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.