Anyone ever have cam one tooth off?

[msservices]

My 87 325is have approx 114k and reads above 150 psi compression on all but one cylinder which is only a tad below that. But, it only pulls 12hg of vacuum whereas another 87 325is (same mileage) pulled closer to 17hg.
The car doesn't run terrible, but it "lopes" while idling. Not violently, but constintently. I have no vacuum leaks, or at least none that could account for a 5hg loss in vacuum. Is it possible to have a cam out of time? I know how to check this but I want to know if someone has or has had the same symptoms.

[strad]

Yes it's possible. When I bought my 325ic four years ago, the shop I had do a timing belt replacement (bavarian professionals in Berkeley, CA) told me that skipped teeth (or sheared-off teeth) is a more common failure than a completely broken belt.

[djb2]

Originally Posted by strad

Yes it's possible. When I bought my 325ic four years ago, the shop I had do a timing belt replacement (bavarian professionals in Berkeley, CA) told me that skipped teeth (or sheared-off teeth) is a more common failure than a completely broken belt.

Either they were completely wrong, or they meant that many belts fail with the outer belt fabric still intact but with inner layer supporting the teeth sheered off.

The belt on the m20 will not skip a single tooth and continue driving the cam. If it skips at all, it's over for the belt.

[fastpat]

Originally Posted by djb2

Either they were completely wrong, or they meant that many belts fail with the outer belt fabric still intact but with inner layer supporting the teeth sheered off.

The belt on the m20 will not skip a single tooth and continue driving the cam. If it skips at all, it's over for the belt.

That's the truth!

YOu can adjust the valve timing somewhat by adjusting the cam via moving it one tooth, I wouldn't do it more than that, I forget exactly how many degrees that moves the timing, but it's quite a bit. Advancing the cam will move the torque curve down the rpm scale some, giving it more low rpm grunt, at the expense of some top end power. Most of us could use more low rpm torque in our 325i engines.

[strad]

Originally Posted by djb2

Either they were completely wrong, or they meant that many belts fail with the outer belt fabric still intact but with inner layer supporting the teeth sheered off.

The belt on the m20 will not skip a single tooth and continue driving the cam.

I highly doubt you know more about this subject than a shop that's done thousands of timing belt replacements and works on M20s every day. But besides that, I've seen more than once on this very forum that somebody's found that their timing belt is one tooth off. Now htf do you suppose that happened?! Either they are complete idiots and set the timing wrong in the first place (possible) or the timing belt skipped a tooth (also possible).

[fastpat]

Originally Posted by strad

I highly doubt you know more about this subject than a shop that's done thousands of timing belt replacements and works on M20s every day. But besides that, I've seen more than once on this very forum that somebody's found that their timing belt is one tooth off. Now htf do you suppose that happened?! Either they are complete idiots and set the timing wrong in the first place (possible) or the timing belt skipped a tooth (also possible).

Most, if not all, of being "one tooth off" is during the cam belt change, it's a very easy mistake to make. If the belt, tensioner, and sprockets are in proper order the belt cannot skip one tooth and remain functional. With enough slack to skip a tooth, lots of teeth on the belt will sheer off with catastrophic results.

[msservices]

Thanks for the feed back. Yes if the cam is off by one tooth it happened when I changed the belt three years ago. If the torque curve theory is correct, then I must have retarded the cam by one tooth because the car has good top end, torque is marginal. But would that confirm my loss of vacuum?

[amd4me]

I had a lobe come off a cam in my hand.
That sucked.