Re: Prop, flywheel bolts

Jay Scheevel

From: <> On Behalf Of Mick O'Connor via
Sent: Saturday, February 20, 2021 2:27 AM
Subject: Re: [JabCamit] Prop, flywheel bolts



Your link leads to #10-32 screws ?

They are very small and not flywheel type

On 19 Feb 2021, at 23:19, Jay Scheevel <jay@...> wrote:

Went back and checked a past order that I made. I had to buy a box of 100 (genuine Unbrako), but the price was not bad from this outfit.






From: <> On Behalf Of Steve Rance via
Sent: Friday, February 19, 2021 2:13 PM
Subject: [JabCamit] Prop, flywheel bolts


Several years ago I was asked to remove the broken studs in the 2200 crankshaft, the prop departed on climb out. Aircraft fortunatly was high enough to turn round and land back on runway. What happened was the owner had put longer bolts in after fitting a supplied spacer behind the prop hub, the bolts bottomed out at the same time as lightly gripping the prop. Always check thread depth by inserting all bolts and measuring there is sufficient grip of at least 2 -3 full turns before bottoming out.

I have done several flywheels and prop hubs in the meantime and also found it impossible to find Unbrako UNF cap screws. All the big suppliers want to sell you a large expensive box which has to be specially ordered. That aside having done several flywheels and prop hubs in only one case found bolts marked UNB, presumably for Unbrako and that was an early engine. All of the subsequent 3/8” Bolts were marked YFS or TMS of origin unknown, so I assume the manufacturers by buying elsewhere are saving money or Unbrako supplies unavailable, another problem is stocks of Unified screws are drying up and only metric fasteners are readily available in UK.

 I have had an old box for years of Unbrako screws (wrong size) marked with the usual approvals and made in Brazil so they can be made anywhere to keep costs down.

Reminds me years ago we had a new Mill delivered at our works, we were having a quiet break when there was a loud crack like a gunshot, it took a while but it came from a M16 capscrew that let go off the milling machine bearing flange, snapped right under the head, it was unplated but clearly flawed.




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