400 Vibration
 

Hey all. I have about 1900 miles on a rebuilt 400. It was bored .030 and has tmeyer pistons and a mild cam. Broke the cam in using the machine shop recommended oil and procedure. Changed out the oil after break in and am now running Joe Gibbs HR-1 15-50, also recommended.

I feel a vibration throughout the truck, '78 150 4X4 4sp, when approaching 3k RPM. It seams to be worse when in 2nd gear than 3rd and its not always there. Yesterday I was tinkering with the carb and noticed that when I rev it I feel no vibration on the carb, intake,valve covers, or block but I do feel it on the power steering fill tube and the rest of the truck. I put a stethoscope to the block, valve covers, alt, water pump, and power steering pump and all is quite. All the pulleys look like they are running true.

The only thing I really noticed is that the fan ,non clutch, starts buffeting as the rpms come up.

As for everything else. The flywheel was cut before it went on the new motor with a new clutch and throw out bearing. The balancer shows no signs of spinning on the hub. The motor mounts looked good when I pulled the motor so I reused them.

Any thoughts on where to look next? New motor/tranny mounts?

Very first thing is take all of the belts off, then run the motor and see if you still have a vibration (don't do this for very long or it will overheat - duh)

Is it a steady or pulsing vibration? Does it get worse as the RPMs increase or go away at some point? Motor mounts rarely cause a vibration unless they are totally hammered. Usually you get a nice clunk instead.

Where do you feel the vibration? In your butt? Feet? Steering wheel?

It's steady not pulsing. I feel it as Im accelerating and the RPMs pass about 2600 to 3000. I shift it at 2800-3000. Havent really reved it past 3k yet as it doesn't have much milage on it.

I feel it in my feet, the gear shift, and the steering wheel. The truck is lifted so If I'm standing outside it and lean in to work the gas with my hand I feel it in the side step and sill plate. About the only place I don't feel it is on the engine.

It's also worse if I'm driving than when revving in neutral. No real change when revving in neutral with the clutch in or out. Also definitely worse in second gear than third. And then theres some days I don't feel it at all which is whats most frustrating.

If I can, I'll try to pull the belts tomorrow and run it.

So curiosity got the best of me. I pulled the belts, started it and gave it a minute for the oil to move around a bit. I pressed the gas pedal slowly with my right hand while I had my left on the steering wheel and my hip on the door sill/side step. I found the following.

Idle pretty smooth for a cold engine.
Off idle stumble to 1500 pretty smooth
1500-1600 a little vibration
1600-2900 smooth
2900-3100 vibration
3100-3900 really smooth
Didn't want to rev it much past that

The vibration was felt the least in the gas pedal and most in the wheel/body side step.

I reinstalled the belts the belts and fired it back up. Other than it being much louder with everything turning there wasn't much difference in the vibration. Man that fan is loud.

Now. I was reading another thread in the '73-'79 forum about power valves in Holley carbs that made me suspect that mine may be bad. I seated the driver side mixture screw and sure enough she kept running. I doubt that has much to do with the vibration but I want to get it fixed and try these tests again.

oil question. 15/50.
 

good oil but for more of a extreme application. what are your bearing clearances. i notice in winter i go with a lighter oil for cold weather startups. not sure on your temp situation but 15 50 seems a little heavy for your application. makes truck a little sluggish with the heavier oil Maybe 10w40 or 10w30. depends on the bearing clearances in mains and rods. .001 to .0015 don't need heavy oil in this engine for your application. this is my question. that is a good oil you are using just questioning the application.:-blah

I thought so too but that's the oil the builder recommended. I was planning on going down to rotella 10w40 after 3k.

Depending on what intake you're using you may have to crank both idle mix screws in all the way to see.

If the carb is creating a misfire at certain loads/rpms that could very well be what you're feeling. Get the carb sorted and then go from there. Is it new or rebuilt?

Power valves don't normally leak unless there is a backfire through the intake that ruptures the diaphram.


If you're running a flat tappet cam I would only use the Joe Gibbs oil, Valvoline VR-1 or Comp Cams "Hot Rod" oil. Rotella or any of the other shelf oils do not have enough ZDDP.

Viscosity would depend on what your bearing clearances are.

Was the crank balanced when it was rebuilt ? There is no way it wouldn't need it being as the pistons were changed out.

It was. Twice as a matter of fact. They had issues with the first set of pistons and ordered a new set. No issues with the second set as far as I know.

I ordered the carb parts last night so once I get it sorted I'll try it again.

Thanks for all the input.