69 Camaro COPO 3963512 Block align bore issues - Team Camaro Tech
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post #1 of 9 (permalink) Old Jan 2nd, 17, 07:52 PM Thread Starter
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d
 
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Cool 69 Camaro COPO 3963512 Block align bore issues

I am trying to help a friend of mine that is not as computer efficient as I. He is building a 69 COPO and the block is at the builder's shop. The block only needed honed at the machine shop. When they went to install the timing chain, it was too loose. He ordered a Cloyes .010 under and tried it as well and it was still too loose. The engine rebuilder believes the center to center is .020 or .025 too short.

What options do we have as to not destroy this original COPO block? We were told Cloyes use to carry a .015 under, but we cannot find one. Does anyone know of any other options? Would a gear drive work if someone machined the bottom gear .020? I believe a belt drive would work, but he is trying to keep this as original as possible. Does anyone build custom timing chains?

Thanks for all the help!

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post #2 of 9 (permalink) Old Jan 3rd, 17, 04:29 AM
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What's your budget? It may be possible for a machine shop and a 3D CAD designer to custom design a top gear that uses an existing chain but increases the diameter very slightly to take up the slack. Then machine it from a billet and heat treat it. For an original COPO block not out of the question. Maybe 2 thousand dollars.
I was told by my engine guy that this is actually how Cloyes does it on their sets. The chains pitch doesn't change, just the sprockets.
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post #3 of 9 (permalink) Old Jan 3rd, 17, 04:53 AM
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Re: 69 Camaro COPO 3963512 Block align bore issues

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Originally Posted by dt69usa View Post
The block only needed honed at the machine shop. When they went to install the timing chain, it was too loose. He ordered a Cloyes .010 under and tried it as well and it was still too loose. The engine rebuilder believes the center to center is .020 or .025 too short.


Thanks for all the help!

The first rule is to determine what exactly is the root cause and your "the engine rebuilder believes" leaves concern in that area. I would expect a knowledgeable engine builder to precisely determine that root cause and offer what needs to be done. A question would be if this block was a rotating working engine prior what was used then? Does your friend or engine builder have parts from a tear down?
My concern again would be first step, find root cause and if engine builder cannot your friend may want to stop action and check with some other shops. It is also concerning obtaining a .010" under timing chain without apparently knowing if it was going to work.
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post #4 of 9 (permalink) Old Jan 3rd, 17, 05:13 AM
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Re: 69 Camaro COPO 3963512 Block align bore issues

It would be good to know what all is going on with the block. Its not that tough to measure. I dont know if there is a reference source for existing engine centerline dimensions and chain pitch combinations but a lot of research is needed. You might want to look into a custom Jackson gear drive if you can take the racket and the angles work.

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post #5 of 9 (permalink) Old Jan 3rd, 17, 06:40 AM
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Re: 69 Camaro COPO 3963512 Block align bore issues

#1. Need to determine the root cause as stated above.

If the block only needed honing who align bored it?
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post #6 of 9 (permalink) Old Jan 3rd, 17, 07:42 AM
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Re: 69 Camaro COPO 3963512 Block align bore issues

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Originally Posted by Vega$69 View Post
#1. Need to determine the root cause as stated above.

If the block only needed honing who align bored it?
As the others mentioned, need to find out just what is wrong here. I would call Cloyes if you need a solution as they list other variations. I don't see a .015 shorter timing set but there are several verisons of blocks, that may get you out of a bind. http://www.cloyes.com/Images/CloyesHP_Catalog.pdf

This may be a question for Larger Dave.

Don
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post #7 of 9 (permalink) Old Jan 3rd, 17, 08:20 AM
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Re: 69 Camaro COPO 3963512 Block align bore issues

A post like this one just begs for questions. Assuming the stated premise is correct and the only thing wrong is the cam location, which is rather odd,...... it is an interesting gearing problem. .025 is likely just far enough off to not have an off the shelf solution. I hope Larger Dave chimes in. I would be curious if something like this sets up harmonics on the cam and snaps them.

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post #8 of 9 (permalink) Old Jan 3rd, 17, 09:47 AM
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Re: 69 Camaro COPO 3963512 Block align bore issues

20 thousandths of an inch on the length of a timing chain seems immaterial. Any cam timing issue could be degreed in to resolve. And I can't picture in my mind how much chain slack it would cause but it is such a short length difference that it seems like it would be easily less than the chain might stretch in its normal still usable life. Am I wrong about this and is it a bigger deal than I am picturing in my mind or are we talking about a different unit than 10-20 thousandths?
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post #9 of 9 (permalink) Old Jan 4th, 17, 06:44 AM
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Re: 69 Camaro COPO 3963512 Block align bore issues

Long ago when we raced each weekend we had issues like this after a block was cut. It was too late to find fault , We would try to move the crank center line away from the cam hole by using different size bearings, thus tightening the timing chain. .

In one case ,we used an oversize bearing on the cam side and a standard or undersize on the opposite. It worked but after the race, our motors were tore down for inspection. When working with ,.010-.020 clearances, this sometimes worked.
This was not the norm, but we made it thru the race day.

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