TheSamba.com :: View topic - Copper head gaskets or cylinder spacer question.

Fri Sep 24, 2004 6:51 pm

Ok I am assembling a 36hp Okrasa with 83mm Porsche 912 Mahle P&C's. I calculcated that a .060 deck height would give me 8.4 CR. Now I did mess up when I ordered the spacers and forgot to add the .060 to the size, duh.
So basically I have the Pistons reaching the top of the cylinder maybe a few thou. under.

To get my deck height do I
(A)
Get new cylinder spacers cut with the .060 added in or
(B)
Get custom copper head gaskets cut of .060?

These are custom sized P&C's so they would have no head gaskets at all unless I get some made. Given that I was leaning towards B but have never used custom head gaskets.

-Craig

Fri Sep 24, 2004 7:10 pm

I would toward the copper. I have always had good luck with them sealing the cylinder properly (knock on wood), even though I have heard a couple of people say that they didn't care for them.
I would just make double sure they fit snugly in the head bores and clear the pistons properly if you are using them to compensate for a too high deck height.

Thu Sep 30, 2004 11:39 pm

If you flycut the head beautifully like it is supposed to be done, you will not need a gasket.

But what does a drill press contraption do to the heads other than rough it some more? And you really expect that to seal?

It takes a $1200 boring/flycutting head to do this operation. At least that is what I use to flycut my case and heads.

You can use shims. It is all up to you what you are willing to put up with on sloppy machining.

Peace.

Fri Oct 01, 2004 4:57 am

nsracing wrote: If you flycut the head beautifully like it is supposed to be done, you will not need a gasket.

But what does a drill press contraption do to the heads other than rough it some more? And you really expect that to seal?

It takes a $1200 boring/flycutting head to do this operation. At least that is what I use to flycut my case and heads.

You can use shims. It is all up to you what you are willing to put up with on sloppy machining.

Peace.

Just what does flycutting and a drill press have to do with adjusting his deck height?
He asked which would be best, shims or a head gasket.

CoolairX2, I think whatever is most convenient for you will work fine.

Fri Oct 01, 2004 6:49 am

Depending on your piston configuration, i think i would lean toward new shims under the cylinders.
if you try the copper head gaskets, and they are just slightly off or tend to squeeze in, you may need to trim the top of the piston down to make sure if you extend past the intended deck, you dont hit a wall of copper with the edge of the piston.
probably wouldnt be a real problem, but it would always be in the back of my mind.

Fri Oct 01, 2004 7:45 am

I have used four different sets of copper gaskets so far and they have all been slightly narrower than the jugs themselves - after being compressed by torquing the head studs. Not that it doesn't happen, but it doesn't seem likely to interfere with the piston travel if they are properly cut. Hence my original statement of "make double sure they fit snugly in the head bores and clear the pistons properly". My experience has always been with the pre-made gaskets for 94mm jugs - I can't lie, I can only recommend them. Even great cut heads can leak slightly because of imperfections in the jug surface and or head surface, but not with copper gaskets. The only time I have heard people having problems is when they have been re-used.

Fri Oct 01, 2004 8:11 am

I guess if i was going to get that close when using copper gaskets, i would probably bolt the case together, then bolt the cylinders and heads on one side and torque them down and then go thought the other side and see how the gaskets squish. although this wouldnt compensate for the hot squish that will happen when the head expands. it would probably need to be a judgement call.

Fri Oct 01, 2004 11:25 am

Another option would be to flycut a step in the head .060 deep. I think it would actually have to be a little deeper to maintain the correct cc's. You would basically add whatever the total cc's are from the deck and the combustion chamber and have the step made deep enough to cover both, since running zero deck yields zero cc's.

Steve

Fri Oct 01, 2004 4:44 pm

They recommended that I angle cut the edge of the piston. My deck height that I have would not allow the piston to hit anyway but this is a little added insurance. They also mentioned that it would reduce the chance of carbon building up on the piston edge and interfering with the head gasket.

The shop selling the gaskets is a VW race shop. They stated that they run zero deck height on all their race engines and adjust the CR with copper gaskets.

These Okrasa heads have been opened up to there max to run the 83mm Porsche pistons. The edge of the stud holes show in the head's piston bore and I wanted to make damn sure it is sealed.

I don't know where that comment came saying I was doing this myself with a drill. It is being done by a damn good shop that have been doing VW's for decades.

-Craig

Fri Oct 01, 2004 6:14 pm

nsracing has been around the forums for a while, it's just his way of saying that he feels that he does the job right. I think that he thinks that all other machinists are hacks and that they use drill presses as milling machines to fly cut the head... hence the $1200 tool comment. I'm sure it wasn't directed at you.

Sun Oct 03, 2004 1:24 pm

I like Mike's assesment on the shim under the cylinders instead of the top. I think this is the most effecient way to set deck height.

Now if you insist on putting the shim up top to set deck, the shims better be accurate enough to sit in the heads and not wobble. The heads would have to be bored so the shim cannot move around by 1/1,000 inch. If these shims are custom made, they can machine them to match the wall thickness of the cylinder. Since the shims cannot move by 0.001 inch, it is very unlikely that you will hit the piston edge to the gasket. You can make the gasket from Bronze or softer copper if you want and machine them one by one to size.

If the shims are stamped, then yes, I can see where the need to hack the pistons off the corners. But geez man, why would you do that to the beautiful pistons? So you will do all the necessary machining and re-balancing of the pistons to accomodate a $1 copper head gasket?

You are better off as Mike said with the shims on the bottom. You can have these shims made to size for whatever deck you desire. Have them machine the shims to about 0.0005- 0.001 clearance around and just seal the bottom part. You do not even need to seal the top the shim if machined this way. It is a simple lathe operation.

If you do not like the machined finish of the top of the cylinders, have them true it with a toolpost grinder on a lathe. The finish will be super smooth like the finish on the valves after a regrind. This all depends on the stone grade used and coolant system.

These processes have been out there for decades through several world wars. The machine shops should know these.

regards.