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Hi all, I just did a timing belt replacement on a rather new to me Porsche 944 Turbo S. The belt replacement wasn’t easy to me, found it hard to tension and to fit the belts. Ultimately ran into belt slaps.
It was my first attempt at a belt change, and I did the belts with the twist and wp method. I checked the belt again by manually rotating 2 revolution on the engine before starting it. When starting without the belt covers on, I saw the belt slapping against the belt guard, with quite a bit of oscillation and the tension is looser than I had set it before tightening down things (can’t gauge properly, idler and guard blocking)
So here’s a sequential list of events:
- Fit on belt with cam sprocket 1 tooth ahead
- Rotated crank clockwise by 1 tooth to align timing
- Set tension, twist at most to 90 deg and able to turn water pump by force using 1 hand
- Snugged down spring tensioner bolts
- Rotated camshaft by 1 revolution, rechecked tension and alignment
- Fit on all other parts without front belt covers and cranked, engine ran for 1-2 minutes till I saw the problem.
- Saw belt slapping and oscillating but water pump was still spinning (video of what I saw as attached)
- Twisted belt and felt looser than I had set, water pump was similar to as I set it though.
FWIW, I checked the belts and did not see any scarring yet. Just wondering which step could’ve gone wrong in my assembly. If the spring tensioner bolts loosened up, I should be getting more tension on the belts?
I’ll be removing the idler and belt guard to check tension by twist and trying to relief the bolts on spring tensioner to let the spring tensioner work more. Will probably want to check timing too. Can this work be done with the balance shaft belt in place?
Release the belt tensioner and see if it takes up more slack, then tighten tensioner. It may be sticky or not pressing the belt enough, but can't see it in the video.
With a new belt tensioned properly, engine off, the water pump should be fairly hard to turn, i.e. you have to get a really good grip on it to turn the pulley..
BTW, did you replace all of the idlers and tensioners? I saw your video where the belt is slapping the idler pulley, but the audio sounds like a worn/loose bearing?
Last edited by PaulD_944S2; 10-18-2021 at 12:33 AM.
Only thing i can think of is that when you tensioned the belt and checked it, it was tensioned “ one way” always rolling it over in the direction of running rotation. What i mean by that is when you tension the belt, to roll the engine back and forth..
think of a bicycle chain.. when you're peddling there is always tension on top and slack on the bottom.. if when you're checking its always tensioned in one direction once the engine is running and “ free wheels” the slack is moving.. anyhow.. food for thought. All i can think of now. Good luck!
p.s. when you do that “ back and forth” use the same pulley and i always pull the plugs to make it easier of course..
Why not pick up a tension measuring device? yeah, it seems expensive, but it’s not as expensive as a failed timing belt. Not getting it right can have a pretty awful result, and the twist method is pretty subjective.
The procedure you listed is correct, but for some reason your spring tensioner is not holding. I can think of a few items to check (1) your spring tension is off, (2) there is an oval lock washer on the right adjustment nut that isn’t there or (3) the nuts aren’t holding due to over torquing of the nuts (steel studs in the aluminum spring tensioner body). If it were me I’d definitely use a tensioning tool to check the spring tensioner and check all nuts and mounting studs on the spring tensioner.
Thank you all for the inputs! I will be re-tensioning it coming weekend hopefully. I didn't replace the pulley and idlers, but I did check the pulley and idlers and they were rotating smoothly. I heard the sound as well, but thought it to be the belt slap, the sound was not present right before the belt change.
I would like to think that GPA951s got it right, hopefully too, then it would be human error and I've escaped with a bit of luck. I have rotated it both directions, but using different pulley and kept the cam to crank portion tight throughout. I thought that was the better way to tension because the slack would be there though...
While I agree that the tool would be useful, sad to say I skimped on that because it seems like a special purpose tool, specialised to the 944. Would the Arnnworx tensioning tool be good for other vehicle belts as well? This did scare me a little. I'll be sure to check the spring tensioner too!
Stuckheng, the tensioner is a specialized tool. But I noticed that you have a turbo S, as I do, and they are special cars that do not come around very often...but you probably know that and numbers are dwindling as time goes on. You got lucky that you didn't take your car our for a spirited drive but had the good sense to check your work and noticed the belt slap. The spring tensioner should be able to set the tension correctly (I do check mine with the tensioner and have made slight adjustments) which is why I think that your tensioner is somehow not holding the correct position. In any case good luck and don't let that belt skip...the results can be catastrophic to your engine (which by the way is pretty tough to rebuilt correctly these days).
Do you have photos of the belt area during the process?
Did you remove the front pulley and balance shaft sprocket from crankshaft before installing the timing belt?
All good suggestions so far. I would also suggest that @stuckheng should post pictures of the timing belt tensioner as it sits now, after the belt covers are removed. This might give us a clue of what is going on.
Do you have access to the Porsche special tool 9200? This is also used for counter-holding the balance shaft sprockets, and is quite useful for working the timing belt tensioner back and forth and feeling the spring tension.
I did dial the spring tensioner back because I thought it was too tight. Someone also meddled with the spring tensioner before, such that the riveted rod-end looking thing is bent slightly. I assembled it anyway because I saw a post of another 944 having the spring tensioner installed without it's spring.
Very helpful suggestions thus far, even the ultimate tensioning tool . That tool's what I'd want to get though, being an engineer at work. I'll get some photos in this weekend once I work on it so we can try to get to the bottom of it. I didn't remove the front pulley and balance shaft sprocket, it was very difficult to insert the belt. Very grateful for this community, hope to be able to share some good news soon
I didn't remove the front pulley and balance shaft sprocket, it was very difficult to insert the belt.
Is it possible to have damaged the belt while forcing it between sprockets? The way that the belt jumps in the video suggests a possible inconsistency in the belt.
The correct procedure is to remove the front bolt, steering pulley and balance sprocket from the crankshaft.
Stukheng, ok new information here on your spring tensioner. That part is critical to the health of your engine and it’s intention is to allow the spring to set the tension of the belt as it’s properly installed and locked into place by 2 nuts on you spring tensioner at 15-17 foot pounds. At 1,000 miles or so, you must retention the timing belt by releasing the tension on the timing belt with the same 2 nuts. Spring tensioners are generally reliable and I check mine with a specialized tool just to be sure. But, is somehow your tensioner is not functioning correctly (for instance no spring, a bent rod perhaps introducing friction, stripped aluminum from previous owners) then you should acquire a new part or certainly make sure that the spring tensioner is functioning…I believe they can still be purchased new from Porsche or used (if used I would definitely check the tension with a belt tensioning tool).
In addition, since this is your first time, be sure that the belt has not been damaged (they are cheap to replace) and that your belt area is clean without oil, coolant or rubber debris. If you were to see mine, it’s really clean because fluids can encourage a belt to skip just as much as under tensioning the belt. Good luck and posting photos will help.
I had a hard time putting the belt in, but I only used my hand in that procedure, hopefully I haven’t damaged the belt. The belt still looks fine visually.
Yea I think the spring tensioner doesn’t work well now, hence I took on a more manual way of tensioning. I dialed back from the spring tensioner’s setting then tightened it down. The spring tensioner is mostly too tight if I just let it do it’s job.
So I did get to work on it. I took out the distributor rotor cap and had a look at it again. Turned it to TDC and guess what? The belt is tighter and closer to spec than what I had felt. So while rotating the engine over with the belt installed, I realise that even while rotating in the same direction, the belt is looser and tighter in some spots. Anyway, I retensioned again based on the loosest position. Now, the tension seems okay by twist at both TDC and at other parts of revolution. Water pump is harder to rotate now, takes 2 hands, but it moves. I then put everything back and now it’s much better.
Anyway, I attached a picture of the belt tensioner and also a video of the belt running with the new tension. I gave this a short drive and it’s been okay. Let me know how it is before I take it out for longer drives it possible. Thank you guys so far, it has been very helpful
I think it looks and sounds right except the oval washer with the tab actually fits into the square corner of the spring tensioner…rotate washer to the right about 45 degrees after you loosen the bolt, then retighten. The nut which locks the tensioner angle in place should hold while you do this.
10-17-2021, 09:43 PM
Timing belt slapping belt guide
. That tool's what I'd want to get though, being an engineer at work. I'll get some photos in this weekend once I work on it so we can try to get to the bottom of it. I didn't remove the front pulley and balance shaft sprocket, it was very difficult to insert the belt. Very grateful for this community, hope to be able to share some good news soon 
