Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
Dave Plowman (News) wrote:
In article ,
The Natural Philosopher wrote:
I had to fit new big end shells and main bearing shells to a Rover V8
engine about ten years ago.
Only the worst of ignorant ****s would fit new bearing shells to
anything. If the shells need replacing, the bearing surface is also
worn/damaged.

No.
Crankshafts are hard steel,. bearing caps are IIRC lead indium
plated, they wear much sooner.
Fallacy. And I thought you knew something about cars.

http://www.austin-healeys.com/austin...ine-details-2/

says I am in fact completely right.

Eh? All it does is give a list of specifications. I already have the
BMC/BL workshop manuals. Who certainly don't mention changing bearing
shells at some specific mileage. As I said, the only time you can do this
and they will last, is if you change them before they are worn. So totally
pointless.

If you let them wear to the coppper backing of course you WILL score
the crank.
And copper is harder than hard steel?

Dont be silly, the copper is plated on the steel shells first then the
lead-indium is plated onto that. But if you can see the copper the
bearing is finished and its LIKELY the steel shells have started to
score the crank.

So one softer metal doesn't wear the crank while another will?


essentially the shells are hard carbon steel. The same as the crank so
they wear the crank as fast as the crank wears them.

Even water will in time wear away much harder rock. Its not a binary
thing Dave, despite your brain being wired that way.

Cranks are hard, shell casings are hard, a sacrificial layer of lead and
indium is plated onto the shell inners to provide a lower friction and
sacrificial surface for the crank to run in. Get it? IF you replace
shells before they are totally worn out the crank will NEVER need
regrinding until well beyond the engines other lifetime limity, like
having been rebored a dozen times.




I'm wondering if they based this on the original version of the A Series
which had bypass oil filtering. Changing the shells as a precaution
*might* just extend crank life. But all A-H and MGs used the later
version(s) with full flow filtering, so it is a pointless waste of money
and time.


No. Its plan good engineering practice, Bearing shells wear about ten
times faster than cranks do.

BTW, it's a common mistake that where you have one hard and one soft
material in a plain bearing, only, the soft one wears.


Its a common truth. Not a fallacy The soft one wears FASTER. That
doesn't mean the hard one doesn't wear at all.

Otherwise why bother to have soft bearing shell coatings at all? after
all MOST of the running is dine on an oil film .


And I've got not a few steel in bronze bearings clapped out on electric
motors to prove it.


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