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jamesjedi's Avatar
Join Date: Aug 2004
Location: The Brink
Posts: 2,120
Machine Early 964 Cylinder or Used 993 Cyliders?

Thought I would just check for something I keep asking myself.

My engine is out and on a stand. I am addressing an exhaust port and replacing that head. Engine does not have any history of leaking at the cylinders. I am considering having the heads and cylinders machined for a groove to have a sealing ring.

However, would it be better to replace the cylinders with used ones from a 993 and then machine the head to have a better mating surface?

Thanks for any input.
Old 02-09-2018, 09:10 AM
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Join Date: Jul 2016
Location: Ayrshire, Scotland
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Personally if it was me presuming that your cylinders and Pistons have been measured and found to be within spec I'd have the cylinders and heads machined flat and rebuild as is with new piston rings.
You said that you had no problems prior and it would be an unnecessary expense to ditch a perfectly good set of P's and C's

If they're marginal with regards to condition then I'd bite the bullet and get a new set and have the heads machined to accept the sealing ring.
Old 02-10-2018, 11:42 AM
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The issue with 3.6 cylinders is not really about the sealing ring. 3.2 and 3.3 engines did not have sealing ring and did not have the same problems because the stud spacing is smaller. With the 3.6 engines the stud spacing was increased to accommodate the 100MM cylinders. Because the forces on the head were now further from the edge of the cylinder this allowed the heads to "bend" as a result causing a sealing problem. FYI 3.0, 3.2, 3.3 3.6 cylinders all have the same outer bore diameter at the head. The change with the later 3.6 involved more than just a sealing ring. The later 3.6 cylinders are flat across the top all the way past the stud holes. Early 3.6 cylinders are like all 3.0-3.3 cylinders. To use the later 3.6 cylinders requires machining the heads flat as well. Because the clamping force was no longer concentrated on the sealing surface of the cylinder a gasket was required. Good explanation with pics at link below.

Understanding 964 Head Gasket Modification

Old 02-10-2018, 12:59 PM
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Join Date: Feb 2002
Location: At the Airport Kentwood, MI
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You are referring to technical service bulletin 9404 where the early heads are machined out to 145mm a fairly easy and straight forward task

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Twinplug, head work, case savers, rockers arms, etc.
Old 02-14-2018, 07:29 PM
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