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MG MGB Technical - Engine mounting spacer

I've either mislaid, or never had, the engine mount spacer fitted to the LH mount. What is it there for? (or in my case, what will I be missing?)
Richard Coombs

Hello,

A perfect aligment.

Cheers,

Jean G.
Jean Guy Catford

Well thanks Guy. But I was hoping for a bit more than that.
Cheers
Richard
Richard Coombs

Chrome bumper mounts and chassis mounting brackets have round holes that bolts are inserted in, but the distance between the chassis mounts has a certain amount of tolerance. Unless the chassis mount spacing is spot-on the engine will either sit higher or lower, and the holes won't exactly line up to allow bolt insertion. On wide-spaced mounts the engine could be raised so the bolts could be inserted, but when released the rubber mounts will be in shear and possible stretch rather than compression and so will fail earlier. On close-spaced mounts unless you can force them downwards enough i.e. by compressing the rubber you won't get the bolts in. The spacer(s) compensate for these variations and allow the engine to sit in the vee of the chassis mounts i.e. the rubber mounts are only under compression while still allowing the bolts to be inserted.

Rubber bumper and V8 cars have slotted chassis mounts, partly to compensate for different spacing but partly because the rubber mounts have studs that must fit into the slots as the engine is lowered, rather than a bolt being pushed through afterwards. They also have spacers, to make sure the engine sits in the vee such that the mount bolts aren't on the bottom of the slots with wide-spaced mounts, which causes the aforementioned shear and stretch forces. However they also have location plates under the chassis mounts so ensure that the mount bolts can't sit too high in the slots, which causes other problems like the engine being too high for the bonnet and prop-shaft angles.
Paul Hunt

I replaced the mounts in my 80LE and couldn't get proper alignment afterward. Might have been because a previous owner left the spacers out and the mounts wore out due to the added downward weight of the engine. After seeing a pic of the spacers in a catalog, they looked identical to the bottom metal part of the motor mounts. I separated the bottoms from the rubber on the old mounts, cleaned, painted and dropped the engine back in with a perfect fit. Thus, if you're replacing your mounts, use the bottoms of the old mounts to save money and time waiting for new spacers.
Rick Penland

Richard,

Sorry to have been so brief. But Paul gave a more encycopedial answer. In fact it is easy to make a spacer with 1/8" metal plate. I have to do that once when ordering delay were too long to enjoy a MGB.

Cheers,

Jean
Jean Guy Catford

Thanks gents. All is clear. Good idea Rick.
When it comes to installing the engine is the 'test' simply to lower the engine fully into place without spacers to see if the mount holes line up? If they do, no spacer; if not the add a spacer. And is the rule only to add a spacer on the LH side? From Paul's description I don't see why either, or both sides can not be used.
Cheers
Richard
Richard Coombs

Workshop Manual only shows one, on the carb side, and the Parts Catalogue only specifies one, possibly because the tolerances on the chassis rails are such that only one should ever be required on undamaged bodies. Maybe it's specified that side as it is easier to fit with the alternator installed. On the V8 it's usually the other side that has to have a spacer added, to stop the exhaust manifold hitting the inner wing, as the torque of the engine compresses that side, and clearance is minimal.
Paul Hunt

This thread was discussed between 24/06/2009 and 27/06/2009

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