Dave,
In a message dated 96-10-03 14:20:44 EDT, ahrendt@atla3.agfa.com wrote:
<< ..... The DPO of my TC apparently had the crank welded up and then
reground. ..... A few years ago on the way to the Burlington, VT GOF the
crank broke at the rearmost main bearing. When we took it apart and examined
the crank I saw that the welder/grinder made no effort to radius the edges.
The grind was a perfect 90 degree edge right up to the counterweight. And
thats exactly where the crank broke. ..... >>
Actually these crankshafts are pretty beefy considering the moderate loads in
these engines. The sharp corner at the bearing journal probably didn't have
anything to do with it, the metal being so thick there as to attenuate the
stress considerably.
I had one crank break on me in 1989, cruising east on the interstate out of
Mobile. The break was across the web between the front main and #1 rod
journal. I wasn't sure what it was at first, the MGA was running about 4000
rpm with the cruise control on at the time, made a lot of noise and kept on
running. After a quick external inspection I nursed it down the shoulder of
the interstate for 6 miles to the next exit. I pulled the pan, checked the
bearings, turned the engine with a wrench on the front crank nut, could find
nothing wrong at the time. Figured it must be a cracked piston of loose
wrist pin. Took out #1 spark plug, noise went away, drove it another 30
miles into Pensacola. Upon further inspection later that evening I found the
break in the crank. It took 3 days to get the parts, 12 hours to get it back
on the road again.
A few years later the starter mounting bolts came loose, statrer motor fell
out, starter pinion gear jambed up the ring gear, broke the crankshaft at the
front of the rear main journal. Can't blame that one on the crankshaft.
Over the last 10 years and 90,000 miles on the MGA I have had a crankshaft
reground, or used one that was, at least 5 times. In fact during that time I
have never used a crank that wasn't reground. I autocross a lot, often run
the engine past 7000 rpm, have never broken a crank while racing. I do
however lose a rod bearing occasionally from the high speeds, but only after
many race dates. If caught early it sometimes gets away with just new
bearing shells, occasionally it needs a regrind. This is the first time I've
tried welding one, and I hope it doesn't develope any stress crack form the
welding. It's an automatic MIG welder feeding a very small wire, so not a
lot of heat involved. I'm going to have it magnafluxed when it's done just
to be sure.
Barney Gaylord -- 1958 MGA
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