Jusii

Yes it is, clarks has a good explanation.

http://clarks-garage.com/shop-manual/eng-08.htm

Sysgen

It doesn't mention on clarks garage if it's possible to have the v marks on the sprokets aligned and at TDC, and still be 180 degrees off? Is it possible? How can it be? I did this 2 years ago and I've had this vibration for a long time and before I plunge into it again, I'd like to know.

I checked last week and my alignment v marks were spot on when at TDC. Could one of the shaft still be 180 off?

Jusii

Yes it does.

In both cases it's assumed that the v marks are aligned, it's about the "O" marks on the sprockets.

"Mechanics who weren't previously familiar with 944s and who didn't pay close attention when they disassemble the balance shaft assemblies naturally assumed that on both shafts the "O" should go on the woodruff key. This causes the lower balance shaft to be 180 degrees out of alignment."

"the groove with the "O" goes on the woodruff key on the upper balance shaft and the groove with nothing stamped beside it goes on the woodruff key on the lower shaft."

Sysgen

That's the assumption I was not making.

"So, the important thing to remember is that on the later cars, the groove with the "O" goes on the woodruff key on the upper balance shaft and the groove with nothing stamped beside it goes on the woodruff key on the lower shaft."

Anyone have a picture of what is meant here? I can't picture it in my head. I guess I'll find out when I check them AGAIN

Jusii

Sorry, no pictures. But I'll try to explain better.

On the balance shafts there's one woodruf key and on the sprockets there's a groove that fits there.

But the problem is that the sprockets have TWO grooves so there's two ways to install them. So on the upper shaft you have to align the sprocket so that the groove which has the "O" mark is aligned with the woodruf key on the shaft.

And on the lower shaft you have to align the groove which has NOT stamped "O" next to it, to the woodruf key.

On the upper sprocket you should see the O mark facing up when at TDC. And with the lower sprocket it should be facing down but there's a chance that you can't see them, due to those sprocket covers.

So if one sprocket is installed with the wrong groove to woodruf key and the v marks match, then you'll have 180 degree misalignment.

Sysgen

Wow, great explanation Thanks

I've found these pictures and from memory, my upper sprocket is as pictured and my lower sproket is also as pictured with the O in the bottom. So it's possible that one of my balance shaft is in the wrong groove and the only way to find out is to take them out or use a strong wire and feel around the back of the sprocket.

Sysgen

OK, I've removed the covers/belts etc. And I have a question, in the above picture, does KEYWAY means that the woodruf key is in that hole ? And is the picture taken from below the car on the bottom sprocket?

This means that both woodruf key point upward, right?

I think mine points down on the bottom shaft !!

Sysgen

OK, never mind, I've reread everything and I think I've got it, this means that my lower balance was 180 off

Byebye vibrations

Sysgen

Just came back from a little spirited drive !!!!!!!!!!!!!!!!! Wow, so that's how it is supposed to run ! To think I've endured this for two years

Runs like a new car !!!

Good night all

Jusii

So you've got like a new car

Luis de Prat

Stephane,

I'm having the same issue after replacing both belts and all the sprockets/rollers. I've read through the thread but am still unclear because I never removed the balance shaft sprockets during the belt and roller replacement.

The engine was set at TDC with the cam markings lined up. Is it possible for the balance shaft sprockets to become misaligned without ever taking them off the engine?

Thanks!

Sysgen

I do not beleive so, the woodruff key would prevent this.

Are the alignment marks correct? The upper one points up and the lower one points toward the bottom.

Also check with a wire as I did if the woodruff keys are both in the top hole. Just remove the retaining bolt, very easy to do.

Maybe one of the shaft is wrong and it was installed 180 degrees off from the alignment marks the last time it was done

Luis de Prat

I thought so. That would be rather wild, since the timing belts were last done a whopping 11 years ago by a very experienced Porsche mechanic and I hadn't had any engine vibration until now. This car had barely done 36K miles since then, but I chose to replace everything due to the years gone by.

I'll pull the belt covers to see what I find. IIRC, the balance sprocket covers have windows to view the markings so I don't have to loosen the sprockets, don't they? Thanks again.

DarylJ

Luis - did you check what was lined up where before you started? It's entirely possible that someone put the lower sprocket on upside down and just lined it up properly, not using the actual timing mark.

Sysgen

That's what I was trying to say in my previous post but couldn't find the right way to say it.

In the top cover you should see the O through a round hole and you should see the bottom O through a rectangular hole.