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MG MGB Technical - Motor-mounts... Bad habit of falling apart.

I have an 1980 B, modified engine (alhough I almost never drive it hard) And of the past 10 years, Ive gone through probably 5 motor-mounts. Its always the one of the left that breaks... First it starts to sag on the right side, which puts the mount in a bad-looking state (the plates are off-center, and the bushing gets stretched into a paralellogram) Now, Im not sure why the engine is to eager to fall down on the right.. but I know its not correct. The oil filter assebly sits VERY close to the frame rail when it does this, and will even tap the frame-rail a bit if the car has any run-on at all after I kill the engine.

After a few months of this right-side sagging, the rubber bushing starts to peel away from the mounting plates, and eventually falls of if i dont replace it.

So...

-Why does my engine not want to sit correctly in the bay? Why is the right side so eager to drop down? It seems like the motor-mounts locate it for the most part... WHy are they having such a hard time!? all the other mounts on the trasmission seem totally normal...

-Is there a better motor-mount that can be used, which is easy to install? Im fairy certain I have the v8 mounts, or tried them... I should note that as far as comfort goes, the mounts have always been PLENTY soft. I could tolerate white a bit more engine shake / vibration, if it meant I could stop fussing with mounts. Im not sure if harder mounts would be hard on the car though. Ive read about "chaining" the engine... but really, this isnt a 300HP V8... Chaining it seems like a bandaid fix... Id rather find a motor mount that can handle a searing 110-120hp. *rolling eyes*
Ben

Ben,

Do you think it could be an alignment problem? When I installed my rebuilt engine back in December, I noticed that there was a twist on the mounts that was stressing the rubber. I slacked all of the mounting bolts and shook the engine/trans with the lift or a jack. That got them lined up without the preloaded stress. I've only put 8 or 9 thousand miles on it since then, so I don't know that I won't have your problem yet.

Also, I think there are some shim plates that were put in some cars if needed. I think they went between the frame mounting point and the steel bottom of the mount. They looked like the metal bottom of another mount, so you may have plenty of them around if you have saved your old mounts.

Otherwise, maybe you are not getting good quality parts?

Charley
C R Huff

I forgot the exact name for it but the plate on the engine that the engine mount mounts to could be bent. I would say buy a new one but I believe there is something in the archives about them being off as well but I could be wrong. Hopefully someone chimes in on that. You also deserve a medal for changing the left motor mount on your 80B that many times. One time is too many. Have any tricks up your sleeve? Or just slow and steady wins the race?

James
James

Well... the drivetrain has been out 3 times durring the course of the mount failures, and the problem persists in the exact same manner. I'll definitly get under there and see what else can be done. It does have the shim plates, but the "adjustment" they make is not the right direction to solve my problem... Ill take a few pictures in daylight when I get a chance... That may help... Regarding the actual bracket being bent or located wrong... Its a possibility, but I have no idea how to determine of its as it should be. Ill see if I can find some measurements, but Im almost certain those are spot-welded to the frame-rail arent they? If I was going to need to remove the original, and weld a new one on... I would probably want to use a more relaible type of mount, and fab up an adapter bracket to weld in place of the original. NOTHING would piss me off more than going through all that trouble, only to watch that stupid mount peel apart again. Someone would be eating that mount for dinner if that happened!

Regarding mount removal / reinstalation tricks; Erm... a good set of deep, thin-wall sockets, and a extention with a U-joint. I'm also a pretty small guy, so navigating under an MG, and getting my arms and fingers where they need to go it probably a lot easier for me. Other than that, it was just as hard last time as it was the first. It always manages to throw me a new curve-ball... But its the same idea as installing the lower seal on the windshield frame, and installing the windsheild frame on the car... Just temper-control, don't force it, and eventually if you poke at it enough, you'll shake something just right, push at the right angle, take the weight off something you didnt realize had jammed, or whatever... If it fit once, and wasnt damaged while it was out... It will (should?) fit again!
Ben

Ben,

This response may not help any; in fact it might only p*ss you off, but I rebuilt the engine on a '76 B back in about '92, tuning it a bit, and proceeded to drive it 11 years and 66K miles with no engine mount failures. Bear in mind, I'm not trying to prove anything. I had heard that the right side engine mount was failure-prone, but beyond that, I did not know what I was doing. The only point is that these engine mounts are capable of sustained service.

So what did I do to make them last so long? I have NO idea! I do remember that with the tricky left mounts, I found I could reach in along the steering pinion with a hemostat and grab the bolt, holding it in position while I changed the mount. Obviously, the flimsy little hemostat would not allow me to snug the mount down very firmly, but I figured it wasn't going anywhere anyway. In retrospect, do you suppose it was the not-so-snug tightening of the mount that made it last so long?

Also, could there be something askew with your engine restraint rod? If the rod were not doing its job, I can see how additional tension on the engine mounts might ensue.

Grasping at straws here, but I hope it helps.

FWIW,
Allen
Allen Bachelder

I have posted the reasons for this - and the fix - numerous times over the past several years. Sorry, I don't have the time to do it again. The last time was a month or so ago. Try to find it in archives. If somebody can remember the thread title(s), it might be easier. If that fails, email me direct.
FRM
FR Millmore

I was curious so to save you the trouble try:
http://www2.mgcars.org.uk/cgi-bin/gen5?runprog=mgbbs&access=&mode=archiveth&subject=71&subjectar=71&thread=200709150331077284

or search the archives for the phrase "prestress the brackets"
Steve Postins

And I didn't grab the "bolt" with the hemostat, I grabbed the NUT.

Nobody has ever called me a bolt!

...Allen
Allen Bachelder

"Just temper-control, don't force it, and eventually if you poke at it enough, you'll shake something just right, push at the right angle, take the weight off something you didnt realize had jammed, or whatever... If it fit once, and wasnt damaged while it was out... It will (should?) fit again!"

Reminds me of losing my virginity :)

Simon
Simon Jansen

Careful Simon, you may remind someone of those Kiwi jokes!!

Regards
Roger
Roger T

You can always trust an Aussie to come throw in something underarm, err, I mean underhand :)

Simon
Simon Jansen

Ouch!!

Roger
Roger T

I think it's legal if you declare you are changing from an OHV to sidevalve action before you buy the car, but it is not considered to be in the spirit of how you should post on the board, or am I confusing cricket and MGs?
On the engine mounts, mine ran it's originals until 1995 when they were changed because the engine was out and I lost my nerve, the new ones went back with the same shims and so far so good.
Stan Best

Since we've probably lost our American viewers at the first mention of cricket they might find this useful:

http://en.wikipedia.org/wiki/Underarm_bowling_incident_1981

It's amazes me just what is on Wikipedia these days!

Simon
Simon Jansen

Simon, Thats a very generous description of events. Was it really that long ago?

And if our American friends could only understand cricket, they might be less confused/confounded by us (and Lucas!!)

G'day Stan, and , yes, I think it is quite probable that an Englishman might confuse cricket with MGs - or anything else for that matter. (LOL, and I hope accepted in the good spirit of safety fast in which it is made!!)

Regards
Roger
Roger T

Did you know that the English were one of the first to recycle news papers? They wrapped their CHISH & FIPS in it.That means they sold old news papers.
Sandy
Sandy Sanders

Well it looks like iI got about as sidetracked as everyone in here :) thanks for the info Millmore, and the fellow who posted the link... I'll check that out.

--
"Also, could there be something askew with your engine restraint rod? If the rod were not doing its job, I can see how additional tension on the engine mounts might ensue."
--

While doing a hasty check-over of the mounting-points the other day, I noticed the bushing on the restraining rod has turned pretty mushy. (It had some oil on it, which looks like it softened the rubber a lot) I ordered a new bushing, athough I dont think its probably the cause, as that bushing was replaced in 2000. But something I did notice... I unbolted the solid-mounted side first, and even with the engine slightly askew as it is now there is absolutly no tension on that rod... But I was guessing that rod was there to keep the fore and aft movement of the engine in check... The odd positioning of the engine seems to have to do with it being incorectly rotated on 2 axes. First, its not horizontally level (x axis). right side hangs down 1/2". It also seems to be slightly rotated on its vertical axis (z axis) so the right mount is stressed down and back, while the right one is *normal* or stressed slightly up and forward.

Anyway... Thanks for the help, and Cricket education guys. I'll see what I can figure out! I'll see if I dont have some better luck wrenching on my car overhand... I'll just have to get it up a little higher off the ground!
Ben

You could also try using the V8 engine mounts. These are supposed to be made of a better rubber, although in every other aspect they are identical.
You might also consider putting in an engine restraint bar.
My car is now a V8 and I used the "under the gearbox" bar and mounted it on the top of the footwell, across the back of the engine.
Peter

V8 are harder rubber, I believe, rather than 'better quality'. I replaced mine which were probably original and had sagged quite a bit when I swapped the engine mounting plates over to the correct sides. The passenger side pulled apart quite soon after, indicated by the gear lever making wild movements on even quite gentle acceleration. The replacement for that side has been OK for some time now.
Paul Hunt

If you can understand cricket I think you'll go a long way to understanding the 'logic' that goes into a British car like the MG!

Simon
Simon Jansen

I was told more heat resistant Paul, but if they are harder as well they might also be less inclined to sag. There is not allot of difference in price so it might be worth a shot.
I know you can put these in the "other" way.
Stud down, not up. I've fitted mine stud up so that they compress and need to be knocked down to come up against the ledge on the bottom of the body bracket and compress a little. I don't remember now what the "correct" way is, this is a V8 set up. Could this be the cause?
Peter

Ben, You said:"First it starts to sag on the right side, which puts the mount in a bad-looking state (the plates are off-center, and the bushing gets stretched into a paralellogram)...

I wonder, have you positioned the gearbox crossmember into the correct mounting holes in the rails? from your description it sounds as though one (left side of car?) or both might be mounted too far forward/backward, depending on how forces are shaping your parallelogram.

There are four mounting holes each side, or at least there are in my 69 - if it is different on the 80 somebody will let you know. I can't remember whether mine uses the first and third (from front) or second and fourth. I can check if you need me to.

It is possible to employ the incorrect holes, especially if the crossmember is mounted back to front. Could be worth a check on this aspect.

regards
Roger
Roger T

On the V8 at least the stud is always fitted in the lower-most position. Even so I still had to twist my engine one way then the other to get first the one stud in the slot and then the other, they wouldn't both go in together when lowered straight down. With studs up I can't imagine they would go in at all. There is a spacer on the engine side plus a locating plate on the chassis rail side, without either of those you may get them in but there would bound to be other issues. Either that, or the faces of the chassis rail plates are too far apart for some reason, or the flanges on the engine are too close together. With repeated breakages then I would think one or other of these two possibilities is quite likely.
Paul Hunt

This thread was discussed between 16/05/2008 and 25/05/2008

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