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Join Date: Mar 2009
Posts: 1,780
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Need base gasket advice
Last fall I did a top end rebuild on a 79 engine that turned out badly. The goal was to install 964 cams and higher compression 81-83 cylinders/pistons. Not a real fire breather-just trying to overcome some of the inherent CIS deficiencies.
I had previously put this same engine top end together a few years back with .25 base gaskets and all 79 parts, but I had sent out the heads to a machinist and they were shaved .10 to obtain a flat mating surface. I did the required piston to head clearance checkat that time with no issues. So, on the second top end job I skipped the clearance check, and sure enough, the engine wouldn't rotate past top dead center. So I took it apart and put in some 9.5 JE pistons that I had been saving, that had deep pockets-still no joy. So then I swapped out the 964 cams for stock and finally got the engine to rotate. But none of the project goals were achieved. I will have some time this fall to restart this project-so I was thinking of getting several sets of base gaskets of various thicknesses and using some combination of base gaskets to get the original project done. So-how high can you stack base gaskets? How many can you use? I was going to get 2 sets each of 1.0 and .5 mm, and I have a bunch 0f .25 in hand. And if I do the squished solder test-what is a good clearance goal? Lastly-am I going about this right or wrong? Thanks in advance for your answers. |
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Join Date: Jun 2009
Posts: 1,241
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I can't advise on your component package as to their compatibility, but I have used 1.0mm shims, the engine doesn't know but it does know clearances. I have heard that you can go .030'' piston to head, but I don't go more than .040'' and checked in numerous places on the piston. Depending on use, valve to head is .060''-.080''. On an over rev, E will hit first. I am not an ''engine builder'' though have built a few. These days just my own. Good hunting. Bob
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Join Date: Oct 2008
Location: Nash County, NC.
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What was your Carrera cam timing goal, 1.25 is spec.
Is the .1 shaved in inches or metric? Cam timing is the problem with the shorter heads as the factory parts all work together in my experiences. Bruce |
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Would like to know answer too
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Join Date: Jul 2013
Location: Brisbane, Australia.
Posts: 2,610
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Interesting.
What's your deck height? Did you install your pistons upside down? Pics might help diagnose...
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Join Date: Mar 2009
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Thanks for the discussion. Have not yet started teardown, just ordering gaskets and supplies at this point. I will keep this this thread updated
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When I got my cases and heads back from machine work, it really forced me to completely recalculate everything. It took me hours measuring, test fitting, remeasuring, test fitting, repeating, testing, etc to get it right. It even reduced my combustion chamber volume a lower value than I thought as well. So the engine will eventually tell you what it wants.
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Join Date: Dec 2014
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964 cams @ 1.25
Intake - .470 lift and 240 duration Exhaust - .430 lift and 230 duration Sorry, don't have the lobe center in degrees. For comparison's sake, here are SC cam specs: SC cams @ (1.00-1.40) Intake - .455 lift and 229 duration Exhaust - .402 lift and 220 duration Lobe Centers - 113 degrees
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