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High EGT after cylinder replacement

Well, do they know why the piston chafed or is there a risk this could happen again?

Are the pistons on that engine oil-cooled?

Last Edited by Aviathor at 08 May 19:13

It probably won’t be a coincidence that the two problems happened on the same cylinder. That’s assuming the EGT probe has been swapped, to check it is not that.

Shoreham EGKA, United Kingdom

I asked them to first exclude an indication problem by swapping the probes. I will talk to them tomorrow. In what fashion could the camshaft be the source for this high egt reading and could it be that my new cylinder suffers from the same chaffing if the camshaft is the problem?


The camshaft would have to be seriously shagged to be doing this. But if they pulled a cylinder, they could have inspected the lobes.

Shoreham EGKA, United Kingdom

placido wrote:

In what fashion could the camshaft be the source for this high egt reading

The only thing I could think of is that the exhaust valve opens prematurely. That would mean that one cam has shifted. I do not believe that is possible. And it would not explain the overheating of the piston which I understand must have caused the running of the piston against the cylinder.


Have you got oil sample data on this engine
How many hours on the engine/cylinders
Is it hangared
Is it flown regularly
Engine monitor fitted, any recent data
What condition are the valve guides in.

I had a similar engine in a TB20GT with cylinder/piston scuffing and partial seizure as in your pictures all caused by internal corrosion.

The EXhaust valve failure may not be related to the scuffing. They could be two separate problems.

And yes, the compressions can go to zero in 3 hours even with overhauled cylinders.

Difficult to comment further without knowledge of my questions above.

EGNS/Garey Airstrip, Isle of Man

No oil sample data
The engine has 2500hrs. 1000 h since complete top overhaul, no TBO yet. The cylinder should be an ECI with about 1000 h on it
Not hangered, flies about 100 hrs per year but hardly during winter where it can sit for 3 months.
For whatever reason my G2 has stopped recording a few years ago. Apparently, I need to update the software.
The valve guide of the new cylinder should be good.
The least oil I have flown the TB21 is on 7 quarts just briefly. Never seen extreme temperature readings. On a hot day climb out I could see 410 degrees CHT but this is completely within limits.

I don‘t see the connection where a camshaft could impact EGT. How expensive is a camshaft for a TB21?


A camshaft is a few k.

One thing which occurred to me is that if you take the normal peak-EGT 65% operation to be say 1550F, 300F above that is 1850F and that is a physical impossibility with 100LL, assuming

  • there isn’t preignition
  • the exhaust valve is working and you don’t have lots of burning fuel reaching the EGT sensor

So one needs to do one thing at a time, starting with changing the EGT probe.

Shoreham EGKA, United Kingdom

Apparently, the 300 degree difference is a low power settings. I asked to swap the probe. I‘ll check tomorrow but it looks they went through this exercise and could not stop the issue.


I had exactly this problem with the engine in a TB20GT. One cylinder lost compression like yours and when that cylinder was removed to find scuffing of the piston and cylinder as you have. An internal inspection of the engine was carried out whilst the cylinder was off to find three other scuffed cylinders, camshaft spalling and cam follower damage and a lot of corrosion. I cannot be too specific because courts got involved and a subsequent agreement was signed.

At the time I did not do oil sampling so I had no data which would have alerted me to the problems, high aluminium for example. Unfortunately, nor do you. I knew something was wrong because on two occasions the engine faltered, just for a second. I was shocked to have it confirmed that these episodes are a sign of partial seizure as one instance occurred halfway between England and Denmark over the North Sea.

Exhaust valves do go bad in normal operation or even when new. I’m not familiar with ECI cylinders but there have been stories and I’ve experience of exhaust valves leaking badly (40/80) at 250 hours on Conti cylinders. George Braily, a well known aviation expert in the US wrote an article saying he tested exhaust valve/guide alignment on new and reconditioned cylinders and found a small proportion unserviceable Straight out of the box mainly due to malaligned guides and valve seats. In other words, bad manufacture.

I don’t think there is a connection between your exhaust valve problem and the scuffing. They are separate issues IMO. At least that is how I’d be looking at the problem.

From what you said above, your aircraft engine has a high corrosion risk. 3 months of inactivity left outside in winter conditions really is quite an extreme corrosion risk environment.

If it was my decision how to proceed I’d have the engine borescoped initially through a plug hole which might give you a clue on the health of all the cylinders. Unfortunately, this does not tell you the whole story. Through the plug hole only lets you see the swept part of the bore. Scuffing more often than not starts below the area swept by the rings and the only way to see that is to remove a cylinder and borescope the engine through the cylinder hole in the crankcase. This gives you access to the cams and cam followers too. I would not spend another Euro until you can establish the general condition of the rest of the engine.

Once you have this clear picture of the engines health from a corrosion standpoint you can then make decisions how to proceed. Just solving issues on one cylinder may not be the best use of funds if there are suspected more serious underlying problems particularly as TBO is ever present at the hours on this engine.

Look, I hope I’m wrong but everything points towards corrosion being the biggest problem not the valve issue.

EGNS/Garey Airstrip, Isle of Man
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