FlyingDog

For some reason my timing belt has started making a chirping noise. The belt has not been over tensioned. All the bearings except the lower idlers are new and appear to be running true. The belt is wobbling about 1/8" forward and backward, but almost perfectly centered on the cam sprockets. The noise occurs when the belt going from the oil pump to the crank changes from moving forward to moving backward.

The two possible problems I can think of are bad (warped?) allignment washers on the crank sprocket, or the balancer is somehow contacting the belt. There are no marks on the belt to indicate contact.

The car is not cooperating in letting me remove the crank bolt. I wanted to ask this question before I go back down to the shop to get the slave cylinder removed (have to partially remove lower bell housing which is a PITA with MSDS headers) to install the flywheel lock.

PS: Since the last time I posted this problem I have replaced the tensiona arm pivot bolt and I think the tensioner boot is finally sealed.

mark kibort

why do you need to remove headers or bell housing. the headers shouldnt get that close to the slave cylinder. i remember changing a slave cylinder with my old MSDS headers. all you need is that thing removed and the flywheel lock just is put right in there, flush with the bell housing.

mk

Old & New

Matt,

IIRC, the consensus would be an alignment issue.

You should take this seriously and deal with it quickly since there isn't consensus on whether your engine will intersect piston-valve upon throwing the belt ;-)

Maybe pull the covers and run it for a look?

FlyingDog

I think I found the chirping. Apparently the oil pan gasket is leaking more than I thought. With the front end higher than the rear, the situation was even worse. The oil level was low. When I added oil, the chirping ended and oil pressure dropped. It used to run 4-5 at idle. Now it's 3 at idle.

Mark, I don't know whether my hardline is bent wrong or what, but the slave piston will not retract enough to remove it from the lower bell housing without dropping the bellhousing about an inch.

Old & New, I'm running without any timing covers. All I can see is that the motion seems to be coming from the crank sprocket area.

FlyingDog

The noise is back, it wasn't the oil pump. It's coming from behind the crank balancer.
https://rennlist.com/forums/928-forum/227059-violent-surging-at-2000rpms.html

SteveG

Does it chirp once/rev of the belt or the pulley? I guess this would be obvious, but are the crank washer and nut torqued down flush? Sounds like the chirp is coming from something out of line (something flanged like a pulley) forcing the belt to walk. I know torqueing it down should make it flush even if it didn't start that way, but stranger things happen. When I got the shark it ran fine but the TB age was unknown, so I dove in. Found a mouse sized ball of TB fuzz in bottom of the cover, small amount of fraying to belt; don't know what was going to be the result, but probably not good and all and all glad I was finding it sooner rather than later. Changed the belt, haven't seen any fuzz since.

FlyingDog

The odd thing with my belt is that there is no sign on the belt that it is touching anything. It still looks brand new. I'm going to pull the oil pump tomorrow and may pull the balancer to look behind it.

Ketchmi

If you can see it, check that the oil pump gear is straight. If it isn't ,it could push the belt into the washers behind the balancer and cause the chirp you are hearing. If the belt runs fine on the cam gears, the alignment is good up to that point. If the driver's side cam gear is bent, it will be moving back and forth onto the oil pump. If the oil pump gear is bent the belt will be going onto it striaght but coming off wavering back and forth.

Good luck!

FlyingDog

It moves forward and backward on everything. That's why I'm having so much trouble figuring out what is causing it. The oil pump or crank seems to be where it is the worst. It would make more sense to be the oil pump since the belt travels over it first.

Daniel Dudley

If everything checks out, suspect the belt. Does it always wobble on the same part of the belt ? I havent ever run a bad bearing or skewed gear, but alignment issues generally cause a belt to ride to the front or back. 1/8'' back and forth in the center sounds like the belt was cut funny, not square to the teeth.

FlyingDog

I pulled the oil pump. It looked almost new. No broken parts... no scratched parts... just a little light polishing here and there. All of the corners were full of black metallic sludge similar to what was on the magnetic drain plug. I cleaned everything with Q-tips, lubed it up with Mobil 1 and reinstalled.

Oh yeah, there was one other thing... My original oil pump sprocket was (aluminum or magnesium?) alloy. The one I bought from 928Intl is steel. There is a 1mm shim behind the woodruff key that is only for use with alloy spockets.

After reinstallation there was no chirp. Oil pressure took about 2 seconds to come up. The belt still wobbles, but seems to do so slightly less. I'll keep an eye on it.

Daniel, I hadn't thought about it being cut wrong, but I was wondering if it got stretched in some strange way when I first had a bad (wobbling) spider behind a cam sprocket.