Thread: Piston at TDC

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The 331 Hemi that were rebuilding is a work in progress and I have a question. How important is it that the piston @TDC is at .000? Can I go .010 or .015? I need a final deck clearance equal to the head gasket thickness of .040 because if I go larger than .060, the advantage of quench disappers.

Denny I'm not going to spend another dime. We have all the parts and the head gasket is .040. This was suspose to be a 4 person build but two have backed out because of money issues and that leaves me and a buddy who neither have done a complet engine rebuild fron the bottom up.

Denny Let me ask you another question. First of all I picked a wrong motor to do a complet engine rebuild. Second of all, the 4 of us got together on this project to do just that and then they backed out leaving just Bill and myself. I'm really beginng to hate myself for buying this engine. Always wanted a Hemi and the price was real good(that should have set off the red flags). We got the engine torn down and found it has a spun bearing and the number 3 cylinder is in 3 pieces. The cylinder wall on # 3 is going to have to be taken down more that what I was planning on of .030. Beside that all looks great!!!!!!!!!!!!!!!!. Now I just have to decide if I want to put more money into the block. All the parts that were needed for this build up came with the motor except the cam. In your opion, is it worth it or should I sell it as is?

Actually the real expert to talk to would be Bob Walker over at Hot Hemi Heads.

Been one of those long days here so I may not being understanding your question properly, but I'm going to assume that you are talking about .000 as a 0 deck height (i.e. the top of the piston being level with the block deck at TDC). If this is the case you might want to read


http://www.rbracing-rsr.com/squishcalc1.html

Which will basically tell you in paragraph 4 that quench does not really apply to Hemi heads.

My 331 has a negative deck height and my 354 is running a positive deck height. The driving factor as it applys in this case isn't what the deck height is ( + or - ) but rather effectively what that deckheight does in reguard to the COMPRESSION RATIO. Your 2 main concerns when building this engine should be final compression ratio and secondly valve to piston clearance with the cam your going to be running.

I know you posed the question to Denny in regards to if it's worth rebuilding or not, but I'll take a shot at the answer too. What you do is up to you, but I personally, if I had a set of .030 over pistion and 7 cylinders that cleaned up at that and one that didn't I'd have a sleeve put in the bad cylinder (usually around $100-$150).

It's your decision on what you spend, but as I brought up more than a few times there is no such thing as building one of these on a budget. As expensive as they are to build you have to much tied up in them by the time you get them running to cut corners and have them blow up because you "saved" a few buck here and there by being a penny pincher.

Thanks Denny. Thanks Mike. Didn't know quench didn't apply to Hemi heads. I do now. Interesting article. Guess I'll sit down and rethink what I want to do. Little mad at myself right now.

one sleeve or one bigger piston it will not know it has 7 .030 and 1 .040 if it will clean up at .040 i put sleeves in all the time and would be happy putting them in all day. some guys think sleeve are bad. but if done right they work geat .you can. i have saved blocks that cost more than +3000. dollars. on you hemi they are getting hard to find? more than the big block chevys and have put more than two sleeves in one block and a new crank rods pistons.and get them line bore all the time if you can get better then sell it. but do you think you can get a better engine for the money you paid for the one you have

Bart, to answer your question:
When dealing with a quench head/piston arrangement like a small block Chevy, yes, you can pop the piston crown out of the bore at TDC and use a little thicker gasket to achieve your 0.035" to 0.040" squish. You can also achieve the correct squish with the piston slightly down in the bore by using a thinner head gasket. For instance, I saw a 0.016" gasket sold by Chevy. With that gasket and the piston 0.024" down in the hole, you'd have your 0.040" squish. Or, like I say, if the piston was popped out by 0.020", you could use a 0.060" gasket to achieve your 0.040" squish. Hope this helps.

Thanks Bob,Mike Denny, Richard,Pat for your input. Really enjoying myself on this project. Going to sleeve the cylinder. Done it before on a flathead so there shouldn't be a problem. I also have a top mechanic here in my city thats whats to buy it for what I put into it. He a machinest so he's going to let me do the bore job on it. I'll just wait and see how everything goes.