Balance shaft alignment?
 

I just did timing and balance shaft belt replacement on 86 NA. It was upgraded by po with a different camshaft and chipped. Don't know exactly what they were.

After the work car starts and runs fine... until I hit about 1800rpm and again just past 4K rpm. get a hard vibration, I can feel it in the gearshift lever even! I have gone past 4K and it starts to smooth out a little but don't want to take it too far.

I'm thinking I might be off somewhat on the balance shaft alignment. Has anyone had similar symptoms?

Balance shaft alignment?
 

Your thinking is probably correct. Including an image, thanks to John/Arizona. Double check alignment after tensioning and be certain to adjust the tension roller clockwise.http://forums.pelicanparts.com/uploa...1410101648.jpg

If your balance shaft sprockets are in proper alignment and you still have the vibration, check that the sprockets are properly aligned on the balance shafts themselves. The sprockets are identical, and use different keyways for the upper (O) and lower (U) shafts.

some sprockets don't have the 'u' stamp so note that the 'o' is showing in the slot at the 6:30ish position on the lower assembly. you really have to pull the lower cover up a bit to see the cover tab/ cog slot on the lower shaft. I wasted 30 minutes with mirrors and cameras until I just pulled the cover back a little.

if your over and under marks are good and she shakes below 1500rom, you may need to check your motor mount height.

if the vibration persists, check your ignition components and injection pattern. my car was off a few teeth on the upper.

Here is a visual guide. I hope that helps.

924Board.org :: View topic - How to set the timing and balance shaft belts on a 924S/944

If you are still experiencing the vibration, check that your shifter is tight and and mounts are good. All engines have torsional and non-sinusoidal vibration, even straight sixes which are considered smooth. Mounts are are what keep you from feeling those annoying vibrations inside the cabin.

^^

Impressed by detail.

Another question.
How are your motor/engine mounts?

The RPM range you mention can also be caused by bad engine/motor mounts.

OR

A bad rotted rubber clutch disc will start to vibrate at about 2900 to 3300 and up.

Cheap URO mounts will last only 12 months.

J_AZ

I had a similar experience when I had replaced the belts. It was the balance shaft alignment. I had it incorrect.


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+1 likely your lower balance shaft is 180deg out. It's a quick fix.

1) Keyways face up.

2) Align timing notches on sprockets with marks in cover and slip sprockets on.

3) Ensure things remain aligned when tensioning belt.

That's it. Teutonic simplicity.

Thanks
 

Thinking its the alignment on bs. Just hate get back in there. Not much room, big hands!

Jc

Balance shaft
 

Set the top position and set the belt and then do the bottom one from under the car .

I used a small mirror to line up the bottom sprocket marks, couldn't see them straight on from under the car.

Do you need to be at TDC when aligning these ?

I think I am a tooth or two off on my Balance Shafts from when I did my belts a few months back.

Easy enough to set again I guess...Just curious if it is required.

Yes, absolutely. Make sure you're at TDC.