428 vibration

[rblong]

I have a slight vibration on my 428 at idle (about 800 rpm). It isn't consistant. The engine had 6300 miles and on it when I bought it. I have put a few hundred on it since I got it and can't seem to determine what it might be. The vibration kind of comes and goes. No sound change, but you can feel it in the steering - not extreme, but your can just feel it every so often. Almost feels like belt flutter (as if you had a loose alternator belt), but the belt is not fluttering. As soon as your off idles it is smooth. Almost feels like a resonance vibration. All temps/pressure are great. Does it have something to do with being externally balanced? Any help would be appreciated.

I guess I should add I have not checked the obvious things yet like water pump bearings, alternator bearings etc. I guees I was tryiog to determine if this is usual to a 428.

[SCOBRAC]

It makes no difference how things are balanced as long as they are balanced. The 428 has no more or less issues with balance than anything else with hundreds of moving parts.

That it seems less at higher rpms is more a symptom than a cure. It is still vibrating, and vibrating more, but so is everything else.

You might try removing the pullies rotating them 45 or 90 degrees and seeing if that cures the problem. Quite often during a rebuild they are reinstalled slightly askew. Look for loose or missing or mismatched fasteners (one bolt longer than others) I know this seems pretty picky but it helps. Make sure if the pully looks like it had a weight welded onto it it still does.

It is possible but unlikely you got a vibration dampner off an scj or even a 390 / 427. They are different than a 428. verify the part numbers before you put the pullies back on.

Second to worse case is a misaligned pressure plate, mismatched bolts on the pressure plate can cause the symptoms you describe. A few grams is no big deal at the centerline of the crank but spread that same few grams to the outer edges of the rotating assembly (pistons or flywheel) and it becomes pounds. Worst case is a rotating assembly balance issue.

[rblong]

Michael - Thanks. I agree with your suggestions. I had a flywheel out once and caused the same thing, but it was at higher rpms only. I know a rotating asembly, is a rotating assembly, etc, but thought I would post it before going deeper. I actually have a vibration analysis/balancing tool I use in my business on all sorts of rotating assemblies. Do you know if anyone publishes recommended vibrations levels for FE motors? This is my first expence with Ford motors and I don't knowwhat externally balanced means. I am accustomed to balancing every components while assembling.

Bruce

[ted]

If the vibration is just showing up at idle and is intermittent or comes and goes, then engine balance itself is likely not the culprit. If engine balance is an issue, it will show up the worst between 1700 and 2100 rpms when bringing the engine rpm's up in neutral. As this vibration is showing up at idle, then check out the accessories such as water pump, alternator, belts, pulleys, etc. Check that the belt pulleys do not have rust pitting within the grooves also.

This particular vibration could also be carburetion related in that you have a carb that's leaning out or surging on one side of the carb and causing an intermittent leanout that feels like a vibration. This would be more noticable on a dual plane intake and not as much on a single plane manifold. You might try cleaning all the air bleeds and see if that helps. A warped throttle shaft or misadjusted blades can also cause this where the throttle plates are not exactly alligned with each other. A vacuum gauge might be of help if this is the problem as you'll see the an erratic vacuum reading or one that's not rock steady.

The harmonic dampers on the Fe's are all zero balanced from the lowly 352 up to the 427 and the externally balanced 410 and 428. Although they may vary in size or weight, they are all zero balanced (SCJ included) and are basically interchangable. The 428 SCJ used a sleeved "pie cutter" counterweight behind the damper in which to compensate for a missing counterweight at the middle of the crankshaft but the damper itself is still zero balanced. The only nuance here is if the balance shop balanced the rotating assembly through the damper (a balance shop no no) and the damper is replaced later. Then you're back to an unbalanced rotating assembly again.

Ted Eaton.

[rblong]

As always I appreciate the feedback from everyone. The coming and going part of it is what seems strange to me also. I am going to put my analyzer on it and it will tell me a lot. I will probably have to have one of my guys help me analyze the data, but I know it will tell me at what frequency, plane, amplitude etc., This should narrow the possibilities.

Bruce