OBehave

I would like to know from the experts,in their honest opinion,What would fail first if the timing belt was grossly overtightened? Please exclude the belt itself. And what the results would be on either 16 or 32 valve engines.Thank You Ed

Edit: Let's assume everything related to the timing belt system is new.

blown 87

My guess would be the water pump bearings would fail first.

I would think you would be ok on a 16 valve, not ok on a 32 valve, as far as valve damage.

heinrich

The belt will not fail. It will only fail if some other component eats, chews, cuts, grinds, or otherwise attacks the belt.

Lesson One

In order of likeliness of failure with an overtight belt on an otherwise old but functional system

1. Water pump bearing, shaft axial play, and tension loss, but more likely total pump failure resulting in total system failure.
2. Roller bushing and roller failure at tensioner roller
3. Excessive wear on aluminium cam timing gears, resultant razor sharp teeth and a cut belt
4. Same as 3. on steel and other gears - ie crank and oil pump (crank first)

But remember .. the above is with an otherwise good but worn system. It is a symphony of components and one weak link will cause a totally different series of events.

Results same on either 16 or 32V except that earlier 16V cars have steel cam timing gears, and other components are also different ... 16V cars USUSALLY do not end in bent valves. 32V cars end with bent valves in 99.9999999999999999999999999999999999999999999999999999999% cases.

Dean_Fuller

Agreed...WP first I think.

Leslie 928 S2

Hey Ed....the most likely failure point would probably be the water pump on an overtightened belt. I know you said to exclude the belt itself, but what belt are you using? We just put a Conti into the S2/S4. It has zero miles on it other than garage miles. But we already have a blinking timing belt light. As said by others, they stretch while in use, but shrink back after sitting, making it hard to diagnose.

HTH! Leslie

heinrich

Your belt will (see manuals) stretch within the first 1000 miles. Normal.

John Speake

Water pump first, then excessive wear on cam gear teeth, even end of cam breaking off (on some 16v?)

Leslie 928 S2

Henrich, very true of Porsche belts. Not true of Conti. At least in our experience. Conti belts will show good tension in the garage, but will stretch out while in use, nonetheless, causing the timing belt light to come on. And then it goes back to the proper window of tension according to the gauge afterwards. What a PITA.

We're living the dream (nightmare) right now, baby!

Only Porsche belts for us from now on!

YMMV, of course.

OBehave

See Edit:

OBehave

The cam would break first?

Jim R.

My $$$ would be on killing the WP bearing first. Sure, you will wear the gears, bushings, rollers also, but that WP bearing seal is the weakest link. I would also think the belt itself is now suspect after being run at a "high" tension.

Jim

heinrich

Dude read our lips .. you can tow a 928 with that belt.

OBehave

I'm aware how strong the belt is,and,Dude read my post,Exclude the belt itself.
As far as Sterling's reply that I quoted,I was questioning if his opinion was that the cam would break first?

heinrich

First, before WHAT? If you want advice, drop the attitude

FBIII

Your putting words in peoples mouths. Water pumps first, cams can break. No one said cams will break first.