Another Vibration Question @3100 rpm - not balance shafts?
 

Vibration is gone. See page 2.


Trying to track down source of vibration. I have read it could be the balance shaft issue. Can someone confirm from my pictures that it is not the balance shaft out of position. Looks correct to me, but want to be sure.

Also, what else could it be. All vibration is right at 3100 rpm.

note that the "0" is in the round opening in upper pulley and in the rectangular slot in lower pulley.


http://forums.pelicanparts.com/uploa...1414169160.jpg

Upper Pulley
http://forums.pelicanparts.com/uploa...1414169205.jpg

Lower Pulley
http://forums.pelicanparts.com/uploa...1414169234.jpg

i see this all the time. i went through it with a shop that did these cars all the time too, and they still screwed it up.

just because the gears look to be in the right place because of the marks, it does not mean that they are. there are 2 key ways on each pulley. if both of them are not pointed up when the marks are in the right positions, there could still be a shaft out of position. unfortunately i don't think you can see the keyways without removing the disk on the front of the gear

The top one is right, you can see the "O" mark (meaning over). You should not be able to see that same O mark on the bottom. It should be U or just blank. If you have two "O" marks showing, you are 180deg out.

Removing the bolts and the metal covers on the balance shafts can be done under belt tension- to check and see what mark is lined up with the woodruff key.

it's not really about the "O".

you can have the pulleys in the right place, but still have a shaft out of position. this is because they use the same pulley for both locations, and it has 2 keyways. that means that regardless of whether the pulley is in the right position or not, you can still have a balance shaft 180 out by merely putting the keyway of the shaft in the wrong slot in the gear.

you have to look at the keyways. both keys in the shafts need to be pointing up when the gears are in the correct locations.

full lower pulley picture
 

here is the full picture of the lower pulley. "0" is visible in the slot not in the circular cutout

http://forums.pelicanparts.com/uploa...1414172134.jpg

thanks - i will pull the covers and check the key locations and report back the results

Few things - I have never seen a "U" stamped pulley, ever, on any model of 944.


The picture angle is hard to tell but your lower shaft might be out of time - the 0 should be visible in the rectangular slot as it is in that picture, but with the gear's notch lined up with the belt cover's finger thing, the 0 should be at an approximately 5:00 position relative to vertical.
The top gear should have the 0 at the approx. 11:00 position at TDC.

guys! forget about the "O", the notch, or any of that until you verify the position of the key way!!!!!!

you can put all of the other stuff in position and STILL not be right.

see this pic - note the darkened keyway in each shaft versus the open one:

http://forums.pelicanparts.com/uploa...1414173259.jpg

I ain't trying to be knit-pickey , but if the shaft key way is in the wrong slot of the gear doesn't that mean the pulleys are not in the right place? By place, I mean orientation. We all get that they are the same pulley for top and bottom.

Slot with O on top, slot without O on bottom. That's what the marks are for.

Also, those metal covers should have a protuberance for the empty slot, so if you have it lined up right the O is visible through the hole on top and through the tiny slot on the bottom, which looks like his situation.

Compare what I am saying to OPs picture and the diagram that was posted and it will all make sense. You can tell that his shafts are aligned properly.

update with pictures - covers removed
 

here is the upper pulley -


http://forums.pelicanparts.com/uploa...1414175665.jpg


Here is the lower pulley - no key in this keyway next to the 0

http://forums.pelicanparts.com/uploa...1414175702.jpg


Here is the lower pulley other half - see the key in the keyway

http://forums.pelicanparts.com/uploa...1414175770.jpg

Flash, I apologize, I think I get the point you are trying to make... If the person who did the alignment put both pulleys exactly backwards then the notches would line up... That would put both balance shafts 180deg out. You would have to turn the balance shaft by hand though as the key way wants to sit facing up on the top on at TDC, if you rotate it by hand it sort of bobs back and forth... You'd have to be a dingus, but it's possible.

Also, PorscheEngineer, that is correctly installed.

So unfortunately I have a vibration from another source. Any thoughts?

Very smonth except around 3100 rpm.

I feel it in the shifter.

Does it vibrate at 3100rpm when sitting still with the transmission in neutral and clutch pedal up?
What about clutch pedal down?

^ This. You may have a torque tube bearing out of position and/or damaged.

I will have to put the car back together perform some tests and report back the results; however, from what I remember when I push the clutch pedal in the vibration goes away.

Are you using a stock shift knob? Those have rubber isolators, otherwise you're going to feel the engine buzz.

the shafts are the same top and bottom, but you can literally have the shaft in either position, and put the gear on and have the marks in the right place, and be 180 out.

that's why the key itself is the thing to look at first. then, you put the gear on with the marks correct.

people get it wrong all the time though, and have one shaft with the key pointed up, and the other with it pointed down.

Everything on the car is stock. I did notice what would be the sound of a bad bearing while coasting - i assumed it was the TT so that was eventually on my list to replace. Could the two be related ?? At that specific RPM??

thanks for all the help pelicans!!

i can see the woodruff key, i think, on the bottom pulley. it is at the 'O', which is wrong. the second picture is not showing the woodruff key, it is showing a tab. i am betting that if you stick a small allen key in the hole in the first photo of the bottom roller, you will find that the woodruff key is in there and it is wrong.

a bad bearing while coasting is probably a bearing at one of the wheels. if it gets worse while cornering one way or the other, you found the bad bearing.

3100 RPM's is, IME, the magic number for vibration with an out of sync balance shaft. i've experienced it twice: i test drove a 1986 NA, PO did a new cylinder head, and the other was when the shop did it with my 951, which was the last time i let a shop do the timing on my 951.

i used nynor's suggestion and used a small allen wrench to test for the keys and i Just confirmed that the woodruff keys are in the proper location per flash968's diagram. the top pulley has the woodruff key at 0 and lower pulley has the woodruff key in the key slot opposite the 0. the allen wrench went in the other key slots approximately 3/4 inch.

thanks again.

I guess since i am this far disassembled i could go ahead and pull the belt and pulleys to be 100% sure.

Probably put on a new belt as well?

hmm.... how bad is this vibration? does it go away at higher RPM's?

you would only notice the vibration if you were driving with your hand on the shifter. as a passenger you would not notice. its like a bell curve from 3000 to 3200 with the peak being at 3100. higher rpms are smooth. as i dont track the car and drive pretty conservative around town, i spend quite a bit of time in that range - just really annoying.

that isn't balance shaft. the balance shaft out of whack is ridiculously annoying. as in, i didn't know if my engine could continue to rev past about 3400 RPM's.

i am leaning towards torque tube bearings, along with the others that chimed in.

i'm not saying that it is the balance shaft, but what the vibration feels like depends on how far out the balance shaft is. if it's only a tooth or two out, which can happen if the balance belt is not retensioned as it should have been, then the vibration is more focused on that rpm point, and not so much the whole range, like when it's 180 out.

from the pictures he provided, that balance shaft belt is spot on.

i can't see the woodruff keys, so i can't speak to that.

the man says that the woodruff keys are where they are supposed to be, after given good information by you. the pictures show the rollers to be spot on.

i am willing to bet that the belt and rollers are right where they are supposed to be.

ah - ok - i didn't see that. if the keys are in the right spots, then i tend to agree about the rest.

When I got my 83 na years ago I had a vibration like you describe and it turned out my timing belt was 1 tooth off.

you might have a resonance in your exhaust...are your hangers supple?

your timing looks spot on.

thomasryan - All new 3" ss exhaust. Hangers are in perfect condition and nothing touching the drivetrain.

zedsn - did the timing belt being off have other effects besides vibration? like misfires or create less power. Did you see a great improvement when it was corrected?

The prior owner had the timing belt break and had some hack put this thing back together and I got it pretty cheap because there was a vibration after it was fixed that wasn't there before I imagine. I would have a vibration start at about 3K and get worse at about 4k but no loss of power and no backfires and the only reason that I found this out is because the hack put the belt on too tight and the water pump started to leak not too loong after I bought the car and I found this out taking it all apart to do the water pump replecement.

Engine mounts. I had the same issue with mine - a vibration at around 3100-3200 rpm, but no real perceptible vibration at idle. I was sure it was the balance shafts but I checked the alignment multiple times and they were definitely fine.

Eventually I inspected the engine mounts and they were way out of spec (using the measuring procedure in Clark's Garage). I replaced those and the vibration went away. That's when I also noticed I had had a vibration at idle really, but hadn't noticed it because it had crept up on me so gradually.

Worse case scenario... I've found that worn-out rod-bearings will cause a vibration in the mid-range that comes in through the shifter...

i had a customer that took his car to a shop that does belts on these cars all the time. they swore they got it right. i made them take the covers off and look at it twice. it "looked" right. in the end, i made them take off the front washer thingies (tech term) and sure enough, it was off.

i would take it down and look at it again, this time with those thingies removed.

Same happened to me, only the reputable shop re-did the car *three* times. I took off the belt covers, removed the pulley bolts and washers, and BAM, one of them was out 180 degrees.

Vibration is gone! Everything appeared to be perfect and everything lined up according to all diagrams and input from brother pelicans. I checked one last item - balance shaft belt tension. The belt seemed a little loose, so after some research I properly tensioned the belt and there was the problem staring me in the face. After proper tension the lower balance shaft was off one tooth. I adjusted and what a major difference - absolutely no vibration whatsoever.

Thanks to all who helped.