Timing belt issue

After reading numerous subjective opinions on timing belts, I thought of an analytical approach.

Today, I installed new timing belts on my 88 TR, while doing the major "plus" service. I decided to take measurements of the belts, both old and new.

I measured the thickness of each belt, first, the thickness of the belt including the "tooth", and then the thickness between the teeth.

The old belt measured 4.9 mm and 2.1 mm.

The new belt measured 5.1 mm and 2.2 mm.

Thus there is wear of both the belt, and the teeth. Maybe one could use these measurements, as a check for belt wear. Of course, this would not take into account any fatigue factor. But, it may help someone make sure that the belts where, in fact, replaced prior to purchase.

This was done on an 88 TR, with about 30K miles on the belts.........last service was done in 1997.

Are you sure both your new belt and old belt were the same size when the old belt was new? You need to measure both belts before they are used then measure them both when old. Even the unused one to be sure that aging of the unused one ie. drying out is not a factor. Just a thought.

No, I am not sure if they where of the same size. I thought it was a safe assumption that "some" wear has to occur.......since steel is riding on both sides of the rubber belt. Maybe the old belts where thinner????? Still, there must be SOME sort of wear on the belts!

Since the lettering can many times still be read on the back of belts even after 60K miles, obviously it is unlikely significant material has been removed. As I am sure JRV can attest, there seens no logic in belt lifing, I have seen 308s with ragged and cracked belts still working, others with "new" appearing that failed. The 12 cylinders are much easier on belts, the criteria for them is different just as for a Honda or VW or Porsche. Like 3x8, the 944 Porsche was notorious, you have to go with belts at 45K or pay the price.
Just my $0.02
Brian

I'm agreeing with Brian here. There really doesn't seem to be any way of knowing when or even why some belts fail and others don't at x miles.

My guess is there is quite a number of determining factors, a few being, tension, heat, use patterns and likely even more that aren't as easy to define.

I gave up trying to second guess belt life long ago. There just wasn't anything I could get a handle on that would give me the true insight needed. Determinates like thickness just doesn't seem a foolproof enough determinate to risk a blown engine on. Some things in life we just have to accept that we will never know the answer too, how many more miles before that belt breaks and how long is a piece of string are just two of those.

Regards, JRV

When I did my belts, I was surprised that they ended-up not being very tight. If I had been left to my own devices (no tensioners) I would have left them tighter. With them being so "loose" I could see them lasting longer, but tending to "jump" easier.
Has anybody else questioned this tightness? or has anybody considered a different spring to make the belts a little tighter?
Mark

Well from my experience it depends on where the cams are for how tight the belt is. I know it should be uniformed but it isn't. You can feel the tension when the engine is a TDC and it feels great. Then rotate the engine a little and you will get a little more slack in one section. I spent hours/days trying to figure out what could be wrong, played with the belt, cam timing, etc. and it would still do it. Granted when I mean looser I mean it in a small way, not like falling off of the cam pulley. Anyone just something I noticed on 308s.