JPTL

Today as I got out of the car leaving it idling in the driveway, I heard a new noise. Faint, but something new:
It's pretty consistent and it is emanating from the top of timing belt cover on the left (passenger) side. I used a mechanics stethescope to isolate it.
It's not a grinding clicking or crunching sound. It's not metallic, or the sound of metal or hard plastic knocking against hard casing...
It's a constant, softer flapping sound - more like the sound that a fan blade would make rubbing against a leaf or piece of cardboard, and it's somewhat muffled as though it's coming from near the cam seal or the distributor.
It was dark, so I wasn't able to see much. I also haven't moved the probe around to see if I could isolate it better.
Tomorrow I'll take a peek at the belt thru the inspection hole - maybe with a timing light to see if there's any fraying of the belt. I'd be surprised if that's the case, but I'm going to check anyway.
What in the area near the distributor/cam gear could make this sound?
I may be able to record it with my video recorder using my mech. stethescope, but I figured I'd throw this out in case it sounded familiar to some of you...

Bill Ball

If it's a fray on the cam belt, that would be pretty low frequency, due to the length of the belt, at about 1/8th engine RPM. Cam gear would be 1/2 RPM. Distributor rotor would be same as cam gear. I haven't had any experience with a problem like this in that area. I'd just go ahead and pop the belt cover off that side and look at the inside of the distributor cap as well as the belt and gear. I can say that air pump sounds from crap that gets drawn into it transmit all over the place and can be hard to localize. In a couple of cases, cutting the air pump belt was all that helped locate it.

JPTL

Good advice, Bill. Cover's coming off as soon as I have a little time. I hope it's coming from the air pump..that seems to be the least problematic situation.

Mrmerlin

for the passenger side noise
First remove the air pump belt, if no change,
THEN
remove the cap
and rotor
and cover,
check the timing belt tension with the engine cold,
also see if the idler bearing is spinning freely, and check the torque of the cam bolt IIRC its 46ft/lb

JPTL

I could use some experienced eyes here (pic)....
Is this an acceptable amount of inward belt travel on the cam gear (the visible teeth are toward the front of the car)?
I assume that even if it is, the disparity between the right & left belt alignment on the cam gear isn't acceptable. I can only assume that the sound is my belt chafing against the tensioner arm(?) considering that the migration of the belt is greater on the passenger side - the side of which I'm hearing this sound.
Note: considering the scale to which I've enlarged the view, the variation isn't huge..a couple of mm's...but it clearly exists.

Since I haven't checked my tension since I did the TB job combined with what I'm seeing here thru the inspection/breather holes is going to force me to delve in. But what should I be prepared to address here? Is it common for belts to migrate a bit like this when they've become broken in & lose tension? Or is this a sign of something more serious like a bent roller shaft bolt?

I did my first complete TB job a couple of years ago & a couple of thou. miles ago (new belt, new WP, new roller & rebuilt tensioner) w/out problems...or so I thought. I found Pirtles writeup in conjunction with Kelly's manual made the job go much, much quicker without oversights...or so I thought. Since I'm not seeing one in Kelly's manual, is there a step-by-step writeup for checking belt tension on '87 + up, detailing hoses to pull, wires to disconnect, components to remove, etc. all the way to the proper procedure using the Kemph tool?
I'm not sure what needs to be removed in order to get to a proper belt tension.

SeanR

The only thing that could make the drivers side run forward is the water pump pulley. I'm not liking that.

JPTL

If that's true, then I'm not liking it either. Pump has less than 3k on it.
But I wouldn't consider the D/S being more forward than it should be. It's the passenger side that's migrated toward the back of the car (away from the front of the gears/car). If anything, the belt on the driver's side would appear to be lined up pretty well (assuming that a mm or two of visible gear teeth is acceptable). Aside from the differential of visible gear teeth between the two sides, the mm or two of shiny gear tooth surface peeking out says that this belt has moved back recently - or is dynamically moving fore and aft as a belt in need of tensioning might do.
This picture is of the left & right breather holes as seen by leaning over the front bumper.

Mrmerlin

FWIW if the passenger side is going to move,
its going to move to the front of the car as the tensioner pivot bushings wear, the tensioner will try to twist to the front and run the belt into the rearside of harmonic dampener.
For what you need to do to look at things ,
its easier if you drain off the coolant then remove the top rad hose,
then the dipstick housing,
then the cap
then the plug wire harness 2 screws
then the top cam cover,
you want to check the tension with the engine at TDC and with it cold,

NOTE if you have Kempf tool you should also have gotten instructions on how to use it

NOTE Seans diagnosis is spot on,
the driverside belt looks a bit too far forward and this is due to what he said.

B4 you start jumping to conclusions you need to inspect the belt tension and report back ,
if its really loose then a new WP may be in your future

worf928

+1 What Sean wrote. The water pump pulley and crank gear (with its two big washers) are the only things that locate the belt on the left-side sprocket.

Your 3k pump? Rebuilt? Or New new?

The good? news (if it's a metal impeller pump) is that the pulley is migrating forward and not into the block.

Edit: It is also possible that there's something not quite right with the sprocket. Before you start taking the car apart, with the engine running, look down the vent hole and see if you have run-out on the sprocket. A very, very slight amount - just enough that you're not actually sure - is ok. When you have the belt off, mark and pull the sprocket, and inspect, very carefully, the aluminum "spider" behind the sprocket. It comes off easily for a close inspection.

JPTL

(I clarified the picture a bit by indicating the back of the car)

So you guys feel that the width of visible gear on the driver's side isn't enough, huh? I thought if anything, I was seeing too much gear (i.e. the belt running a wee bit too far back). How much of the gear teeth should be visible?
Mrmerlin, you say that the belt as it rides on the p/s gear tends to move forward as the bushings wear, but the belt has moved toward the back in this case, right? Could this be due to the waterpump pulley moving out and misaligning the belt to the point that it tracks inward on the p/s cam gear?

So I may possibly have 2 things going on:
An issue with the p/s sprocket - possibly the spider..
and the possibility of the w/p pulley starting to migrate off the shaft - or the shaft migrating thru the bearing?
I know it's premature to start in on the pump until I get in there, but it's a rebuilt (Porsche casting) from 928SP with a plastic impeller. The original seemed really tight, but I was following the "change your pump with every other timing belt change" philosophy. In hindsight I probably should have left that original pump in. No telling how many times the shaft on the rebuilt has been pressed on and off.

worf928

The amount of gear showing in either picture isn't worrying and both are showing gear in a normal way.... except for the fact that they are not even.

The prima facie evidence of the belt walking is the "shiny" area visible on the passenger side. The driver's side has probably walked forward, but you won't know until you pull the cover.

In my experience the amount of gear shown on the passenger side is more normal than that shown on the driver side. However the "shiny" on the passenger side indicates that originally it was tracking closer to the front of the gear and tracking just like the driver's side. So, the belt was tracking in the same place on both gears a couple of K-miles ago.


Since you indicate that you have a rebuilt pump (sourced in what year?) my bet is that the pulley is migrating and that you do not have a problem with the sprocket.

JPTL

Well, I'm hearing from 4 guys who know from experience how a timing belt should be tracking & how it shouldn't. Although not the news that I wanted to hear, the info that you guys have provided at least points me in the right direction: determining if a catastrophic but avoidable component failure is looming.
My new knowledge of the potential causes for the belt tracking this way before I dig in is like having the right tools all laid out before starting the job.
..thanks for the tools !

AO

Directions on how to re-tension can be found here. Hopefully this will help.

http://www.928gt.com/pc-35-10-tool-9...oner-tool.aspx

Bill Ball

The passenger side belt does ride further back due to the Hall plate behind that cam gear that is not on the other side. So, that doesn't alarm me. That said, I do see what looks like a CHANGE in the wear pattern on the passenger side, as evidenced by the exposed shiny area, as Dave noted. It appears the belt is moving around a bit. How does it look with the car running? Does the noise coincide with belt movement?

It would be worth popping both covers and investigating. I can tell you that canting of the water pump pulley from bad bearings can be hard to spot. I missed it one time, looking down at the pulley with the left side cover removed, but it became obvious once the center cover was off and the pulley was fully exposed that it was bad.

Mrmerlin

anyway, since you didnt pull off the air pump belt do that first ,
then run the car see if the noise goes away.


IF not then pull the timing cover on the passenger cylinder as outlined above