Engine shakes the cab at idle.. but why?

AA_Ezra · 04-13-2011, 11:53 AM

I have had this engine shake since i purcahsed the car about 5+ years ago and it just won't stop shaking it feal like when i car is goign to stall whiel in the cab.

Woul love some suggestiosn from the grop even those that are uncommon

Here is what I think it might be, pleasee add if i missed one

Motor mounts ?
Ballance shafts out of alignment?
Timing? ( dont see how)
Bad DME?
Distributor cap,rotor,plugs, coil?

Ballance shaft bearings?

Recent service:
Timing/balance belts replaced ( took extra care to align balance shafts)
Replaced a motor mount i should have purcahsed 2 thought only 1 was bad

My motor moutn on passenger side was toast, i thought the drivers was good but i guess not look at the pic. instaled new mount on drivers and put old drivers on pass side.

The good, the bad, the ugly

thanks

krystar · 04-13-2011, 12:30 PM

betting on balance shafts. real easy to screw up and time em 180deg off

AA_Ezra · 04-13-2011, 12:41 PM

Would that only cuase low rpm shaking or higher rpm as well?. I will go out and check that right now.

balcsgirl · balcsgirl's Garage

Would a bad ground cause that too???

AA_Ezra · 04-13-2011, 01:57 PM

ok checked out the ballance shafts the bottom is perfect the top is off by 1/8th of an inch which i think would be ok. Took off the sprocket and it apears to only go on one way so i know i got that right. Are the bottom and top sprockets interchangeable? maybe they were mixed up when the Previous owner had the belts change?

krystar · 04-13-2011, 02:17 PM

the real question is...are the sprockets keyed on the balance shaft the right way?

the early sprockets had two key slots. O and U. O is upper BS. U is lower BS. way i remember is O=over, U=under. the sprockets were interchangeable but u had to use the right key slot. only way to check as far as i know is to remove the sprocket.

AA_Ezra · 04-13-2011, 02:35 PM

Ok i will have to check them again. My sprockets only have an ( 0 ) and no ( u ) of any kind.

according to PET upper and lower balance shafts are the same and the sprockets are the same.

Krystar, thanks for all you're input so far. Been dealing with the shaking for too many years and i've reached my limit today.

BUt i did put the key on the (o) position on top balance shaft and the key on the bottom balance is on the ( u) position if it had one. im just glad i scribed a TDC mark on my aluminum flywheel.

Going to check the correct torqe for the shafts and turn on the car the safts are alined a little better now

krystar · 04-13-2011, 02:39 PM

i remember reading that early (definition of early blurry) sprockets have both O and U stamped. later sprockets only had O stamped, the U slot is still there, just unmarked. ...as you've already discovered. doubt they changed part numbers because U isn't stamped hehe

AA_Ezra · 04-13-2011, 04:31 PM

Update:
re-aligned the balance shafts toqued and ready to go
Took off the alternator and A/C belt ( just in case it was causing vibration)

Turned the car on seemed to be a little smoother (maybe i wanted it to)

Re-attached the A/C and Alternator belt Turned it on seemed about the same.

Small improvent but the shakign is still there.

Double checked my timing and its on the money Camshaft lines up and the Flywheel TDC is lined up with the outher edge of the Aluminum timing thingy that sticks out

John_AZ · 04-13-2011, 05:04 PM

My '88 would shake at idle -950rpm-- a couple years ago.

I could not believe it would be the MMs ~60K on odometer.

I had enough and went cheap on the MMs---Hamburg Technic (Deutsche Parts ebay)

I put both on and for a couple of months no vibration.

Then the vibration came back. DO NOT BUY CHEAP MMs

I got another set of MMs-----OEM Porsche $$$ Vibration gone for 2 years +++

Update: Techno Duck just put on a set of Rein MMs. He said they are the same as OEM ----except they grind the part number off. Not cheap but reasonable. Pelican sells Rein.

Picture if you want to measure your old MMs. Measure base to base--no shoulders.

GL
John

AA_Ezra · 05:54 PM

Well looks like my middle motor mount in the picture is wasted just by eyeballing those measurement. You know, I glanced over that page but did not really read it. after readign it I didnt know there was a " pull down test". That middle motor mount didnt really have any ply like the new one. so that one is probly shot.

Don't remeber the brad of them but they were 80$ or so each and lasted me about 5 years so those were a good run.

I alread installed the Uro mount so i don't think i can return it. so i'll just have to ride it out as i have no icome right now. And i still need to order another for the passenger side maybe i might order the more expensive one if i'm able to sell some gear

John_AZ · 04-13-2011, 06:05 PM

The passenger side always fails first. Exhaust manifold heat.
(This is why you will see single MMs for sale on ebay saying "left side-used".)

Some members will swap the "good--??" left and put on the right for a while. I did this when my cheap Deutsche Parts MMs failed early. I kept the new cheap Deutsche parts MM on the drivers side and put back my original drivers/left side OEM old MM on the Passenger side.

I measured the OEM MM to make sure it was still in spec first.

Helped for a while. Just a thought.

GL
John

AA_Ezra · 04-13-2011, 06:41 PM

Quote:

Originally Posted by John_AZ

The passenger side always fails first. Exhaust manifold heat.
(This is why you will see single MMs for sale on ebay saying "left side-used".)

Some members will swap the "good--??" left and put on the right for a while. I did this when my cheap Deutsche Parts MMs failed early. I kept the new cheap Deutsche parts MM on the drivers side and put back my original drivers/left side OEM old MM on the Passenger side.

I measured the OEM MM to make sure it was still in spec first.

Helped for a while. Just a thought.

GL
John

that's exactly what i did New URO on the Drivers Old used (???) on passengers side.

Looking at them under the car I do notice that the new mout is pretty much vibration free while the old used one does vibrate.

Makes you wonder how badly the engine acutaly shakes with solid mounts

alfadoc · alfadoc's Garage

When I got my S2 going (bought it non-running) it had a dreadful vibration. It made the hatch rattle at idle. Double and triple checked the timing and balance shafts, which were correct. Then installed cheap eBay motor mounts that I had purchased before I knew better. That got rid of most of the problem. I still get the occasional buzz out of the door panels at cold idle, but it is a 3 liter four cylinder after all.

These mounts only have 1500 miles on them. When they go bad, which I know they eventually will, I'll replace them with genuine Porsche mounts. I suspect that some of the vibration that I still have will go away then.

p-talk · p-talk's Garage

Vacuum leak? Timing and balance belts too tight?

AA_Ezra · 04-14-2011, 04:06 PM

Timing belts need to be tightened again as they were just recently installed so I'll see if that helps.

Vacuume leak. My exhaust is too loud to hear it. And I don't really now what the best way to check it, propane, brake cleaner, water and soap? I don't want to make the rubber worse

John_AZ · 04-14-2011, 05:28 PM

Quote:

Originally Posted by AA_Ezra

Timing belts need to be tightened again as they were just recently installed so I'll see if that helps.

Vacuume leak. My exhaust is too loud to hear it. And I don't really now what the best way to check it, propane, brake cleaner, water and soap? I don't want to make the rubber worse

Begin by reading Post 7 "Vacuum leaks"
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/458680-idle-drops-low-then-stabilizes.html

I occasionally use "Starting Fluid" for a quick check

GL
John

mayPOR944 · mayPOR944's Garage

mine used to shake really bad at idle, even the whole steering wheel would vibrate like crazy, replaced motor mounts best thing i did for that car

AA_Ezra · 08:20 PM

Quote:

Originally Posted by John_AZ

Begin by reading Post 7 "Vacuum leaks"
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/458680-idle-drops-low-then-stabilizes.html

I occasionally use "Starting Fluid" for a quick check

GL
John

Thanks that helped alot i will have to get a different tip for my propane torch as the current one i have automaticaly lights ( BOOM)

didn't know about the 02 sensor that makes sence i would have tried with it still connected

John do you have all these post's bookmarked or is it just from memory that you search for the post

AA_Ezra · 04-14-2011, 08:19 PM

Quote:

Originally Posted by mayPOR944

mine used to shake really bad at idle, even the whole steering wheel would vibrate like crazy, replaced motor mounts best thing i did for that car

I'm hoping it will be that simple but i've replaced them both before and it was still the same, Then again i have dotn alot of work to the car to make it run smooth since then.

We will find out once i get the other motor mount and the other test others have suggested