correct grit for polishing crank

V

V848 Ford

Member
I micked the crank in my 255 block and can only find .ooo2 out of round so I think I will put it in the lathe and polish it. What is the correct grit to use?
 
If you dont have a belt polisher for the purpose make a clamp out of 2 pieces of hardwood.
That way you will polish it straight and flat.
 
Sounds like .0002" is within service limits.
Exactly how do you propose to polish only the high side of the journal and not touch the low side.
Suspect you will do more damage than any perceived correction by attempting to polish.
 
You can buy crank polishing belts from Goodson and others. But, unless you can offset the crank as it would be in a crank grinding machine it will be difficult to do a proper job.
 
You can use the method shown in the photo below. It is taken directly out of the Chevrolet "Power Manual". It uses the chosen paper cut in strips and a short length of rope. This method does NOT require "spinning" the crank!

It does work but takes some practice to get the "feel". If you "play" with some "600" grit paper you won't cause any damage or remove any material.

Thanks, Gary in N.Y.

P.S. We have a "dedicated" belt-style crank polisher, uses "240", "320", "400", or "600" grit (we rarely use the 600). I will also add .0002" (2 tenths) is a "non-issue", you will find more "error" than that in new brgs.
 

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I agree with 34PKUP, leave it alone. If you really don't know what your doing, you can cause more damage to the crank. .0002", I wouldn't do a thing.
 
If you can polish it correctly its an inprovement.
Done incorrectly it can result in a worse then before status.
A standard belt for a crankpolisher is supposed to be running highspeed and to corse for handpolishing in a lathe.
That woodpiece trick aint to bad in a lathe...many Scania truck cranks was finished that lowtech way in production ;)
Its basicly the same idee as using a block for sanding you get a flat surface.
 
First off, how sure are you that the mic you are using is accurate to that degree. Second, it is within tolerance and you can only make it worse by accident so just leave it alone, you won't be making it any better.
 
I'd worry about getting all the abrasive and filings out of the oil passages afterwards. Leave it alone! :)
 
Why don't you post a couple pictures of your journals? I'd like to see them - just to see what condition they are in. If they are good, don't screw with it.

If not, take it to a crank grinder and have them polish it the right way. Why take a chance with a method that is suspect at best . . . especially since you're probably buying a new set of bearings. :)
 
GOSFAST said:
You can use the method shown in the photo below. It is taken directly out of the Chevrolet "Power Manual". It uses the chosen paper cut in strips and a short length of rope. This method does NOT require "spinning" the crank!

It does work but takes some practice to get the "feel". If you "play" with some "600" grit paper you won't cause any damage or remove any material.

Thanks, Gary in N.Y.

P.S. We have a "dedicated" belt-style crank polisher, uses "240", "320", "400", or "600" grit (we rarely use the 600). I will also add .0002" (2 tenths) is a "non-issue", you will find more "error" than that in new brgs.
Click to expand...

If you tear strips of crocus cloth to the width of the journal, place them on a 3 foot piece (or so) of gaff tape, you will have a long run of the crocus cloth.
Now, put the crank on end. Maybe with the flywheel or in a vise.

Walk around the crank while you pull the crocus strip from side to side.
I've done this lots of times and it works great... Don't forget the compressed air to clean your grit from oil passages.

Karl
 
If you really think that it needs a polish go down to the local machine shop and buy a crank polishing belt and take it home and use it as described and be done with it. The cost of the belt is less than a burger at McDonald's and 320 or 400 is all you need.Never mind the crocus cloth voodoo and all the rest here just get the belt they come in a 91" x 1" length or 72" or 64"as a common size cut it for the ease or operation clean it up well after u are done and you are done far from rocket science.

R
 
Thaks for all the info. guys I am going to practice on a junk crank first. I have standerds for checking my micks out so i don't screw the crank up.
 
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