bgrabner

I replaced my Tbelt and WP a few weeks ago, replacing the timing belt tensioner pulleys and bushings, and while i was in there I replaced both my cam gears and oil pump gear. Tension checked out great, the car starts and runs great, and no timing belt warning light at all.

So here is my question - with the engine running i did a visual inspection through the passenger and driver cam gear covers and noticed the belt does not track completely straight - as it moves through the rotation the belt has about 1mm of travel variation. It is nowhere near the front or back edge of the cam gear, and I took the passenger side cam cover off to inspect the belt and it is obviously not rubbing on anything. Other than the tracking of the belt, everything appears normal - cam gears are tracking straight, tensioner looks good, etc...

I guess what bothers me is that on my other shark the Tbelt tracks completely true - no variation at all. I PM'd with Bill Sanders and he said his GTS Tbelt doesn't track completely straight either. Does anyone else have this issue, and is it a concern? And what would cause this? I would think over time the belt would eventually track true. I think because of the motion of the belt and the minimal travel it isn't wearing the teeth of the belt in a side-to-side motion, but since this is my first Tbelt job I guess i am a little paranoid.

Thoughts/opinions from the group?

Bill Ball

Mark the belt through the inspection hole. Start the car and observe the mark. If the mark comes around at the same exact phase in the wobble path each time, then you know the belt is not dead straight. If the period of the wobble does not match the belt rotation, then you have another issue, such as a bad bushing or incorrectly assembled tensioner arm.

bgrabner

Thanks Bill - i tried that last night but the belt and cam gear are moving too fast. Guess I will have to pull the cam cover and manually rotate the engine. Wouldn't I get a tension warning if the belt wasn't tracking straight though?

aggravation

I'm just venturing a guess here but, it seems to me that if the belt itself was just a little less than true then there would be no tension issue and thus no reason for the light to come on.
Imagine if you took the belt off and laid it on its edge on a perfectly flat table and saw that there was a section of the belt that didn't quite touch the table yet installed it tracks consistently without putting undue friction on the teeth or actually sliding around then it would be ugly to watch but it would be working fine.

As long as the same parts of the belt are always landing on the same parts of the teeth then there wouldn't be any unusual stress and the tension wouldn't be affected.
My biggest concern would be the integrity of a belt that somehow was created with a bit of warp to it....
I probably would change it unless a bunch of the more experienced members around here started adding comments like 'It happens all the time, no worries!'

Chris

I recently went through this and replaced everything and it turned out to be the damn belt, I tried Bill's method of marking on the old belt but it did not sync up with the mark either.

It would seem to me the belt not tracking straight would be less than optimal, for me, once I had seen it it drove me nuts and it needed to be fixed.

Chris

atb

I've heard that a worn crank gear can also cause the belt not to track straight.

Chris

Yes Adam is right and this part is often overlooked as the wear is not so obvious as the cam gears. Tom and I were looking over Dave's GT this weekend and it needs a new crank gear along with the cam gears.

Chris

JKelly

What brand?

My new belt (continental) is going in today. I laid my belt side-down on a flat metal desktop to check for inconsistences. It was perfect all the way around on both sides.

Maybe another way of checking the belt to see if it occurs in a certain area of the belt itself, would be to have one person looking through one cover hole and another person looking through the other one and then calling out when the warp passes by.

Bill Ball

Yeah, the crank gear is steel, whereas the original oil pump gear was aluminum (replacement is steel) and the cam gears are aluminum. So, that gear is rarely replaced. It does need to be inspected if the T-belt can't be nailed down as the culprit, as is most likely.

JKelly

If the crank gear was worn and causing a belt to not track straight, wouldn't the old belt be riding to one side or the other of the gear and be noticeable when you were changing it?
or maybe be rubbing heavily against one of the thrust washers?

dr bob

Reminder that the belt needs to be installed so that you can read the lettering from the front of the car looking back.

Also- don't be afraid to use a timing light to try and isolate the tracking to points in the engine rotation. You have eight plug wires, they fire 90 degrees apart on the crank, 45 degrees apart on the cam. If you see the same tracking each cycle with the timing light, your problem is mechanical and not the belt.

----

The period of the belt on the crank gear is probably in the 6" range. (PI*diameter of the crank gear) The period on the can gears is twice that of the crank gears. Recognize the period of the tracking problem and you can isolate whether a worn gear is causing the problem. You can use a wax crayon held through the vent hole to mark the edge of the belt as it tracks in and out. You can use the same crayon to mark the cam gears to see if the belt tracks relative to cam gear position, but this is easier identified using the timing light since the cam gear is at 1/2 crankshaft speed and always indexed to the crank.

Chris

Wobbly belt was Continental and so was the replacement which was OK, I laid the belt on a flat table and could not see any issues.

Chris

bgrabner

It seems like the consensus so far is that the belt really should be tracking perfectly straight if all timing pieces are operating optimally? I don't recall if the previous belt was tracking perfectly, but I know when I removed it it looked brand new, so I don't think it had any undue wear from the crank gear.

kmascotto

Hi, I was doing a little research about belt wobble and I found this thread. I noticed my belt also had a 1 mm tracking issue. I replaced everything when I did the TB/WP (all gears too). If its just a belt that is not 100% true (Gates belt) should i be concerned?

I am about to go back in to check the tension (about 1000 km to go)

Is there a better way to test and isolate the reasons for the alignment issue?

tx