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MG MGB Technical - Transmission engine restraint rod question

1977 MGB roadster.

While under the car I noticed the nut on the engine restaint rod was not tight. This is the nut on the cross member end. I tightened it up pretty tight. Now I'm getting significant vibration from the engine while accelerating. I'm assuming I've overtightened the nut.

My question is how tight should that nut be?

Thanks in advance for any input.

Brian Denis
Brian Denis

I think that bar is there to stop the engine/gearbox from moving forwards when braking. The nuts should be done up so that you're not putting any tension or loading on the engine mounts. At least that's the logic I used! I can't remember off the top of my head if those nuts are those domes ones (a bit like nylocks) so they don't come undone by themselves?
Simon Jansen


It should have rubber mountings, look at the Moss catalog on line.

Bob Fisher

Simon, great post, thanks. You started me thinking and I took another look at the rod. The forward nut is screwed all the way in. When I tighten the back nut I am probably pulling the engine rearward. Tomorrow I'll slaken the forward nut and see if I get some give, then I'll tighten the rear nut against the rubber mountings and therefor the forward nut.

Bob, thanks for the input. Actually it was the VB catalog that was most helpful. Moss doesn't show the nuts on their gearbox mount page, VB does. It was the forward nut and it's purpose that I was overlooking. I was just cranking on the rear nut without even considering the purpose of the forward nut.

Thank you both again for taking the time to help out.

Brian Denis
Brian Denis

I deleted the stayrod 30 years ago and have never had a problem. If your motor mounts are in good condition, the stayrod is redundant. RAY
rjm RAY

And then you hit the right pothole, or have the slightest bump to the front, and the fan eats the rad. Rough railway crossings are good! I've replaced a few.
If all the parts including the spacer tube are present and good, the restraint should be tightened with no fore/aft preload on the mounts. The nuts are tight on the tube.
Different years have differing arrangements, so check that you have a "set" of bits.

FR Millmore

I've seen some engine mounts that have an extra steel angle bracket that serves the same purpose as the rod. I noticed it after I installed a rod to a car that didn't have one. So, I guess now it has a belt and suspenders.

Also, doesn't that rod have some adjustment so that it can be tight on both ends without pushing or pulling the engine?

C R Huff

Thanks for the input, all good stuff.

It's been 5+ years since I've looked at the tranny area other than to watch the front & rear seals slowly drip oil. I have no recollection of the spacer being installed. I've ordered a complete set of buffers and the spacer and will install them correctly. When I pieced the car together I probably didn't give this area enough thought. I've always had a vibration on initial acceleration and I'm hopeful this could be where the problem lies.

Brian Denis
Brian Denis

I think all the aftermarket books are incomplete or wrong, but certainly don't have pics of all the pieces. There seem to be two different versions of the angle brackets Charley mentions; they were on c70-74 cars, a result of the scandal of the day "unrestrained engines causing unintended acceleration"! I can't remember all the details, but it may be instructive to tell you that these were frequently badly bent from the engine moving forward, despite the car not having been crashed. And they got left off a lot, since it made getting the mount bolts out/in much more slow/difficult, in the days of flat rate mechanics.

77 will have the latest type, with the vertical pin and bushes for that, in addition to to the stay rod and assoc. parts, and the main gbx mounts. This is a demented assembly, and you will be when you get done. It is possible to get some pieces in backwards, such that they put wrong loads on other parts. Keep switching stuff around until it all lines up; I can't begin to tell you how to do it without one in hand, so good luck!

FR Millmore

I've never seen the brackets Charley and Frank talk about actually on a car of that era, probably for the reasons Frank mentions, and although they are shown in the Parts Catalogues none of the usual suspects in the UK have ever heard of them. I've been fortunate ... so far.
PaulH Solihull

Paul -
There was a lot of flap about vehicles having "uncontrolled acceleration" about then, just like a few times since. And if course just like today, it was a few poorly maintained and operated vehicles causing the trouble. And the US Gov started passing regulations. The problem was bad or broken motor mounts letting the engine rotate, causing the rigid throttle linkages to go wide open. Never a problem on the cable operated linkages, but you couldn't explain that, and the associated for/aft movement was becoming a problem with the first "no damage" requirements for low speed crashes. So BL came up with the brackets as a quick fix, kept them under the legal radar in the US. Other companies subsequently came up with motor mounts that actually ARE much better at restraining engines under all conditions, BL managed to make it worse with the intro of the round mounts with bad brackets and horrid serviceability.

- that's Fletcher, don't know how or why my revised signin has reverted to the earlier form.
FR Millmore

Of course, Fletcher, sorry about that. My selected options also change or revert from time to time.

It's to prevent the fan chewing up the rad that I'd like to insure against. Ordinarily the inch and a bit clearance should be enough, but if a mount parted (which I've had on the V8 but that has electric fans) it almost certainly wouldn't be.
PaulH Solihull

This thread was discussed between 06/09/2010 and 11/09/2010

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