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MG MGB Technical - Stretched motor mount , cause?

1977 MG MGB.

Today I replaced a motor mount with only 2k miles on it, passenger side. It was stretched about 1/2" rearward. The rubber was compressed to about 3/4" with cracks in the rubber. The drivers side was elongated toward the engine but not pulled back. The installation appeared normal when I put them in last summer. The car has no apparent accident damage. However, the body plate the mount bolts into is indented 3/8" on the bottom.

Based on how difficult is was to install the new one, and how I can already see the new passenger side stretching back I expect it to happen again.

I'm looking for suggestions on the cause and cure. One possibility is the transmission support bar. There are three holes on each side of the undercarridge and my bar is bolted as far back as possible. Is this correct?

Any ideas are appreciated.
Brian Denis

Brian. My experience is that the transmission, when bolted up to the crossmember, will determine which set of holes are used. I only remember two sets of holes and captive nuts per side, but I may be wrong on this.

If the engine and motor mount do not line up, there are a couple of reasons.

First, the car has been hit and one side of the frame has been moved backwards. Check the rails in front of the engine and forwards to see if you can see signs of accident damage.

Second, the front engine plate is bent. If so, the rear bolt for the motor mount would not fit in and the bent front plate should be very obvious.

Third, the transmission cross member is bent and is skewed to the driver's side, pulling the passanger's side of the engine rearwards. It has been two weeks since I have been under an MG, and I am getting older. But, as I remember it, the drive shaft is centrally located in the tunnel. If it were a problem with the tranny cross member, I would expect the rear of the tranny to be out of line, the front of the prop shaft (Brit for a drive shaft) to be out of alignment and your U joints to develop problems rapidly.

Thus, my best guess is accident damage. This can best be discussed with a body shop or mg specialist. They can tell you what needs to be repaired/replaced to correct the problem. They can also tell you how safe to drive the car would be with this type of damage. The back up plan would be to relocate the hole in the right hand motor mount so the engine is sitting correctly. This may require the fabrication of a new mount, or simply welding in a filler piece for the old hole and cutting a new one in the existing motor mount.
Les
Les Bengtson

Les, thanks for the suggestions... I'll look into all of them.

I don't suspect accident damage because I've been all over the car in 2+ years of refurbishing and see no evidence. Also, the original mounts that I took off did not show this stretching which makes me think it's something I did.... or something related to replacing the engine.

The engine is a refurbished one and I did have to swap the front engine plate. The mount brackets that bolt to the block are another suspect that I plan on replacing. I removed the two shims on the passenger side this time to help alleviate the compression on the mount.

Any other suggestions are welcome... thanks!
Brian Denis

I am bound and determined to find a replacement for stock rubber bumper front sngine mounts. The left side is just awful.
BL ought o be ashamed! [or whomever is responsibile]

I am open to any and every suggestion.

Safety Fast
Dwight
Dwight McCullough

Dwight,

I have been through changing the mounts on both my four banger 1.8 and today on my 3.5. When I had the four cylinder I managed to fiddle in the nut on the left rubber mount when the engine was out.

With the 3.5 V8, it couldnīt be done that way so I took the steering out. The steering came out with a little persuation. After that it was a piece of cake to bolt up the mounts, even with the engine in the car.

Regards
Erik
Erik

If these are the round type motor mounts, did you try spinning it around 180 degrees. The single mounting screw that bolts to the crossmember is offset to one side.
William Bourne

The mounts are the round variety and I tried them every way possible. They are installed with the bolt offset "up"... meaning the bolt is high and the bulk of the mount rubber is down.

I have considered changing to the original square ones to see if that makes a difference.

Thanks for the input William.
Brian Denis

My V8, which uses the same mounts, came with the gearbox cross-member bolted to the front two holes one side, and the rear two the other! If I tried to use the same holes both sides the mount was pushed one way or the other as you describe. In my case the mounting plates that bolt to the block were on the wrong sides of the engine - they are handed but there is nothing on them to indicate it, and the difference is about 1/2". The crank pulley also tended to foul the (thicker) anti-roll bar under heavy braking, but the main resolution only came when the sump started leaking where it had been resting on the cross member and worn through! Swapping those plates over with the engine in-situ was quite a challenge. Funnily enough a couple of weeks after I resolved it I went to a classic car show where they were reshelling a V8 with one of the first V8 bodies from BMH. They were obviously having problems getting the engine in, and I could see they had the plates on the wrong sides. They swapped them over and all was well. FWIW when on the correct side of the V8 the engine is in the rearward of the two possible positions, I've no idea if the 4-cylinder is similarly affected.

I've had to replace the rubbers twice, and managed to fiddle the nut and washer onto the chassis rail side of the driver side rubber by 'glueing' them to a spanner and getting it started by rotating the mount, then bolting the mount to the engine plate, then tightening the nut 1/2 a turn a time by turning the spanner over. Even then it needs a slim spanner.

Because the studs on the mounts are angled mine would not drop straight into the slots as they fouled the outer ends, so I had to twist the engine a bit around its crank axis to get one in, then twist it the other way to get the 2nd in, then straighten it up. The other thing is that the old rubbers were distorted as if the bottom steel plate hadn't slid far enough into the Vee of the chassis plates, so I smeared a bit if oil on the new ones and tapped them down a bit with a hammer and drift after the engine was sitting on them.
Paul Hunt

This thread was discussed between 02/04/2005 and 05/04/2005

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