Timing Chain Slack
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 3,461
Likes: 18
From: cooper city florida
Timing Chain Slack
I was manually turning my engine over on my L79 with a breaker bar at the crank pulley, and there seemed to be quite a bit of slack in the timing chain. Is there a measurement of slack when its time to replace the chain. I broke a timing chain one night on my 289 hipo. Needless to say, it was a very ugly, not to mention, expensive scene. My Fairlane was 6 years old when it happened. My vette is 45 years old.
Le Mans Master
Joined: Sep 2008
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From: Lake Minnetonka, Mn
2018 C1 of Year Finalist
If it is wearing through the cover, it is time to change it. Has this been replaced before? Does it have a replacement nylon gear? If you think there is too much slack, it probably has too much slack......
Race Director
Joined: Feb 2004
Posts: 14,984
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From: CT
I Agree, there should be hardly any slack at all in the chain.
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 3,461
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From: cooper city florida
Thanks for the reply guys. Dan I have owned the car for 3 years and I really don't know much about the history. It's not hitting the cover, but it does seem to have an excess amount of slack. I'm going to see if I can get some sort of measurement tomorrow.
Safety Car
Joined: Feb 2003
Posts: 4,068
Likes: 27
From: St. Joseph Mo
Since you have it that far apart and as easy as it will be to change it. Why not?
Cost isn't much either when compared to bent valves and such.
I had a new chain break on a 325 hp 383 Mopar after it ran 30 minutes. Bent two intake and two exhaust valves not to mention the need for another set of head and intake gaskets.
Cost isn't much either when compared to bent valves and such.
I had a new chain break on a 325 hp 383 Mopar after it ran 30 minutes. Bent two intake and two exhaust valves not to mention the need for another set of head and intake gaskets.
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 3,461
Likes: 18
From: cooper city florida
Hope this might be of some help:
How To Measure Chevrolet Timing Chain Wear==>LINK
How To Measure Chevrolet Timing Chain Wear==>LINK
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Thread Starter
Melting Slicks
Joined: May 2007
Posts: 3,461
Likes: 18
From: cooper city florida
Since you have it that far apart and as easy as it will be to change it. Why not?
Cost isn't much either when compared to bent valves and such.
I had a new chain break on a 325 hp 383 Mopar after it ran 30 minutes. Bent two intake and two exhaust valves not to mention the need for another set of head and intake gaskets.
Cost isn't much either when compared to bent valves and such.
I had a new chain break on a 325 hp 383 Mopar after it ran 30 minutes. Bent two intake and two exhaust valves not to mention the need for another set of head and intake gaskets.
Tech Contributor
Joined: May 2005
Posts: 15,576
Likes: 118
From: Conroe Texas
I actually don't have it apart, but I think I soon will. I was just moving the balancer around to TDC manually, with a breaker bar and a 5/8 socket on the bolt in the middle of the damper, and noticed how much I would rotate the balancer, before I would feel the pistons move. It certainly didn't feel right.
Last edited by 62Jeff; Jan 27, 2010 at 12:25 AM.
Thread Starter
Melting Slicks
Joined: May 2007
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From: cooper city florida
Hmmmm. Good point Jeff. I see what you mean. What the heck is that slack I'm feeling? Also when I rev my motor up to about 3500 and hold it steady, with a timing light on it, the timing mark fluxuates around on the balancer and is not steady. I thought that would also indicate a bad timing chain or maybe to much end play on the distributor shaft.
Race Director
Joined: Jan 2003
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From: Central Arkansas
How are you "feeling the piston move"? When a piston is at TDC or BDC it's not going to have much vertical movement component in relation to crankshaft rotation. It may seem like there is slack when there is really just very, very slight up or down movement. From your description of timing the motor, it does sound possible your missing the balancer key, the ring is slipping, or something is moving - but I wouldn't think it would be dancing around greatly - it would just be off the timing marks.
Team Owner
Joined: Mar 2003
Posts: 26,118
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From: Greenville, Indiana
Hmmmm. Good point Jeff. I see what you mean. What the heck is that slack I'm feeling? Also when I rev my motor up to about 3500 and hold it steady, with a timing light on it, the timing mark fluxuates around on the balancer and is not steady. I thought that would also indicate a bad timing chain or maybe to much end play on the distributor shaft.
If you can feel 10* as read on the balancer just by moving the crank, it's probably not wasted money to change the sprickets and chain. I wouldn't use the method described in the link to watch the distributor rotor. False test as the distributor rotor movement in relation to crank movement is also dependent on the amount of distributor shaft end play. You could have a new, tight chain, spec on the distributor shaft and still have crank rotation without distributor rotation.
Contrary to what you commonly read here, I don't believe a distributor shaft that has end play will affect timing or cause fluctuations. When the engine is running, there is a hard enough drag from the oil pump to cause the distributor shaft gear to be forced hard against the bottom of the distributor housing and it will stay there as long as the oil pump is pumping oil. It doesn't just rattle around and jump up and down.
Check the top distributor bushing/shaft for wear. Loose breaker plate, faulty vacuum advance and condition of the points for the timing fluctuations.
Last edited by MikeM; Jan 27, 2010 at 07:37 AM.
Team Owner
Joined: Mar 2004
Posts: 24,202
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Simple! Pull one of the valve covers, and rotate crank back and forth some. This will reveal chain slack!
If there are doubts, and the engine has over 60k, it may be suspect. Of course I have seen good running engines, with chains that were shot!
Install a good double roller timing chain MADE IN USA
If there are doubts, and the engine has over 60k, it may be suspect. Of course I have seen good running engines, with chains that were shot!
Install a good double roller timing chain MADE IN USA
Pro
Joined: Jan 2007
Posts: 524
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From: Auckland New Zealand
This was what mine looked like when I pulled apart a supposedly reconditioned engine. Use a good quality double roller chain & sprockets, not the horrible silent chain as seen in above shot.
I also put a button on front of cam to stop any possiblity of for-aft cam movement.
Le Mans Master
Joined: Sep 2008
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From: Lake Minnetonka, Mn
2018 C1 of Year Finalist
Good luck. BTW, how many miles on the engine?
Race Director
Joined: Feb 2004
Posts: 14,984
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From: CT
On an Olds Cutless I once had the chain slipped a few teeth due to too much slack and it wouldn't start. It drove me crazy for a few days unitl I put a breaker bar on the balancer and it moved back and forth about 20 degrees each way until resistence was felt. It was only then that I realized the chain needed to be replaced.
On the Corvette I use a Cloyes double roller. You don't need a cam button with a flat or hydraulic cam as the slight pitch on the lobes to keep the lifters turning puts the pressure to the read of the engine not the front. With a roller cam the button is needed.
On the Corvette I use a Cloyes double roller. You don't need a cam button with a flat or hydraulic cam as the slight pitch on the lobes to keep the lifters turning puts the pressure to the read of the engine not the front. With a roller cam the button is needed.
Thread Starter
Melting Slicks
Joined: May 2007
Posts: 3,461
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From: cooper city florida
A visual is not that difficult if you want to pull the cover and look. I would want to do that as opposed to anything else. As someone said, if that chain jumps time, you will have serious issues to deal with. The replacement nylon gear that GM used to sell (OEM on later models) will strip, too. Very expensive proposition, in some cases, if that fails.
Good luck. BTW, how many miles on the engine?
Good luck. BTW, how many miles on the engine?