Vibration at 4000 RPM
#1
Burning Brakes
Thread Starter
Join Date: Dec 2002
Location: Houston,Tx. Texas GreaseSlingers
Posts: 949
Likes: 0
Received 0 Likes
on
0 Posts
Vibration at 4000 RPM
The main issue with the new car is a bad vibration right at 4000 rpm. PO said it started right after the water pump and belt job.
So, logic would lead one to think balance shaft belt.
Geo, Jenkett944 and me pulled the covers today and went exploring.
Alas, the belts, rollers and timing seem to be right on.
We buttoned it all up and went for a test run. I had not run it up to anything near 4000 rpm before this, as I wanted to check the belts beforehand. Sure enough right at 4000 rpm it shakes big time. Gear shifter, gas pedal, whole damn car, you can feel it in your bones. Feels very mechanical, not like a fuel or electrical related issue and only does it under a load, not when you rev the engine in neutral.
I just drove it 20 minutes. Runs like a top at anything under the 4000 rpm. Although it feels a little sluggish compared to my other 84, but that could just be tune up related stuff or that it has sat for a while.
SO,,,What next ? Torque tube ? Anyone experience what a "bad" one feels like ?
PO had a used tranny installed. Don't know why. Could something with that process/repair done wrong cause this ? One of the PO's work orders had written on it "Balance Shaft is Bad". We kind of wonder how they would determine that without an engine teardown.
Has new half shafts/CV's, rear wheel bearings and a complete clutch job, Any of those items possibly related ?
We will probably go back in, remove the balance shaft belt and drive it to see if it changes the situation. Before that however, I thought I would post it here to see what y'all might think.
Geo & Jenkett944, feel free to add any feedback from your visual or driving experience with it today to help explain the sensation/problem.
Chime in, think outloud, conjecture or guess....all thoughts and replies welcome
So, logic would lead one to think balance shaft belt.
Geo, Jenkett944 and me pulled the covers today and went exploring.
Alas, the belts, rollers and timing seem to be right on.
We buttoned it all up and went for a test run. I had not run it up to anything near 4000 rpm before this, as I wanted to check the belts beforehand. Sure enough right at 4000 rpm it shakes big time. Gear shifter, gas pedal, whole damn car, you can feel it in your bones. Feels very mechanical, not like a fuel or electrical related issue and only does it under a load, not when you rev the engine in neutral.
I just drove it 20 minutes. Runs like a top at anything under the 4000 rpm. Although it feels a little sluggish compared to my other 84, but that could just be tune up related stuff or that it has sat for a while.
SO,,,What next ? Torque tube ? Anyone experience what a "bad" one feels like ?
PO had a used tranny installed. Don't know why. Could something with that process/repair done wrong cause this ? One of the PO's work orders had written on it "Balance Shaft is Bad". We kind of wonder how they would determine that without an engine teardown.
Has new half shafts/CV's, rear wheel bearings and a complete clutch job, Any of those items possibly related ?
We will probably go back in, remove the balance shaft belt and drive it to see if it changes the situation. Before that however, I thought I would post it here to see what y'all might think.
Geo & Jenkett944, feel free to add any feedback from your visual or driving experience with it today to help explain the sensation/problem.
Chime in, think outloud, conjecture or guess....all thoughts and replies welcome
#2
Balance shafts are out of time by 180*. 50% sure.
edit: the other 50% is I'm talking out of my ***, and have no clue what your problem is
edit-edit:changed statistics after you made your second post
edit: the other 50% is I'm talking out of my ***, and have no clue what your problem is
edit-edit:changed statistics after you made your second post
Last edited by iloveporsches; 08-29-2004 at 04:01 AM.
#3
conjure what? if i could conjure the answer for you i would. alas, i cannot, therefore, i conjecture...
i think a balance shaft is 180 out. its still possible, i think, don't they have two identical markings?
i think a balance shaft is 180 out. its still possible, i think, don't they have two identical markings?
#4
Burning Brakes
Thread Starter
Join Date: Dec 2002
Location: Houston,Tx. Texas GreaseSlingers
Posts: 949
Likes: 0
Received 0 Likes
on
0 Posts
This was what we were expecting to find.
BUT.....
The "O" and the "U" seem to be in the correct positions and the marks line up exactly.
Wouldn't they be off it it was out 180 degrees?
edit...thanks Erau, spell check only works if I type in the correct word to start with...
BUT.....
The "O" and the "U" seem to be in the correct positions and the marks line up exactly.
Wouldn't they be off it it was out 180 degrees?
edit...thanks Erau, spell check only works if I type in the correct word to start with...
#5
#6
i had my bottom roller on bachwards. the face of the roller was facing toward the engine, an easily made mistake i guess. but it made it so that the roller was about 6 teeth off. and I had the exact vibration you speak of at 4000 rpms.
if not that, in 86 the bottom balance shafts changed so that the O does not go the same way as it did in 85. so make sure that your directions you used were for the same year your car is.
if not that, in 86 the bottom balance shafts changed so that the O does not go the same way as it did in 85. so make sure that your directions you used were for the same year your car is.
#7
UAE Rennlist Ambassador
Rennlist Member
Rennlist Member
Take OFF the balance shafts and re-install them
I had that problem (at 3,300rpms) and everything looked fine.
After removing the belts, found that they were not installed properly........
Just double check it.
I had that problem (at 3,300rpms) and everything looked fine.
After removing the belts, found that they were not installed properly........
Just double check it.
Trending Topics
#8
Race Director
Originally Posted by hosrom_951
Take OFF the balance shafts and re-install them
I had that problem (at 3,300rpms) and everything looked fine.
After removing the belts, found that they were not installed properly........
Just double check it.
I had that problem (at 3,300rpms) and everything looked fine.
After removing the belts, found that they were not installed properly........
Just double check it.
BTW, they rollers cannot be backwards if we see the O and U can they?
#9
Rennlist Member
Originally Posted by Cass944
i had my bottom roller on bachwards. the face of the roller was facing toward the engine, an easily made mistake i guess.
Symptoms were like this: Cruising in 5th, downshift to 4th to accelerate, and the car had no pick up at all, plus a nasty vibration.
#10
Addict
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Join Date: Nov 2001
Location: Dayton, Ohio
Posts: 7,262
Likes: 0
Received 0 Likes
on
0 Posts
To rule out the possibility of the balance shafts, just remove the balance shaft belt and take the car for a quick ride. The car won't idle as smooth but it won't be too bad. If the 4K vibration is gone, it's the balance shafts.
#11
UAE Rennlist Ambassador
Rennlist Member
Rennlist Member
BTW guys, i have an o-ring leak comming from behind the cap-to-camshaft housing....
Anyway, we took it off today, and found that o-ring needs to be replaced, anyway while looking and taking off the rotor, that allen bolt has chewed threads...........
Now this is a wild guess, but if that allen bolt thread was chewed, could that cause ANY sort of minor play/problem at a certain rpms?
I know that MAY not be related, but just a wild guess, since that bolt doesn't seem 'perfectly' bolted to the rotor..............
Anyway, we took it off today, and found that o-ring needs to be replaced, anyway while looking and taking off the rotor, that allen bolt has chewed threads...........
Now this is a wild guess, but if that allen bolt thread was chewed, could that cause ANY sort of minor play/problem at a certain rpms?
I know that MAY not be related, but just a wild guess, since that bolt doesn't seem 'perfectly' bolted to the rotor..............
#12
Rennlist Member
Originally Posted by hosrom_951
BTW guys, i have an o-ring leak comming from behind the cap-to-camshaft housing....
#14
Rennlist Member
Originally Posted by hosrom_951
That is what the previous owner said, and the bills say that too...
P.S. Was the PO a fellow from Portugal? He had a car just like yours in the UAE and hasn't posted in a long time. Got a new FIAT, or the like.