Balance shaft bearing replacement

[944imraan]

I've got a early 944, and in the last few months noticed a mild "clunking" sound like a pair of shoes in the drier. Since the weather has warmed up lately, I changed oil from 10W-30 to 20W-50, and the noise is now suddenly a clanking, most noticeable at idle, and tapering off with increases in RPM.

The guy who owns the race shop where I get some of my parts thought it was probably the balance shaft bearings going bad. (I suppose that the extra clearance and less-lubrication provided by the thicker oil would make it worse.)

In case it's relevant: it's been running roughly recently also, so I've got a new distributor cap, rotor, etc. on order that should help.

I'm just trying to determine the scope of the problem, as I see three potential options:

1) cut the bal shaft belt and put up with vibration (upgrade motor mounts to prevent them from going bad?)

2) pull the shafts, replace bearings, change and retension timing and bal shaft belts, and water pump ($$$, 12k since timing belt +wp change)

3) just rebuild the engine (might not be much more expensive than #2)

or am i barking up the wrong tree?

[ae1969]

To be honest I have only seen one car that supposedly had bad balance shaft bearings ......and that was a stretch I don't think that was the problem before the tear down...

Assuming it is the balance shaft bearings you may be out of luck. The bearing bridges are probably out of round....replacing the bearings may give you a temporary fix before they begin to fail again. If the bearing bridges are bad this = new motor. The one side is machined on the block.

If you are looking for the quick diagnosis.... YOU hit it on the head. Remove the balance belt. If the problem goes away leave the belt off..... and you are right, the vibration will worsen your mounts pretty quick.

IMO You have better chances having a bad rod bearing than a balance shaft bearing.....not that this news would be more comforting to you...

Have you checked the drain plug for metal shavings? You really need to isolate the sound.

By the way... . welcome to the board.

[Porsche-O-Phile]

Well, I suppose you could have it machined rather than replacing the entire motor right? Although either way, it'd be a lot of work.

[todwic]

If yer shaft bearings failed, those little bits are floating in your engine oil. Making bad things happen. yer prolly better off with a new/used engine. I found a core engine and rebuilt that in my '84.

[944imraan]

The drain plug had some metal filings on it, but not significantly more than the drain plugs I've seen come out of other cars, though I haven't seen that many. As for where the sound is from specifically, I'd have to say that area of the block under the intake manifold--right about where the upper balance shaft is.

If I were to remove the balance belt, are there other motor mounts that I could use? Anything else I'd need to adjust/replace to handle those vibes coursing through the frame?

[ae1969]

If you feel up to it remove the belt.... and lets see if the noise goes away first.....

[944imraan]

That's probably the wisest thing to do right now. I wonder if there is enough time left in this weekend to do that.

I'm just a little concernecd about the motor mounts...

[944imraan]

Hmm. I was doing some other work on the engine, (distributor cap +rotor replacement), and, while it did not solve the problem I was trying to, i no longer hear the noise. Not sure what that means, but...

[fast924S]

You will have alot of problems dealing with thte fibrations due to no balancing shafts. When I rebuilt my enigne I made the mistake of running one balance shaft 180 degrees of timming because of the 2 stupid timming marks on the pully. Anyway I ran it for like 4-5 weeks. I was new to Porsche and didnt know it wasnt supose to run rufff like that. Anyway I went threw 2 power steering pumps, the virbration tore them up. 2 motor mounts Poped from vibration, 4 drive belt tensioners, agian vibration killed them and it cracked the fuel dampener off my fuel rail. I dont know if having it 180 degrees off made the vibration worse then not running balance shafts but I think it will kill stuff fast as it did in my case. But hey I learned from my mistake and man its 100 times beter when you have those shafts timmed right. HEHEHE

[944imraan]

Wow, that would just about double the vibration. It would definitely make it worse, as, instead of throwing the weight to the side that would stop the vibration, it throws it to the side that makes it worse.

I'm working on some tuning issues now. Think it might be a little rich during acceleration.

[1.2gees]

I will just second that it's not too likely to be your balance shaft bearings.
Ahmet