Timing belt split

[will81vw]

Hello! So I have been noticing that since I last replaced my timing belt on my '81 rabbit 1.6, that it likes to ride on the very outside (away from engine) edge of the can and IP sprockets. Apparently it has worn itself out prematurely from this, after only about 20k miles it has split lengthwise and now is about a third skinnier than it was. However, it still rides on the very edge of the pulleys like it wants to ride itself off and it is only saved by the fact that the tensioner and int shaft pulleys are recessed and keep it from doing so. Has anyone else ever had this or a similar problem? I am not sure why it is doing this...belt too tight? My crankshaft has become slightly eccentric, I can see it wobble at low rpm slightly, I was thinking this might be making it want to migrate off the sprockets? Obviously I will have to replace the belt, but does anyone else have any idea how to stop this from happening next time? Thanks so much!

[coke]

Usually it means the bearing in the mainshaft of the IP is going bad. Sometimes however it can just be the IP is misaligned. This happened to me on a new pump. Some maneuvering up and down and backwards and frontwards fixed it.

[82vdub]

x2 what Coke said. Is the crankshaft timing belt pully wobbling, or is the crankshaft V belt pully setup wobbling? If the cogged sprocket for the timing belt is wobbling, I would suggest that this situation be investigated a lot closer before something happens. Also, get that timing belt replaced asap! These are an interference motor, so if the belt goes, the valves get mashed into the pistons.

[will81vw]

Thanks for the replies. I did replace the IP with a used one at the same time as the timing belt, so it could be misaligned. How can I tell if I have the proper alignment? By 'maneuvering' do you mean loosen the IP bolts and try to center the belt on the sprocket? How else can I test if it is the mainshaft bearing going out? Why does a bad pump bearing cause this situation?
It is the V-belt pully I notice wobbling, however I havent looked at the sprocket with the pulley removed and the engine running to see if the sprocket wobbles by itself.

[82vdub]

When you install a new timing belt, you turn the engine over a few times by a wrench on the crank (a must do before you use the key!) and observe how the belt rides on the pullys. If it rides to one side or the other, it's typically an issue with the IP.

A bad bearing on the main shaft of the IP will let the main shaft wobble, which will allow the IP pully to not be true with the remainder of the pullys on the engine. That's one reason why it's important. You should be able to take the main shaft of the IP and see if you can move it from side to side or up and down (without a belt on) and see if there's play in it. To get the belt to center, you will need to adjus the IP, or see if you can find a bent piece or some dirt or something between the IP and bracket. If it's missing the bracket at the high pressure end, this could cause it to be off center too. If the IP pulley isn't exactly square to the reminder of the pullys, it will cause the belt to ride on one side or the other of the pullys.

[rabbit_man]

You can center the belt by lifting the high pressure end of the IP. That could mean loosening ALL of the IP bracket bolts, meaning the engine mount/IP mount plate and the "L" shaped bracket that braces the engine mount bracket.

Play with 'em and try to get the sprocket end to tilt down and the output end to tilt up.

[Fatmobile]

libbybapa posted the procedure for centering the belt,
if your sprocket can't be moved alot with the belt off.

[Quantum-man]

Use a straight edge to check face of pump pulley 'square' er parallel with other pulleys

[will81vw]

Today I finally worked on the car. I removed the IP and found that one bolt was missing on the front bracket on the right side. Also one was not very tight on the side bracket. I shifted the front mount bracket so that the side that holds the high pressure end was up a little higher and then put the pump and belt back on. The good new is that the belt stays centered on the cam, and although it still rides the edge of the IP pulley the belt is flush with the edge rather than sticking out a little like before. But on the crank sprocket the belt does stick out from the edge about 1/16 inch. I think the crank sproket is closer to the engine than the other pulleys somehow. So, what do you think, is this OK, or what to about it? I was even thinking of putting some washers between the sproket and the pulley to make a gap to accomodate the lip of the belt sticking out so it cant rub. The IP pulley has a tiny bit of play but not much, so I think it is OK for now. So, I am thinking about finishing putting it back together and hoping for the best. What do you guys think? What do you think about the washers between the crank sporcket and pulley idea? Thanks for the help.

[Quantum TD]

Couple of thoughts:

1) Washers behind the crank sprocket is a bad idea, if you can even do it at all. You run a serious risk of having the sprocket spin and the pistons eating your valves.

2) If the belt is running off, I'd suspect some over-tightening at some point. This can lead to failure of the intermediate shaft bearings. I'd check those out while I was in there.

3) Go and buy a new crankshaft sprocket and bolt. They're cheap as hell (like $20-30) and at least you'll know that you're covered there. While you're in there, examine the nose of the crank. Is the slot for sprocket all wallered out? It might be a bad sign.

4) I'd replace the tensioner bearing while I was in there. You never know what may have happened to it, or if it was part of the problem.

5) Does your car have the small reinforcement bracket that connects the alternator and/or AC bracket to the injection pump bracket? On MK1 cars, this bracket also supports the front edge of the timing belt cover. Be sure to LOOSEN the bolts to this when the belt is off. Check to see that the IP bracket is STRAIGHT, and then tighten the bolts back down.

Then, set your injection pump so that it's sitting right in the bracket and tighten the bolts down.


Having said all that, I'd reiterate what others have said. 99% of the time, belts running off is caused by a cock-eyed injection pump. The belt will ride in and out as it rotates. So long as it's not riding on the edge of the tensioner, you should be fine.


You've probably already solved the issue, but if you wanted to cover all yer bases.....

[will81vw]

Thanks for the thoughts. I wasn't thinking behind the crank sproket, but in front of it between it and the pulley, to prevent the pulley from rubbing the belt. Tensioner is pretty new. My crank nose had some damage previously, which I fixed by using an oversize key and keyway, there is a post about it on this forum. Seems OK so far. Im definately glad I keep the upper timing cover off or I wouldnt have noticed my belt wearing. So, is the belt sticking out off the crank sproket a little bit after hand cranking something to worry about or not?

[Fatmobile]

So the belt is in the center of the cam but riding to the outside on all the other sprockets?

I see you understand that lifting the rear of the pump will help the belt run farther to the inside.

The 2 bolts holding the injection pump bracket to the block are the bolts you want to loosen, adjust, tighten,..
not the 4 bolts that hold the pump to the brackets.

[will81vw]

Yes the belt is centered on the cam sprocket, flush with the IP sprocket and a bit off the edge of the crank sprocket. I took off the pump and adjusted the bracket. Is it better to do with the pump on? There is not much space to reach those two bolts with the pump on.

[Fatmobile]

I don't know how to tighten those 2 bolts with the injection pump on.

When I do get them adjusted right,
I have to go back and remove the pump one more time,.. when I put blue locktite on those 2 bolts,..
and the 2 bolts holding the rear bracket to the injection pump bracket.