Another Vibration Question @3100 rpm - not balance shafts?

porschengineer · 03:19 PM

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.

Upper Pulley

Lower Pulley

flash968 · 10-24-2014, 09:03 AM

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

Bradical · 09:18 AM

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.

flash968 · 10-24-2014, 09:24 AM

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.

porschengineer · 10-24-2014, 09:36 AM

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

porschengineer · 10-24-2014, 09:38 AM

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

v2rocket_aka944 · 10-24-2014, 09:45 AM

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.

flash968 · 10-24-2014, 09:55 AM

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:

Bradical · 10:33 AM

Quote:

Originally Posted by flash968

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.

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.

porschengineer · 10-24-2014, 10:38 AM

here is the upper pulley -

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

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

Bradical · 10-24-2014, 10:45 AM

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.

porschengineer · 10-24-2014, 11:24 AM

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

Very smonth except around 3100 rpm.

porschengineer · 10-24-2014, 11:25 AM

I feel it in the shifter.

DannoXYZ · 10-24-2014, 12:07 PM

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

sausagehacker · sausagehacker's Garage

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

porschengineer · 10-24-2014, 01:50 PM

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.

edredas · edredas's Garage

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

flash968 · 10-24-2014, 02:46 PM

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.

porschengineer · 10-24-2014, 04:31 PM

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!!

nynor · 10-24-2014, 04:58 PM

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.