Polishing crankshaft

[pennine]

Hi

I'm in the process of rebuilding my engine and awaiting the return of my block from the workshop after the re bore. The crankshaft has had a 10 thou regrind in the past and the surfaces are perfect but I want to polish the surfaces ready to take the new bearings, my question is what grade paper should I use ? I thought crocus paper at first but then was told 1200 grit and then told emery ??

Help

[richardthestag]

imported post

^^

Polishing his crankshaft

snigger :P

When I did my Anglebox I used emery cloth, very gently indeed - but then had the crank regound anyway - not really sure if that is helpful.

When your crank was taken down 10 thou was it re hardened ? if not you may wish to consult with specialists for confirmation. Who is doing your block can they advise?

Happy Christmas

[V Mad]

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Whether you use emery or wet & dry paper is unimportant, its the grade of grit thats crucial and the method you use. Don't use anything coarse: 1200 is OK.

But are you sure theengineering company to have not already polished it whilst on their machine?

[pennine]

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Thanks for the replies guys, the crank has not been polished this stripdown it was re groundpreviously by an unknown company. It has been checked by the company doing my re bore and all I know is that it was 10 thou taken off ( the bearing shells are marked as such also ). The engine was a quiet one but an oil burner, some 5 thou wear on some bores which is why I'm having the rebore and new bronze valve guides and stem oil seals. Back to the crank as I said the bearing surfaces are perfect and I cannot see or feel any marks at all, I just want to take the shine off for the new bearings to bed into, so as suggested I only need 1200 grit. .

Can't wait for the bill just before Xmas.

[mjheathcote]

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When I got my crank back from a regrind and hardening I tear dropped all the oil feed holes with a dremel type tool and then gave the crank a polish with emery cloth.

That was over 18 years ago though so I can't remember the grit number!

I basically followed all the procedures in an engine blue printing book at the time, including polishing all 8 conrods removing all the casting marks (took me days!), then having the whole lot balanced.

I've post up some pictures so you know what I mean.

Cheers,

Mike.

[pennine]

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Mike that is an immense amount of work, I take my hat off to you.

I spent all morning switching the pistons to the con rods and then fitting the rings, to do what you have done will probably take me a year.

[V Mad]

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pennine wrote:

. Back to the crank as I said the bearing surfaces are perfect and I cannot see or feel any marks at all, I just want to take the shine off for the new bearings to bed into....

Bedding in is definitely a standard process in regard to fitting new pistons/rings in the cylinders, and the bores should be cross-honed to assist this process. A shiny bore with new rings will not bed in properly. But I have not encountered this recommendation for crank bearings. I think the smoother the finish the better on a crank and shiny is good. Don't forget the bearing shells have very soft metal surfaces, and any abrasion by the(very hard) crank surfaceswill accelerate wear.

One thing I can recommend is the use of plastigauge when refitting the crank bearings. It is a final confidence check that the correct clearances are obtained. It's so easyfor mistakes to creep in(wrong size shells, poor tolerance control etc).

Good luck with the rebuild. It's a great feeling when you first fireup one of your own rebuilds

[Sheepdip]

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I just had my crank repolished prior to refitting. There were some marks on it which worried me and I wanted professional judgment (turned out to be water marks).

It didn't cost much.