3.2SS top end rebuild - compulsory newbie questions

[Alan L]

You better check your valve clearance first.
Alan

[KTL]

If you're going to go without a base gasket, i'd be sure to dress the sealing surfaces of the engine case and the cylinder to avoid any leaks. On my current '86 3.2 engine rebuild, these surfaces show a bit of corrosion. So I plan to lap them together with some valve grinding compound to smooth them out.

If no copper base gasket, I definitely would use some non-hardening sealant like Curil T or blue Hylomar to seal that area, just to be sure you don't end up with a pesky weep leak. With the new base gasket i'd leave it dry. In the one instance that i've seen base gaskets reused (heads were taken off, cyls left in place to do valve guide replacement) and they still don't show any leakage 20K miles later.

Neil makes a very good point about the fire ring zone that creates additional void space beneath the combustion chamber. Although over time this area gets partially filled up by carbon deposits collecting on the cylinder wall (actually considerably thick here) and a little bit on the periphery of the piston above the uppermost compression ring. What that means to me is a newly built engine has that void space which reduces the compression ratio. Then as the carbon collects it increases the compression ratio. The space never gets completely filled because the movement of the piston keeps the buildup at bay. So maybe account for 1/2 that void volume and call it 6mm tall by 0.5mm thick?

The same can be said for the carbon that grows on the piston crown and the cylinder head. This carbon on the crown & chamber is much more prominent than the fire ring carbon. So that too increases the compression ratio over time. Should we compensate for that as well?

Here's some pictures from the 80K miles engine i'm working on right now




I don't know if this is something that is taken into account with the original engine design. In other words, did Porsche slightly reduce the compression ratio in the design, knowing that the carbon buildup will eventually increase the compression ratio?

Or you can just let your valve guides leak and that'll keep things cleaner? These pics are taken of the same engine at cylinder #3 that had a very leaky intake valve guide. Note the small pool of oil on the closed intake valve and the very fouled, but still operational spark plug.

[Nux]

Just to update:

Heads are now completely re-built. Cleaned (not blasted). 12 new high end valves, seats CNC machined. New retainers, springs and guides. Basically like new.





And I finally got my custum made rings as well. Naturally, Mahle does not provide replacement rings for their Max Moritz conversions. And to further complicate things, they are 1.2, 1.2 and 3.0mm - which no other company uses apparently.

So here we go: New 1.2mm compression ring, 1.2mm Napier 2nd ring and 3 piece oil ring:



It does feel good knowing it's all in proper order though. Now it's time for assembly. Thanks again for help and guidance.

[lvporschepilot]

Good stuff. keep it up!

[Nux]

So I've CC'ed the heads to 89-90cc, pistons to 33cc isch, deck hight 0.9mm with base gasket.






So with somewhat crude measurements I have calculated my CR to 9.2:1 - which is pretty close to the 9.3:1 that Mahle states for the 3.2ss kit.

If I remove the base gasket, I will get CR around 9.5-9.6:1, but with a deck hight of only 0.6-0.65.

So unless you guys advise me differently - I'll stay with the base gasket. Correct?

[David 23]

Originally Posted by Nux

Just to update:

Heads are now completely re-built. Cleaned (not blasted). 12 new high end valves, seats CNC machined. New retainers, springs and guides. Basically like new.

Exactly what valves did you use?

[Nux]

Originally Posted by David 23

Exactly what valves did you use?

Those are quality valves from Intervalves Technologies in Switzerland.

INTERVALVES TECHNOLOGIES AG