Lycoming Exhause Valve Guide SB

ronschreck · #1 08-14-2009, 10:56 AM

A friend of mine discovered some serious exhause valve damage to his O-360
and during the repair process he uncovered a Lycoming SB that addresses the issue of carbon buildup on exhause valve stems. I'm curious, how many have performed the inspection described by this SB? Also, what are the chances of having problems with carbon buildup when useing electronic ignition and running mogas? Comments welcome....

Here is the SB on the Lycoming valve guides: http://www.lycoming.com/support/publ...dfs/SB388C.pdf

And here is the Service Instruction # 1425 with reaming instructions: http://www.lycoming.com/support/publ...fs/SI1425a.pdf

Andrew M · #2 08-14-2009, 11:22 AM

I have done it on a small contenital engine. I dropped the exaust valve untied into the cylinder and cleaned the guide with emery cloth and a "Swizzle stick"(slotted bamboo or dowel). Fishing the valve back into the guide was done with two people using a magnet and two pair of forceps working through the spark plug holes.

The first one is a little scary, after one is done it's no big deal.

Andrew

az_gila · #3 08-14-2009, 08:22 PM

...with a 600 hr Lyc. reman engine.

I failed two cylinders in the other direction - valves too loose - and did a top overhaul.

It is a worthwhile test since a loose valve can be just as bad as a tight one.
This is a picture of my Lycoming tool, but the SB gives dimensions for a DIY tool.

The above tool is usually modified to use a dial indicator to get direct readings. As shown above, the small screw on the right is adjusted to be close to the valve stem extension and a feeler gauge is used to get readings.

The tool depresses the valve a small amount as it is tightened down on the cylinder head - this lifts the valve off the seat without removing the valve springs. The version that Spruce sells does not do this.

Note that the SB also calls for cleaning the hydraulic lifters.

Quote:

Originally Posted by ronschreck

A friend of mine discovered some serious exhause valve damage to his O-360
and during the repair process he uncovered a Lycoming SB that addresses the issue of carbon buildup on exhause valve stems. I'm curious, how many have performed the inspection described by this SB? Also, what are the chances of having problems with carbon buildup when useing electronic ignition and running mogas? Comments welcome....

Here is the SB on the Lycoming valve guides: http://www.lycoming.com/support/publ...dfs/SB388C.pdf

And here is the Service Instruction # 1425 with reaming instructions: http://www.lycoming.com/support/publ...fs/SI1425a.pdf

Ironflight · #4 08-14-2009, 08:42 PM

As Gill well knows (as do many other Grumman refugees here in RV-land...), this SB was a constant source of discussion and frustration in the Grumman world for quite a few years. I left that world behind when I slid into my RV-8 for the first time, and have always been amazed that even with the same engines, no on in the Van's world ever mentions the thing - or valve failures for that matter.

I have never really figured out the difference - except that there seems to be fewer cooling problems in the RV's than in the Grummans as well....

Paul

az_gila · #5 08-14-2009, 08:51 PM

...consistent.

A local Tiger with an O-360 right at TBO borrowed my tool and his valves were all within tolerance....

My engine even has the hi-chrome "improved" valve guides, his did not...

We've measured a few RVs with O-360's and they have all been OK so far.

Quote:

Originally Posted by Ironflight

As Gill well knows (as do many other Grumman refugees here in RV-land...), this SB was a constant source of discussion and frustration in the Grumman world for quite a few years. I left that world behind when I slid into my RV-8 for the first time, and have always been amazed that even with the same engines, no on in the Van's world ever mentions the thing - or valve failures for that matter.

I have never really figured out the difference - except that there seems to be fewer cooling problems in the RV's than in the Grummans as well....

Paul

Radomir · #6 08-14-2009, 08:55 PM

Maybe how you operate your engine has a lot to do with the end result? Just a thought...

az_gila · #7 08-14-2009, 08:58 PM

Quote:

Originally Posted by Radomir

Maybe how you operate your engine has a lot to do with the end result? Just a thought...

...but the previous owner did 500 of those 600 hours - as well as the factory instrumentation that didn't even include a CHT guage...

I now have 4 cylinder EGT/CHT monitoring....

David-aviator · #8 08-14-2009, 09:01 PM

Quote:

Originally Posted by Ironflight

As Gill well knows (as do many other Grumman refugees here in RV-land...), this SB was a constant source of discussion and frustration in the Grumman world for quite a few years. I left that world behind when I slid into my RV-8 for the first time, and have always been amazed that even with the same engines, no on in the Van's world ever mentions the thing - or valve failures for that matter.

I have never really figured out the difference - except that there seems to be fewer cooling problems in the RV's than in the Grummans as well....

Paul

Could be SI1485A has something to do with fewer reports of valve problems. Lycoming switched to a better valve guide in 1996 and since March of 1998, all engines have been shipped with the improved guides. The inspection time was increased to 1000 hours, or half way to TBO, on engines with the new guides. That does not account for RV's flying with older engines, but many RV's do have later engines, much later than those on the Grummans. They've been around for a while.