U20 vibration

[kilro]

I have a rebuilt U20 with a vibration at 1500 rpm. New motor mounts and vibration damper. Engine runs fine otherwise. Transmission is good new u joints,new axle bearings, new ss exhaust from Jim Tyler. The only thing I still need to replace is 8 blade cooling fan . The Roadster is a 1966 1600 with 1969 U20 engine and drive train.

Please Help
Kilro

[Linda]

What does the person who rebuilt the motor have to say?
Were the carbs synced well?
Linda

[bossbob]

x2 on Linda's comment, was the rotating assembly balanced, drive shaft? Do you feel the vibration in the seat or the steering wheel. I built a 393 motor got it installed with a used trans and had a similar vibration, couldn't figure it out, changed the angle of the trans, rear end, balanced the drive shaft, turned out to be a bad input or output shaft on the trans. New tranny, and vibration was gone.

[Gars68]

While revving the engine to 1500 RPM's, with the tranny in neutral, is the vibration still there?

[fj20spl311]

Check to see if the timing is stable. Could be the springs or weights in the distributor or a loose shaft.

[greydog]

All good guesses.
Would help to isolate the problem.
As Gar sugvested, is the vibration present in neutral both with clutch engaged and not?
Or, only when moving? All gears or only 1? Specific speed? When vibrating, does it continue with clutch pushed in? What about turning left or right, uphill or down, braking or not?
Lots of causes for vibration, the better you can exactly pinpoint conditions, the better our chance of helping.
Dan

[Gregs672000]

I suspect the fan just based on the rpm... the fan clutch is engaged at that low RPM but would freewheel once the engine reaches a certain RPM, right? I don't know because 1) my car never had one being a 67.5 and 2) I run an electric fan now and have for years. I had a BMW straight 6 have a low rpm vibration that was caused by a broken fan blade... went away as the fan freewheeled.

[theunz]

I suspect the fan just based on the rpm... the fan clutch is engaged at that low RPM but would freewheel once the engine reaches a certain RPM, right? I don't know because 1) my car never had one being a 67.5 and 2) I run an electric fan now and have for years. I had a BMW straight 6 have a low rpm vibration that was caused by a broken fan blade... went away as the fan freewheeled.

Easy to check, remove fn belt. If that fixes the problem then it's either the fan, water pump, or alternator.

[kilro]

Thank you for your sugestions. In answer to questions I rebuilt the engine, Vibration is there in gear and neutral,new carbs and synchronized. no clutch on fan just spacer. Will check stability of timing and also run engine without fan belt.

Thank You
Kilro

[bossbob]

Any update on your vibration problem?