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Dimple On Crankshaft Bearing Face?


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#1 jonlad

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Posted 14 January 2022 - 12:42 PM

Hi all

Some advice please. Rebuilding a 1275 A+ I foolishly assembled with main caps on the wrong way around (180 degrees out).

 

I span the crank only a little - enough to realise my mistake, but upon stripping, one of the bearings has "picked up" a little on one of the crank bearing faces. 

 

i.e. there is bearing material deposited on the crank.

 

It's maybe 1mm x 2mm and my initial thought is to use a dremel and a small burr or grinding bit to put a dimple on the crank bearing face, making sure all sharp edges are removed and all everything is below flush. My thinking is that there are through holes in this face for oil feed so what I am suggesting isn't too drastic?  Of course I'd get some new bearing shells too!

 

Engine is not intended to be a high power race engine, just a stage 1 weekend cruiser.

 

I'm sure worst has been done back in the day when minis were cheap and cheerful?  I'm on a budget and trying to avoid a £500 crank!

what do you folks think?  and I'm ready for the "what are you thinking, only a new crank will do" but really? 



#2 GraemeC

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Posted 14 January 2022 - 01:04 PM

If you only spun the crank by hand, I very much doubt that the bit of bearing material has fused itself to the crank that well that it wouldn't pick off with a bit of care



#3 jonlad

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Posted 14 January 2022 - 01:21 PM

Thanks Graeme,

I must have been tired, when it didn't move by hand, i put the crank bolt in and turned it just maybe 15 degrees with a socket and ratchet before realising something was amiss.

the "chip" seems pretty well attached, there was a score mark on the bearing where the material has come from

 

still, all the work i do on minis i do myself so that I can learn, and this might be a valuable lesson...  :shy:



#4 KTS

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Posted 14 January 2022 - 01:36 PM

the bearing material is much softer than the stuff the crank is machined from, so should come away without having to resort to a dremel - a scrap bit of copper or brass or even hard plastic, should be fine to use as a makeshift scraper

 

worth investigating whether the bearing has actually picked up on something that's embedded in the crank journal..



#5 jonlad

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Posted 14 January 2022 - 03:06 PM

Thanks KTS, will have a go at scraping it off and see whats under it 



#6 Ethel

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Posted 14 January 2022 - 03:36 PM

Acrylic is good, snap it and you'll get a nice sharp edge to get some purchase.



#7 jonlad

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Posted 15 January 2022 - 09:01 PM

Success! Thanks for the advice, the chip came off with a sharp edged piece of hard plastic. There doesn't appear to be anything under it in or on the crank. I'll reassemble with new shells, turn it over BY HAND! then maybe take it apart again and check the shells for marks

#8 mini13

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Posted 16 January 2022 - 02:06 PM

Surprised it picked up, did you assemble dry?

#9 jonlad

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Posted Yesterday, 08:48 AM

Surprised it picked up, did you assemble dry?

no, everything oiled!



#10 bpirie1000

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Posted Yesterday, 10:33 AM

Any pictures as this may assist and educate...

Good luck nd well done for seeing/feeling it... possibly saved fro scrap pile..




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