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MG Midget and Sprite Technical - New Vibration-symptoms=diagnosis?

Hi Folks,
Here it is-New, rebuilt engine last spring, 1000 miles a week all last summer, 300 miles a week September -end of october-smooth strong. Changed the oil before I put it to bed for the winter.
Driving it since March-smooth strong engine. Last week I thought I heard a sound like a clicking while excellerating in 2nd or 3rd (can't recall exactly) but then I never heard it again and no further symptoms till this morning.
First 15 minutes of the trip-no noticable concerns, slowed to a stop to turn left at a light... 1st gear smooth acceleration to 3krpm, shift to 2nd and quite noticible vibration throughout the range to 3.5k. Shift up to 3rd same, and to 4th same. Blends in to the normal feeling vibration in 4th around 3.5k.
I tried to experiment a bit. Taking my foot off the accelerator pedal I don't believe I could notice the vibration-eliminationg possible tire problem (I think). It seems to roll smoothly. If i have to lift to slow for the common variences of traffic, when I re-apply pressure to the gas pedal the vibration returns.
So...could it be either transmission or axle fluid level (it's raining so I can't get under the car today to check :( )Could a transmission bolt have vibrated loose? Is the engine really not idling smoothly and I have a bad spark plug? (gonna check the plugs after it cools down) New longflo air filter-could it have anything to do with the fuel/air mix, even though it hasn't presented itself for the past couple of months?
Just hoping for some suggestions and the simplest, cheapest possible problem. Keeping my fingers crossed...Mike T
Mike Taylor

Sounds like a misfire to me - i.e., one of the cylinders not working.

Have you tried pulling individual spark plug wires while idling? If you remove a lead, and the idle doesn't change, you have a dead cylinder.

In the meantime, verify that all your ignition leads are pressed on tightly.

-:G:-
Gryf Ketcherside

Hi Gryf,

That's first on my list. I'm battling a terrible sinus cold and the weather here is crap, but I'm going out in a bit to check that very possibility while keeping my fingers crossed!!


Mike T
Mike Taylor

...and do a compression test.
Dave O'Neill 2

Pulled the plugs 1st since the engine had cooled sufficiently. Normal wear-light gray brown color, .027 or so gap throughout all 4. Started the engine and removed 1 lead at a time-slight loss of rpm on each occasion. So, not that. Looking in the Haynes did bring up a concerning possibility.....worn u-joint/s. I'm still hoping theres a cheaper cause becuase I have absolutely no spare $$ till God knows when :(
Mike Taylor

Can you get it to make the sound while the car is stationary? If yes, check your motor mounts. Had a similar problem some years back when a (new) motor mount failed. Took forever to track it down.

Richard
R J Reeves

Thanks Richard-one of the first things I looked for when I got to my destination this morning. I had a suspision that it was in the drivetrain somewhere, Haynes fault diagnosis seems to be the thing this time I'm afraid.
Mike Taylor

You can usually diagnose worn UJs by simply crawling under the car and rotating the driveshaft by hand, looking for any play in the joints. Been there...

-:G:-
Gryf Ketcherside

Thanks Gryf-yea, just waiting for the weather to dry out. I'm so convinced that that's the problem I ordered 2 Duralast U-Joints from auto Zone last night. 2 year limited warranty total cost with S&H $27.48 Might be here with the sunshine by this weekend. Any tips?
Mike Taylor

This thread was discussed between 12/05/2010 and 13/05/2010

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