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MG MGB Technical - main bearing caps

main bearing caps front and rear refuse to go back in. any ideas
les

These are a tight fit in the block at the best of times. Make absolutely sure that the faces of the caps are scrupulosly clean and that the block is clean as well polosh with fine emery to make sure and then tap the caps down into place. Make absolutely sure that both caps are positioned flush with the block faces when finally in position.
Iain MacKintosh

Try putting the caps in the freezer for an hour or two, it could make them shrink enough to slide in.


My first post here by the way, I just signed up as a member! Have been reading a lot here for some time, though.
Johan Garmer

Put one side of the cap into the block by about 10 thou and hit the other side smartly with a copper hammer to start it then beat it down with the hammer - keep a finger on the shell, it sometimes will jump out, but get your finger out of there before it gets hurt!
Chris at Octarine Services

Be sure to heed Chris' admonishment. I use a couple of long pieces of threaded rod to jack the cap into place.
Cheers - Dave

David DuBois

Oooops! Still, at least there is one less finger nail to get oil under!

Threaded rods OK for later engines but not on the early ones with studs instead of bolts for the main caps.
Chris at Octarine Services

A useful tip, get hold of two main cap studs from a studded B series block and use them to guide the caps into place.

Peter
peter burgess

Chris - We were discussing that very thing last night with some friends. I told them that after nearly three years, I still stop at that finger when I am trimming my nails. In truth, I didn't sacrifice the finger to an engine, rather a hydraulic log splitter (it was just a good follow on to your admonition to get the finger out of the way). Cheers - Dave
David DuBois

Les-
I prefer to shrink-fit both the front and rear crankshaft main bearing plates in order to ease the assembly process. This will make for ease of proper alignment. Spray the main bearing plates with WD-40, seal them in a Ziploc bag in order to prevent ice from forming on them, and then chill them thoroughly in a freezer overnight with the thermostat set as low as it will go. When they are well-chilled, fit them into place. Simply place the crankshaft main bearing plate into its respective slot at the end of the engine block, and then, using a pair of long ½”-20 UNF machine bolts to align the crankshaft main bearing plates, turn each retaining bolt about one-half turn at a time until the crankshaft main bearing plates are almost seated. This will produce a rate of descent of .025” (.64mm) per half-turn of the machine bolt, which will be within the distortion tolerance of the cast iron engine block. As they descend into place, change to shorter machine bolts. When they are almost fully seated, use the factory machine bolts, again turning them a half-turn at a time, in order to fully seat them.
Steve S.

Dave,

Nice to see you are in good humour!

Steve,

Wow, you have just way too much time on your hands - it takes me less than one minute to fit the shell to the cap, lubricate it, tap it down into position and align it fore & aft, lubricate & drop in the bolts (or washers & nuts) and torque up !
Chris at Octarine Services

Chris-
As a former Tool & Diemaker, I see the risk of damaging precision-machined mating surfaces, plus distorting the engine block, and the idea of pounding them into place with a mallet just makes me shudder. I know that that's the way that commercial garages do it all the time, but for them time is money. My time costs me nothing, and so I do it the safest way possible.
Steve S.

This thread was discussed between 27/03/2009 and 29/03/2009

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