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MG MGB Technical - Crank case nut/bolt

Hi all, just started stripping this engine that I got, so it is a 5 bearing circa 1970 GH. I have it on a nice new engine stand great I thought I can reach nearly all parts. But now loosening the crankshaft pulley bolt or nut, how can I stop the crank from moving? I could I suppose drop the pan now and jam some rags into the crankshaft area itself, or is this a bit un-scientific? Alternatively, perhaps I can manufacture a bar to bolt(using the flywheel bolts )to the flywheel end. I need to stop the whole engine from attempting to move. The central bolt on the engine stand attachment does not seem 'man' enough to resist movement! Mike
J.M. Doust

Mike. Use an pneumatic impact wrench on this bolt. Far and away the best method. Trying to remove it using a socket and breaker bar will be frustrating at best.

Les Bengtson

My engine was seized, so that was no problem. But the impact would not shift the crank nut. In the end I used a 3 ft pipe wrench around the socket. In your case the safest way would be to bolt some angle iron across the flywheel nuts.
Art Pearse

I found an innovative idea on another site. Rotate the engine until #1 piston is about 5 degrees past TDC. Remove the #1 spark plug and insert enough rope into the cylinder to fill it and leave the end hanging out. Turn your socket or wrench counter clockwise letting the rope compress enough to lock the crankshaft in place and loosen the bolt.

Rick Penland

Just wait until you take the sump off and then place a piece of wood between the crank and the crankcase then slacken the nut with a socket and breaker bar.
Iain MacKintosh

That's softwood (3x2 pine?) Iain is suggesting, for those that have not seen some of our hardwoods.
Roger T

If you don't have an impact wrench, you may need to review whether you can leave the engine on its stand. When I undid the crank bolt on my midget engine I had to put it on the floor on its side and use a long breaker bar. I doubt whether the engine stand I had it on would have survived.
Steve Church


I had exactly the same issue about 4 week ago. I tried my air impact wrench (not an expensive one) no go, I tried a cheap electric wheel nut remover (used to good effect on my Midget) no go. I realised I wouldn't be able to use leverage while it was on the engine stand but I didn't want to take it off as the head and sump were already off. What I did was bolt a long stout bar to the front engine plate, using 2 bolts, that went straight down to the ground. I then put a piece of wood (ramin as I think pine is to soft) between a crank web and the crank case (this assumes the sump is off). This allowed me to use a socket and breaker bar with a piece of pipe on the end of it. Having the bar bolted to the front engine plate allows the load to be transmitted straight down to the ground putting almost no load on the engine stand. If my description isn't good enough let me know and I'll take a picture as the engine is still on the stand, I had a setback when I found the head was cracked.

Bob Davis

You are going to remove the sump anyway, so the block of wood is the go.
Try and get it as far towards the front of the crank as possible so as not to stress the rest of the crank
Holding the back of the crank and applying heaps of force at the other end isn't all that smart of an idea.
Just jam it up the front there and get someone to support the engine while it's on the stand and you shouldn't have a problem

Don't forget to bend the locking tag back first


I have always given the end of a tommy bar a "sharp" tap and this usually releases it. Engine doesnt need to be locked. Need to be a couple of really sharp taps on the end of a 12 to 18" bar and you need to be holding the socket and bar against the nut so it doesnt fly off. Failing that the block of wood up against the crank wo sump is the next best. Not sure if it needs to be softwood as Ive usually used an old hammer handle with no issues to date. I don't like pine as it splinters into the block etc.

A J Ogilvie

I use an inlet valve bent at 90 deg to lock the flywheel. Just put the stem through a bolt hole, and then wedge the head in the ring gear. Been using it 30 years!!

Actually it was an inlet valve from a 2.0 Ford Pinto, for what it's worth!

Colin Parkinson

Thanks Gentlemen, I have enough food for thought. The sump is not off yet but I like the sound of the piece of wood (soft)between the crank and web, and the front plate supports idea. I will keep you posted! Mike
J.M. Doust

Don't have an impact wrench? Use a standard box end wrench and then rap it sharply with a BFH. Like using an impact wrench, the sharp rap and inertia will loosen all but the most stubborn fasteners (they will usually break loose with a second rap). Cheers - Dave
David DuBois

This thread was discussed between 22/12/2010 and 10/01/2011

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