Der Cupmeister

So, who has a story about their valves being bent due to a loose cam belt ? Is the culprit more likely a siezed waterpump, bad roller, tensioner stud breaking off, belt breaking from not being changed, etc..... I use the "tool", many use the Kriket, and just as many use the 90 degree twist theory. If this adjustment is so critical it seems we would have lots of "loose belt" horror stories due to these different techniques being employed literally around the world.

Thoughts ??
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afx

I had my valves break because my timing belt lost some of the teeth. I am not sure if it lost the teeth because of an incorrect tension, or old age... but I would bet old age. It seems to me that most of the times people have their belts break is when the wait too long to change them, not because they were not tensioned correctly. I have heard of many people using the "twist" method and having no problems at all. I think that the age of the waterpump/belts/rollers has a lot more to do with failure then the correct tension (as long as it is somewhat close).

ahofam123

My neighbor worked on Ferraris, Porsches, and old Jaguars and said that the guys down at the shop always tensioned the belts by hand. When he came over to help me tension my belts he said that the $15 kricket was a waste of money because your hands could do as good of a job. I kept the kricket however because I felt that $15 is a lot cheaper than a rebuilt head.

iloveporsches

Your hands can do just as good of a job, only if you know what you're doing/ feeling for. I have no idea how tight I belt should feel, so I used the Kriket.

SoCal Driver

Timing belts. Two times. Don't ask!

Both times timing belt separated -- no lost teeth.

First timing belt replacement, well before the two breaks, I had missing teeth. Caught it before it jumped and did any damage. Found the teeth on top of the filter. Came in through the vent hose from the belt cover.

The straight long side where the belt comes off of the crank pulley to the cam pulley is the tension side.

The tension side on any "gear" belt application has a tendency to slap when the distance is a large as what is on the 944 engine. This is why there is a smooth "idler" roller (not a pulley as it does not contact the belt) and the addition of the fence on the new water pumps; to keep the belt from slapping in one direction and the fence to keep the belt from contacting the teeth going the other way.

Which is where the missing teeth come from -- a loose belt hitting itself going the other way.

So a loose belt is not too bad but an overly tight belt will eventually break. Which takes us to the auto tensioners.

The idea of an auto tensioner has been around as long as timing/gear belts. Why Porsche thought it could get away with out one is anyone's guess. The spring loaded one the later model 944's seems to a far better job than no tensioner. The hydraulic loaded one on the 968's seems to do even better.

I see some rebound harmonics with the spring tensioner but little rebound with the hydraulic because of it's inherent dampening.