Titan 0-340 Burnt Intake Valves

[Tim Lewis]

I had a valve rotation discussion with Lycoming tech support in October 2017. Lycoming tech support told me (in the context of an IO-540-C4B5) that the rotator cap does *not* impart rotation onto the valves. The valves *can* rotate, but they don't have to.

Here's a good article on different types of valve rotators designs, including the (non-positive) thimble valve rotator, whose description matches the parallel valve Lycoming cylinders I've worked on:

https://marineengineersblogs.blogspo...ators.html?m=0

Note that the thimble valve rotator design *permits* rotation (when the valve is open) but does not *impart* rotation.

[rv6ejguy]

The Aviation Consumer, around 10 years ago found that over 20% of new cylinders inspected had non-concentric valve seats with irregular contact. I believe these were factory Lycoming. They'd heard of many cylinders going soft in only a few hundred hours and seen leaking and burned valves on a number of these.

Their recommendation was to disassemble these new cylinders and check/ correct before putting them in service.

I'm not saying that's what happened here but most cases of burnt valves can be traced to hot gas leakage caused by improper seat contact or the valve being held open slightly for some reason.

[theduff]

Thanks Tim for a great article explaining how the rotator caps work on a Lycoming:
“Note that the thimble valve rotator design *permits* rotation (when the valve is open) but does not *impart* rotation”
I didn’t know that engine vibration was the force that caused the rotation after the caps release the valve. Not intuitive at least to me.
To Ross’s comments on the concentric problems of valves and seats even on new cylinders. When LyCon does their port-flowing of cylinder heads they also redo the valves and seats even on new cylinders using a Serdi precision valve machine that has an accuracy of portions of thousands of an inch. The contours of the valve and seat are responsible for a portion of the HP increase seen by their port-flowing. When I see an old fashioned Sioux grinder with arbor and grinding stones used by most cylinder overhaul shops I’m amazed at the operator skill and technique to get even a reasonably accurate job.


Back to the OP: Consider pulling your cylinders and having all the valves and seats redone by a shop with a Serdi machine. If Ross is right that might cure your problem.

[Mike Macon]

Duff -

I am sending the two cylinders with burnt intake valves, that includes the one that was replaced 50 hrs. ago, and the two that have not failed out for repairs and reconditioning to Aero Sport.
My apologies to Doug if they do not advertise here.

[Jim Ball]

Please note that the Continental SIL007 only refers to replacement cylinders for Lycoming(R) engines. The Lycoming 340 has a different diameter cylinder barrel. The Titan 340 has the same diameter cylinder barrels as a 320. The 320 cylinders CAN be used on the Titan 340. Most Titan 340 engines have tapered cylinder barrel fins to reduce weight and direct more cooling air to the heads and a venturi design intake valve seat. Other than those differences, the Titan 340 cylinder is the same as a 320.

[theduff]

Thanks J B for piping in. I made a bad assumption about the 340 cylinder dimensions. After talking to a very knowledgeable source I learned that when using the 340 stroker crank they make up the difference in deck height with the piston ie a 7:1 compression piston ends up being something like a 9:1 compression ratio. They do this with a stock length 0320 rod but they do some extra machining on the large end to clear the crankcase.
So back to the OP: Factory Lycoming 0320 cylinders would be an option.

[Mike Macon]

Thanks guys, that's the info I have been searching for and knew this website was going to be my best resource. VAF comes through again.