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Old 01-16-2008, 06:00 AM   #1
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Default Timing Belt LENGTH - Does it Actually Affect the TIMING?

A co worker and I are having a debate, or an exchange of theory.

We are debating if installing a longer or shorter timing belt (let's say 1 tooth extra/less) would actually throw the timing belt off on an engine.

The exact scenario we're using is a 1993 Honda Accord engine. He bought the car with a broken timing belt, and rather than buying a brand new belt we were looking through our shop for "take-off" belts for free to slap on the engine just to make the car mobile until he scavanges parts on the car for another Accord of his.

The Accord belt he would actually need is a 113 tooth belt.

I found a good condition take-off belt that came from a VTEC 2.3L Accord engine that has one less tooth, at 112.

My theory is that installing the shorter belt will not change the timing at all. Sure he'll need to run the tensioner in all the way, and the belt will be tighter than it should be, but I think the timing would stay on time.

For some reason he thinks the change in belt size/length would throw the timing off, or at least he's not 100% it wouldn't throw the timing off.

I likened it to a bicycle chain. Toss a longer chain on, but leave the sprockets the same size, and the ratio remains unchanged. Same with extended swingarm/longer chain motorcycles with stock sprockets - sure the chain is way longer, but the ratio remains the same.

I told him that unless you change the cam or crank gear I can't see how timing could be affected.

Thoughts?
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Old 01-16-2008, 06:31 AM   #2
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Default Re: Timing Belt LENGTH - Does it Actually Affect the TIMING? (B18C5-EH2)

I would think that you are correct in that it will keep time, but I do not know from personal experience. Although I would make sure the lengths are really that close and it does not have larger teeth to compensate.
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Old 01-16-2008, 08:55 AM   #3
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Default Re: Timing Belt LENGTH - Does it Actually Affect the TIMING? (91DA9)

given your exact situation you are the one that is correct, not your friend.

be sure that the teeth in the belt are the same size and that they sit snug in the wells on the pulley cogs.
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Old 01-16-2008, 09:57 AM   #4
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Default Re: Timing Belt LENGTH - Does it Actually Affect the TIMING? (89s1)

I agree with the above posters. its exactly like the bycicle analogy. the only thing that will change the timing is changing the number of teeth on the gear. the timing belt is a 1-1 transfer of motion(as long as tension is retained). the gear teeth on both sides are what cause it to be a 1-x transfer of motion.
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Old 01-16-2008, 12:15 PM   #5
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Default Re: Timing Belt LENGTH - Does it Actually Affect the TIMING? (B18C5-EH2)

I wouldn't recommend mixing and matching timing belts, you can get into a world of trouble.

The first thing is that the size of the teeth and the distance between the teeth on both belts have to be the same, otherwise you risk jumping a tooth on one of your pulleys or loosing the belt entirely. And on an interference engine it's not good when that happens.

The length of the belt DOES make a difference. It's similar to when your timing belt stretches, it still works, but your timing starts to get slightly retarded the more it stretches.

In order for that 112 tooth belt to be a completely identical fit belt, in terms of timing angle, it has to be shorter than the 113 tooth belt by a distance of exactly 1 tooth (tooth to tooth length, or one tooth and one valley). If the belt lengths are the same, or the difference in lengths isn't 1 tooth, you just threw your timing off.

Think of it this way. Imagine the distance of the belt from the crank, around the exhaust cam gear, and to the intake cam gear. Now count the # of teeth the belt has in that distance. Now if you put on another belt, and the number of teeth on that belt is different over the same length, say 1/2 a tooth, your intake cam is now off 1/2 tooth rotation from the crank. The exhaust cam will be off as well but by a lesser amount.

As your OEM timing belt stretches, the length of the belt over the same number of teeth gets longer. This causes the cam gears to slowly start falling behind the crank. 1/2 a degree, 1 degree, and etc. as the belt stretches more.

It doesn't cause a catastrophe per say, but why knock the timing off your car and hurt your performance by installing an incorrect belt? Not unless you're trying to save every $ you can. You might be able to correct your ignition timing, but your valve timing is hosed.

Modified by court76wi at 3:42 PM 1/16/2008


Modified by court76wi at 4:15 PM 1/16/2008
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Old 01-16-2008, 05:29 PM   #6
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Default Re: Timing Belt LENGTH - Does it Actually Affect the TIMING? (court76wi)

Quote:
Originally Posted by court76wi
Think of it this way. Imagine the distance of the belt from the crank, around the exhaust cam gear, and to the intake cam gear. Now count the # of teeth the belt has in that distance. Now if you put on another belt, and the number of teeth on that belt is different over the same length, say 1/2 a tooth, your intake cam is now off 1/2 tooth rotation from the crank. The exhaust cam will be off as well but by a lesser amount.
If the belt has the same number of teeth per foot(i.e. tooth spacing), then the number of feet away the belt is has no effect on the rotational speed of the gears.

You are correct in that if the tooth to tooth spacing is off, the timing might be jacked up. that is because there might be some slip in the belt, or a tooth gets skipped on the pulley which will cause the pulley to not rotate as far as it should if all the teeth are being used on the other one.

Since the op never specified whether tooth spacing was identical, either theory could be correct. If tooth spacing is the same on both belts, the belt would be proportionately longer to incorporate the extra tooth, and not change the timing at all if the tensioner is doing its job. If the tooth spacing is different, then the potential for play in the the belt, or uneven tooth seating might cause timing issues.
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Old 01-17-2008, 04:42 AM   #7
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Default Re: Timing Belt LENGTH - Does it Actually Affect the TIMING? (sanimalp)

Okat let me clarify a few things:

The teeth spacing is 100% identical. Both belts are genuine Honda belts, intended for F series SOHC engines. One for the VTEC, one for the non-VTEC. the belts are literally identical save the one tooth difference.

Also for those telling me I'm risking the engine this engine is more than likely junked already - this is literally to make the car mobile again to pull it in and out of our shop rather than pushing it.

If belt tension is a concern, and if a loose belt causes a change in timing, then if anything this overly tight belt would cause timing to be better than a looser correct belt, no?

Click the image to open in full size.

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Old 01-17-2008, 06:48 AM   #8
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Default Re: Timing Belt LENGTH - Does it Actually Affect the TIMING? (sanimalp)

Quote:
Originally Posted by sanimalp

If the belt has the same number of teeth per foot(i.e. tooth spacing), then the number of feet away the belt is has no effect on the rotational speed of the gears.
sanimalp, I didn't say the length of the belt or its distance affected the rotational speed. Differences in spacing become more apparent over a longer distance. So any "visible" differences are easy to notice it's called a mental image of what is happening. Having a spacing difference of 1/2 a tooth would give you an idea of how advanced or retarded your cam timing is. However the same number of belt teeth still go around the crank per revolution. So yes, the speed doesn't change.

If rotational speed actually changed you would no longer have a 1:1 ratio, your motor wouldn't run.
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Old 01-17-2008, 12:34 PM   #9
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Default Re: Timing Belt LENGTH - Does it Actually Affect the TIMING? (court76wi)

Quote:
Originally Posted by B18C5-EH2
If belt tension is a concern, and if a loose belt causes a change in timing, then if anything this overly tight belt would cause timing to be better than a looser correct belt, no?
the main reason I mentioned belt tension is because if the tensioner can't do its job, then the belt can either slip because its too loose, or be slowly shredded because it is too tight. only one of those issues will cause problems in the short term.
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