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MG MGB Technical - Engine Mounts
|I am re-installing a newly rebuilt engine into my 77 mgb roadster. I have thoroughly searched the archives and have found a wealth of information on the rounded diamond shaped spacers inserted at the motor mounts. However, I have not found anything on the square spacers (shown in the Moss catalog between the rubber mount (item 91) and the washer and nut. My question is simple - does the square space go on top of the mount that is welded to the chassis(i.e., under the plate of the rubber mount, or inside the chassis mount? It seems that it should go inside, with the stud from the rubber mount going first through slot in the chassis mount, then thru the hole in the sqare spacer, then through the lock washer, then through the (well-documented-nearly-impossible-to-get-started) nut on the drivers (LH) side. The depth of help available from the members on this site is truly appreciated.|
|You will note that the square washer has an offset hole. The mount stud goes all the way at the bottom of the slot on the frame (tap it down with some weight on the mount), and the square washer offset is to keep it there so it can't move upward under any (loose) condition. Put the square piece in (yes, under the bracket - sorry)so that the widest part is uppermost, it just fits up against the top edge of the cavity. then figure out how to get the lockwasher and nut on!! Run a die over the threads before starting this so the nut is absolutely free-running - the threads are usually bunged up. Use anti-seize on the stud. It helps a bit if you can get the underside of the frame bracket clean (Brakleen or lacquer thinner) and use something sticky to hold the square washer up while you deal with the nut and lockwasher.|
A further tip: Have you replaced the brackets on the engine? They commonly are broken, and if not near new are cracked if not broken. Look very carefully at the 90deg bend at the front edge, and around the lower bolthole to the block. You DO NOT want to do this again soon! To greatly increase lifetime, Put 1/8" of spacers between the block and the lower bracket, and a heavy washer under the lower bolt head. You will have to grind this to fit securely in the channel at that point, and you need a slightly longer bolt. Be sure that the longer bolt will tighten against the stack of spacers and bracket without the lockwasher, then fit the lockwasher. If this bolt is bottomed in the hole the bracket WILL break, and the threads WILL be damaged when you remove it. This procedure prestresses the mount bracket and the rubber mount in a favorable direction and increases the life indefinitely. I've never replaced one I did like this, but have done dozens done as original.
|Thanks so much for the concise description and the additional tip. I had put the square spacer in the right place, but upside down (stud-hole at the top). Looking forward (ha) to getting it fitted correctly this week-end!|
|Hmmm, my car (a 78) didn't have any square plates inside the mounts. Mind you mine also didn't have a nut on one side either so that isn't surprising! Are these plates absolutely necessary?|
Not really, and many are missing due to the difficulty of getting all the pieces in. Just make sure the mount is hammered all the way to the bottom of the slot, else the mount is stressed badly (too much shear and not enough compression) and will fail even earlier than usual. Put a big round flat washer on to cover the slot. And the nuts have to be tight!
|OK, thanks. I did all that when I put them in and just to make sure I will check the nuts are really tight this weekend!|
This thread was discussed between 14/09/2005 and 16/09/2005
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