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?


Having rebuilt more engines than I can remember in my time, I've never
found a case where replacing shells only when there are signs of
bearing problems works. Only time I'll replace bearing shells without
a crank grind is when carrying out other work which requires splitting
the bearings. Because they are cheap, it makes sense to replace them -
in much the same way as you fit new gaskets.

In the bad old BMC days I used to replace big ends at 30k, mains at
60k and have a bloody good look at the crank and bores at 120k, if
the whole car lasted that long.

You replaced them on spec - or when there was signs of wear?

It turned out to be the same thing Dave, I'd drop the sump and if I
could find any rock in the big ends I'd drop the caps and replace the
shells - not a big job.

You dropped the sump on spec?

at 60K I replaced the mains on spec, and that too is doable - by
dripping the main bearing caps - just.

I did this because the haynes manuals of the time recommended that you
did.

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.

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.

--
*Why is the time of day with the slowest traffic called rush hour?

Dave Plowman London SW
To e-mail, change noise into sound.