Which cylinder base gaskets should I go with here?

[BGCarrera32]

Hi guys:

Deck height question here (regarding top edge of piston at TDC to top of cylinder)...doing a pretty straight up rebuild on a 3.2 Carrera motor using new Mahle 10.3:1 Euro/ROW pistons in 95mm jugs as opposed to the US 9.5:1. It's a compression bump, that's it. Case has not been decked or machined.

For checking "deck height":
Dropped a P and C on #4 with a .25 mm stock base gasket thickness.
Dropped a P and C on #1 with a .50 mm gasket thickness.

For the .25 mm gasket measuring 3 places around the piston it is averaging .96 mm with some repeat measurements returning at 1.08 to 1.28 mm.

For the .50 mm gasket measuring 3 places around the piston, I'm seeing a deck height average of 1.19, with tries reading 1.21 to 1.53.

Obviously, this assumes my measuring is decent, so let's say it is.

My rebuilt heads have had .004" (.10mm) removed . Will perform a valve clearance check, etc.

Question here is which gasket to go with? In understand factory was .25mm, again no case machining done. I want to make sure I'm not leaving power (compression) off the table. What do you think- what would you do?

Thanks
BG







With .25 mm gasket:

[PeteKz]

My view: With 1mm deck clearance, that's plenty. Use the .25mm base gasket. I eliminated my base gasket in order to get deck clearance down to .030"/.75mm on my current 3.2 long-stroke engine. I like to keep the combustion chamber tight, not so much for the increase in CR (which is pretty small for just .25mm change in deck clearance), but to improve combustion chamber squish and turbulence.

But, I also measured the point where the piston contacted the inside of the head, to make sure I had at least .75mm there too. There are several ways to do that--use clay, a piece of solder, or assemble piston to cylinder and set the piston deck clearance at 1mm, then put the piston/cylinder on the head and measure how much further you can push it into the cylinder before it touches the head. In my case using the same Mahle Sport P/C's you have, my clearance to the head was the same as the deck clearance, .75mm.

[BGCarrera32]

Thanks. A few more data points as I had some time tonight; I did the solder method and using the .25 mm gasket installed, I placed my solder on what appears to be the highest spot of the dome and a spot across from it. The solder was around 2.5 mm unsquished. When I rotated the engine over twice, it didn't squish at all.


I then moved the solder to a couple of alternate spots, just for giggles, and in one spot it did squish. When I removed it measured 1.21 mm. I think this is confirming that the .25 mm gasket is good to go.




Also, and I've run into this before, I am getting these striations on the cylinder wall when turning the engine over. They don't feel like scratches when hitting them with my fingernail, but I can't wipe them away either. I took great pains to ensure eveything was clean, rings were deburred as necessary, etc. and have plenty of Joe Gibbs break-in oil lubing the Ps and C's. Have you run into this before as well or am I overthinking it? Again, they look like scratches but not really feeling anything and nothing is binding when I turn the engine over by hand. How do I mitigate or avoid this?

[PeteKz]

Those vertical lines are normal. That's the rings starting to wear against the cylinder walls.

[mikedsilva]

Def use the 0.25 gaskets.

[BGCarrera32]

Thanks guys

[Jeff Alton]

Good Advice already given!

Cheers