Engine Vibration

[fb1411]

I have a 70 C-20 350 when the RPM's are between 1200 and 1500 the engine shake and can be felt in the cab and seen in the steering wheel. I have check the fallowing.
spark to all cylinders at these RPM's
disconnected from trans
removed all moving parts from front of engine including harmonic balancer
shaking always the same

any ideas

[stepsider]

stick or auto ? Many be in tranny. flywheel, pressure plate or internal problem with torque converter. check the bolts to those items.

[SIXTY9]

Did you check the flex plate or flywheel?

[BluTrukker]

Try unhooking one plug wire at a time to determine which cylinder is not firing or misfiring, assuming the issue is just one cylinder. Pull the valve covers and roll the engine over slowly to verify that all of your valvetrain is operating correctly too.

[71K20chevy]

Make sure if you try the spark plug method that you wear thick welding gloves or something, 40,000 volts doesn't feel good. Don't ask how I know...

[Andy4639]

I would check the engine mounts first.
Have U ever seen the chains tieing down a motor? There is a reason for it. The V-8 is a great motor but it has a problem of viberation when running!
Why all this about spark plugs when U haven't said anything about it running bad?

[hamjet]

Also something to think about, the exhaust might be resonating a harmonic back pressure at that RPM. I use to drag race many years ago and when I removed the exhaust from the headers I got what seemed like a vibration at a certain RPM.

[chewychevy67]

I had a 454 with a vibration problem once. For over a year I tried to figure it out. The engine ran well gut at 2000 rpm and up it would vibrate. Finally I chsnged tne engine balancer and that was the problem. It had moved on the rubber just enough to untrue the balance. It was hard to time properly as well due to this.

[stepsider]

Clutch Fan ??, usually Vibs in steering wheel means front rims,tires,balance, Ect.

[Wrenchbender Ret]

Its probably a mismatch of parts. You may have a harmonic balancer or flywheel from a small block 400. Or the truck has a 400 engine in it with the balancer &/or flywheel from a 350.

[BluTrukker]

Originally Posted by Andy4639

I would check the engine mounts first.
Have U ever seen the chains tieing down a motor? There is a reason for it. The V-8 is a great motor but it has a problem of viberation when running!
Why all this about spark plugs when U haven't said anything about it running bad?

This is a quick and easy way to determine if a cylinder is misfiring and causing the vibration. If it is, when you pull 7 of the plug wires one at at a time, it will run worse. The eighth one there will be no change. That will be the one with the issue. If this doesn't produce any results, than you are able to look elsewhere for the vibration.

[67 chevelle]

Originally Posted by Andy4639

I would check the engine mounts first.
Have U ever seen the chains tieing down a motor? There is a reason for it. The V-8 is a great motor but it has a problem of viberation when running!
Why all this about spark plugs when U haven't said anything about it running bad?

Agree , chevy did not "fix" their fireing order mistake untill the ls engines came out