Ok. Quick "why" question about the timing belt.

[supergoat]

I go to check my oil today and since I just recently did a timing belt job, I check the tension on that as well.

Ok. The tension was very loose. So I was not happy. I'm talking about almost a full inch of play. Also, strangely enough the dowel pins were both pointing up to show tdc. So I move my car into my work area, yes I know it was stupid to crank the car with so little tension but I had to.

For shits and giggles I check the tension again after moving it and it's tight! It's tensioned pefectly, 1/4in of play at most. I set it back to TDC and it's still perfect!

What would cause my belt to have a loss of tension like that, until I crank the car?

 

[92redman]

Is it still loose when the car isn't running? When you finnish the job, you are supposed to turn the engine over by hand a couple of turns because that gives the tensioner a chance to take the slack out of the entire belt, not just the part where the pulley is touching. If it is tight now, I would go back and check to make sure that the autotensioner is protruding the correct amount. The other possibility, and this is what happened to me, the auto tensioner was bad and I when I started it up the crankshaft jumped a tooth or two. So what I am saying is check the auto tensioner, if it is protruding farther than when you set it you probably need to redo it and tighten up the tensioner pulley more, and if the belt is loose and the autotensioner is protruding less than when you set it, that needs to be replaced.

 

[supergoat]

It's tight now. just fine. I took everything off and the tensioner was set just as I left it. Cranked it over by hand a few times and it was perfect.

Also when I did the waterpump and re-installed the belt, I cranked it over quite a few tiems by hand and all was ok.

I dunno, it seems perfect now. But this morning it was unusually loose. Like not much tension at all. But I checked everything over and all was fine, and it's nice and tight.

 

[BUCK]

My best guess would be the T/Belt idler Pulley Binding intermittently - I wouldn't blow this off too quickly...

 

[Defiant]

I'd guess rock-back from the engine shutting down, and momentarily turning backward for part of a revolution.

 

[supergoat]

The pulley seemed to be fine. Spun freely with no signs on friction or anything.

Defiant, I hope that's all it was.

 

[bottledgt]

that is perfectly normal to be loose then tight at different times after shuting the engine down. it has to do with the way the cams lay over when you shut it off. if you stop it in the right spot, both cams may be trying to spring towards each other, causing the slack you experienced. again ,if you stop it , the cams may this time be at a neutral state or pulling away from each other, and the belt will be tight this time. if you did everything right and used good parts(tensioner) dont worry about it.

 

[Defiant]

I recall the first time I tried to turn the cam in a Datsun head while it was out of the car. My god. First, you can't do it unless you have it clamped down- HARD. Then, once you do get it to turn, about halfway through the first set of lobes that're being used, it'll try to whip back on you. HARD. Amazingly hard, the first time you experience it. I'd not be surprised to find the cams take a good 20hp to turn at speed.

If engines didn't already exist, and weren't already running, I'd never believe they were possible. I don't get how you can burn fuel fast enough at 5,000 rpm, nevermind the Formula 1 and racing motorcycle stuff. It's just miraculous.

 

[jrivard00]

Originally posted by Defiant
I recall the first time I tried to turn the cam in a Datsun head while it was out of the car. My god. First, you can't do it unless you have it clamped down- HARD. Then, once you do get it to turn, about halfway through the first set of lobes that're being used, it'll try to whip back on you. HARD. Amazingly hard, the first time you experience it. I'd not be surprised to find the cams take a good 20hp to turn at speed.

If engines didn't already exist, and weren't already running, I'd never believe they were possible. I don't get how you can burn fuel fast enough at 5,000 rpm, nevermind the Formula 1 and racing motorcycle stuff. It's just miraculous.

You should try cranking the heads on a V8 that has been build for truck pulls. My friends uncle had one that was producing 1600 hp and was using SS springs with 800 pounds of pressure with 305 degree cams that dropped the valves 1 inch.

 

[Defiant]

Originally posted by jrivard00
You should try cranking the heads on a V8 that has been build for truck pulls.

Hah, V-8s. No, I only like to work on one motor at a time! :laugh: