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MG MGB Technical - Crankshaft straightening?

I have been reading Peter Burgess' book on "How to power tune MGB 4 cylinder engines" and noticed in the Crankshaft section, a comment that "Steel cranks cannot be straightened and will have to be grounded straight". I would have thought the steel crankshafts in the early engines could have been straightened but the later cast iron ones could not be? Any comments?

Is there a source for new crankshafts other than fully machined steel billet cranks?
Mike
Mike Ellsmore

I dont know if there is anything different with the steel B shaft but back in the 50s we used to straighten them. In fact when I did my external 3rd year exam, 3rd year was engines, that was one of the tasks I was given, and to check the bearing tunnel alignment. We never bothered to try with a cast shaft. In fact some of the early cast shafts although good in use could break in half if they fell over on a concrete floor. Moss UK still list them but under ring for a price, maybe a billet. Denis
Denis4

I wonder whether 'cannot' refers to the minimal chances of getting the journals correctly aligned by bending it straight.
Paul Hunt

Im no expert but I think you could be right Paul H.

Forged steel cranks are known to be straightened with a slight amount of pressure applied in the right place, but would you get it perfect?

I had a hard time myself with a broken journal until I sourced a 10/10 polished nitrided later type forged crank to replace my early type (which at later date ill get repaired)on EBAY for 50 USD plus international postage which was far cheaper than buying a new/used reground one from a vendor.

I think the billet steel cranks cost double what they should- perhaps someone will pick up on that and start selling quality billet cranks from say- SCAT Industries- with tailored throws or a range of cuts to suit different specs.


JS Ahlund

I have had confirmation from Peter Burgess that this was typo - it should have read "cast iron cranks can only be straightened by grinding".
Mike
Mike Ellsmore

The book is due for re-release around about September/October, thanks to Mike for bringing it to our attention the section on cranks will say....
Forged steel cranks can be straightened, but cast iron ones cannot and are best rejected.

Peter

Peter Burgess Tuning

'can' being the operative word I think! For the cost and peace of mind I would prefer to reject any bent crankshaft!
Hal Adams

I had a bent and damaged crank in the '75 MB 300D I purchased some years ago. The 5 cylinder Diesel engine had spun a rod bearing and bent the crankshaft while severely damaging the #4 journal. I was going to simply replace it until I got a quote of $1,300 for a replacement unit. A lot of money at the time. So, I sent the old crank out, to a large machine shop that I used for big projects, to see if they could decide whether it was worth trying to repair or discard. I got it back 5 days later in like new condition. They had straightened it and built up the damaged journal. Finally, it was cut .0200" under size. I put over 70,000 miles on that engine before eventually selling the car due to relocation reasons. I was amazed at the quality of the workmanship of the shop and the longevity of the repaired part. RAY
rjm RAY

Hi Hal

If one has a crank tuftrided, which involves heat, the crank can 'think' it is back in the forge and bend, this has to be corrected by bending it back to its post forge straight state. No problems with this.

Peter
Peter Burgess Tuning

This thread was discussed between 03/06/2013 and 05/06/2013

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