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MG MGB Technical - Five-main Crankshafts

I'm looking for a crankshaft to build up an 18GB five-main engine. My MGB factory parts book shows 12H 2524 covers all years from '65 up through at least '76. But I understand there were some differences. Are there? And if so, which ones are best?

TIA!
Allen
Allen Bachelder

Lots of different cranks available over the years. Both cast and forged. Early 5 mains were forged, later ones were cast. Different balance factors as well. From my research the best 5 main crank was the cast "flat side" crank and that is the one I used in my rebuild of an 18GB engine. I believe that Peter Burgess's book also recommends this crank. Very easy to spot as the throws are indeed flat. Others are the more common pork chop look.

HTH Ron
Ron Smith

Allen, the following link covers the three types of 5 main bearing cranks. As noted many prople prefer the middle years flat sided crank.
http://www.mgexperience.net/phorum/read.php?1,424307,424616#msg-424616

Clifton
Clifton Gordon

As noted in the link that Clifton provided the floating pin rods with the larger end caps are also prefered as they provide more meat on the cap for balancing. These as noted are rather rare, late middle year as I recall. My 18GB specs, .060 over bore, flat side crank, floating pin rods, piper 286 cam and lifters, aluminum large valve head, non dished pistons with head chambers taken out to 53cc. Used both Weber side draft with a Mallory dist and stock SU's with header. Much more power than stock but still flexible in traffic. Getting harder and more expensive to find all of the good parts now.
Ron Smith

In 30 years of doing MG repairs I have had 2 flat sided cranks that broke and another 2 that were cracked. I have been told by an English chap that the early 65-68 18GB crank that was forged is modified & used in the Rover 2L engine for racing purposes because it is stronger. I always get my motors main bearing tunnels line honed when rebuilding them.
Garth
Garth Bagnall

I thought MGB cranks were always forged, it is the cranks in 18B and 18V engines for other applications like the Marina that were cast.
Paul Hunt

Thanks guys. Lots of useful information here. I appreciate your help.

Allen
Allen Bachelder

This thread was discussed between 18/07/2008 and 19/07/2008

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