3K RPM Vibration

[Chris_B]

I had my 02 motor rebuilt by a local indy shop a couple of years ago. I had the block honed and installed a set of +1 sized Mahle 9.5:1 piano top (E12 head) pistons, with new rod and crank bearings, and had the head rebuilt with new seals, etc. What I did not do is have any balancing done. The motor now has about 9K miles on it, and is very strong with a Motorsport 300 cam, and dual 45DCOE carbs.

Unfortunately, it vibrates a fair amount at about 3K RPMS. You can feel it a bit in the car when driving through the steering wheel (and see it in mirror vibration). In particular, if you put your hand on the motor and rev it up to that RPM range when the car is stationary, it noticeably vibrates. This is a fairly high frequency vibration (the motor does not visibly shake) and fades out when the revs climb (maybe effects the 3K-4K RPM range). I don't know if I should worry about this or if this is harming the motor.

Any opinions?

[dubois]

It is hard to tell, but if it is only in certain rpm range, it could be the harmonics for that particular engine. You would think the flywheel would dampen the vibrations, the M10 crank also has some nice counterweights. I believe mine vibrates too, but after 5 years, hasn't broken apart. I have only driven very few 2002's that would rev like a six or a boxer engine, the four cyl, are naturally unbalanced. I personally wouldn't worry about it.

[Guest Anonymous]

I'm sure you have checked every possible thing but you might try looking at the pressure plate bolts. If one is missing or different weight it can introduce a nasty vibration.

[nbristow01]

Sounds more like the flywheel, pressure plate or the front pulley. Thats if there is even an issue. These motors generally don't rev as smooth as the new cars do nodays from what I have read and seen

[Chris_B]

I have observed enough 02 motors in operation to say that this vibration is unusual. Again, not horrible, but you can definitely feel it in a fairly narrow RPM range about 3K RPM. It seems to me that this didn't develop until the motor was broken in, but I could be wrong about that.

I have had the front pulley off a few times since the motor was rebuilt. Had it powder coated and then pulled it again to reposition the front seal (was leaking a tiny bit). Seems like it can only go back on one way...?

I guess I can pull the sheet metal piece off of the front lower part of the tranny and inspect the flywheel bits with a mirror. Will give that a try on the out chance that a bolt has come out (or wasn't put in).

[JerryC]

Loose bolts can contribute to vibration at certain speeds, also. Make sure all the exhaust and intake manifold and starter bolts are tight. That all-important exhaust transmission bracket could be a culprit. My tii had a broken intake support bracket that eliminated a lot of vibration after it was fixed.

-Jerry

[TobyB]

Worth rebalancing your carbs, especially if it really shows up at no- load.

The webers can really fuel differently at low loads...

cheap easy thing to eliminate.

As are spark plugs, wires, cap and rotor.

hth,

t

[allbim]

It might just be your exhaust system vibrating (resonating)

[MMII73]

I've had a similar vibration in my car since I've owned it, it occurs at about 3800 RPM, I feel it in the floorboards and seat mostly. It used to bother me, but after 8 years I pretty much ignore it.

I've changed the head, carb, fan, trans, distributor (not chasing the vibration) and it hasn't changed. I haven't changed the clutch, alternator bushings or motor mounts yet.

I'm curious to read other ideas, for now I just try to avoid that RPM range. The car really smooths out above about 80.

[PatAllen]

anything bolted to the engine can act as a vibration transducer/amplifier.

3krpm is the natural vibration "hot spot" of the M10 (+- few hundreds of rpm).

Start looking at what has been taken off the motor for the rebuild. It can be realy anything.

-shifter plaform

-exhaust braket/heat shield

-alternator mounts

-intake manifold oem bracing to the starter

-air cleaner

...

-loose connecting rod about to get out of the block by a new opening

-missing nuts on the flywheel

...

personnaly i dont think it is because it wasnt re-balanced. normaly all good sources of pistons are already weight matched, and you dont say you changed the rods or the crank so i would look for something else.

[bfletcher]

@Chris_B

Did you ever figure out what the vibration was?

I'm trying to solve the same thing. Mine showed up after I changed the oil pump. I have been in there since, and nothing is loose. 

I have found a lot of loose accessories, but tightening them did not fix it. I'm going to check the pressure plate bolts next. 

[Chris_B]

Nope. Then again, I haven't done much investigation. I am about to start a 5 speed install project, so I will be able to check out the clutch assembly, but my guess is this is something internal to the motor. The motor runs well other than this annoying problem, so I am reluctant to tear it down just for this. 

 

I am wondering whether it is worthwhile to have the flywheel/clutch balanced (or whether it is even possible). 

[rcf925]

I highly recommend getting the the rotating mass balanced, Crank,pistons,rods,flywheel.  I did mine a year ago and it makes motor so smooth it's well worth it especially if your going to be running it hard

[bfletcher]

@rcf925 that is a great suggestion!
I will make a note to have that done next time the motor is apart. I would be inclined to ignore this vibration entirely if it didn't show up over the course of a 6-hour drive. I have eliminated all of the accessories and the transmission as the causes of my issue. I'm down to checking the pressure plate and maybe the cam gear bolts.

[AustrianVespaGuy]

Remember the M10 is and I4 that doesn't have a balance shaft that runs at 2x crank speed, so it'll never be perfectly smooth.  And I do think that ~3000 RPM tends to be one of the natural resonance frequencies of the engine system.  That said, they can still be pretty smooth too.  My old rusty stock(ish) 76 used to be pretty darn smooth actually.  My current '75 had pretty noticeable 3k vibrations, and they did improve when I rebuilt and balanced the engine, but they also didn't go away completely either; certainly not as smooth as the 76 was.  I've wondered if this might have something to do with the exhaust though, as the 75 has had Supersprint 4-2-1 headers and Ansa resonator/muffler since I bought it, and the 76 was always stock exhaust.