Re: engine vibration

Posted by Joe on February 26, 1998 at 14:44:56

In Reply to: engine vibration
posted by Joe Koehler on February 26, 1998 at 13:48:04

The problem is, when the engine is running at any speed above idle speed ,the vibration seems to be excessive. Maybe the crankshaft/flywheel are out of balance?
Could be...
I would guestimate the problem to be (in decreasing order of likelyhood)
1. Former owner neglected to dynamic balance the v-belt pulley, crankshaft, and flywheel/clutch assembly as a unit.
This is very likely since most shops can't afford the cost of dynamic balancing equipment and it is difficult to find someone to do it or know if it is done right.The fanbelt pulley, crankshaft, flywheel and clutch pressure plate (without the disk) should be done as a unit if possible.
2. Flywheel housing out of alignment with the crankshaft axis.See MAFCA books "How to Restore Your Model A" which will tell you how to insert shims to minimise distortion of the flywheel housing and check for alignment.The engagement/disengagement of the clutch with the transmission in neutral should give you a clue here.If the vibration changes dramatically as the clutch is disengaged, look further into this.
3. Your original two bladed fan may be headed for centrifugal destruction.The low speed at which you describe the vibration beginning might tend to indicate this is the problem since the fan spins faster than the engine does.I prefer not to run an original "airplane blade" fan since it is hard to know if it is safe.You can remove the fan belt and run the engine for a short time without the fan or generator and see if this makes a difference.
4. Your engine may be missing at higher speeds.Short out the spark plugs one at a time with a screwdriver.If you short out one and no change to the engine speed or apparent ease of operation results, that is the missing cylinder.
5. Check your engine supports to be sure they are firmly bolted to the frame.Sometimes just the thrashing around of a slightly unbalanced engine magnified by a loose connection will make things worse.This is a good idea even for smooth running engines.
6. Center main wiped in some way.Usually this is a "knock" rather than a "vibe".Hard to check for sure without tearing down the engine.
Of course, the Model A being the *non-precision* machine that it is, is likely to have a lot of rattles and rolls that our modern ears are not used to.Otherwise, there would be no market for the "Float a Motor" and other fixes that have come to be used through the years.
(Taking the other tack) Also keep in mind that "If it don't sound right, it probably ain't".If the problem is getting worse, it isn't normal.
Hope you find out what's going on.Let us know.
thanks,
Joe

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