How many cylinders will you remove?

[Bill Hart]

A few years back I had low oil pressure and couldn't figure out why, after removing the engine and splitting the case I found the the main journal was cracked across the oil port. The general consensus at the time was that the crack developed due to improper torquing duing a cylinder removal. My question to the group is if you were having to pull multiple cylinders, how many cylinders would you remove at one time?

[Bruce Fenstermacher]

I'd remove as many as I needed then retorque them correctly. What is the difference between installing all six at engine overhaul or installing one later. No difference that I can see.

[mit]

Doesn't matter if you re-torque correctly that's how they get assembled.

[KS170A]

Some studs are actually through-studs that help secure opposing cylinders. When installing cylinders that utilize these through-studs, care needs to be taken to ensure the opposite cylinder remains torqued as well.

[hilltop170]

On Wed Dec 3, Mike Busch will be giving a webinar about this very subject. Participants need to register prior to the event.

Cylinder removal webinar

[Metal Master]

A few years back I had low oil pressure and couldn't figure out why, after removing the engine and splitting the case I found the the main journal was cracked across the oil port. The general consensus at the time was that the crack developed due to improper torquing duing a cylinder removal. My question to the group is if you were having to pull multiple cylinders, how many cylinders would you remove at one time?

The issue with replacing all six or all four cylinders on an aircraft engine comes from loosing clamping pressure on the main bearings during the replacement or prior to replacement because of case fretting. This can come from two different sources. If the engine has bad fretting between the case halves then clearance at the main bearings will become tighter when the new cylinders are installed. This can be so bad that it locks the crank shaft when the cylinders are torqued. I have seen this happen. Another instance is if the cases are fretted and all cylinders are removed at once the main bearings can rotate in their bores and the Indexing tabs on the bearings rotate out of position and then when the cylinders and case half’s are torqued it binds the crank shaft. This happens because the engine has to be rotated to get the Cylinders off of the crank case and get the piston pins out. In either case if it does not bind the crankshaft when the engine is re- torqued the engine is doomed to failure because you cannot tell very easily if these conditions exists and bearing clearance is reduced. Of course there is the possibility that no case fretting has occurred and there is no problem. A smart thing to do before removing the cylinders is to re-torque all cylinders and through bolts prior to removing the cylinders to see if an issue exists prior to even buying new cylinders or having cylinder work performed. And then only remove two cylinders at a time to keep from losing clamping pressure across the crank case halves. The problem with this is staging the process as you mostly want to get the job done and taking all of the cylinders to the shop to be reconditioned is better than doing it onesies twosies. Another way of doing it is to have spacers made of the same thickness of the cylinders base flanges and re-torque each of the through bolts as each pair of cylinders is removed. Lycoming has a process for the older narrow deck engines that require the of hanging of a weight on the propellor blade and checking the rotational torque (weight) that it takes to turn the engine to be within a certain specification. And then checking the rotational torque after the cylinder replacement to be within a certain specification then if does not you have to disassemble the engine and have machine work performed to return the clearances at the main bearings. The older Lycoming engines and even newer Lycoming engines are more prone to case fretting than the smaller Continental engines. However I have seen both Lycoming and Continental engines have fretting issues that required machine work determined during cylinder removal. Owner Operator Beware.
Regards,
Jim

[mit]

A few years back I had low oil pressure and couldn't figure out why, after removing the engine and splitting the case I found the the main journal was cracked across the oil port. The general consensus at the time was that the crack developed due to improper torquing duing a cylinder removal. My question to the group is if you were having to pull multiple cylinders, how many cylinders would you remove at one time?

The issue with replacing all six or all four cylinders on an aircraft engine comes from loosing clamping pressure on the main bearings during the replacement or prior to replacement because of case fretting. This can come from two different sources. If the engine has bad fretting between the case halves then clearance at the main bearings will become tighter when the new cylinders are installed. This can be so bad that it locks the crank shaft when the cylinders are torqued. I have seen this happen. Another instance is if the cases are fretted and all cylinders are removed at once the main bearings can rotate in their bores and the Indexing tabs on the bearings rotate out of position and then when the cylinders and case half’s are torqued it binds the crank shaft. This happens because the engine has to be rotated to get the Cylinders off of the crank case and get the piston pins out. In either case if it does not bind the crankshaft when the engine is re- torqued the engine is doomed to failure because you cannot tell very easily if these conditions exists and bearing clearance is reduced. Of course there is the possibility that no case fretting has occurred and there is no problem. A smart thing to do before removing the cylinders is to re-torque all cylinders and through bolts prior to removing the cylinders to see if an issue exists prior to even buying new cylinders or having cylinder work performed. And then only remove two cylinders at a time to keep from losing clamping pressure across the crank case halves. The problem with this is staging the process as you mostly want to get the job done and taking all of the cylinders to the shop to be reconditioned is better than doing it onesies twosies. Another way of doing it is to have spacers made of the same thickness of the cylinders base flanges and re-torque each of the through bolts as each pair of cylinders is removed. Lycoming has a process for the older narrow deck engines that require the of hanging of a weight on the propellor blade and checking the rotational torque (weight) that it takes to turn the engine to be within a certain specification. And then checking the rotational torque after the cylinder replacement to be within a certain specification then if does not you have to disassemble the engine and have machine work performed to return the clearances at the main bearings. The older Lycoming engines and even newer Lycoming engines are more prone to case fretting than the smaller Continental engines. However I have seen both Lycoming and Continental engines have fretting issues that required machine work determined during cylinder removal. Owner Operator Beware.
Regards,
Jim

Specifically you have seen an O-300/C-145 do this?

[Metal Master]

Specifically you have seen an O-300/C-145 do this?[/quote]
Tim,
I have done only a few O-300's one was a complete overhaul and the others were only removals of single cylinders. And my own which I removed the 2, 4 and 6 cylinders. On mine I checked torque on all of the cylinders before I removed them. Removing a single cylinder created no problem. The O-300D I overhauled needed no case work. It was 2,000 hour engine that had never been overhauled. I have seen the problem in a number of Lycoming engines and numerous big bore Continentals. But I have also heard of several main bearing web failures of C-145's and O-300's but it is only hear say other than those I have seen pictures of here on the 170 Association forum. We found the problem of severe fretting on my friends 172-TD w/ 180 Narrow deck O-360. He ended up deciding to purchase a new Lycoming wide deck engine because Lycoming would reduce the core value if we split the case on the narrow deck returned as a core by $2,000. The new wide deck roller cam Lycoming introduced a whole new can of worms and it took a year and a half to get the engine running correctly again. But that as they say is another story.
Jim