944 hissing/whining sound (video)

[rex LT]

My 1984 944 has been running well for the last few years. All belts have been changed about 3 years ago (15k miles ago) by the previous owner. (have receipts)

Few days ago I noticed a rattle from the exhaust, only happened at around 3,000 rpms. Today, the rattle seems to be gone, however, a new problem developed. There is a very noticeable high pitched hissing/ whining sound (a bit similar to a super charger whine) when the engine runs. It's most noticeable at idle, but it is also there are the rpm's increase.

I've been reading that this could be a balance shaft belt. But would a sound like this happen all of the sudden? Engine has been perfect for the last 3 years, only belt that I have touched/changed is the alternator belt a few weeks ago. From my understanding, balance shaft belt whining usually happens after changing/tightening the belt.

Link to video: https://www.youtube.com/watch?v=wXZK2SsCWnM&feature=youtu.be

Car runs and drives fine, no loss of power.

Any input is appreciated.

[Tom944]

I certainly does sound like the belts. If you can not do it yourself I would have an independent mechanic experienced with 944s take a look. Could be a roller or bearing issue. You certainly don't want to risk the timing belt breaking.

[rick13]

Maybe time for belts, idlers, and tensioners.

[mytrplseven]

Rick's right. If the balance belt was too tight (usually the one that makes this noise) it would have shown up right after it's initial installation. This sound more like rollers or idlers.

[rex LT]

Little update: I removed the alternator belt to make sure that the alternator bearing is good, which it is. The high pitched noise is still there when the alternator belt is off.

The noise is always there, even as the rpms increase. It is high pitched/ whiny

Originally Posted by mytrplseven

Rick's right. If the balance belt was too tight (usually the one that makes this noise) it would have shown up right after it's initial installation. This sound more like rollers or idlers.

Is there a guide/how to/process for diagnosing bad rollers/idlers?

If it is bad rollers/idlers, how immediately do I need to address them? I currently daily drive the 944 about 10 miles on the highway to work.

[dgcantrell]

The only true way to diagnose them is to replace them. It's cheaper than a rubber band break. Much easier to fix. You can remove the belts and spin them by hand. Any of them that feels stiff and makes ANY noise whatsoever needs to be replaced. I made the mistake once of trying to oil the smooth idler that rides on the back of the timing belt. It was fine for a while but suddenly locked up unbeknownst to me... Rubbed the timing belt gradually to where it was so thin is snapped.......

[rex LT]

Originally Posted by rex LT

Little update: I removed the alternator belt to make sure that the alternator bearing is good, which it is. The high pitched noise is still there when the alternator belt is off.

The noise is always there, even as the rpms increase. It is high pitched/ whiny







Is there a guide/how to/process for diagnosing bad rollers/idlers?

If it is bad rollers/idlers, how immediately do I need to address them? I currently daily drive the 944 about 10 miles on the highway to work.

I drove the 944 for about 10 miles today. When I pulled in the driveway the whiny sound was gone. I then restarted the car and the sound is present again.

Does this mean anything? The sound went away after some driving, but immediately came back when restarting.

Is this still inline with having bad rollers/idlers?

[dgcantrell]

If it was the belt, it would whine all the time. This certainly sounds like a bearing on one of the rollers.

[Leo944]

Rex,

I had a similar whine, here's what caused it:



It was not a cheap repair. Recommend you spend a little to replace the rollers rather than a lot when one finally gives out and takes the valves with it.

Good luck!

[88Silver924S]

It sounds like bad bearings on one or more of the idlers or tensioners. If the person who replaced the belts did not replace the idlers and tensioners then you may want to just replace them all. Even if they did replace them maybe one went bad quickly. Is there any leakage from the water pump weep hole?

Since you asked if there are ways to test the rollers here goes. Turn off the engine. Remove the top belt cover. To check the idler roller lift the belt off the idler and spin the idler: it should have a viscous drag (from the grease) and NOT spin fast, if it spins freely the grease is gone, and/or if you hear or feel clicking (a broken ball), you need a new idler. With the engine off if you feel any looseness or wobble in the water pump pulley it is probably a worn out bearing.

To check the bearings of the tensioners while the engine is idling: very carefully use a mechanics stethoscope and touch the tip of the stethoscope to the stationary bolt on idlers and tensioners to listen for a bad (noisy) bearing. Whenever you are working around moving belts/parts be stone-cold sober, focused, deliberate, and steady handed so you don't get hurt. On moving parts like these I do not like to use the long screwdriver with the handle to the ear method since turning one's head and maintaining accurate contact with the stationary bolt may cause the screwdriver to slip into the moving belts; with a stethoscope you are looking straight at the target the whole time. They cost about $15. If you are not comfortable working around moving parts, please don't do it.

How many miles on the engine? Have the rollers and water pump ever been replaced?

[rex LT]

Update: Took timing belt cover off, to find a broken/damaged balance shaft belt that has slipped off from the rollers.

Timing belt is still there and appears to be in good shape.

From my quick research I can drive the 944 without the balance shaft belt without any damage. Can anyone weight in on this?


How difficult is it to change the balance shaft belt?

Pictures attached:

[dgcantrell]

Umm.. Dude.. you got extremely lucky on that. As long as the timing belt is ok, you should be ok. Time for new rollers and belts though. The balance shafts are timed but all they do is dampen the vibrations of the engine at idle. You should have had a bit of vibration at idle along with the whine.

[88Silver924S]

"My 1984 944 has been running well for the last few years. All belts have been changed about 3 years ago (15k miles ago) by the previous owner. (have receipts)"

That belt shouldn't grenade in 3 years/15,000 miles. I would be suspicious of the quality of the workmanship with the timing belt too. The timing belt idler looks older than 15,000 miles and the water pump looks old too (may be the original)? The alternator belt looks like a 15,000 mile old belt, maybe the PO just did the alternator belt? Several missing teeth on the balance belt; any idea how it "came off" it's rollers?

Good luck.