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By Dooley - 4 Years Ago
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Hi all, I’ve been trying to sort out a bad vibration it’s bad enough to make her un-drivable. Vibration starts through out rev range, stationary, clutch in or out. Things I’ve already done: machined & balanced flywheel, clutch & pressure plate, engine mounts, rebuilt Damper, spark plugs etc, cab bolts & engine mount bolts all tight. Vibration doesn’t seem bad under the hood but really noticeable in cabin, steering wheel vibration is real bad & cab shakes & rattles. It’s getting real frustrating as even local mechanics are scratching their heads. Cheers
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By Ted - 4 Years Ago
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You don't mention how long or when this problem started which could help in determining the cause. How about disconnecting the belts and cranking up the engine to eliminate a vibration originating from one of the engine accessories? Another option is performing a compression test on the engine which would help to rule out a weak or dead cylinder.
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By Dooley - 4 Years Ago
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I purchased it with the issue thinking I was an easy fix. I’ve removed the belt and no change, number 2 piston is down lower compared to the rest but not way down.
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By Deyomatic - 4 Years Ago
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Does it happen when it's moving? I had an unknown vibration in my old 55 Fairlane where the driveshaft was slightly out of balance and first took out my driveshaft yoke/ tailshaft seal- so I replaced the seal. Within a couple of months the vibration was unmanageable. Turned out that unbalanced driveshaft took out my tailshaft! Ended up getting a used tranny and having a hot rodder buddy make it fit.
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By Dooley - 4 Years Ago
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Vibration the same when stationary.
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By 55blacktie - 4 Years Ago
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Internal balance? Did the seller provide any history? How long had he owned it? When did the vibration begin?
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By 55blacktie - 4 Years Ago
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Does it get better/worse with change in rpm?
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By Dooley - 4 Years Ago
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Seller won’t return phone calls unfortunately. Gets worse with higher rpm, a friend said it might be main bearings? I’ve had it just under a year and been trying to sort it out ever since. I’m convinced it’s internal balance issue as I’ve tried everything else I can think of.
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By Ted - 4 Years Ago
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If the engine was rebuilt or throwed together with a hodgepodge of parts, then an imbalance due to a mismatch of parts would be high on the list. If the oil pressure is good, then worn main bearings is low on the list. Check the head casting numbers on the heads to verify that both heads are the same. At this point, there’s also the probability that one head is milled much more than the other. While this has likely already been performed, check the spark plug wires for having the correct firing order. You don’t mention valve lash but that should also be double checked.
I’ll still suggest performing a compression test as that may give a better idea of where to look when the engine is torn down for examination. While the spark plugs are out for the compression test, examine them closely for any irregularities in the color or burn patterns.
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By panel driver - 4 Years Ago
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You mentioned that number 2 piston is down lower than the others. Maybe mismatched connecting rod length,
or bent connecting rod. Try checking running compression. Just a stab in the dark.
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By DryLakesRacer - 4 Years Ago
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Sounds like one 312 rod which would cause imbalance if a piston is low in the cylinder An hydrauliced rod would just have a “ess” in it if you removed the pan. I had a 283 go over 100,000 miles with a bent rod.
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By rladams65 - 4 Years Ago
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Since the frame shakes, I would have guessed drive shaft balance (and possibly the yoke / u-joint) - but if it happens in neutral, then I am less apt to pick there.
It is realtively easy to pull the heads and weigh them.
At this point, everything else I can think of is a a lot of work to diagnose. For instance, you could measure the shake on the engine top while it is in the car vs. on a stand ... to isolate/debug the connection between those major system groups.
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By oldcarmark - 4 Years Ago
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What are the actual Compression readings? High to low should be within 10% of each other.
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By Dooley - 4 Years Ago
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Happens when stationary and moving
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By Ted - 4 Years Ago
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Have you performed a cranking compression test?
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By Dooley - 4 Years Ago
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I have mate, number 2 piston was lower than all the others.
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By Ted - 4 Years Ago
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Actual compression numbers would be helpful. Performing a leak down test would provide some additional information before actually taking the engine apart. If the leak down test indicates 5% or less leakage, then cylinder sealing would at least be eliminated from the list of possibilities. While performing a leak down test, do all the cylinders and not just #2 so you can get a range of values.
Assuming cylinder leakage is within acceptable limits, removing the right bank cylinder head and measuring piston to deck clearances could potentially indicate a short or bent rod or even possibly a piston with a different wrist pin location. If the deck heights check out okay, then you may be simply dealing with an out of balance rotating assembly with an odd ball weight piston being at the top of the list.
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By Dooley - 4 Years Ago
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Thanks Ted, I will keep you posted once have have time to work on her again.
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