Believe me Neil, I feel your pain! I've been at this for over 30 years
and had my share of incorrect parts from folks who should know better.
In fact, I was planning on finishing rebuilding the tranny in my '65
over the long Fourth of July weekend, had assembled all the necessary
parts from one of our beloved suppliers, and as I began the first step
of replacing the bearings in the laygear I discovered they had sent the
wrong ones! End of project for that weekend!
I'm no expert on three main bearing MG cranks although I have much
experience with three main VW ones. The VW cranks are subject to less
vibration due to the horizontal configuration, and I think German
metallurgy is somewhat better than British, especially British from the
'50's. Impurities in the steel lead to imperfections in the crystalline
structure than can cause premature failure. There are shops that will
balance VW cranks by adding significant amounts of metal to help dampen
out natural vibrations. Amazingly, you can even have one custom milled
out of a solid billet, but I digress, none of this helps you any.
Given the metallurgy, there is no reason to expect greater longevity
from your NOS crank versus a good used one, in spite of what logic tells
you. If I were in your position I would check the availability of NOS or
used Mk I and Mk2 cranks, get two or three of which ever is available,
and expect to be replacing cranks every so often. I wouldn't modify the
block unless you can get your hands on two more good Mk II cranks.
These three main cranks will last longer if you don't ask for too much
torque all the time, they like to spin, so run it up before you shift
and stay in a lower gear when you need torque. Make sure you have good
oil pressure, and when you see it dropping over time replace the
bearings!
How about dropping the whole idea and popping in an MGB five main
engine!? ;-)
Keep at it, this sort of thing builds character, I think.
--
Stuart MacMillan
Seattle
'84 Vanagon Westfalia
'65 MGB (Driven since 1969)
'74 MGB GT (Restoring)
Assisting on Restoration:
'72 MGB GT (Daughter's)
'64 MGB (Son's)
Parts cars:
'68 & '73 MGB, '67 MGB GT
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