Removing Pistons and Cylinders for head stud replacement, take out together?

[cabmandone]

I've read several threads about removing the pistons and cylinders and find some saying you need to remove the piston and cylinder together. As I understand, it has something to do with the way the cylinders and pistons break in. I'd like to get a look at my rings while I'm doing this but if it's really a big deal I'll keep them together when I remove. It appears I have to remove the pin from the rod and take the piston and cylinder out as one.

[Flat6pac]

I always pull them apart. When you put them back together space the rings, there really isn't much to see but more convenient to handle.
The thing you don't realize is, after spacing the rings and running the engine a short time the rings settle in where they want to be.
Bruce

[cabmandone]

Originally Posted by Flat6pac

I always pull them apart. When you put them back together space the rings, there really isn't much to see but more convenient to handle.
The thing you don't realize is, after spacing the rings and running the engine a short time the rings settle in where they want to be.
Bruce

That's what I'm hoping for. I've read some threads where guys said they had a bad ring and didn't know until they separated the P&C's

[Lapkritis]

Always separate to clean and inspect. Great time to get rid of carbon etc..

If everything inspects out then you can return the now cleaned rings to the exact place they were before. Maintain ring matched to piston to cylinder and which side is up.

[Henry Schmidt]

When the piston/pistons are in hand it's important to do more than "inspect" the pistons and cylinders.
Measure everything as precisely as possible
.
It is also important to load the ring lands with pressure to determine that the material is not damaged. It can be deceptive. The material between the rings can appear to be in tact and yet still be damaged. The picture shows obvious damage but damage can be much more subtle.

[Lapkritis]

Good point of clarity by Henry - part of an inspection is checking for wear/damage with precise gauges.

[Speed Buggy]

I had one of my Pistons with a broken land between the two compression rings. No symptoms, found it while replacing rings.

[Henry Schmidt]

Originally Posted by Speed Buggy

I had one of my Pistons with a broken land between the two compression rings. No symptoms, found it while replacing rings.

This phenomenon is very common on US delivery 80-83 911 SCs. These cars run a "lean burn" (smog) engine with 9.3:1 compression and combined with higher operation temps, poor fuel and the propensity for CIS to run leaner at cruise, the net result is an engine that wants to detonate.
Damaged ring lands is a common result of detonation.

[cabmandone]

Great feedback from everyone. I read several threads where people said "don't remove the pistons from the cylinders" It seemed odd to me not to since you'd have no idea what condition things were in unless you did. I believe several were quoting Wayne's book as the reason not to remove pistons from the cylinders.

I really appreciate all the comments.

[Dpmulvan]

They're referring to alusil cylinders when they say don't take the piston out.

[cabmandone]

Here's what Wayne had to say about this in a thread about Nikasil vs Alusil

"If you are tearing apart your engine for reasons other than worn out rings or valve guides, then you might opt to reuse your Alusil cylinders. This would be the case, for example, if you were tearing down your engine to replace broken or pulled head studs. If this is the case, I would recommend that you take your pistons and cylinders off of the engine, put them high up on a shelf, and don’t touch them until you are ready to reassemble. Don’t pull the pistons out of the cylinders and don’t dislodge or disturb the rings. Of course, you are taking a risk here that you will have worn rings in the near future. However, if your engine is a 3.0L, with 100K on the odometer, then there is a good chance that you can get 100,000 additional miles or more out of your set of rings, cylinders and pistons. I don’t necessarily recommend playing the odds like this, but if you’re rebuilding a good running engine with excellent leak-down numbers for the purpose of replacing head studs or some other non-wear problem, then it might be a good bet."

So it sounds like I should identify my cylinders before tear down.

Something I just read about. According to a thread here on Pelican, Mahle have 11 cooling fins where Kobenschmidt have 10. It implies you can tell what cylinders you have by counting the cooling fins. Accurate??

[Turbo_pro]

Originally Posted by cabmando

Here's what Wayne had to say about this in a thread about Nikasil vs Alusil

"If you are tearing apart your engine for reasons other than worn out rings or valve guides, then you might opt to reuse your Alusil cylinders. This would be the case, for example, if you were tearing down your engine to replace broken or pulled head studs. If this is the case, I would recommend that you take your pistons and cylinders off of the engine, put them high up on a shelf, and don’t touch them until you are ready to reassemble. Don’t pull the pistons out of the cylinders and don’t dislodge or disturb the rings. Of course, you are taking a risk here that you will have worn rings in the near future. However, if your engine is a 3.0L, with 100K on the odometer, then there is a good chance that you can get 100,000 additional miles or more out of your set of rings, cylinders and pistons. I don’t necessarily recommend playing the odds like this, but if you’re rebuilding a good running engine with excellent leak-down numbers for the purpose of replacing head studs or some other non-wear problem, then it might be a good bet."

So it sounds like I should identify my cylinders before tear down.

Something I just read about. According to a thread here on Pelican, Mahle have 11 cooling fins where Kobenschmidt have 10. It implies you can tell what cylinders you have by counting the cooling fins. Accurate??

The important thing to remember is that Wayne is not an engine builder. His experience is primarily limited to research not hands on rebuilding.

[cabmandone]

Originally Posted by Turbo_pro

The important thing to remember is that Wayne is not an engine builder. His experience is primarily limited to research not hands on rebuilding.

Point made, point understood.

[KTL]

An often touted issue with Alusil and its rings is that many claim re-ringing Alusil is a crap shoot. Meaning, yes you can put in new rings. But getting them to seat with the cylinders is the concern. Many claim that you can't get the new rings to seat well due to the cylinders having already been "bedded" with old ring material and that is not conducive to the new rings being able to seat. So you end up with new rings promoting high oil usage and combustion blowby.

I personally think that advice about foregoing the ring replacement is very risky on account of what Henry pointed out. If you're neck deep in the engine service, it's unwise to avoid dealing with the pistons & rings. You never know what you're going to find unless you take a look.

I recall in the past there's been some info shared here on the forum dispelling the 11 vs 10 fin thing. Easiest way to tell is to find the Mahle or KS marking on the cylinder usually covered by the air guides) and also look at the color of the cylinder walls. Alusil is light grey and the cross hatching is usually quite faint. Nikasil is darker and slightly golden/yellowish with a more prominent cross hatching.