jamesld

I recently changed my TB and I have a more noticeable vibration at idle. I noticed a painted mark on the outside pulley attached to the crankshaft, which has small metal weights attached to it. Unfortunately, I noticed it after I removed the pulley and cleaned it. I also noticed two red paint marks on each of the cam sprockets indication TDC. When I reassembled the crank pulley I oriented the paint mark to the bottom because I assumed that by looking form the top of the engine all of the marks should be visible, i.e.,. I could see both the timing marks on the cams and I could see the mark on the crank pulley if it was rotated to the bottom of the engine. However, I was wondering if these marks (look factory) should be aligned by looking form the bottom of the engine instead, meaning that I should have rotated the crank pulley to the 12 o' clock position. Does anyone remember how theirs were marked and it which position they should be oriented. Thanks

Jim bailey - 928 International

To the best of my knowledge Porsche did not use paint marks for any cam timing .

Bill Ball

The title of this thread says dampener orientation, but what you are describing is the multi-belt pulley. I'm not familiar with any specific orientation for that pulley. Of course, the dampener is keyed and is critical.

I am not aware that the factory weight balanced the pulley. It is so light compared to the dampeneer and all the other rotating mass, I can't imagine balancing it to have any effect. Sounds like somebody did. Unless someone comes upo with something to indicate otherwise, I'd probably just knock the weights off the pulley.

Does the pulley rotate true?

The cam gears are not paint marked. They have a notch to indicate TDC. Many people dab paint there for better visibility. It would be important to make sure the paint mark is in the correct location.

Garth S

There are two belt pulleys adjacent to the harmonic dampener: the inner one is yellow-znic plated, single belt and drives the AC compressor: this pulley often has one or more balance weights welded to it - a note of Porsche **** perfection. I suspect this is the item referred to. The outer unit is multi-belt, painted black, and would not be additionally balanced.
There is no specific orientation for either regards a keyway IIRC - the only caution on reassembly is that any welded weights on the inner pulley do not interfere with reassembly. If the pulleys rotate without 'wobble', it is OK.
The cam drives often have paint marks applied by the previous maintainer to mark either or both of the 45 deg and TDC points: The 45 deg is more commonly marked, as the crank is locked in here on 32v engines for dissasembly: the belt is initally reinstalled at this 45 deg point, and without a factory 45 deg cam drive reference point, the paint mark had been previously added (forsight to get the timing correct.
Other than the 'wobble' issue, cannot equate a vibration problem: what kind of vibration,?, at what rpm?, how severe?, ...?

Jim bailey - 928 International

The crank pulley is not indexed by any key so should be balanced independent of the engine and it would not matter where it is . The Harmonic balancer with the grooves for timing marks is located by the key and only fits in one location (unless you put it on backwards) but it too is balanced separately from the engine. Quite often paint marks are used by mechanics in a hurry to mark where the balancer and cam gears are located before changing a t-belt so the simply return it to where it WAS . Their thinking it drove in it will drive out just the same no matter if it is correct or not . Sometimes marks can be used to identify 45 degrees off TDC to make it easier to get the timing closer .

WallyP

The crank dampener will only go on in one position.

The next pulley out - the large diameter single-groove A/C pulley - has no keyway, and will go on in any position. That pulley had two small balance weights on my '90 GT. My assumption is that the pulley is balanced - but that it is balanced so that it doesn't matter where it is oriented. There is no "external balance" on the 928 crank.

If the increased vibration is due to pulley installation or orientation, the only thing that I can think of would be if you got one of the pulleys off-center - and I think that would be hard to do.

It is pretty common to have paint marks on the cam gears either at the same location as the factory "V" marks, or at the 45 deg BTDC position, to make changing the belt easier. None of these marks would have anything to do with balance.

Bill Ball

Ooops, forgot about the AC pulley. Mine has a single weight too. We all seem to agree orientation should not matter providing the pulley seats and rotates without a wobble.

Jim bailey - 928 International

Wally about once every two weeks I get to ask someone if they put the balancer on backwards. That comes after they tell me the engine will not run but the timing marks are all lined up. Usually it is a 2 valve motor and not much of an issue. If something will go on two ways sometimes it does happen. Same is true with the crank washer which is one reason they sometimes come off!

jamesld

Thanks for the input here guys.

I feel confident that it doesn't matter what orientation the a/c or multi-belt pulleys are reassembled regarding if they are weighted or not. It appears that my a/c pulley is not weighted, but I have a couple of small weights added to the inner rim of the multi-belt pulley.

So, it is not likely that the vibration is due to a misoriented belt pulley. With the engine turning, there seems to be no wobble associated with the belt pulley assemblies.

I was just trying to narrow down any possible reasons why I seem to have more vobration form the engine at idle entering the cabin than before. Maybe some other issue. It just seems to feel like it running rougher. RPM's hold solid at idle no searching and engine noise seems constant with no other unusual noises.

Bill Ball

Checked the motor mounts recently?

jamesld

The motor mounts will be something to consider. I did not notice the oil pan setting unusually low when I was changing the TB and other under carriage work. I did noticed this morning that the car will idle even more roughly after driving it a little agressively. I have replaced all of the rubber hoses on top of the engine, all vacum lines with elbows, new ingintion wiring, news coils, new distrubutor caps/rotors, knock sensors, idle stabalizer, throttle position switch and all fuel lines/dampeners/rising rate fuel regulator. I had it checked out after reassembly and everything was in spec. The only thing I have not changed yet is the CO2 sensor and the hall sender. Just to give anyone a better idea of what to suggest to check next. Cheers