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Discussion Starter #1
I am aware that a timing chain has a maximum allowable deflection tolerance of 1/2 inch before a change is recommended.

I tested my deflection per the shop manual procedure, and my deflection was at 1/4 inch.

I have no performance issues to speak of. I have the timing cover/water pump off to replace the seals due to oil leaks that are starting.

I don't see any broken teeth, no gear wear, nothing that looks too fishy.

I am not sure of the mileage on this chain, that is the only wildcard.

The part cost isn't the issue, I see I can get chains of various quality anywhere from $30-$90 dollars. I honestly am not sure of the quality of what I have on mine currently, though I did see on the chain it was Made in USA- which I am hoping means better quality.

I have everything open, it isnt a terribly horrible job, but I am one to not mess with what is working fine.

Is a 1/4" deflection all that far from what the deflection would be on a new timing chain that would be newly installed on a '66 289? I think what I have right now is totally fine, I certainly can spend the $50 bucks that I was thinking of spending for a middle of the road timing chain/sprocket set on another project.

Torn wheather to replace or not- I know most will say replace, but there may be no good reason to do it, other than to think I have bought some free insurance-which with the quality of anything built now, may not be such a guarantee.

Replace or leave it alone at 1/4" deflection?
 

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I'm thinking it's still in good shape, why change? Keep in mind if the engine has been rebuilt and line bored this may change the distance between the crank and cam, moving them closer and making the chain slightly looser. For race engines they do make timing chain set specifically for this application to keep the chain tight.
 

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Discussion Starter #3
Thanks for your reply, I am going to take the path of more work and change it out, even though it probably is totally fine. I chose the Edelbrock model that CJ PP sells.

Still interested in what the deflection will be on a new one freshly installed, I guess I will create my own answer when I change it out.
 

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Just some guy
67 coupe, 69 Sportsroof, 86 hatchback
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I think you'll find the new one to be about the same. If the chain didn't have a little slack it would be impossible to install. That said, unless I put it on myself and know the chain's history I'm in the habit of just putting on a new timing set if I am working in that area. I don't know if I've ever seen 1/4" though on a used engine. It's usually more like "My God, why hasn't this poor thing jumped time?" kind of slack and tooth wear.
 

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Using the timing marks to check how many degrees of slack are present is a better method to check for wear.
Rotate the crank clockwise to bring the marks to the end of the timing scale then rotate the crank counter clockwise very slowly until all the slack is gone. Read the marks then determine how much slack is present. If there are 6 degrees or more present, replace the chain and gears. You can watch the distributor for signs of just beginning to move if it's not practical to look at the cam for movement with the timing cover in place.
 
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