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Old 05-29-2010, 07:58 PM
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How to PROPERLY polish crankshaft journals yourself?

Hey guys, what is the best "do it yourself" method of polishing crankshaft journals?

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Old 05-29-2010, 08:48 PM
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i wouldnt begin to comprehend even if someone explained it bc if im not mistaken. journals have to be perfectly round. if u can somehow come up with the "polishing belts FOR crankshafts" and make up a "gizmo to rotate the crankshaft" I would say do it but it all depends on how extensive the damage is.
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Old 05-29-2010, 09:37 PM
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You need to make like a stand for the crankshaft to sit in . Take a 2x8 and cut to the length of the crankshaft you need , 36" ? Take two 2x 8 and screw them into the base , you need about 6 inches in height to clear . So thats one 2x8x36 and two 2x8x6 im just figuring on 36 inch lengths your might be different but you get the idea. Put 400-600 emery cloth around journal. Put masking tape around emery cloth snuggly. FOLLOW ME ? Put RAWHIDE SHOESTRING, AROUND OUTSIDE OF MASKING TAPE. you have to stand over crank and pull one side of the shoestring then pull the other side. Make sure you have long enough RAWHIDE shoe string. Make sure when you are pulling string you are getting the emery cloth to make at least 2 turns.
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Old 05-29-2010, 09:39 PM
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You can put oil on the emery cloth or do it dry , start with 400 and go up from there. I like to go to 1000. Its alot of work but you will like it when you finish. It takes practice to get it right , like just making sure the emery will snuggly fit into the journal and get it to make a couple turns but youll get it
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Old 05-29-2010, 09:46 PM
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I forgot to mention you have to cut a v like in the ends of the 2x8 stock for the crank to sit in . Its jUST HARD TO EXPLAIN. I could draw a picture if you need it , i gave my stand away, but they are easy to make.
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Old 05-29-2010, 11:08 PM
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Havn't needed to do this procedure in a long time but when I did I used thinner, kerosene, even diesel on the wet/dry sand paper. Need to keep it wet just like block sanding a body panel. The grit you start with depends on the condition of the crank, but if it's real bad then just get it 10-10'd at the machine shop.
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Old 05-29-2010, 11:17 PM
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personal prefference i guess.
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Old 05-30-2010, 07:00 AM
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I think that I wouldn't do that by hand unless all you want to do is possibly take the discoloration off the journal. You can buy rolls of different grit cloth, but the fact that you have to have a strop that totally goes around the journal at least once and a bit more, and the two ends passing will make for a sanding band that's very narrow, i.e. less then half of the width of the journal and will tend to dig an edge in the surface and possibly do some damage. Depending on what the journal looks like (a minor scratch that you can't "feel" with a fingernail) you might just be best off leaving it. If you can run that fingernail across and "feel" it, then it should be left for the grinder. We used to do 220/400 grit stropping on gas turbines and generators, but we had an 8 up to 20 inch diameter shaft to work with and a fair bit of allowed clearance.

Here's where you can buy rolls of paper if you are determined to do that job:http://www.mcmaster.com/#sandpaper-rolls/=7ba0w9
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Old 05-30-2010, 09:39 AM
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even my local engine builder polishes crank journals that don't need turned by hand.. and the above procedure is also how I was tought
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Old 05-30-2010, 09:40 AM
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Quote:
Originally Posted by Irelands child
I think that I wouldn't do that by hand unless all you want to do is possibly take the discoloration off the journal. You can buy rolls of different grit cloth, but the fact that you have to have a strop that totally goes around the journal at least once and a bit more, and the two ends passing will make for a sanding band that's very narrow, i.e. less then half of the width of the journal and will tend to dig an edge in the surface and possibly do some damage. Depending on what the journal looks like (a minor scratch that you can't "feel" with a fingernail) you might just be best off leaving it. If you can run that fingernail across and "feel" it, then it should be left for the grinder. We used to do 220/400 grit stropping on gas turbines and generators, but we had an 8 up to 20 inch diameter shaft to work with and a fair bit of allowed clearance.

Here's where you can buy rolls of paper if you are determined to do that job:http://www.mcmaster.com/#sandpaper-rolls/=7ba0w9
If you have discoloration , then you have a problem, spun bearing perhaps??? No then you need machine work. Im talking about just polishing up here, with a decent crankshaft. There is no such thing getting it too smooth. Yes you have to be ( carefull )
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Old 05-30-2010, 10:10 AM
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Quote:
Originally Posted by crystalbluevib
If you have discoloration , then you have a problem, spun bearing perhaps??? No then you need machine work. Im talking about just polishing up here, with a decent crankshaft. There is no such thing getting it too smooth. Yes you have to be ( carefull )
There is always a bit of oil discoloration between the two journal bearings. You can knock that off with crocus cloth and a lubricant which doesn't remove any metal. If the journal has a spun bearing there is more then just discoloration - like transferred babbit and gouges. Been there too many times.

Matt - unless you are 'experienced' my suggestion is - don't. The engine builder (Prattsville??) will use some 400, a bit of kerosene and strop the stone marks - but has done it probably for many years and has the 'touch'. Lawn mower, other small, low load for its' size, engine, not a problem!!!
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Old 05-30-2010, 10:42 AM
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Quote:
Originally Posted by Irelands child
There is always a bit of oil discoloration between the two journal bearings. You can knock that off with crocus cloth and a lubricant which doesn't remove any metal. If the journal has a spun bearing there is more then just discoloration - like transferred babbit and gouges. Been there too many times.

Matt - unless you are 'experienced' my suggestion is - don't. The engine builder (Prattsville??) will use some 400, a bit of kerosene and strop the stone marks - but has done it probably for many years and has the 'touch'. Lawn mower, other small, low load for its' size, engine, not a problem!!!
There is a line you can see between between the two yes, thats not what i would refer too as discoloration
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Old 05-30-2010, 11:58 AM
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The "proper" way of polishing the crank is done by spinning the crank and using a polishing belt to polish it in the same direction of rotation as the engine runs.



I've "polished" cranks to remove slight surface rust by hand using solvent wetted emory paper wrapped around the journals and spun w/a lace double-wrapped around the paper. This isn't meant to be a replacement for proper machining of the crank if it's needed.
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Old 05-30-2010, 12:04 PM
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Quote:
Originally Posted by cobalt327
The "proper" way of polishing the crank is done by spinning the crank and using a polishing belt to polish it in the same direction of rotation as the engine runs.



I've "polished" cranks to remove slight surface rust by hand using solvent wetted emory paper wrapped around the journals and spun w/a lace double-wrapped around the paper. This isn't meant to be a replacement for proper machining of the crank if it's needed.
Hmm, i wonder if the op owns one.
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Old 05-30-2010, 12:39 PM
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Quote:
Originally Posted by Irelands child
Matt - unless you are 'experienced' my suggestion is - don't. The engine builder (Prattsville??) will use some 400, a bit of kerosene and strop the stone marks - but has done it probably for many years and has the 'touch'. Lawn mower, other small, low load for its' size, engine, not a problem!!!
engine builder is actually in Grand Gorge a few miles away.. my small town doesn't have much of anything except a grocery store, lawn mower/ ATV shop and 2 auto repair shops.... but the builder in Grand Gorge does most all of the dirt track motors, as there is quite a few racers in the area, and a chassis shop in the paint shop of the now closed down Chrysler dealer

I'v done it the above way on a few cranks.. with the emery cloth wrapped around the journal and pull the string.. just until the crank is nice and shiny and smooth. and this is after I mic them to make sure the cranks are within spec for roundness as per the manuals.
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