Timing Belt tracking way off on ONE pulley

[MarkRobinson]

I've done probably 14 timing belt changes in the last 15 years but have never seen this before:

Performing entire "front end" service on my racer-buddy's 928: '85 Euro.

With the new tensioner parts (idler, tensioner bearing, shoulder bolt & both bushings), the t-belt is riding out on the driver's side pulley with about 3/16" overhanging the front of the sproket, but rides just fine on the passenger's side sproket.

At the tensioner, C-clip is in-place, idler is new, bushings for shoulder bolt and the shoulder bolt are new, thick spacer-washer was placed between idler and tensioning pivot assembly: diagrams & parts were double checked.

Tensioner pulley is in alignment with the crank pulley, both crank pulley washers are in-place, crank pulley was fully pressed onto crank: so nothings "obvious"

No, crank pulley is not on backwards (read that on rennlist): not even sure how that's possible as one end has chamfer to allow it to slide onto crank.

I'm going to pull it all apart again tonight & ensure the c-clip didn't dislodge. I've heard of bent tensioner arms: perhaps this is bent: the belt was tracking forward when I started the project on the old belt, and the shoulder-bolt bushings were still in decent shape, though original it appears.

Thoughts??

Mark

[Mrmerlin]

does the engine have the correct cam pulleys on it? all round tooth
I might suggest to swap the pulleys left to right or atleast examine them side by side,
if you can compare the distance from the back side of the water pump front pulley its possible this is sliding off the shaft.
Or the shaft is canted in the pump housing did the tensioner seem to require a bit more tightening than when you removed the belt??

[chesireIsugaree]

I saw an oil pump meltdown destroy a motor.... it had some play in it and the gear was worn oddly on the teeth.


Are your cam gears 100% perfect on the teeth?

[s928s]

If something is off slightly it will change the belt trac. The motor spins clockwise while facing the engine. So in theory as the crank rotates it pulls the left cam and all else follows. Slack is taken up on the back side of the crank rotation.
1. Tensioner arm is bent
2. Idler tensioner on the waterpump housing is not fully seated.
3. Cam gears are worn
4. Oil pump. ( check for binding without belt tension, can r/r to inspect impeller, pack with grease on reassembly)
5. beveled washers on crank installed backwards. If outer washer and crank pulley are not installed, It may also walk some.

DAVID

[Mrmerlin]

you could also have broken cam snout thats still connected enough the turn the cam and keep the engine running,
the driverside cam is the weak link in the belt run to keep the belt centered the belt is guided over the right pulley via the crank guides and then the waterpump is the guide for the driver side cam

[MarkRobinson]

I resealed the whole front of the engine, cam seals as well.

Waterpump as a rebuild unit, resealed the oil pump as well.

large guide washers front/back of the crank pulley were removed, inspected, double-checked, reinstalled (there were no issues). Crank pulley is all the way on the front of the crank

It IS tracking incorrectly as the the front of the belt is starting to show small freys even after 10m of idling, so something's pressing/rubbing. I'm starting to suspect the idler arm or possibly the c-clip was not seated. I need to drain the coolant (again) to check this so I don't get a gallon of coolant runnnig down the front of the engine when I remove the tensioner.

[Mrmerlin]

note the tensioner isnt connected to any coolant but it is connected to an oil return.
But the pivot bolt for the tensioner arm is. as it is screwed into the waterpump
the front timing cover lower long bolt might leak coolant as it goes into the waterpump
I would suspect it may be a watepump issue as the tensioner arm if its bent will usually drive the belt into the backside of the crank damper and start chewing up the front edge of the belt before the water pump if the belts off after the waterpump then the pump may be bad or there is a problem with the cam or pulley on the DS

[MarkRobinson]

Yes, the shoulder-bolt penetrates a water passage: you remove it, coolant comes out. I've seen this on every t-belt job. Ok, you refered to this as the pivot: correct.

[stepson]

Just a silly question here, Mark, but could you have put the cam gear in question on backwards? They do have an offset after all.

[MarkRobinson]

I checked, but I can check again. The longer "nose" on the cam gear faces outwards if memory serves.

It's not that it's merely riding off the front of the driver's cam gear: it's being deflected to ride in that position, as the front of the belt is starting to lightly frey from the deflection.

[Mrmerlin]

a picture would be a good thing here

[porken]

Water pump pulley migrating outward?

[MarkRobinson]

Yes, that's what it was: WP Pulley was not properly & fully pressed back on the shaft. It stuck out 5mm past the one that came off the car: see pictures.

Notice that the shaft for the WP is exposed on the existing, but not on the new one.

This picture: larger part of my mic is where it touched the pulley on the existing water pump: huge difference.


Just check your WP's before you install them: this could easily happen from any reconditioner.

[Mrmerlin]

I suggest to buy a a new Laso pump from Roger,
hes got a good priice on them and they are brand new and are plug and play,
glad you found the problem.
Just a note the old pump is also damaged in some way,
the pump shaft should be flush with the pulley with the shaft sticking out the way it does it will hit the inside of the timing cover

[MarkRobinson]

I've probably installed 12 rebuilt WP's over the last 15 years, have never seen this before. My faith in the rebuilt units is strong.

[Mrmerlin]

I have replaced a few rebuilt units so far,
one on my own car and also a new factory pump on my car with only 1500 miles of service. IIRC the new laso is about 230.00 well worth the price of admission and now they are coming with plastic impellers