Crankcase Fretting, Installing Cylinders and "Oh CHIT"

[Steve Pierce]

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/showt...-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.

[Broncoformudv]

Thats great info Steve! I never thought to hand turn the prop once the engine was warm but will be sure to give it a try every now and then to keep an eye on things. I always do it when cold just to see how things feel prior to using the starter.

[Rick]

Hi Steve,

We never stop getting an education. Some are EZ and cheep and some are on the other end of the scale.

Your comment "Got out the wobble test fixture" leaves me to ask what dose it look like? I make fixtures for everything, but I have not made one for checking valve to guide clearance. Could you please post a picture of your creation.

And yes, Ken is a wealth of knowledge and has always shared it with me when I call for guidance. I have also toured his facility and I recommend them all the time. a very professional operation.

Rick

[at7615]

https://www.lycoming.com/node/15787

Gotta have that oil hole @ the exhaust valve!

[Steve Pierce]

The fixture I have was given to m by an old mechanic many years ago and coincides with Lycoming Srvice Bulletin 388C. https://www.lycoming.com/content/ser...lletin-no-388c
IMG_20200609_073247.jpg

IMG_20200609_073252.jpg

[Steve Pierce]

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.
IMG_20200609_083457.jpg
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.
IMG_20200615_172806.jpg

IMG_20200615_172824.jpg

You can see where the front main was starting to fret up to about midway.
IMG_20200615_172857.jpg

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.

[at7615]

Good save Steve!

[Pacerfgoe]

Just curious how you now deal with an engine that now has a different case serial number than the data plate, do you just make a note of it in the logs and move on?

[Steve Pierce]

Just curious how you now deal with an engine that now has a different case serial number than the data plate, do you just make a note of it in the logs and move on?

Just changing a part like a crank shaft, cylinder or even a fuselage.

[JPerkins]

As far as the FAA is concerned the only part of the engine that IS THE engine is that data plate. Rest is parts of it.

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