA bantam (45 years ago)  would go into pre-seize tight running whenever it got warm. The problem started  after a full seizure which occurred a few weeks after  I had had it re- bored. The guy who rebored it  said the first seizure had  probably  smeared aluminium from the piston into the hone  grooves resulting in insufficient piston-cylinder lubrication.   He also  thought that the first seize might have been due to  adding too much 2T oil to the fuel. He said too much oil  can increase fuel viscocity  and make the engine run too lean.

Just for info really.  Not saying  you've had smearing pistons - if you had you'd almost certainly have seen smear lines on the piston walls.

BobP


David Amsler
 

Depending on instrument the oil pressure sensor is connected to, the pressure spikes from an oscillating PRV may also result in a rise in indicated pressure, Any sudden change in oil pressure either up or down is a pretty good indication of oscillation of the PRV. 
David A.

On Thu, May 6, 2021 at 10:05 AM <jabcamit@...> wrote:
A good check to see if the PRV is oscillating is to  closely monitor oil pressure whist slowly increasing and decreasing rpms.  If/when the PRV goes unstable you will see a sudden slight dip in pressure as rpms increase and  (at a slightly lower rpm value)  a step increase in oil pressure when the PRV closes with slowly decreasing rpms. Monitoring the voltage across the pressure transducer  (meter on ac millivolts range)  is an even better test.



My BSA bantam (45 years ago)  would go into pre-seize tight running whenever it got warm. The problem started  after a full seizure which occurred a few weeks after  I had had it re- bored. The guy who rebored it  said the first seizure had  probably  smeared aluminium from the piston into the hone  grooves resulting in insufficient piston-cylinder lubrication.   He also  thought that the first seize might have been due to  adding too much 2T oil to the fuel. He said too much oil  can increase fuel viscocity  and make the engine run too lean.

Just for info really.  Not saying  you've had smearing pistons - if you had you'd almost certainly have seen smear lines on the piston walls.

BobP


Mick O'Connor
 

Bob,
FWIW, my PRV is running great, reliable stable pressure with no oscillation 

Mick

Sent from my Commodore 64 TerraTurbo

On 6 May 2021, at 15:21, David Amsler <EnergyHawk@...> wrote:

Depending on instrument the oil pressure sensor is connected to, the pressure spikes from an oscillating PRV may also result in a rise in indicated pressure, Any sudden change in oil pressure either up or down is a pretty good indication of oscillation of the PRV. 
David A.

On Thu, May 6, 2021 at 10:05 AM <jabcamit@...> wrote:
A good check to see if the PRV is oscillating is to  closely monitor oil pressure whist slowly increasing and decreasing rpms.  If/when the PRV goes unstable you will see a sudden slight dip in pressure as rpms increase and  (at a slightly lower rpm value)  a step increase in oil pressure when the PRV closes with slowly decreasing rpms. Monitoring the voltage across the pressure transducer  (meter on ac millivolts range)  is an even better test.



My BSA bantam (45 years ago)  would go into pre-seize tight running whenever it got warm. The problem started  after a full seizure which occurred a few weeks after  I had had it re- bored. The guy who rebored it  said the first seizure had  probably  smeared aluminium from the piston into the hone  grooves resulting in insufficient piston-cylinder lubrication.   He also  thought that the first seize might have been due to  adding too much 2T oil to the fuel. He said too much oil  can increase fuel viscocity  and make the engine run too lean.

Just for info really.  Not saying  you've had smearing pistons - if you had you'd almost certainly have seen smear lines on the piston walls.

BobP