Lycoming O235 Continuous burnt Valve problems

I"ve owned my PA 12 for over ten years with around a 1000 SMOH. But in that time I have installed two new Lycoming cylinders, and overhauled the two other cylinders and it is continuous battle against burnt valves. What gives. The two new Lycoming Cylinder assembles are now looking like they will need attention soon. I'm not alone here. Another 12 next hangar over same darn thing. 2 to 300 hours at most then failed low compression and burnt intake or exhaust. Any suggestions? I put an average 100 plus a year.

Checking for proper valve lash/ range when installing push rods? Maybe go for widest setting so as valve/seat wear the valve don't get held open...


Might check if you have proper lash left on bad cylinder before removing....

We have done this. We were thinking that the cold settings just we not enough for the expansion and as a result the expansing was closing the gap, but haven't seen any change . Are they notorious for this, ours sure are. We lapped the valves last time and so far so good. Seems the front right runs a little leaner than all the rest but here again not sure if there is a relationship. What are the major causes for burned or leaking valves.

Motorcycle mechanic-NOT aircraft engine mechanic. free advice and all.. but your getting into the nuances of engine problems when things run fine for a while and then have premature wear.. So one thought of many.. Be sure and check valve stem to valve guide clearance. The valves conduct heat away from the seat and then up the stem where the heat transfers to the valve guide. Excessive valve guide-to-valve clearance will cause overheating of the valves. I offer this since you say it can be either intake or exhaust so maybe an over-cautious-about-valves-sticking mechanic reamed extra clearance. Of course your damned if you do and damned if you don't ;-) . There is the other stuff: over leaning (extra fuel cools the valves), How about this: maybe full throttle enrichening device on carburator is bad? Every take off would overheat the valves a little and over time? , tight tappets, valve seat problems, hot rod cam, etc. Hopefully Lycoming mechanics will chime in with "experienced" focused suggestions. dave

Fortysix12 said:

I"ve owned my PA 12 for over ten years with around a 1000 SMOH. But in that time I have installed two new Lycoming cylinders, and overhauled the two other cylinders and it is continuous battle against burnt valves. What gives. The two new Lycoming Cylinder assembles are now looking like they will need attention soon. I'm not alone here. Another 12 next hangar over same darn thing. 2 to 300 hours at most then failed low compression and burnt intake or exhaust. Any suggestions? I put an average 100 plus a year.

Click to expand...

You might be running to lean. Some panes we set the fuel flow higher to get better cooling of the engine. It wastes more fuel but the engine will last longer and run cooler

The 0-235 engine is a just a POS.....

Why did I know you were going to say that Luke...

I ran an O-235-C1 to 2600 hrs since new with no problems. I adjusted the mechanical valves regularly and replaced the carburetor when the venturi AD came out. It finally started using a quart of oil every 2 hours so I replaced it with a mid-time engine. When I tore the original engine down the only thing wrong with it was that the taper was worn out of the rings. It burned 6.3 gallons an hour and ran great after I figured out to lean it all the time except in the climb to keep from having to clean the plugs every 25 hours. That was the most economical airplane/engine I have ever owned and luckily it was my first.

O235c1 with 1500 SMOH, runs good and only put a quart oil in every 12 hours, how often do you need to adjust the valve clearance? I have flown it 25 hours, would like to make sure the rockers are set correctly.

Thanks

Edit:
Found SI1068

https://s32.postimg.org/6jpz4e8wz/si1068a.jpg

fuel at high power settings is important. If you are just slightly low you run at peak egt... and things go bad fast.

Those were the engines that would always swallow valves?? The exhaust stem gets too hot and bends or breaks. You can lap it to fit, but it won't last as the valve is bent at the stem. Those valves could be 60yrs old. Do the new ones do it?? Run it rich especially at takeoff. JMO.

My 2010 post still holds true for me.

Steve Pierce said:

I ran an O-235-C1 to 2600 hrs since new with no problems. I adjusted the mechanical valves regularly and replaced the carburetor when the venturi AD came out. It finally started using a quart of oil every 2 hours so I replaced it with a mid-time engine. When I tore the original engine down the only thing wrong with it was that the taper was worn out of the rings. It burned 6.3 gallons an hour and ran great after I figured out to lean it all the time except in the climb to keep from having to clean the plugs every 25 hours. That was the most economical airplane/engine I have ever owned and luckily it was my first.

Click to expand...

Hmm, got lots of time behind an O-235-C1 and maintaining them and never had any issues.

Tango Cub said:

You might be running to lean. Some panes we set the fuel flow higher to get better cooling of the engine. It wastes more fuel but the engine will last longer and run cooler

Click to expand...

Hi guys ! I think Tango is right!
You might be running too lean!
A very easy way to know is to look the end of your exhaust pipe?
If it's white you are running too lean!
Black too rich
Coffee color.. perfect for the engine and pilot
Hope this help!



Sent from my iPhone using SuperCub.Org mobile app

Google "AOPA Anatomy of a valve failure", at the bottom of the article is a nice colored chart detailing the progression of a burnt valve. The headline is that valves burn because they fail to seat properly. That detail is the responsibility of the guy that built the cylinder. A few hundred hours into the engine run no one remembers his name but his poor workmanship has shown up and it's the pilots fault because he leaned the engine. I would like to see some hard bonafide data that leaning causes burnt valves. Maybe someone can post the chart because I cannot. No offense intended to you cylinder builders out there, Jim

https://www.aopa.org/-/media/files/...ety/14fn0000-asi-valve-safey-poster_final.pdf




Sent from my imitation glass cockpit.

There is lean and then there is too lean. No different then a sled, puii a plug and check the color.

Glenn

Thanks for pointing this Cruiser and thanks for sharing Farmboy!
Very interesting!
It must be a combination of the valve seating
And the leaning ( make the valve too hot) that burn the valve!


Envoyé de mon iPhone en utilisant SuperCub.Org