In a message dated Tue, 31 Dec 1996 09:29:47 -0600
william.eastman@medtronic.com writes:
>> I was intrigued be a recent post concerning using an MGB harmonic
balancer on an MGA. I have loads of questions on this general topic.
>>
>> I have heard that 1600's are prone to crankshaft cracking. <
You have heard a common statement, but hard to tell statistically how
common the problem actually is. I did have an MGA 1500 crankshaft break
on me several years ago. I was on vacation at the time cruising east on
the interstate about 20 miles out of Mobile, Alabama. The engine kept on
running, I managed to nurse it down the shoulder for six miles to the
next exit, got it up on a hoist and pulled the oil pan.
The break was between the front main bearing and the #1 rod bearing,
broken at an angle across the web, not at the journal. The separated
stub in the front was being carried in the front main bearing, the rest
was carried in the center and rear mains. The larger part of the crank
kept pushing the little piece around to drive the timing gear, so it kept
on running with no other damage. Under moderate throttle the crank would
flex a bit and make nasty knocking noises.
I put the oil pan back on, topped it up with oil, put the #1 spark plug
in my pocket (ran nice and quiet on three cylinders), and proceeded to
drive on another 35 miles to Pensacola, Florida. Big town, better
services and parts availability. Was grounded for a few days at Motel-6.
Rented an engine hoist across the street, yanked the engine and tore it
down in the parking lot. Made some calls, got another crankshaft from a
club friend in Raleigh shipped down on Greyhound, got the new bearings
and gaskets locally. Had all the parts on a Saturday at 4:30 pm, had it
running again by 4:00 am.
The engine had been rebuilt a few years earlier, only had about 15,000
miles it, was in great shape otherwise. I suppose the advice here is
that when (and if) you ever have your engine apart, have the crankshaft
magnafluxed, especially if you're about to do a rebuild. Even the
tiniest crack can be found by magnafluxing. If you find any crack, it's
time for a replacement crank. These cars are always getting older, so
maybe fatigue cracks will be becoming more common with time. Since you
can still buy several used crankshafts for the cost of a new one, I still
opt for buying used parts.
>> Could the addition of a harmonic balancers on later models be in
answer to this issue?
Probably not. Internal loads on a running engine are a couple orders of
magnitude higher than the stress of vibration. If it's going to fatigue
and crack, it would be from internal stresses, not from the vibration.
>> I read somewhere that 1500 and 1600 cranks were differant yet Moss, et
al sell the same crank for both engines. What gives?
1500 and 1600 engines are nearly identical, difference being the 1600
block has larger bores and pistons, period. I think all other parts are
identical.
The MGA 1600-MK-II engine is a different beast, has a 1622 engine that is
considerably different. The 1622 has a different crankshaft, main
bearings, connecting rods, pistons, block, and a head with larger valves.
>> Will the later 5 bearing con rods fit a 3 bearing crank?
No. The 3-main 1800 rods are the same as the MGA 1622 rods. That's it.
>> In American engines, the harmonic balancer is often counter weighted
to make up for an inherant imbalance of the crankshaft. Is this true for
the MG balancer?
No. The MG crankshafts can be balanced alone with no other parts
attached. I'm having one balanced now, currently in the shop. The front
pulley (or balancer), flywheel and clutch assembly are all symmetrical
and can be balanced alone.
The MG "harmonic balancer" is in fact not a balancer at all, just a
vibration damper. It's made of two pieces, a small internal hub and a
heavy external ring. In between is vulcanized a bit of soft rubber.
When running, the outer ring does a little dynamic dance about 90 degrees
out of phase with the ambient vibration, effectively canceling out much
of the vibration. Serious racers probably wouldn't use one (it's a bit
heavier than the plain pulley). Occasionally the rubber in the balancer
can delaminate and let the outer ring come off, probably happens about as
rarely as a broken crankshaft.
>> Where can I buy a harmonic balancer and MGB front cover? Moss doesn't
carry the front cover and, since I only have MGA catologs, I don't know
if they carry the balancer.
Check out your nearest British car bone yard, still lots of used parts
available.
>> What model balancer should I get? Will I need a separate pulley?
will it still line up with my present accessory drive (water pump,
generator)
The pulley groove is part of the balancer. The one you want is from a
late production MGA MK-II 1622 engine (after engine 16GC\8263. You can
also use one from the early MGB 1800 engines 18G through 18GF, 1962-1968.
They all bolt right up, belt grooves all in the same plane. You may
also install the timing cover from the same engines, these having a
rubber oil seal in place of the original MGA felt seal ring. If you
change the cover you also need the seal and oil thrower to match.
>> Since 1600 cranks are a bit pricey, anything that I could do in the
way of prevenatative medicine would be of great interest to me.
See "magnafluxing" above. Otherwise not much. That's about it,
otherwise don't worry unless it actually happens to you, it's not very
likely to break.
Barney Gaylord -- 1958 MGA
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