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MG MGB Technical - crank nut size

What size socket do I need to turn over the engine using the crank pulley nut - preferably the nearest metric size as they seem to be the most common in the motor factors.
Steve Church

Steve. The correct size is 1 5/16". Removing and replacing the nut, during engine rebuilds, when the harmonic balancer goes bad, or when you need to replace the seal on the timing chain cover is a bear. Using the nearest metric size might do for simply turning over the engine. But, for some of the maintenance required the correct size is a must. Might as well pick up the correct size now and only have to purchase one socket over the years. You should be able to find a good quality socket, of the correct size, on line if you cannot find it locally.

Les
Les Bengtson

Steve-
Place a 1 5/16” wrench / breaker bar against the right chassis rail (as you are facing the engine from the front). Put some wood or something thick and soft against the left chassis rail in order to prevent it from being scratched. Your wife's pillow is good for this (she won't mind you borrowing it for such a worthy cause). Take care to disconnect the High Tension (HT) lead from either the ignition coil or the distributor cap so that the engine cannot start. Blip the starter briefly, and the retaining bolt will be jarred loose. When reinstalling, note that there is a flat on the middle round section of the harmonic balancer pulley that you must hammer the tab of the lock washer down onto. This holds the tab onto the harmonic balancer pulley wheel, and you can then tab up the head of the retaining bolt as normal. Be aware that the retaining bolt of the crankshaft’s pulley wheel on the harmonic balancer (harmonic damper) in the end of the crankshaft is not standard Whitworth, but is of Whitworth form: Diameter 1 5/8"-16 TPI, 1 1/16 Full Thread. If it is found necessary to clean up the threads, the operation must be confined to cleaning up only. These threads are highly stressed and must always be up to full size. Thus, it is not correct to use an American SAE-UNF form tap or die in order to clean up these threads, though you might get by in the end of the crankshaft, but definitely not on the bolt. To my knowledge, apart from the 1/4-inch BSPP (British Standard Pipe Parallel) threads in the drain port on the side of the engine block, this is the only other British form threaded fastener on any of the B Series engines. Note that BSF is 5/8”-14, rather than 16 TPI. UNF is 5/8”-18. CEI starts with 20 TPI at ½" and larger.
Stephen Strange

Hi Steve,

The 1 5/16" socket I bought, many decades ago, has a 3/4" square drive. To save having to buy a 3/4" drive bar I bought a 3/4" to 3/4" square adapter, which fits neatly into a 7/8" ring spanner.

Herb
Herb Adler

Steve - There are a number of BSP and BSF threaded fasteners used on the MGB engines - see the chart , British Fasteners Used on the MGB in the Other Tech Articles section of my web site at: http://homepages.donobi.net/sufuelpumps/ I was not aware that the crank pulley nut had Whitworth threads. I'll have to add that to my chart. Cheers - Dave
David DuBois

Dave-
Thanks for that. I'll incorporate the new information into my book.
Stephen Strange

"...is not standard Whitworth, but is of Whitworth form..."

What is it then, exactly?
Roger T

Roger-
Sometimes standard designs aren't up to the task, so apparently it's an in-house custom design tailored to the purpose.
Stephen Strange

This thread was discussed between 23/08/2010 and 25/08/2010

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