Stacking Cylinder Base gaskets
 

I'm doing a top end on my 1979 SC. I am installing 98mm Max Moritz P&C, 9.3 CR
My deck height was .58 with a .25mm base gasket, so I was going to add a .5mm base gasket to the .25 to get a deck height of 1.08mm. In addition my local Porsche mechanic suggested I use Dow Corning 730 on the gaskets. (He is big into Turbos and doesn't take chances)

Comments? Any problem with using two base gaskets?

Thanks for your input.

dog

I Stacked two gaskets to compensate for milling the deck and have had no problems(no leaks!).

I've been wondering about this also, since there seems to be lots of issues with leaks both between the head to cylinder and cylinder to base on larger higher compression motors.

What size is your motor and what CR?
Did you use any sealer like Curil T at the base?
Did you use any glue or sealer between the shims that you stacked?

Just curious,
To drop my CR for my turbo conversion, I was thinking of stacking 2 shims, which work out with the thickens of 2 cam tower gaskets, keeping everything growing on the same plane.

Subscribing

Re: leaks http://forums.pelicanparts.com/911-engine-rebuilding-forum/457406-leaks-between-cylinders-heads.html

Mine is a stock 2.2e, cr 9.1.

I've had good success when stacking .25mm's on .5mm or 1.0mm but never stack a .25mm on a .25mm. They start to deform and move around a bit.

Don

They are copper, anyone ever sweat them together?

Funny that you mentioned that, because I was thinking the same thing. Providing you can do it Consistently so that they are all the same thickness to each other and all the way around the shims. I thought of sweating them, getting the solder to flow and while the solder is still molten to use a cylinder to weight them down flat and flush together.

I'm not sure if its really worth the effort though, the other thought I had was to use a spray contact cement on the mating surface of both shims and carefully bring them together then press to ensure a 100% bond

There really isn't a need to stack gaskets - you're less likely to have a leak if you use only one, and put Curil T on them (or similar product).

I've even seen some builders recommend Curil K2 on the shim on the side mating to the cylinder, then the Curil T on the side to the case!

Places like Flatout Gaskets http://www.flatoutgroup.com can make shims in whatever thickness is needed in basically no time flat - they make all the ones I supply to my customers, out of copper, stainless, or carbon steel depending on the customer's application.

Although I haven't built a Porsche motor yet (and will be asking lots of questions from you guys when I go back up), I would think stacking gaskets would not be a good thing.

I would think the movement between the two while you torque would cause uneven distribution of pressure. I know in the jet engine world, we were never allowed to stack shims or gaskets of any kind.

But, I'm not an Engineer and have never torqued a 911 cylinder down, so what do I know? :D

I tend to agree with you Tippy and on the same page!

My experience goes back to work on nuclear submarines and we never stacked gaskets or shims either. Very dangerous or at least it doesn't give you that "warm and fuzzy" feeling when you are 900 feet below the surface of the ocean. A leak there could end up killing you and everyone else aboard the ship.

Navarro brings up a very good point regarding getting it right the first time with one being the size you need.

Oh yes, that would be scary! :eek:

Not sure what the factory deck height spec is for dog's 79SC but I'm pretty sure it's more than 1.08mm. My question, is there no concern on geometry, particulary the alignment of the cam box to cam tower and the seal around the cam at the cam box. Would it not put it off center and create a potential for leak?