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MG MG Y Type - Vibration revisited

To continue a discussion from late last year-

I had been fighting a vibration in Y5095 that made driving very far rather unpleasant. A strong rumble that began after a few miles into each trip and seemed to get worse as it warmed up. I have had the u-joints replaced and the drive shaft professionaly balanced, but no improvement.

Willem van der Veer has had what sounds like the same problem, and someone suggested checking the rubber bushings and setting of the "engine control link", or steady bar as some have termed it. Well, after inspecting the bushings and finding them in reasonable condition, I began to think about the setting of the link. I have no way of knowing whether it was ever changed from factory settings, and supposedly the engine has never been out, so I decided to try pre-loading the link by shortening it by about 1/16 inch.

Instant improvement! The vibration wasn't completely gone, but noticeably less. Another 1/16 inch of preload has seemingly fixed the problem (Knock on wood, rub my lucky rabbits foot, etc.). The weather has prevented extended trips but I have real hope now.

Willem, have you tried this adjustment yet?
Paul Briggs

This suggests there is a touch-point on the engine/chassis. Pre-loading the link will not cure any inherent vibration problem, as it will still be present in the rotating masses. The engine and gearbox sit ontop of three rubber mountings. The front one is bolted to the front cross member and the timing chain cover mounting. The two rear ones are loose, with the gearbox simply sitting on them. The gearbox is then held down onto them by a small eye-bolt undernreath. This has rubber top-hat bushes to insulate it.

Touch points can be where the gearbox mountings have fallen to bits with oil contamination, or the front mounting has delaminated. The exhaust pipe can touch the pedal box, and the gearbox cover the top of the bell housing. It needs a good checking over to find the bit touching. The exhaust should be bolted rigidly to the underside of the gearbox, but then flexibly mounted aft of that. Very old and hard rubber water pipes can pass some vibration to the radiator.

By moving over the link by 1/16, you musy have pulled the engine/gearbox unit away from the bit that was touching.

Neil.
Neil Cairns

Paul,

I haven't tried preloading the engine control link, but I think it can be a way to find the vibration. I'm afraid that if the control link is subjected to too much load, the mounting may share? The water pump is also at risk if the link-rubbers are dodgy?
If you shortened the link the cause of the vibration should be on the left side of the engine?

My vibration occurs only at higher revs, cold or warm, also in neutral and I stil have to try if depressing the clutch makes any difference. But because of the juddering clutch I plan to take out the gearbox and than I will be able to have a good look at all the mounting rubbers.
Willem van der Veer

Neil-

You make some very good points, as the vibration always showed up when the engine/trans reached operating temperature, so heat expansion may have caused a touch point. The small amount of repositioning caused by preloading the link may have pulled it away from the contact. With the improving temperatures here I will closely inspect it for contact. I will add that when I was playing with the link I completely disconnected the outer end and rocked the engine by hand to see if it wanted to settle at a different position (it didn't) and did not feel any obvious contact.

I recently rebuilt the transmission so I know the rubber blocks in the mount are in good condition, and the front engine mount "looks" good, but I will inspect it thoroughly.

Your comment on the radiator hoses prompts me to go install the new ones I have sitting in my shop.

Willem - My concern for putting too much force on the link mounts is why I made a small initial adjustment to the link. If I hadn't detected any change I would have quit playing with the link right away. Your vibration problem has some different characteristics from mine but Neil's suggestions are all worth pursuing.

Paul Briggs
Y5095
Paul Briggs

I had a similar problem with my Y-type some time ago. After fitting a new clutch and at the same time fitting new gearbox mounts I had a very noisy vibration/rumble (even with the car stationary) that wasn't there before! I thought it might have been the new mounts as they were really the only relevant thing I had changed. I took them off and supported the gearbox with a jack and presto the noise disappeared! The culprits turned out to be the new gearbox mounts---they were far too hard! I cured the problem by replacing the old mounts and returning the new mounts to a friend who runs an MG spare parts and workshop here. He was extremely grateful (and relieved) to hear of my experience as he had been getting complaints from customers, in particular one very irate TF owner after a gearbox overhaul--he had already removed the gearbox and inspected it and couldn't find anything wrong with it! Again replacing the old mounts overcame the problem!
Barry Bahnisch

Another culprit might be the "pivoting" fastening bolt between the two rear rubber-mounts of the gearbox. It uses exactly the same type of dished washer and dished rubber that the engine steady link (in front)does.
Quite often the dished washer is mounted upside down, thus touching the chassis' crossmember and starting a rattling noice.
Anton Piller

This thread was discussed between 25/02/2004 and 27/02/2004

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