Cylinder Sealing
08-19-2010, 11:26 PM
#1
Racer
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Location: Silver Spring, MD
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Cylinder Sealing
Got an issue with my ongoing rebuild so I thought I would float it out there for comment. I know, I know – some of you are ready to say “I told you so”. 
Got a set of new pistons/cylinders (I think I’ll leave out the manufacturer & supplier names) solely to bump the displacement to 3.8L. No issues with original P/C’s – turned out they are in great shape. Problem is, the new cylinders do not have a base o-ring seal gland or a head seal provision – but they are nice and flat/smooth. Since my engine is a Aug 91 build, I do have the Porsche updated sealing features in my stock cylinder (although part of my leaking problem was caused by one of the cylinder base seals failing). I have been told by the cylinder supplier to use a Curil compound to seal the metal-to-metal base area (no comment on the head seal), since they have seen this to be very successful.
I guess I am at the point where I cannot see taking the risk of developing a future leak just for the sake of a small displacement boost. I guess I have to think that Porsche made the cylinder sealing upgrades for good reason. Believe me, the new P/C’s look beautiful and they are otherwise very well made, so I am torn. But, I and my mechanic are leaning towards just using the stock P/C’s, with new rings of course. I would have to negotiate a return of the purchased P/C’s, hopefully without too much of a restock charge.
Any experience/opinions with this situation of sealed/nonsealed cylinders that may help me finalize my decision? Don’t be too hard on me – this is my first Porsche (just two years of ownership), so I am still in newbie-land.
Cheers.
Got a set of new pistons/cylinders (I think I’ll leave out the manufacturer & supplier names) solely to bump the displacement to 3.8L. No issues with original P/C’s – turned out they are in great shape. Problem is, the new cylinders do not have a base o-ring seal gland or a head seal provision – but they are nice and flat/smooth. Since my engine is a Aug 91 build, I do have the Porsche updated sealing features in my stock cylinder (although part of my leaking problem was caused by one of the cylinder base seals failing). I have been told by the cylinder supplier to use a Curil compound to seal the metal-to-metal base area (no comment on the head seal), since they have seen this to be very successful.
I guess I am at the point where I cannot see taking the risk of developing a future leak just for the sake of a small displacement boost. I guess I have to think that Porsche made the cylinder sealing upgrades for good reason. Believe me, the new P/C’s look beautiful and they are otherwise very well made, so I am torn. But, I and my mechanic are leaning towards just using the stock P/C’s, with new rings of course. I would have to negotiate a return of the purchased P/C’s, hopefully without too much of a restock charge.
Any experience/opinions with this situation of sealed/nonsealed cylinders that may help me finalize my decision? Don’t be too hard on me – this is my first Porsche (just two years of ownership), so I am still in newbie-land.
Cheers.
08-20-2010, 12:24 AM
#2
well since I have only owned mine for a couple weeks I guess I can't say much.
However, I did working on air/oil cooled Porsches for my dad for several years and sown the seeds for KM racing, so maybe I have a cent or two.
What I have found is there are no short cuts with these cars. You either do it right and correctly or you don't do it at all because it will come back to haunt you. Personally, I don't think I would use anything but a set of Mahle cylinder and pistons, which you can do a 102mm bore 3.8... for about $4k plus labor.
I think Porsche only ran the new 3.6 for 1 or 2 years before correcting the problem with a cylinder ring-gasket. It was basically a oil leak problem and not a compression leak or anything of that nature.
Some AM sets are not cut for O-rings.
However, I did working on air/oil cooled Porsches for my dad for several years and sown the seeds for KM racing, so maybe I have a cent or two.
What I have found is there are no short cuts with these cars. You either do it right and correctly or you don't do it at all because it will come back to haunt you. Personally, I don't think I would use anything but a set of Mahle cylinder and pistons, which you can do a 102mm bore 3.8... for about $4k plus labor.
I think Porsche only ran the new 3.6 for 1 or 2 years before correcting the problem with a cylinder ring-gasket. It was basically a oil leak problem and not a compression leak or anything of that nature.
Some AM sets are not cut for O-rings.
