New Timing Belt...Correct Sync? RESULTS

This is a followup, telling the outcome, to my posting last week about a timing belt that might have been installed out of synch. That posting was titled, "New Timing Belt, How To Test Correct Synch? ".
My thanks to those who wrote in.

Mazda MPV, minivan, 1989, V6, 3.0L, 2wheeldrive, 133,000Mi, autotrans
It was really two questions: 1?) If there is suspicion a new timing belt is out of sync, off by a tooth or more, is there a way to test it without disassembly? Everyone answered that there is not. You must remove the cover and look at the alignment of all the marks. 2?) Do the symptoms of my car sound like a timing belt is misaligned, and can a car even run if off by one tooth? The symptoms were that, while the engine with belt replaced actually seemed to run smoothly but it did this: When starting off, it had low power and I had to keep putting my foot deeper into the accelerator, with little increase in speed. Then when it finally built up to a certain RPM, it would wind up to a much higher RPM instantly, faster than you could let off the gas it would be at 4500+RPM and then the auto.trans would do a radically hard upshift. (I don’t know, sounds like the way you might want a racing cam to work.) Everyone’s answer was that it sounded as if, yes, the camshaft was out of sync. One person had personally experienced similar symptoms when mistakenly misaligning the timing belt in their own car. So that was a big lesson learned for me.

RESULTS AND RESOLUTION: It was a tough situation for both me, the customer, and the auto shop. Since my car had been towed in, not running, and an older car, they could not know if it was running poorly before it ever arrived there. And they had absolute confidence in their technician. Upon test drive (after first installing the new timing belt) the technician had noted a hard upshift not knowing the car, he could not really know if the engine felt different (as I certainly did). But the shop could find no other problem with the car, nor could a transmission shop explain the hard upshift. So the shop acknowledged this was a very odd case and agreed to dismantle the front of the engine and look into it. Result: They found the timing was off by one tooth. However, the apparent reason was a failure of the timing belt tensioner. Of course, they had examined that tensioner during the initial job and determined it to be not leaking (hydraulic) and did not replace it (only the tensioner pully was replaced). But on this second disassembly they found the tensioner device was broken. There is a little shaft about a quarter inch in diameter and it had completley broken off. (They gave me that old tensioner.) The failed tensioner allowed the belt to jump off by a tooth (on one of the two cam shafts). We can only assume that the tensioner broke immediately after the timing belt job was complete, because the car’s bad performance was noticed as soon as I received the car and even noted by the mechanic’s test drive. The shop did this second disassembly at no charge, and even did not charge me for the new tensioner ($180 retail!), for which I am grateful. Before doing this second tear-down, it was a difficult discussion for me and the shop owner. We both knew it was a very unusual situation, impossible to say confidently what might be going on. The owner knew he might have his employee dismantle the engine and find nothing wrong, but they went for the option of trying their best to make it right for the customer. They succeeded and I am grateful. The car runs beautifully now. Thanks again to all who wrote in.

Thanks for the follow up. And I am happy to hear that the shop took care of the problem. Good shops are very protective of their reputation and apparently you have found a good one.

Good to hear a positive resolution. Just as an aside, I still haven’t redone my timing belt just living with the reduced power until is convenient to do the tear down.

Good to hear from you guys. To: Pvt public. You have not reset your timing belt, you say. I gave thought to driving mine for a while as it was (since I was so confounded about the cause) but someone reminded me that it could be bad for the valves, perhaps burning them or other unintended consequences. A thought. -TechKnot.

So far just reduced power and gas mileage. No codes or other abnormalaities noticed so far. I don’t drive hard or far at any time too busy working 2 jobs. maybe next weekend.

I’m a little skeptical of the explanation. The tensioner failed and then started working again??? Usually when they fail…they keep failing…

At least they didn’t charge you anything for this…That’s good…I’d just chalk the explanation up to spin…

Mike in NH: Hi, thanks for perspective. Indeed I thought of remote possibility that the tensioner could be a cover story. But I have decided to give the shop the major benefit of any doubt on this. First of all they were willing to dismantle it - when they did not totally believe anything was wrong with the car (it actually ran somewhat reasonably for an old car, but I knew it was way off, being my familiar car). They did not charge for the new tensioner. They gave me the old tensioner. I am analyzing this as a total novice who has never had a timing belt system apart (but seen pic’s in my shop manual). The little tensioner shaft was broken inside of the tensioner unit body and perhaps it was still able to function, to actually still provide pressure along the shaft, if it had not been withdrawn from the tensioner body. I can imagine how this could have been overlooked; it simply was not visible. They made a big point when first disassembled, that the tensioner was showing no leakage, so they were not going to replace it. And even a good mechanic might not have known to pull on the little shaft to see if it was broken. The belt had shredded, but not broken, and they said the strands were all wrapped around everything, and it took work to clear it all out. I wonder if one of those strands got wrapped around the tensioner mechanism and it gave a hard yank as the crankshaft made its final turn. (I was amazed how the engine came to such an instant stop when this happened.) So, as amateur, I can only imagine all the possibilities. And I’ll never know what went on internally with the shop. But as customer, they did make it 100% right for me, at no extra charge. I lost a lot of personal time on this, but they also lost time and money. I think it was a very odd quirk, just one of those things that would never have been imagined. So I’ll go with gratitude that it is resolved. One friend said, “oh, just give up on that car”. No way! I love the car, always driving it very gently, and I knew it runs well. It was worth a big effort to save this care. But if it had not been for this forum and you guys writing in to say that the symptoms definitely sounded like the timing belt out of time, I might not have had the strength or evidence to go back and dig into it further. Showing a printout of all your comments to the service-writer was undoubtedly helpful in this process also. The consensus was very useful to all of us. Thanks again to all. (And I’m still interested in any further comments or theories, if anyone has one.) -TechKnot

Personally, I don’t buy the story you were given and think they’re telling you this as a means of deflecting criticism away from themselves and onto a part that can’t speak for itself.

In mechanicspeak this would be referred to as going into CYA (cover your xxx) mode.

We’re to believe a failed tensioner caused the belt to jump a tooth? If that were the case then I’d think a failed tensioner would cause it to jump more than one tooth; maybe one every so often until the engine quits running.
A jumped belt will usually cause damage to some degree to the teeth on the belt. This means they should have replaced the belt again rather than take a chance.