timing belt tracks itself towards the left

[honduraneclipse]

I have done about 10 timing belts and have not encountered this odd problem yet. Everything seems allright and the car idle fines (except the surging) but the belt tends to walk left towards the spark plug area about 1/4 of a inch which is chewing up my timing belt. I know for sure this is not normal and it concerns me a great deal. any input would be appreciated

new tensioner and tensioner pulley installed the correct way
new idler pulley
new timing belt
Balance shaft removed
new oem cranck sprocket
also the bottom end has been rebuild along with the head

 

[Big Woo]

I have a couple of questions first, if you don't mind
1: Has the cylinder head ever been resurfaced?
2: Have the camshaft housings ever been align honed? (rare but you don't know unless you ask)
3: Is either one of the cam gears bent, does one of them seem to wobble when the engine is running?

 

[honduraneclipse]

1. yes the cylinder head has been resurfaced before, it has 272 hks cams along with the rest of the fancy valve train

2. I dont believe the housings for the hks cams were aligned honed. The place that rebuild the head and block usually just does a touch up clean and then pats you on the back and says goodbye thank you.

3. I did not notice the cam gears being warped. I would take a closer look though next time.

 

[Big Woo]

I have seen this occur on rare occasions when (this is not DSM specific) the head was resurfaced on a plane that was not parallel with the original plane, and/or the cam housings were aligned honed causing some runout of the end camshaft axis.

On heads that are warped badly, it can be more difficult to determine the original plane. Some machine shops are better at this than others. It is more machinest skill than it is hardware, but some equiptment is better than others. This is most common with rolling belt resurfacers, this type of equiptment is intended for resurfacing manifolds, but some shops tend to also use them for cylinder heads when they feel just a touch up is needed. The problem is that there is no means of positioning the head to maintian the factory plane, therefore on OHC heads the cam positions can become misaligned.

This does not mean that this is your problem. First I would check for runout of the cam gears, since it requires minimul work, at least to take a look at. Next you may want to pull the timing belt cover and ensure that everything in place. For example make sure that on the crank snout that the balance shaft belt dirve gear is in place, along with the shim, and timing belt drive gear, ensure that all are fully seated. It sounds like you have done timing belts before so you should know what to look for. also look at the tensioner arm and be sure that one of the pivot bushings has not been damaged. Inspect all pulleys for runout.

You don,'t by chance have a 6-bolt with a 2G tensioner pulley do you?

 

[honduraneclipse]

I dont believe I have a 2g tensioner pulley, how would I tell the difference between the both of them ...
Check runout on the cam gears that sounds like a good idea ... What's the spec on that?

Also when I check this out again I am going to bring my friend that originally teached me how to put on a timing belt on. He has done quite a few of them so I hope he can catch it.

 

[Big Woo]

There should be almost no runout of the cam gears. When they are rotated in the cylinder head, and a dial indicator perpendicular and close the the outside edge of the gear itself.

The 2G tensioner has a larger bearing diameter than the 1G tensioner. Bearing diameter means the actual bearing in the center of the tensioner pulley, not the outside diameter of the pulley it self.

Another set of eyes looking for possible problems is always a good idea, well almost always.

 

[honduraneclipse]

Chuck this one to the DSM gods. The problem was the arm the tensioner rode on. It cupped in so bad it made the timing belt run out of track.WTF
thanks big woo for all the tips. I hope you guys out there learn to check this before installing a new belt on!

 

[steve]

It's uneven pressure across the belt that causes it to walk. As you found out, you need to make sure all the pulleys are square to the block and that you haven't worn out the pivot on the tensioner arm.

There are a couple of posts on the subject in the archives.

Steve

 

[rarest_90_DsM]

Thanks Steve