worn exhaust valve guides

[seebruce]

My planes in for annual and found 2 cylinders with worn exhaust valve guides on the TSIO 360LB Continental. I've been running LOP for about 20 hrs since I bought the plane.The cylinders have only about 260 hrs on them.

Has anyone that's been running LOP experienced this condition? I'm wondering if this is just a coincidence or if LOP is causing excessive ware in the guides. From what I was told the previous owner only ran ROP. The compressions were fine at pre buy. But I have experience this before when the valve will seat correctly when tested and give good compression even though the guides were worn.

[Cruiser]

There are four major considerations for long exhaust valve life:

valve train alignment - You can't do anything about this. The overhaul/builder does. 

lubrication - again, you can't do anything about this. It is determined at manufacture.

oil cleanliness - Change the oil as often as needed based on usage conditions and color. If you check the oil and it appears black on the dipstick, it should have been changed already.

valve cooling - LOP is the single biggest thing to help here. Do it aggressively. The valve cools by transfer of heat to the seat. IF the valve and seat are not perfectly aligned (see the other three conditions) heat transfer is reduced. CHT is critical. The higher the CHT the harder it is to remove the heat from the valve. On the other hand, the lower the CHT the better BUT it will not compensate for the other three problems. In other words, LOP operation is not the cure all OR the blame.........

Where did the cylinders come from? Factory new? overhauled?

Is there a wear pattern? One place? two places across from one another? Look at the rocker arm face and the valve tip. Where is the contact? If the rocker arm pushes the valve stem to the side, rapid valve guide wear occurs. What does the valve seat look like? If the valve does not fit in the seat it will wooble causing guide wear.

[Piloto]

Was the engine started without preheat below 20F?. Starting without preheat after several weeks will cause inmediate wear of the guides and bearings. After a week most of the oil in the upper parts of the engine will run down to the oil pan leaving the upper parts dry. When you first start in cold weather (below 20F) after two weeks it takes about a minute for the oil to warm up and circulate around the valves guides. Clearances in all metal machines (specially engines) reduces at lower temps. This is why in extreme cold (below -20F) you can not move the prop by hand. If you can not move the prop by hand easily you need preheat.

José

  

[seebruce]

These were factory new cylinders. They are at the shop for repair right now and I haven't discussed the condition with them yet. I kept the  CHT on the hottest cylinder  between 350 and 375. The plane came from Arizona so I don't think cold starts are the problem.

[KSMooniac]

It is entirely possible that the valves were not aligned nicely from the TCM factory... there are some in the business (so I've read) that do valve jobs on new TCM cylinders before installing them just to make sure the alignment/centering is correct.

[Cruiser]

How did the Nickel (Ni) look at the last oil analysis? How has it trended since the cylinders were installed? What is it now?

[ovation0219]

one reason we use leaded fuel is for the lubrication of the upper end. If you are running Lean of Peak that lubrication is lean. This engine was not designed to run lean of peak. Temps are not the only concern when running LOP. I think you will be better giving the oil companies a little money instead of saving it for the engine shop.

[danb35]

...and how does the fuel get inside the valve guides to lubricate them?

[seebruce]

I've heard this before. I can see how this would be true for the intake, but I  can't see how it would lubricate the exhaust valve guide.

[danb35]

There are a lot of old wives' tales about LOP operations, but few (if any) of them have any factual basis.

[carusoam]

At the risk of adding to the old wives tales, here goes....

[1] The lead additive in the 100LL is in there for two reasons.  Increase octane rating and to lubricate valve stems.

[2] This is the hear-say part: The soft metal lead and lead oxides are responsible for the lubrication.  They deposit on the surfaces. They will deposit in ROP as much as LOP.  If you run really rich, the deposits are lead balls collecting in the lower spark plug of each cyllinder. 

"molten lead would coat the valves, rings and cylinder walls with a flash coating" 

http://39olds.com/lubrication.htm

[3] Old cars and old planes required the lead lubrication.  Modern materials of construction no longer require this in either planes or cars.  The octane boost is often still appreciated, but the lead lubrication is not.

[4] "Physical compatibility is addressed by the installation of hardened exhaust valves and seats."  - Wikipedia

  http://en.wikipedia.org/wiki/Tetra-ethyl_lead

[5] In the case of Bruce's engine....Why only two cyllinders and not all six?

Best regards,

- anthony -

[seebruce]

I talked with the shop this morning. They told me that they see this problem all the time with Continental cylinders. They are of the opinion that it is the use of inferior material at the factory. I had the same problem with my Seneca cylinders which were also new factory cylinders built back in 96 when it was known that Continental produced a large number of cylinders with bad guides. I would have thought that they would have solved that problem by now.

[carusoam]

Bruce,

What is the shop's recommendation?  Is it as simple as new, good quality, valve guides + valve alignment?

-a-

[seebruce]

That's pretty much it. Hopefully the rest of the guides were done properly.

[seebruce]

That's pretty much it. Hopefully the rest of the guides were done properly.

[ovation0219]

I have heard of all the stories about this engine not making TBO because of the cylinders failing. I had a friend with a seneca with 2400 + hours on both engines with no cylinders being removed. i had a Turboarrow and I put a Victor Aviator engine in it and flew it 1300 + hours before i sold it and it had not had a cylinder removed. I think this engine gets a lot of grief because of poor flying habits. Your problem is probably fixed and now will not have any more problems. Just watch how you fly it.

[KSMooniac]

TCM did indeed have a rash of poor quality cylinders (thanks to some wunder-MBA cost savings) that led to a lot of premature cylinder/valve problems no matter how the operator managed the engine.  Hopefully those days are behind them, but you never know...

[ovation0219]

All Companies have problems expecially when trying to cut costs. This engine gets a bad reputation and is really a good engine.

[seebruce]

ovation0219,

Did those engines that went all that time have factory new cylinders at overhaul?