While I was looking at my car the other day - I examined the main belt to look to see if there were any signs of wear. To my surpise the belt looked brand new. I was then pondering the picture someone posted not too long ago of the belt that had an advanced amount of wear - and wondered why the belt was considered the only factor. What about cam gear teeth? What about the effect of cutting the cam cover to expose the cam gears thereby exposing the belt to the elements of dust and dirt. Could it be that certain brands of cam gears are the culprit? What about the differences in driving conditions? Hell what about ozone?

Thoughts?


[Modified by Phat Bastard, 11:25 PM 7/9/2002]

 

Good points

How many miles do you have on your belt? Is it a stock one or a PE?

 

Stock . 20000 miles so far (not a lot I know)

 

so based on your theory ... i can make the assumption that since i leave my timing belt cover off .. i'm prone to snappage because i'm exposing it to dirt and the likes. This is on ctr cams w/ spoon cam gears. Mmm..sorry but I don't think it works out. With the covers on dirt can still get on and cling to the belt.

Talking with some friends we all agree that people may be setting the tension on the timing belt wayyyy too tight for big lobe cams.

We can theorize all we want though ... we'll more than likely never know the culprit unless Toda makes a statement on the issue.

vpc - who sees this becoming a 2-4 page thread by the time its done


[Modified by vpc, 11:26 PM 7/9/2002]

 

no my point is that exposure of the belt (which in stock form is covered) may lead to more premature wear due to dirt/dust getting in between the cam gears and belt.

i know that improper installation is the leading cause - but the example i saw did not snap - it was heavily worn on the underside (toothed side)

 

by running without timing cover on top, the only thing prone to dirt damage are your engine seals.

The lower cover being removed can be extremely hazordous to your belt since rocks can fly up from the road and hit it, therefore possible snapping it.

dirt and exposure to air are hardly reasons for snapping a belt. cams would be at little more fault.

if you installed cams in your car, and something goes wrong, it was probably your fault. belt was too tight and the belt snapped. cam towers torqued improperly and the cam broke in half. etc.

 

yeah i get what you're saying...another point that you can add to your theory is that the dirt acts as an abrasion between the belt and the gears.

Its a good theory but IMHO I don't think it holds any water...

 

I had my stock belt taken off after 8000 miles. 5000 of which were on OEM and 3000 of which were on toda spec B. My timing belt looked brand new. But i still replaced it with my power enterprise one.

My theory is that people are not being honest when they are telling their stories about timing belts snapping.

 

power enterprise?

tell me more, like, wtf is that?

 

Scroll down about 75% of the way and look at what Jeff at IB has to say.. it goes along the same lines re: tension of the timing belt.

http://forums.clubsi.com/showflat.ph...hs&Main=803980

 

Timing belts break due to fatigue stress. There is two forms of fatigue stress acting on the timing belt:

1. The bending and straightening of the timing belt as it moves around the cam gears, crank gear and tension pulley.

2. The loading and unloading of tension as the crank gears drives the cam gears. When I say unloaded I mean, not completely unloaded but enough to change the stress "felt" by the timing belt.

Number 2 is the bigger factor and is used to calculate the "fatigue life" of the timing belt by the engineers. The stock belt was designed around the tension required to spin the stock cams at factory redline. So if you use aftermarket cams and raise the redline, the stock belt will NOT last as long as the manufactured specs.

That being said, you could get lucky and end up with a belt that last just as long with your setup (just like some Intel chips can be clocked higher than others).

To the person who said that tightening the tensioner is bad. This is false to a point, you don't want it loose or you will be increasing the delta (range) of the fatigue load which would reduce the belts life.

 

Hmmm I hope Jeff comes here to clear this up because the post I just read of his doesn't really fly with me.

There will be more stress on a belt if you are using higher valvespring rates and there will be more stress on the belt the higher the lift on the cams. Combine both these situations found when using aftermarket cams and valvetrain, and there is no question that the torque required to turn the cams is greater than with a stock setup.

Jeff seems to be saying otherwise. His logic at the beginning of the post kinda lost me...

Here's what he had to say:
I do agree however that proper tension would be key to the lifespan of a belt.

Now, is everyone measuring their belt deflections when they install? What are the ideal values? Not having the helms in front of me, how many points should it be measured at? Is it 2?- between the crank and cam gear and between the cam gears?

Hopefully someone who's NOT having problems with breakage and experiencing normal wear can quantify their tension so we can find an ideal value...

Speaking of which, how does one properly measure belt deflection(s) (numerically)?




[Modified by sackdz, 4:51 AM 7/10/2002]

 

I'm taken this from few ITR's I've seen. Ones like my OLD ITR compared to another fellow who had cut the cover so he could adj timing..we both had within 1,000 miles of each other and both tracked the cars. But his belts had already worn on the outside of the belt like it had been heated up and melted some. Mine had no such effects. My guess is the cover acted as heat asorber plus it keeps most elemets away from the belt. I had the samething happen on my CRX which is uncovered but was using OEM belts. Friend of mine that builds race engines for ITC cars said the cover helps keeps the belt away from elements...when water, dirt, rocks and such get in there they wear away belts fast. I would figure he would know since they run those big enduro races..and if belt going to break that be the time to break.

 

ive been running JUN III on my stock timing belt for 20,000 miles the belt is in great condition, tensioned to the proper oem specs. Belt still looks great, but will be changing shortly.

 

stiffer valvesprings are the reason for snapping...
They cause the need for a higher force to turn the cams which puts more stress to the timing belt. That`s all.

 

This is an incredibly good explanation.
Anything regarding timing covers is irrelevant and has no influence unless
you are referring to a foriegn object getting stuck and grinding away a belt.
Also it shuold be noted that belts dont snap(although I have heard of a few
that have) they have teeth removed.

 

I also agree with Jeff's post for the most part... However, some cams do actually cause the rpms to speed up and slow down a little bit at idle... *ahem* *cough* *spec b's,* *cough* *spec c's* *cough*

And timing belts are a "wear" item, so just inspect and replace it periodically..... I've got 13k on my oem belt: 5k with oem itr cams, and 8k with toda spec b's... I have been running a cut cover since getting the spec b's in... and my timing belt is showing *some* lines across the sides of the teeth... I'll post up pics soon...

But many of us run the belts tighter than spec because when shifting at ~9k, you may let off the gas a little and get back on it, and this jerking motion on the belt *can* jump a tooth if the belt is on the loose side...


-the r0cker, who scratches his head and was wondering when this topic would come up again.....

 

Well here is my thoery on this: (I might repeat a few things mentionned on previous posts but hey...)

There is three reasons why the belt would fail:

1-Fatigue stress
2-Tension in the belt exceed mechanical limits
3-A foreign object fell into the protective cover and damaged the belt up to a point
where we end up with reason #2

1-Fatigue stress:
This is caused by the wear and tear of usual and "excessive" driving. This wear and tear will be more evident on more aggressive camshafts / stiffer spring set-up. Also the one important factor of increased fatigue with aftermarket camshafts is the increase in belt flapping due to a lack of tension in the belt.
For those who do not understand the cause of belt flapping, it is very easy: Imagine that there is some slack only in the section of the belt between the intake camgear and the water pump, start turning the crankpulley slowly, the exhaust camgear starts to turn also followed by the intake camgear, now as soon as the tip of the lobs on the intake camshaft clears the rocker arm, the valve springs who are pushing up uses the lobs of the camshafts as a lever to turn the camgear and because there is some slack in the belt, the intake camgear turns faster then the belt for a split second, transfering all or part of the belt slack in the section between both camgears. If you continue to turn the cranckpulley, the exhaust camgear still turns but now the same thing that happened on the intake side, happens on the exhaust side; since there is now slack in the belt right after the exhaust camgear, the belt can't restrain the action of the exhaust valve springs and now the slack is transfer between the exhaust camgear and the cranckpulley. This "travelling" of the slack in the belt is what creates the extra flapping and also extra wear in the belt as it is subject the impact loads everytimes it as to pick up the slack. This also induce vibration that can, after a while, cause slippage of the camgears and bring us a #2 situation. If the belt is inspected regularly, fatigue failure should be avoided.

2- Excessive load on the belt.
First I would like to point out that IMHO putting "to much" tension on the belt via the tensionner will not make the belt snap or shread teeth. What it will do is create extra wear on the different bearing surfaces of the camshafts and crankpulley and also increase the fatigue factor of the belt.
What will cause excessive load on the belt, enought for it to shread teeth or snap, is losing timing on either one of the camgears. If the valves touch the pistons hard enought, the force transfered to the belt will increase dramatically causing the teeth engage in the guilty camgears to shread. If a brand new belt fails, OEM or P.E., chances are this is what happen. Beleive me these belt can take a lot more load then it is necessary to turn a camshaft.

3- Foreign object cutting the belt
This is fairly self explainatory.


Well my fingers are cramping up so that is pretty much what I have to say. If I forgot something or if you disagree with something I wrote, please feel free to let me know. Also forgive any grammatical or typing error, I tried to keep it to a minimum.

 

I always thought aftermarket cam gears always do that to the belts.