chain slack effect on cam

[GN-231]

Is the spring on the stock tensioner weak? I pitched mine after my last cam change and now I was wondering if the tensioner every did anything more than just keep the loose slack of the chain in control.
I would think a camshaft, with all the valve spring loads, would have a tendency to dictate the slack side of a timing chain. For instance, if you had a timing chain that had some slack. Would the tension be biased to one side of the chain as went up the slope of the cam and backlash to the other side of the chain when you came down the backside slope of the cam? Or is one side of the chain always going to be in control of the tension?

I am just wondering since there are a lot of people running double roller chains and no one has a tensioner for doubles...therefore, I don't think all of them would fit like a glove with no slack, even with the slight varitions of timing gear sizes. If the cam moves with slack, then all the cam timing would be shot to crap!

 

[GN-231]

Anyone know anything about this? Not sure what to think, I am sure there are a lot of people running looser chains on the double rollers, I am just wondering how this affects performance. Seems like maybe the tension would always be biased to one side of the chain but I am not sure. Since the cam lobes are symmetric about the lobe center, you should always be ramping up one lobe and down another. However, at the top of the lobes, the forces would be unstable since it would be like trying to balance exactly at the top of the lobes. This event at the top of the lobes may allow a change in tension bias?

 

[Momar]

Well, I just picked up my first gn a couple days ago, and havent messed w/ the timing chain setup on one yet, but the slack on a timing chain or belt will always be on one side of the chain. A chain can only pull, not push. That means that the side that the chain travels from the cam to the crank will be the side that is tightest when running.

Are the crank and the cam the only things on the chains on these motors? I know that there are motors that dont have tensioners such as the sbc, so if it is set up right, it shouldnt be a problem. Maybe someone that has actually dealt more w/ these motors will have more of an idea though.

Ben

 

[Nick Micale]

Originally posted by GN-231
..........................................I am just wondering since there are a lot of people running double roller chains and no one has a tensioner for doubles...therefore, I don't think all of them would fit like a glove with no slack, even with the slight varitions of timing gear sizes. If the cam moves with slack, then all the cam timing would be shot to crap!

Even though I have replaced lots of timing chains and done lots of Buick engine rebuilds, I do not profess to be an expert on chains, but will voice my opinion based upon that experience.

First, it must be realized that the factory timing chain set on the turbo Buick motor is the same one used on the 160 HP economy V-6 for many years [before the turbo motors]. This is important as it was not anticipated that this chain set up would ever be subject to high HP applications.

In the last 20 years of turbo Buicks, I have seen how they wear. A low mileage car that has been run hard will be lucky to have a chain/gear last 50-60K miles. Normal driving, have removed 100-150K mile chains with almost no play.

So, if you plan to do a "performance" build, a very good chain set must be used. Loose chain or worn gear will greatly alter cam timing even with a tensioner. A loose chain can also ruin a cam sensor on a performance motor.

In building a low 11 sec. or faster Buick, only the best chain should be used. In many cases, a line bore due to steel caps install or wear, will require the use of a shorter chain to eliminate slack.

Another problem, especially in 10 sec. and faster cars is the lack of a harmonic balancer. The factory "balancer" is NOT a harmonic blancer, it is a hub for the pulley. If a cast crank is used, it has LOTS of flex which is NOT removed by the stock hub. All this flex is also transmitted to the cam which is at the other end of the chain.

I know this is a long-winded reply, but it is necessary to know and build properly for the performance level desired. Some guys will say "I have stock stuff and run 10's", or whatever. Having seen the disasterous results of under-building for the results desired, this is not too smart, nor inexpensive.

When we do a car upgrade or motor build, we want it to have potential performance a good bit more that actual use. You could call this a "safety factor". Actually cheaper in the long run.

 

[GN-231]

Thanks for the detailed reply Nick. I think chain importance is often overlooked. I would think you don't want to get your chain too loose and you would not want your chain too tight. If it were too tight, I would suspect the bearing life may be influenced.
The chain topic also shows the importance to always degree your camshaft. I never understood why degreeing step was so important, but you need to make sure your valve timing is optimal for a performance engine.
FYI... I have heard over and over that ROLLERMASTER is the only way to go.
I think the best fit chain would line up without much very much, or no slack, so you couldn't move the chain by pressing with your finger? Any specs for how much finger deflection of the chain is bad, seems like that should be measureable?

 

[sumnerw]

Off the top of my head, it seems that "loose" chain would effect camshaft timing by retarding it a little bit but I don't think it would be particularly noticeable with only a little looseness. In the extreme, I suppose that a really loose chain could jump the teeth like on a failed start when the engine might back up momentarily.

Buzz White in Houston, TX

 

[tom h]

Nick,

When you say "... only the best chain should be used", what specific brands or models of chain/gears do you like to use on a stock block V6 ??

Any general tips on setup? eg, how do you judge (or measure) what a correct amount of slack is ?

 

[Mike Licht]

New chains are very stiff and not easily moved upon install. After some running time. (not much) If you remove the front cover you will find that you can move the chain a bit from side to side where you could not before. This is not stretch or even a problem. What is important is that the CAM GEAR cannot be rotated back and forth. Yes Buzz a loose chain will retard timing some. Some engine builders even advance the cam a degree or two to compensate for that. Then we need to talk about perfect aginst the real world. If we advance or retard the cam 1 degree it will have some effect on the way the engine runs but in most cases it will be small to none on these cars. Unless the chain is pretty bad it will not cause huge problems, not that it will not cause any, they will be small however.
Mike

 

[wh1-Denver]

Originally posted by Mike Licht
New chains are very stiff and not easily moved upon install. After some running time. (not much) If you remove the front cover you will find that you can move the chain a bit from side to side where you could not before. This is not stretch or even a problem. What is important is that the CAM GEAR cannot be rotated back and forth. Yes Buzz a loose chain will retard timing some. Some engine builders even advance the cam a degree or two to compensate for that. Then we need to talk about perfect aginst the real world. If we advance or retard the cam 1 degree it will have some effect on the way the engine runs but in most cases it will be small to none on these cars. Unless the chain is pretty bad it will not cause huge problems, not that it will not cause any, they will be small however.
Mike

What is an acceptable amount of slack in a Rollmaster DR?

 

[87grandnat]

I am having main caps installed on my stock motor, i was told that it wouldnt change more than.001 to .002 and the double roller chain(stock measurment) would be ok, but if i could find one that was .002 it would be better, were can i purchase a chain in that size, oh it has to be Rollmaster too.

thanks,
Joshua