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MG MG Y Type - Engine? vibration

OK, here's one for all of you wizard diagnosticians out there in Y land. My Y, Y5095, has a strong vibration at what seems to be engine speed and under load. Idle seems smooth. When still not up to full temp the vibration is muted, but as the engine ( and probably trans, diff., etc.) reach operating temperature the vibration increases to unpleasant levels. It is highest in 4th gear(highest load) but still present in lower gears. It is especially strong on overrun when slowing down. What brought this to a head was a little trip on Thursday when I decided to take it out for a spin and run an errand. The engine ran smooth as glass ( as I suspect all of yours do all the time!) on the way out; about ten miles. After about a 15 minute wait while I was in the store, I proceded home, but the old vibration was back. I have changed out the plugs and wires, checked points and timing, compression, and even changed the coil. All fluids were recently changed, too. New u-joints this spring didn't change anything.

Any suggestions? I want that smooth running back, I have had so little of it since I acquired the car.
Paul Briggs

I had this problem on a 1954 TF, I found that when the heavy vibration was present I would push in on the clutch pedal , rev the engine a little then release the clutch and sometimes the vibrations would go away, I ended up driving from Atlanta Georgia to Tampa bay Florida. This is approximately 500 miles of hard driving with this problem with this problem. I replaced the clutch pressure palate and disk and the problem dissapeared. I cannot remember how many times that I had to repeat that push the pedal rev the motor and release the cluth that it took but I am certain that it made the rubber pad on the clutch shiny. Hope that this might help.
Sandy Sanders
Hudson Florida
conrad sanders

Paul

Does the problem continue when you rev the engine while standing still, or only when in motion?

If no - check your prop shaft bolts for tightness, UJs for play.

If yes, do you have a heat shield fitted? Yes - post your query to the Technobods on our Technical Page on www.mgytypes.org.

If no, are you using a tank of petrol from a gas station you'd not normally use / had a lot of rain in the area recently - could still be water in the petrol, but still worth running past Neil & David as above.

Paul
Paul Barrow

Some interesting things to consider. Sandy, thanks for the info. I am having to assume that this is the original clutch with 88K miles, so things are certainly worn. Perhaps something is so worn, or broken loose, that it has shifted and now the clutch assembly is grossly out of balance. That might explain how it occasionaly miraculously "heals" itself, or disengaging, revving, engaging might help for a while. The vision of loose parts flailing about in there really helps me sleep at night!(Not)
Now to Paul's questions. Yes, the vibration does feel like it is still there when revved sitting still, just not nearly as strong. Back when this vibration first started to annoy me I had the UJs replaced and I have checked the bolts more than once. The new UJs made no difference. I assume you are referring to a carb heat shield? No. As to fuel, this has been an ongoing problem for many months and tank fills, at several different stations, with no noticeable changes, so I rather doubt the water theory. I could try draining the tank to be sure, though.
Paul Briggs

Does it happen in reverse? Check your engine and gearbox mounts also the steady bar to the water pump!
Richard Prior

Some thoughts on vibration: Although I have had a few MG's over the years, I never used a Weber carb. until we installed one on my cousin's 1980 MGB. There was always a vibration period, under load, between 2800 and 3200 RPM, which I thought mechanical. Turns out is it was carburation. The vibration completely dissapeared with the Weber, top end speed increased, and overall perfomance was more like an old pre-emmisions car. Of course we had discarded the Lucas Electronic distributor, and replaced it with a new 1974 points distributor from Moss Motors.
When I overhaul a transmission, I spray Moly Dry Film Lube, Dow Corning #321, on the input shaft spline. It goes on wet, but dries quickly, and works into the steel for permanent lubrication. It allows the clutch disc to move back and forth along the spline with out sticking or galling. I use Moly Pene-Lube on all the gears and bearings, and finally add M(for Molybdenum DiSulfide) Gear Oil Additive, 5-10% by volume to the gear oil. The Moly will actually heal any pits on the gear teeth, prevent metal-to-metal contact, reduce heat and noise, and increase fuel mileage. Add some to the differential oil, as well.
Scott Barrow

This thread was discussed between 23/11/2002 and 18/12/2002

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