Timing belt skipped 5 teeth - how?

honda
accord

#1

First time posting - hope I’m doing it right.

A coulpe of weeks ago I started my '95 Accord EX with vtec engine. It always fires right up and this time was no exception, except for it also immediately died and would not even try to restart. After troubleshooting the fuel system that didn’t seem like the problem and I had good clean spark. So… I thought exhaust obstruction or mechanical timing. Started with mechanical timing and sure enough after pulling the valve cover and setting the belt pulley to tdc on the #1 piston it was very obvious that the mechanical timing was way off. I decided to take it to my mechanic (who’s great) who had installed a timing belt kit 10,000 miles ago. He dug into it and sure enough the belt had skipped 5 teeth. The weird thing is that there was no clear cause for the belt to slip. Everything was intact, functional and operating as it should. The belt had no damage and was in great shape. He reset the belt and it runs as it always has.

Bottom line is my mechanic, his partner and me are completely stumped as to how this could happen.

Anyone have any ideas? Thanks.


#2

Could this Accord have been involved in a flash flood while parked where the water came above the front wheel axle nuts?


#3

When he replaced the timing belt 10k miles ago, did he also replace the belt tensioner?
If not, this problem may recur, and that is not a good thing.


#4

Certain Honda engines are interference. If you skip more than 5 teeth or so the valves will crash into the pistons and then you have big problems. I agree that this needs to be looked into further. If it was just a non-interference engine, then fine, but this is likely not. I always change ANYTHING that touches the belt during a timing belt replacement. Some cars run the water pump off them, then you have idlers and tensioners. Replace them ALL!


#5

Nope, never been in water anywhere near that deep.


#6

Everything that comes in a timing belt kit was replaced, including the water pump. I don’t know if that included the tensioner but he did say that this is a manual tensioner and that when he got the cover off the belt was still correctly tensioned. It wasn’t that the installed tensioner failed.

Everything was as it should be, that’s what makes this so weird.


#7

You’re right, this is an interference engine. As I noted above, a full timing belt kit was installed, not just the belt. As the belt had slipped 5 teeth it wouldn’t even try to start and that’s a good thing but given the circumstance understanding why it slipped that much is hard to understand.


#8

Did this engine have one or two belts?

I’m confused how it could slip. But what really confuses me is that it did slip and it didn’t destroy your engine.

How do you know it slipped? Mechanic show you…or just tell you??


#9

It does have two belts. Timing belt and balancer belt. It didn’t destroy the engine because the mechanical timing was so far off that the engine wouldn’t start. The real question is - how did it get so far off without a failure of at least a part of the system?


#10

Not all timing belt kits are created equal. Some do not include ALL of the parts that can fail a timing belt. Many include the auto-tensioner but do not include the idler pulley(s), and if one of those seizes it can cause the belt to jump teeth. First step would be to verify exactly what parts were in the kit used.


#11

How can the pulley fix itself. OP said all the did was replace belt and it’s running great. Pully bad you’ll probably hear it.


#12

You may want to double check that statement that _“Everything that comes in a timing belt kit was replaced, including the water pump” TB kits don’t normally include the water pump. For that matter, you may also want to double check your assumption that the tensioner was replaced.

My money’s on the tensioner.


#13

Yup!
While I suppose it is vaguely possible that some other problem led to this situation, I think that it is almost surely a case of a bad tensioner.
My theory is that either the tension wasn’t replaced, or it was defective right out of the box.
I guess that a “frozen” pulley could also have been the culprit, but that should have already revealed itself to the mechanic.


#14

Thanks for the replies everybody, much appreciated.

TSM - I had asked that the waterpump be replaced and kits that include a waterpump are readily available.

I agree that it’s most likely tensioner related and will delve into that when I get a chance. Thanks again!


#15

Just because the engine won’t start doesn’t mean the engine couldn’t get destroyed. When you turn the key the piston and valves are moving. If timing is off a valve we’ll be open enough to be hit by the piston. 5 teeth is usually more then enough cause this.

I’m still amazed there was no damage.


#16

I missed the part about running great, that’s how! I need to learn to read, apparently. :wink:


#17

You’re right Mike, I hadn’t thought of that and it is interesting that there’s no damage from cranking the engine trying to start it.

Above you asked “How do you know it slipped? Mechanic show you…or just tell you??”

When I pulled the valve cover and set the #1 piston to tdc it was very obvious that the mechanical timing was way off. The cam sprocket has a spoke stamped “top” that should have been straight up but was advanced almost a quarter turn and the rotor wasn’t even close to pointing at the #1 plug wire. And yes, it was my mechanic who told that that was because the belt had slipped. He reset the belt and the car runs great now. So, other than a slipped belt what else could it be? As I said in the OP, there was no sign of any problems with the timing belt system when he went in to have a look, other than the belt apparently having slipped 5 teeth.


#18

Most probably: He didn’t tension it correctly. Manual tension is usually “over-tight” on a new belt to allow for slight stretching. If he installed another new belt, have it retensioned in a few thousand miles.


#19

Agree.

Or he didn’t tighten the tensioner bolts, perhaps over tighten them and a bolt broke.

If the tensioner pulley did fail he would have had to replace it, he can’t return the car to you with a failed tensioner pulley.


#20

Are You sure it was advanced?
It should be delayed in the rotational direction. Some belt tensioners go slack when engine is turned backwards. Could happen if the engine backfired on startup. Could that have happened?
If the the tension was correct, it would not jump teeths, it would rip them clean off.