Question on timing belt tensioner

[NJTom]

We are replacing the timing belt and water pump in my 1988 924. So far it's going good, had a heck of a time removing the pulley bolt but with a breaker bar,five foot pipe over it and two guys, one pushing the other pulling we got it out. Since this is the first time we've done this we ran into something and are hoping that others who have can weigh in. The upper tension roller spins free and easy, the lower will turn but doesn't spin like the top one. Is this "normal"? Appreciate the feedback and thanks!

[IdahoDoug]

So, just to be clear, your thread name says "timing belt" and your post talks only about the "timing belt" but your diagram clearly is circling two parts associated with the "balance shaft belt". Further, your upper circle is not around a "tensioner" but the actual sprocket on the end of the upper balance shaft.

That aside, if the lower balance belt tensioner is not rolling well you need to replace it. It should spin freely and silently. Many here counsel to replace all these tensioners and rollers if you want to avoid experiencing a failure on a 29 year old car that will instantly destroy the engine.

Doug

[Slam]

You've circled the upper and lower balance shafts themselves, not tensioners, as Doug noted. They should both spin freely.

In some cases the front housing for the lower BS gets replaced if/when the power steering mount cracks. This is an issue, since the housings are machined with the block in a matching set and should not be swapped from one engine to another. Still, it happens.

The trick is to experiment with torquing sequences for the front housing until you can torque the three bolts to spec and still have the BS spin freely. I just went through this with a friend's car and found that torquing the bolt at 7:00 first, then the one at 12:00 and finally the one at 4:00 allowed me to get them to spec and have the shaft spin. Earlier when we pulled the housing off we found the nose bearing had a section that was highly polished, indicating the housing was ever so slightly cocked. It had been changed at some point in the car's life. We knocked the shine off the bearing.

Edit: Huh. You did circle the BS tensioner after all. Serves me right for using my iPhone early in the morning. I got confused - you said "upper tension roller" but circled the upper BS sprocket, and I assumed you'd circled the lower BS sprocket too. Carry on... However, my tech tip still stands and I apologize for any confusion I may have brought to the proceedings.

[NJTom]

Thanks gentleman! I will try and do better next time.

[Pauld_94S2]

You don't mention mileage or condition, but if indeed you are referring to the timing belt tensioners having a different feel, you should strongly consider replacing them.

In fact, if the car is new to you, or, you don't have recent service records that detail parts replaced at the last belt change, you should replace all of the consumables: belts, tensioners, water pump, and any seals or small parts.

However, if you are doing this to test run the engine, then continue with the timing belt.

[Bradical]

haha! There is a ton of hostility in this thread for it to not be about doing a turbo-swap on an NA 944. Dang!

Anyway, you are asking about the relative feel between a tensioner and the balance shaft gear itself, thats why they feel different. Also, that instantly destroying the engine thing- if you want some insight to the massive amounts of timing belt threads sprawled all over the internet- here's what I've figured out about it. I am going to leave my opinions out of it and see if you can pick up the subtle hints I am sharing as I go.



You might have figured out that the older 944s and the later 944s have two different types of tensioners. The spring tensioner is on the later 944s (like on your 924S) and the earlier ones had an adjustable tensioner like the lower one you circled- on a stud, for the timing belt as well.

At one point there was a lot of problems with tech's over tensioning the stud-mounted eccentric tensioner, or at least that what Porsche was saying, and studs where sheering off and causing the belt to slip, the valves to collide and engines to become damaged (under warranty).

So, Porsche came out with a few fixes- the spring tensioner and the P9201 tool, which is an expensive belt tension gauge. Both of these items made it clear that premature timing belt failure is caused by technician error or poor maintenance, and never should it ever be considered to be caused by an original design flaw. Make sure you buy that P9201 tool so you can be certain that the belt is tensioned exactly right!


Furthermore, by way of roller replacement- you should definitely be checking the belt system and replacing the rollers and tensioners as needed. The belts are supposed to be done every 45,000 miles, so by daily-driving standards you'd be replacing these and the water pump every 90,000 and checking them every 7,500 miles when you do your oil change wouldn't be a bad idea either. Especially if you are adding a lot of oil to your car between those 7,500 mile changes because it's dripping on the garage floor-

...Thats the BIG problem- belt contamination. Leaky oil seals, dirty belts and poor maintenance. The teeth on the belt fail from the belt being saturated with leaking oil, or a sheered timing belt tensioner stud on an early 944 are the two biggest things that cause a timing belt to fail.

If the timing belt idler seized it could damage the back of the belt and weaken it, but I am guessing if the thing is seized you'd probably hear it. The only damage that the balance belt tensioner, idler or either of the gears have or even the balance belt snapping is if any of the debris somehow damages the timing belt. You can leave that guy off entirely if you want- your motor mounts prefer it stays on and is properly aligned, though.

I'll finish with this. You are doing the right thing right now- learning how to do the timing belt yourself. You are learning how it works, how it fails, how to do it right and how easy it actually is to do yourself, and if it ever does fail you'll know that it's your fault. Again, not a flaw with the ORIGINAL DESIGN! And if you don't want to pawn your wife's jewelry and dip into your kid's college fund for the P9201 but you can't sleep at night not knowing the exact belt deflection of the upper portion the timing belt between the tensioner roller and the cam gear then arnworx sells a much cheaper one that works great.