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Crankcase Fretting, Installing Cylinders and "Oh CHIT"

Steve Pierce

BENEFACTOR
Graham, TX
So helping my buddy Travis with the annual on his Pacer and on the compression test we had cylinder #2 that was 60/80 and #4 was 40/80. The cylinder that was 40/80 got replaced with new about 4 years ago and the 60/80 was the same last year. Both were leaking out of the exhaust but the valves looked good through the borescope. Tried running it up again, staking the exhaust valves and no change. Got out the wobble test fixture and found both exhaust valve guides worn beyond limits. Looked at the rocker arms and the rocker arms with the oil squirters that should pump oil onto the hot exhaust valves were installed on the intake valve. Cause found now to fix. Pulled the two cylinders and it was obvious that the exhaust valve guides were way loose. Travis took the cylinders to Sal's cylinder shop for new guides. The newer cylinder was no issue but the older cylinder had a small crack in the exhaust port so bought a new one to replace it and another to replace #1 which was an older overhauled cylinder since #3 and 4 had been replaced 4 years ago, now we have 2 new and 2 cylinders with only a few hundred hours since new on a 600 hour engine. Should be good for years to come. All we have to do is put everything back together and start planning a trip to Idaho in a few weeks. Ha. Get the cylinders on and it feels kinda tight. Hmm, what the heck. Text Ken at LyCon to see if he has seen this before. In the meantime we back the torque off the front main, still tight. Back the torque off one nut on the center main and the crank spins like I am use to. About that time Ken calls me and explains that the crankcase has fretted and we just torqued it back to spec and took out that extra clearance that had fretted away. Was hoping for a magic fix but there is none. Reviewed the logs and found all the yellow tags from the last field overhaul but nothing about the crankcase. Nothing in the logbook entry as well, not sure about the overhaul before that. Conclusion is that the engine needs to come off, case split, crankcase sent out to have the halves milled and mains and cam bores bored. Luckily I have an overhauled 160 hp narrow deck crankcase stashed for one of my cores so we won't have to wait for the case to be overhauled but another lesson learned. Travis was researching last night and found this issue referenced in Gordon's thread when he found a crack in his crankcase. https://www.supercub.org/forum/showthread.php?53815-Cracked-O-320-Case-Best-way-to-proceed/page2

I like to say I will know it all when they start shoveling dirt on my face, just another case of something new learned. Now to get to work so we can do some fun flying. Just thought others might like to log these lessons away for the own use down the road. Big thanks to Ken at LyCon for his insight and willingness to share his wisdom with me over the last 20 plus years.
 
Crankcase Fretting, Installing Cylinders and "Oh CHIT"

Thanks learned something! Now how does this dovetail into the thread about cylinder changes and engine failure...... kinda makes more sense now.....
Edit, anyone remember that thread? Got a link?

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Had my first visit to Crow Island 8MA4 (Mass.) yesterday and met a great bunch of people, Cubs of every variety and Bushwheels galore. I heard someone talking about Steve's wealth of knowledge, but I swear someone said he's from Oklhahoma! Are them's fighting words? ;-)
 
Had my first visit to Crow Island 8MA4 (Mass.) yesterday and met a great bunch of people, Cubs of every variety and Bushwheels galore. I heard someone talking about Steve's wealth of knowledge, but I swear someone said he's from Oklhahoma! Are them's fighting words? ;-)
It was a pleasure to meet you WhiskeyMike.Hope to see you there often.
 
Well I pulled out the overhauled 160 hp narrow deck case I had rat holed away since 2008. It was overhauled by Divco and has the dowel at the center main through studs which is suppose to help with fretting issues.

We got Bender's crankcase split and can now see what had gone on. Pretty obvious when you look where the o'ring rode between the two halves and how smooth it is and the lip there compared to the rough texture where the fretting was going on.




You can see where the front main was starting to fret up to about midway.


We got the engine back together and put some time on it late yesterday afternoon and he is flying it some more today so he can head to Idaho tomorrow. Glad we found it when we did.
 
That is just one example of why the early narrow deck engines had only a 1200 hour TBO. Exhaust valve stem diameter was another.
 
Can you elaborate on the exhaust valve stem diameter issue? This engine is a narrow deck B2B 160hp w/ 4 new cylinders.


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Looked at the rocker arms and the rocker arms with the oil squirters that should pump oil onto the hot exhaust valves were installed on the intake valve

Could you explain and/or show pictures? Thank you, good information.
 
Intake rocker arm has a hole near the pushrod end. Exhaust rocker arm has a hole facing the valve stem.


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SERVICE INSTRUCTION
652 Oliver Street
Williamsport, PA. 17701 U.S.A.
Tel. 570*323*6181 Fax. 570*327*7101 www.lycoming. com
DATE:
SUBJECT:
MODELS AFFECTED:
TIME OF COMPLIANCE:
February 25, 2011
Service Instruction No. 1454A (Supersedes Service Instruction No. 1454) Engineering Aspects are FAA DER Approved
Rocker Arm Assembly Replacement Part
All Lycoming engines incorporating parallel valves except O*235 Series, O*290 Series, O*320*H Series and TO*360*E Series.
Anytime valve rocker assemblies are removed.
NOTE
Incomplete review of all the information in this document can cause errors. Read the entire Service Instruction to make sure you have a complete understanding of the requirements.
This Service Instruction identifies Rocker Arm Assembly P/N 17F19357 to be installed on the parallel intake and exhaust valves on all cylinders. Rocker Arm Assembly P/N 17F19357 supersedes Rocker Arm Assembly P/N 17F19353
The supersedure history for the Rocker Arm Assembly is as follows: LW*18790 17F19353 17F19357
Prior to P/N LW*18790 Rocker Arm Assembly, one (1) each of Rocker Arm Assembly P/N 69444 (intake) and P/N 74636 (exhaust) were installed on the respective intake and exhaust valve.
CAUTION
Rocker Arm Assemblies P/N 69444 and P/N 74636 are not interchangeable with one another.
Rocker Arm Assembly P/N 69444 (which only can be installed on the intake valve) is identified by the oil drain hole located under the push rod end of the body. Rocker Arm Assembly P/N 74636 (which only can be installed on the exhaust valve) is identified by the oil drain hole located under the valve end.
NOTE
Before reusing Rocker Arm Assembly P/N LW*18970, refer to the latest revision of Lycoming Service Bulletin No. 477 (AD 87*10*06).
NOTE
The new Rocker Arm Assembly P/N 17F19357 can be installed in either the intake or exhaust valve position without changing the other rocker on that cylinder.
ISSUED
MO DAY YEAR
06 05 91
REVISED PAGE NO. REVISION
MO DAY YEAR 02 25 11
1 of 1 A
[emoji767]2011 Avco Corporation, All Rights Reserved. Lycoming Engines is a division of Avco Corporation.



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Thank you. My 0540-F1B5 rockers same part#
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Exhaust rocker arms have a hole where the red circle is to squirt oil on the exhaust valve to help cool and lubricate it because it runs hotter. If these are mixed up with the intake rocker arm without an oil squirter the guide wears out, the valve doesn't seat and the cylinder fails a compression test.
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Thank you Steve.

I use aircraftspruce.com SB388C fixture. Not great but works.

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Can you elaborate on the exhaust valve stem diameter issue? This engine is a narrow deck B2B 160hp w/ 4 new cylinders.
It is most likely that your cylinders have the 1/2" valves since you installed new ones. The change in dimension was made decades ago.
 
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