Cylinder woes?

[kortopates]

2 minutes ago, bdash said:

The sticky exhaust valve was said to be the cause of the EGT drop that led to me taking the aircraft into the shop. The low compression was something additional that the shop reported seeing while investigating the issue.

Right, if something went awry very recently I'd have not had time to notice a change in oil consumption.

Would something like a broken ring be visible in any form in the engine monitor data?

Not always but often a loss of EGT (decrease in power/combustion) coupled with an increased CHT (frictional heat).

[MIm20c]

2 hours ago, N201MKTurbo said:

It surprises me that nobody repairs cylinders anymore. An exhaust valve and guide is less than 1/2 AMU. If you talk to them real nice, the local cylinder shop can change it in less than a day. I can do it myself for that matter. 

If you have low compression and the cylinder is not scored, just replace the piston and rings. 

Last time we sent a 550 cylinder to a small shop/good reputation it only saved $250 versus buying new. The OH’d cylinder did make it to engine OH but the savings was not worth the hassle IMO.  Not sure what current prices put the break even at. 

[kortopates]

30 minutes ago, MIm20c said:

Last time we sent a 550 cylinder to a small shop/good reputation it only saved $250 versus buying new. The OH’d cylinder did make it to engine OH but the savings was not worth the hassle IMO.  Not sure what current prices put the break even at. 

somewhat an apples to oranges comparison. There are at least 3 entirely different levels of servicing/repairing a cylinder with escalating prices:

1) IRAN - just fix what's broken

2) Overhaul - required replacement parts including new piston, but not to new limits but serviceable limits

3) Overhaul to New limits - with a first time run cylinder should be as good as new and some will argue better than new since a good overhauler will pay more attention to detail in valve lapping and symmetry.  

The price goes up just like between a G5 to a Aspen to a G500 does. 

Also OEM new assemblies typically don't include the rocker arms and shafts that have to be added to the cost of a complete cylinder.

In some cases you can't even get a NiC cylinder without going the "Overhaul to new limits" route since they are unavailable new.

[bdash]

To circle back on this: I asked that the cylinder be borescoped before proceeding. That revealed vertical scoring on the cylinder walls, consistent with broken rings, so I ended up replacing the cylinder.

I’ve flown around three hours since, and am still waiting on signs that the rings have seated. The weather’s looking rough for the foreseeable future so it’ll be at least another week until I’m truly back up and running.

[carusoam]

Great follow-up, BD!

Thanks for filling in the details.

Good luck with the break-in flights...

Best regards,

-a-