Engine Vibration

[thriftychicken]

I've got a vibration coming from the engine that occurs from 1900-2200 rpm. It is big enough that it bothers me, but others who ride with me don't notice it. I can mainly feel it in the shifter and I think I can hear it or maybe I'm thinking I can hear it because I know it's there. The engine builder does not feel it is an issue with the balancer or flywheel, but rather something to do with the rigid motor mounts or a misfire. The vibe occurs in the driveway in neutral with clutch in or out so I think that rules out the trans back. This is a 408 (351W) & TKO 600. Anyone notice something similar in their cars or know what this may be?
Thanks

[Jeff Kleiner]

Were the pressure plate alignment dowels installed in the flywheel?

Jeff

[NAZ]

Engines vibrate and this is sometimes worse at certain RPMs from resonance. You mention rigid mounts -- if you have solid mounts it will amplify even small vibrations. If the vibration hits a natural frequency of the chassis or even body parts it will also amplify the vibration. If you're using an OEM vibration damper these are typically an elastomer (rubber) ring pressed in between an inner and outer hub and are seldom concentric, meaning that they may have a natural out of balance condition built in due to sloppy manufacturing tolerances. They are typically tuned to dampen harmonics at a specific RPM range for use with factory cranks. If used on a modified engine they may not be as effective. You may also experience vibration from engine driven accessories like an alternator or A/C compressor. These can be eliminated as suspects by removing the drive belt(s).

If others can't feel it when you point it out then perhaps you're more sensitive to it than others. If it is a real issue there are companies that balance machinery in the field, they can at least confirm an out of balance condition and quantify how bad it is.

My race car has solid mounts and vibrates with a fairly large magnitude at around 1500 to 1800 RPM as it hits a natural frequency with some of the chassis parts. The noise competes with the open exhaust for which is more annoying but it's not a serious problem and NVH is not a concern on a race car.

[Railroad]

Carb or EFI?

[65 Cobra Dude]

Quick question - did you use the right flywheel? I used an externally balanced flywheel on an internally balanced engine. Got the vibration at the same RPM range.

Henry

[Erik W. Treves]

I am with Jeff... dowel pins?

[thriftychicken]

It doesn't have solid mounts, but I'm assuming the urethane mounts will transmit vibration a little more than stock.
Dowel pins are in the flywheel
It is carbed
It has an aftermarket balancer and 28oz flywheel

[65 Cobra Dude]

Give Mike Forte a call.

Henry