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MG Midget and Sprite Technical - crankshaft damper

Hi,
I have a vibration at 4000 rpm that is causing problems with the carbs ability to deliver fuel. I have several options. Rubber mount the carb. This will just cover up the symptoms. Engine mounts may have gone hard, so I have ordered some new ones (I hope they last). I can strip, lighten and then balance reciprocating parts (I may as well lighten them whilst they are being balanced). And lastly I can fit a fancy crank damper but they seem expensive.
Has anyone any experience on the modern dampers or eliminating vibrations?
Thanks
Dave
Dave Brown

Assuming your is a 1275 engine then the standard front pulley/damper usually works fine. Has the vibration just started or has it always been a problem?
Bob Beaumont

I think it has always been there, I just didn't know that it was a vibration. The damper is likely to be over 40 years old and the rubber must have hardened by now.
Dave
Dave Brown

Dave, they're all over circa 40 years old, and most people aren't having a problem. How have you isolated the vibrations to the crank damper? Is it visibly perished/damaged?

Not saying you aren't right, but it's not that common. -- Is it?
Lawrence Slater

They can play up but its not common plus they aren't available any more to the same quality.

Other things to check externally are the fan, dynamo/alternator bearings,water pump. if it not these then it could be the clutch or badly worn flywheel ring gear but its an engine out for that. More radical would be a crank rebalance but that would mean an engine strip of the bottom end.
Bob Beaumont

I am getting a squeal from the clutch release bearing every now and again so I think the clutch will need looking at sometime soon. So when the engine is out I can check the flywheel. I think I will also take the opportunity to balance and lighten the flywheel, crank, rods and pistons.
The alternator is new and looks ok. The fan and water pump look fine and there are no strange noises so there is no hint that they may be causing the vibrations.
Dave
Dave Brown

If you are having the crank out then its worth giving it a check anyway and or renewing the bearings. A decent bottom end and rods balance does make the engine much smoother and last longer. The factory balance was not bad but over the years it will have had different clutches and the ring gear will have worn. Thereis not much else that moves other than the tranmission. I guess the prop shaft uj's are ok??or is the vibration noticable stationary?
Bob Beaumont

Have you checked the propshaft UJs? Even a worn rear one can seem like the vibration is at the front of the car.
graeme jackson

I had the problem all 3 crank dampers I had for my new engine build where sh*t.
Rubber gone or cracked.

So I went for the cooper s setup available from minispares.
Seperate pulley and damper (MED have more variations but also more expensive)
It needed some work but is now balanced and ready to fit.
Was the cheapest quality option as the normal 1275 damper is NLA
Onno K

I have not checked the UJ but the issue can be demonstrated with the car standing still, in neutral so the prop shaft will not be spinning.
Dave Brown

Dave,
are you sure it isn't a slight misfire?
Guy W

Hi Guy,
It did not show up as a misfire on Pete's rolling road.
Dave Brown

This thread was discussed between 21/04/2013 and 22/04/2013

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