Too much timing chain slack?
03-14-2006, 12:11 AM
#1
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Too much timing chain slack?
I just finished a freshing up/ upgrading my LT1. I'm using the stock timing chain since it only has 30,000 on it and shows no obvious signs of wear.
My question is as follows: When I rotate the motor by hand, at four distinct points in the rotation (N.E., S.E., S.W., AND N.W.) the cam will snap forward, taking up the timing chain slack on the back end.
My valve spring pressure is 125# on the seat and 320# open; Comp Cams Xtreme lobe pattern with lift at 556 I/ 520E. I'm using the Comp Cams 1.6 Pro Mag rr's.
My machinist said that this cam lunge is normal on higher lift/ stiffer spring roller cam motors and I shouldn't worry. Also, the lifters are slightly bled down since they have been out of commission for over a year. Anybody else experience this?
Cheers,
JD
My question is as follows: When I rotate the motor by hand, at four distinct points in the rotation (N.E., S.E., S.W., AND N.W.) the cam will snap forward, taking up the timing chain slack on the back end.
My valve spring pressure is 125# on the seat and 320# open; Comp Cams Xtreme lobe pattern with lift at 556 I/ 520E. I'm using the Comp Cams 1.6 Pro Mag rr's.
My machinist said that this cam lunge is normal on higher lift/ stiffer spring roller cam motors and I shouldn't worry. Also, the lifters are slightly bled down since they have been out of commission for over a year. Anybody else experience this?
Cheers,
JD
03-14-2006, 01:22 AM
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Re: Too much timing chain slack?
Sounds normal when the cam lobe goes on the down side. An LT1 has a little more slack than a SBC.If ya are running an electric WP ya can get the Clowes "oversize" crank gear which is the same size as a standard SBC and take up some slack. NO ya can't run one for a SBC,ya have to get the one for the LT1. This is only if ya are running an ELECTRIC wp.
03-14-2006, 12:54 PM
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Re: Too much timing chain slack?
Does this extra slack adversely affect timing on the bottom or top end? Or is this not an issue since there is constant tension on the chain when operational (assumed)?
03-14-2006, 01:37 PM
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Re: Too much timing chain slack?
Originally Posted by 1racerdude
If ya are running an electric WP ya can get the Clowes "oversize" crank gear which is the same size as a standard SBC and take up some slack. NO ya can't run one for a SBC,ya have to get the one for the LT1. This is only if ya are running an ELECTRIC wp.
03-14-2006, 01:58 PM
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Re: Too much timing chain slack?
Originally Posted by Mikey97Z
Why not run it with the mechanical pump? Seems to be working for me.
Wait and see if it will last.
03-14-2006, 02:00 PM
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Re: Too much timing chain slack?
Originally Posted by SiCk PuPpY
Does this extra slack adversely affect timing on the bottom or top end? Or is this not an issue since there is constant tension on the chain when operational (assumed)?
It does effect it.
Ya can see how much with a degree wheel.
03-14-2006, 10:10 PM
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Re: Too much timing chain slack?
Originally Posted by 1racerdude
It does effect it.
Ya can see how much with a degree wheel.
Ya can see how much with a degree wheel.
I degreed the cam and everything came right on spec. But, when I degreed it, instead of going forward to .050, then turning the motor in the opposite direction to find the halfway point, I simply continued to rotate it in the same direction until it came to .050 after and did my calulations that way. I useda digital dial indicator and verified all the numbers; everything was *****-on with the cam card.
03-14-2006, 10:28 PM
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Re: Too much timing chain slack?
Originally Posted by SiCk PuPpY
I degreed the cam and everything came right on spec. But, when I degreed it, instead of going forward to .050, then turning the motor in the opposite direction to find the halfway point, I simply continued to rotate it in the same direction until it came to .050 after and did my calulations that way. I useda digital dial indicator and verified all the numbers; everything was *****-on with the cam card.
If ya had done it the backup way it would have shown the effect the slack has.
Ya probably don't have too much as they are looser than normal when new. The way I check one is twist and how close the ends come together when squeezed together,this shows the chain pin wear.but that's just me. A new SBC chain will not touch in the middle when pulled together.
03-16-2006, 09:42 AM
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Re: Too much timing chain slack?
Originally Posted by 1racerdude
GM put the slack there to take some of load off of the front cam bearing which has enough driving the pump. Why ya think all the cam bearing trouble?
EDit: BTW, because of potential chain slack is precisely the reason I do not use the piston stop method for TDC when degreeeing cams. The engine doesn't run backwards, so why establish TDC that way?
Last edited by A/G; 03-16-2006 at 09:49 AM.
03-16-2006, 10:27 AM
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Re: Too much timing chain slack?
Originally Posted by A/G
Wait a minute! Let me get this right. You are stating ALL the guys that had bearing failure after cam swaps also installed the O.S. crank gear, or in some shape or form used a chain that was set tighter than typical/OEM LTx? I personally, am not as positive as to why the bearing failures, but really question the tighter chain scenario. This reasoning was influenced by what Cloyes had to say, not from forum grapevines.
EDit: BTW, because of potential chain slack is precisely the reason I do not use the piston stop method for TDC when degreeeing cams. The engine doesn't run backwards, so why establish TDC that way?
EDit: BTW, because of potential chain slack is precisely the reason I do not use the piston stop method for TDC when degreeeing cams. The engine doesn't run backwards, so why establish TDC that way?
The damn front cam bearing wears out on it's own. If ya tighten the chain it says "see ya".
I have talked to an engineer at Cloye's not a salesman,about the ends and out's of this situation and you can question all ya want.
Ya seem to know more than the people who wrote the book on cam degreeing.
03-16-2006, 12:13 PM
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Re: Too much timing chain slack?
Originally Posted by A/G
EDit: BTW, because of potential chain slack is precisely the reason I do not use the piston stop method for TDC when degreeeing cams. The engine doesn't run backwards, so why establish TDC that way?
That is also why I chose to do a heads off degree procedure using a digital depth gauge and rotate in the direction of operation.
03-16-2006, 12:17 PM
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Re: Too much timing chain slack?
Originally Posted by 1racerdude
Ya seem to know more than the people who wrote the book on cam degreeing.
Anyway, could say I got in near the ground floor regarding degreeing. When I first started, the piston stop method was considered an acceptable alternate or second choice, or for the 'backyard' mechanic without access to an appropriate indicator. More? No, but there was no question as to which method was preferred by pros willing to eliminate as many variables as possible. For the guys here that choose the piston stop method, no need for concern, as long as the chain is respectable you'll get pretty close.
Edit: Almost forgot... apparently, the story one gets depends on the Cloyes engineer you talk to. Either that or he was impersonating one.
Last edited by A/G; 03-16-2006 at 12:38 PM.
03-16-2006, 12:39 PM
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Re: Too much timing chain slack?
Originally Posted by A/G
Aren't you kinda old to have such a negative challenging attitude? Me, too old and passive (and maybe too smart) to pick a fight here.
Anyway, could say I got in on the ground floor regarding degreeing. When I first started, the piston stop method was considered an acceptable alternate or second choice, or for the 'backyard' mechanic without access to an appropriate indicator. More? No, but there was no question as to which method was preferred by pros willing to eliminate as many variables as possible. For the rest of the guys, no need for concern, as long as the chain is respectable you'll get pretty close.
Edit: Almost forgot... apparently, the story one gets, depends on the Cloyes engineer you talk to. Either that, or he was impersonating one.
Anyway, could say I got in on the ground floor regarding degreeing. When I first started, the piston stop method was considered an acceptable alternate or second choice, or for the 'backyard' mechanic without access to an appropriate indicator. More? No, but there was no question as to which method was preferred by pros willing to eliminate as many variables as possible. For the rest of the guys, no need for concern, as long as the chain is respectable you'll get pretty close.
Edit: Almost forgot... apparently, the story one gets, depends on the Cloyes engineer you talk to. Either that, or he was impersonating one.
NA, not to old for anything,including correcting info.Old is a feeling, and I have no nevgative anything.It's all good
Well ya know when gears drive against each other the try to seperate. This leaves the cam gear pushing DOWN. When the chain pulls it also pulls down and around.Most of the wear on the front brg is between 4 and 7 O'clock. This is the reason GM spected the smaller crank gear to take off some of the load of the chain on the slack side. Sooooo if ya run the factory WP AND a tight chain it increases the wear big time.
Ya can do what ya want about degreeing,USE the trick of the week,don't care, but the accepted method is IN THE BOOK, especially for someone just learning.
If ya don't watch someone gonna cut your "shade tree" down then what ya gonna do.
OBTW I will bet I have more ,and more up to date"tools" than the majority including sonic thickness tester(bore) and and electronic surface tester(bore and deck surface)
Did the engineer at Cloyes happen to tell ya why GM spected a smaller crank sprocket?
Last edited by 1racerdude; 03-16-2006 at 01:22 PM.
03-16-2006, 02:04 PM
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Re: Too much timing chain slack?
To further explain the 2 methods:
When using the positive stop(doesn't make any difference if the stop is screwed in 1/2")when the piston stops the rod is at an unknown angle,then ya go the reverse way and the same thing happens. When ya half the difference ya get TRUE TDC(rod straight and crank on "0").
When using a dial indicator the piston stops going up(no change in indicator reading). It takes a few more degrees of crank rotation to make the piston start down(change in indicator reading).
Now it is a real guess to try to get the rod straight(with no indicator movement)and the crank on True TDC.That is why I don't use an indicator.
When using the positive stop(doesn't make any difference if the stop is screwed in 1/2")when the piston stops the rod is at an unknown angle,then ya go the reverse way and the same thing happens. When ya half the difference ya get TRUE TDC(rod straight and crank on "0").
When using a dial indicator the piston stops going up(no change in indicator reading). It takes a few more degrees of crank rotation to make the piston start down(change in indicator reading).
Now it is a real guess to try to get the rod straight(with no indicator movement)and the crank on True TDC.That is why I don't use an indicator.
03-16-2006, 02:14 PM
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Re: Too much timing chain slack?
Originally Posted by 1racerdude
When using a dial indicator the piston stops going up(no change in indicator reading). It takes a few more degrees of crank rotation to make the piston start down(change in indicator reading).
Now it is a real guess to try to get the rod straight(with no indicator movement)and the crank on True TDC.That is why I don't use an indicator.
Now it is a real guess to try to get the rod straight(with no indicator movement)and the crank on True TDC.That is why I don't use an indicator.
Excuse me for laughing racer, but are you for real? That is NOT how one uses the indicator to find TDC. Anyone else reading this thread know what racer is doing wrong reading the indicator that way?