Deck Height

73fback · Post by **73fback** » Mon Apr 28, 2003 7:37 pm

I cc'd my heads today for the second time to insure the accuracy. Both heads have 1 @ 48 and 1 @ 49 cc's. My question is, if I use deck height spacers to set my CR, it would require a different spacer on each cylinder of the same head. Won't this cause sealing problems?

I'm also familiar with the technique of shaving some off to gain the extra cc, but I'm a little nervous about doing this.

Also, is this one cc enough to even worry about?

Post by **sparkmaster1** » Mon Apr 28, 2003 9:09 pm

I would flycut .010 off the one head and the cc's should be very close. Ten thousandth's of a flycut just about equals 1 cc . What kind of CR are you looking to run? Tim

rlarkin · Post by **rlarkin** » Mon Apr 28, 2003 9:56 pm

I think what he is saying is the difference is on the same side, not opposit sides.
If that were the case, I don't think you can shim only one jug on a side.
Yiu have to shim both.

73fback · Post by **73fback** » Tue Apr 29, 2003 6:16 am

The differences are on the same head. It will be close to stock CR, it is a stock rebuild.

Post by **sparkmaster1** » Tue Apr 29, 2003 7:31 am

It looks like you need to see if they are flycut to the same depth on each hole then. Are these heads that you have used, or know their history? If they are cut to the same depth you could remove a bit of material in the combustion chamber to try and get them closer. Tim

Post by **Marc** » Tue Apr 29, 2003 7:33 am

Ordinarily you shouldn't shim differently on the same side unless you're correcting for uneven barrel length or case decking - with both barrels clamped down lay a straightedge across the top and make sure it contacts all 4 points (well, within .001" or so anyway).
At ~7.5:1, 1cc is going to make approximately 0.1 difference in the compression ratio which is at the limit of acceptability for a stocker IMO. Ideally you should open up the smaller chamber a little to get them closer but I wouldn't lose any sleep over it if you don't.
Note that if you have a reground intake valve in the larger chamber, replacing it with a new one would help (~¼cc for every .010" thicker the valve is).

Lymkey930 · Post by **Lymkey930** » Tue Apr 29, 2003 11:50 am

Just grind a little out of the smaller combustion chamber to match the larger one. That will allow you to have matching combustion chamber volume and then use same size shims.

jasonb · Post by **jasonb** » Tue Apr 29, 2003 1:58 pm

I think that you should run it with out worrying about it. 1cc is not bad really.

73fback · Post by **73fback** » Tue Apr 29, 2003 2:13 pm

To be honest, part of why I'm worried about it, besides the fact I want it to run as good as possible, is bragging rights

I have some buddies who are looking to buy engines, wether through mail order or locally. I have been spreading the advice of many, and that is to do it yourself, you are your best mechanic. Well, I believe this statement, and this is my first full rebuild.

I just want to prove a point to a handful of buddies, and have as close to perfect specs as I can. Even a bonehead like myself can do this.

BenI · Post by **BenI** » Tue Apr 29, 2003 2:13 pm

I once replaced a jug and forgot to replace the shim-immediatly I heard a whistling sound on startup. I tried to convince myself that it was a ring seating sound but had to face reality when the sound got worse as I drove the car more. Finally I pulled the head and found that the missing shim had caused the head to sit crooked causing really nice head leaks.

Chris V · Post by **Chris V** » Tue Apr 29, 2003 2:19 pm

BenI wrote:Finally I pulled the head and found that the missing shim had caused the head to sit crooked causing really nice head leaks.

Lucky your head didn't crack, which can happen I hear.

Post by **Marc** » Tue Apr 29, 2003 2:35 pm

BenI wrote:I once replaced a jug...had caused the head to sit crooked causing really nice head leaks.

First thing I do after torquing down a head is airload each cylinder and run around the head/cylinder parting line with a lit paper match - any flickering tells you something ain't right; it only takes a couple minutes to check and it's much nicer to find the bad news at that point rather than after it's in the car.