Valve guide diet

[xwildcat]

As an update to my inflight failure...

I removed the rocker box on the #6 cylinder and see what looks like bullet fragments lying in the cover.



So obviously the exhaust valve guide caused my cylinder failure. However, the top plug wire tip was a little corroded.
The bottom plug was gunked up and not firing because of it. I imagine it "expired" during the failure, but there could have
been a couple strikes against this cylinder that just happened to converge on that flight. It was probably sick for awhile.

The plane and I wait (impatiently) now for the cylinder to come back. All is well.

[210TC]

Sure would like to see more pictures.

[UP-M5]

its obviously a good idea to check the other cylinders for similar wear, but it would also be good to check the valve seats in the rest of the cylinders. debris like that can travel around between cylinders in a spooky way.


so give us more info. was it a high time engine? had it been overhauled in the last 30 years?

[xwildcat]

I only know it's history since 1981 at which time it was imported to Canada. The serial number is 52572,
in case anyone knows about this engine. It's a Franklin 6A-350-C1.

It has 960 hrs on it with a top overhaul on 4 of the six cyls done about 500 hrs ago. This was done during
a restoration when everything was apart. This particular cylinder was not done at that time.

I've changed the oil and filter and will also flush the oil pan just to be on the safe side. I've also removed
all the valve covers and inspected the rest of the valves and done a compression test on all the cylinders.

The weird thing is the bad cylinder was still showing 70/80, albeit with a noticeable air leak.

[210TC]

A guy at our airport had a problem with his franklin (was not hitting on all 6). He removed the cyl and gave it to a friend of mine to check out.
The friend told me the valves guides needed to be cleaned and he ran a reamer through them to get the coking buildup out. Valve was sticking...
You should consider checking the valve guide clearance on the other cyl's.
I recomend those of you that run your engine's on the rich side no matter the manufacture to check exhaust guide clearance every 300 to 500 hrs.
Correct me if I am wrong...I think lycoming has a service note on this.
One of the many problems with differential comprssion testing is that generally a sticky valve will not show up. And some time this same issue will not show up with a proper compression check. I use both methods when checking compression. The ONLY way to obtain correct readings is to cycle the cylinder over it's entire working range. Not many years ago ALL of the books recomended differential as a means ONLY to identify the a problem that was found during normal compression test.

[UP-M5]

210tc is right, bad valve guides rarely if ever show up on a compression test. lycoming has a service bulletin that says to check the guides every 400 hrs. and they have a long process. but basically i just remove the valve spring (with the cylinder still on the engine) and see how loose/tight the valve feels in its guide.
some engines tend to coke up and stick valves, while others (like yours) seem to get very loose and worn out.
make sure whoever is repairing your cylinder installs a new valve and a new spring. they must have been beat to death in the last few minutes...
and you might pay special attention to that other cylinder that wasn't part of the top o/h.
good luck, and keep us posted......

[Kirk]

I looked up that SB. You're right, it's a lengthy process.

For those interested here's the link to SB-388C:
http://www.lycoming.textron.com/support ... SB388C.pdf

Kirk

[TomD]

Thank you, Superior Air Parts!!!!

[xwildcat]

As an update...

My cylinder will need to be built back up as it apparently had been reamed out too much, which caused the guide to fail. So that's getting done.

The good news is Greg Lucas in Pauls Valley, OK sent me a new yellow tagged cylinder he had on the shelf. So we installed that and I just got done flying it for the first time. 1.4 hrs and 9 landings. All is well.

Thanks also to Wup and Bill at AK Bushwheels for loaning out the Franklin cylinder base nut wrenches! I'll get those back to you guys ASAP.

BTW, the oil analysis came back to day with no abnormal wear.

Thanks for everyone's concern and advice after my engine failure!