Rebuild Questions (This Horse is Not Dead Yet)

Superman · 01-24-2002, 09:59 AM

I'm going to try and resume our conversation, now on Page 2, about rings and stuff. My cylinders are still on my engine because I am still cleaning the case. When I remove them, I will carefully record the exact positions of each ring and ring gap. I will measure ring gap and piston ring lands. If the rings are still in spec or close, and particularly if the ring lands are widened, I plan to re-use the old rings. I really don't want to buy new pistons or cylinders and my engine showed compression readings from 192-195 psi before disassembly.

Now, to answer Wayne's question (I know you already know this, Wayne so I'm not trying to 'teach' you anything), the reason one would re-use old rings is that these engines commonly smoke if you change rings but not cylinders. It doesn't sound like the smoke during breakin and then quit. It sounds like they just smoke. So, without suggesting new P&Cs, I'd like to hear more comments on putting fresh rings in old P&Cs, versus re-using old rings. I know JW has repeatedly warned that new rings on old cylinders tend to smoke.

BK911 · BK911's Garage

I'd like to jump in on this topic with an additional question:

If your ring land is out of spec, how much will new rings reduce the gap? For example, if I get a measurement of .006", will new rings put me within spec? Any ideas?

Thanks!
BK

Early_S_Man · 01-24-2002, 12:19 PM

Question #1 for Super Jim ... are they Mahle's or KS?

BK ... rings don't wear much, since they are hard alloys of iron, it is the ring grooves in the softer aluminum piston that wears, and will be out of spec.

BK911 · BK911's Garage

Not exactly what I wanted to hear! But thanks anyway!

Superman · 01-24-2002, 12:57 PM

I don't know yet. It seems to me that someone said they have different finishes. Mine are very silver. Like that silver paint we used to use on our model cars' headlights and bumpers. Anyway, I'm likely to conclude soon that the case is clean enough and it's time to remove the P&Cs. Then we'll know. Or perhaps I'm missing markings taht are already visible, but I think the markings are on the piston sides, rather than the tops or bottoms.

KTL · 01-24-2002, 01:05 PM

Aren't pistons and cylinders matched? That is, Mahle pistons=Mahle cylinders, Kolbenschmidt pistons with Kolbenschmidt cylinders. Cylinders have markings on them which determine type, as do pistons i'm sure. Then you'll know if your pistons are forged (M) or cast (K) I think. SC Spec. books should give you the details of what was used for what year and type, right?

I'm just going by what I recall from my Carrera spec. book. That's the shallow depth of my experience!

jabb · 01-24-2002, 01:52 PM

I believe you can put a magnet inside the cylinder if you feel a slight attraction to the cylinder it is a Mahle.....

Superman · 01-25-2002, 08:30 AM

The cylinders are KS.

The top compresson ring lands will accept at .003" feeler, but not a .004" feeler. This means they are not only within wear spec, they are within installation spec! I have not measured end gap yet, but I expect this will be in spec too. Since I liked the way this engine ran before teardown, I am still very likely to re-use the old rings. Again, I think they are nearly new dimensions and they do not smoke. New rings would be about the same, except that they might smoke.