Remetalling Crank Timing Side Bearing (Babbit)?

[Peter Gee]

I have a either factory fitted or good British replacement steel backed A7SS crankshaft bush in my engine, but the crank timing journal  is slightly oval (say.002) and the bush has lost all it's babbit (if it ever had) ,showing a coppery surface underneath.  I can't
 get lead bronze where I am in Africa, which I would have preferred to phosphor bronze for a copy to be turned. Also BSA dedicated line reaming of bushes is unavailable- nor the specialized reamer.

However a competent engineer here does re-babbitting. Is this a reasonable alternative, since babbitt is so soft it could even be  sized to a re-ground crank, just removing the ovality, say .003 total - simply by scraping and engineer's blue use?

My idea would be, after  grinding the ovality of the crank journal, to ask the engineer to re-babbit my original bush, itself having been honed to perfect round, then re-babbitted and honed  again with a .001 clearence for the journal,. Then by using blue and bolting up the crankcases, any high spot could be detected and scraped using a traditional method? In any event white metal is so soft it's hardly likely to seize??

My idea being that since the steel bush is original and a perfect case fit, I should get good alignment?

Sounds weird but is there a principle that it can't work?

[Rex]

Babbit bearings are relatively thick, so would it be satisfactory applied in a 2/3 thou layer over other metals?
The World's a smaller place with Net, so why not spring for the correct item from somewhere or other and save potential unnecessary strip-downs?

[Greybeard]

Peter says he will not be able to get the bush reamed in-line. Although I'd have thought someone with a milling machine could do the job.


Peter, if it helps I'll purchase a bush here and post it to you.

[Peter Gee]

Dear Greybeard,

That is very kind, and I could if needs be get one from UK ( presumably solid Phoshor bronze)..however my idea was since I know my original steel backed bush is  perfect and existing  crankcase fit, I won't get any misalignment due to shrinkage, only minor on the babbitted surface, which could be easily scraped down, eliminating need for line reaming?

A  new UK one might not be a perfect crankcase fit, thus needing line reaming (scraping bronze would be tough)..that's my line of thinking...

[RichardL]

Peter,

There is a thread on this topic that I think will interest you. I didn't go back and read all the posts in the thread, but I think you could start reading here: http://www.a7a10.net/forum/index.php?topic=3003.msg20855#msg20855

Richard's (Orabanda's) fixturing for line boring the crankcase is pretty amazing, but we must remember he has many A7/10s to justify such effort. There is also discussion of renewing bushing material.

Richard L.