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Old 01-12-2009, 04:34 PM   #1
C3Paul
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Default How do I polish my cast iron crankshaft?

I am rebuilding an engine for my 1980 and while the block is in the machine shop I have the time to do some cleaning.
I have started cleaning the casting marks and rounding off all the sharp edges on my cast iron crankshaft before it gets balanced and reassembled.
How far do I go with cleaning and polishing?
Thank you, Paul
Click the image to open in full size.

Last edited by C3Paul; 01-12-2009 at 04:47 PM.
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Old 01-12-2009, 05:20 PM   #2
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How far do I go with cleaning and polishing?Thank you, Paul
Cast crank ... Not very far ... mostly a waste of time ... but DO pay the shop to polish the journals just prior to your install. Polishing leaves behind some fines. You should spray clean it with brake/carb cleaner & air ... after you get it back but just before assembly.

tip: if you let a crank lay around for awhile, it's prone to rust on journals ... polish just before install.
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Old 01-12-2009, 05:28 PM   #3
gofastvette
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.
Get yourself a roll of fine emery cloth and go at it....
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Old 01-12-2009, 07:19 PM   #4
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Polishing without equipment to keep the journals 'true' is a waste of time. At best, you can just smooth and shine up the surface a bit by hand. Leave this work to the shop.
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Old 01-12-2009, 07:43 PM   #5
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I assume the reason you want to polish the crank is to increase the fatigue strength? Preventing it from cracking. This usually only happens in the fillet radii next to the bearing journals and polishing will not help much. The best benefit comes from either shot peening or fillet rolling the radius. Not sure where you can find a fillet rolling machine but there are lots of people who do shot peening. It should be done after the journals are machined and finished. The bearing journals are then masked with duct tape so the shot doesn't dimple the area. Care must be taken not to nick or scratch the radii after the process as this can cause a stress concentration.
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Old 01-13-2009, 01:11 PM   #6
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Polishing without equipment to keep the journals 'true' is a waste of time. At best, you can just smooth and shine up the surface a bit by hand. Leave this work to the shop.
+ 1 on that.
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Old 01-14-2009, 07:28 AM   #7
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Thank you for your replies.
I will leave the journals to the machine shop however, is there anything I could do to the counter weights?
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Old 01-14-2009, 09:25 AM   #8
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There is nothing to do on the counter weights...unless you see some loose metal or "hanging" burrs on some machined edges (sometimes you see these on balancing drill-outs). If so, use file or Dremel to de-burr that area...just to remove any loose stuff. If the repair shop is planning on cleaning the crank (and they would have to after polishing it), there's nothing else for you to do on it.
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Old 01-14-2009, 09:26 AM   #9
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Thank you for your replies.
I will leave the journals to the machine shop however, is there anything I could do to the counter weights?
Yours not a highly stressed race motor, right?
Yours is an OE or replacement-grade cast crank, right?
Yours will be balanced, right?

I say leave your counterweights alone ...
whatever you might do ain't gonna add enough to matter ...
it might even hurt it if you make a mistake ...
and the CWs SHOULD end up with welding and/or drilling or both resulting from balancing ...
then it may not LOOK so smooth either but you will not alter it then, right?

Suggest you communicate this same question to your local guy who's gonna do work on your crank.
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Old 01-14-2009, 10:10 AM   #10
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He wants to polish his shaft........Wide open on this one, I am surprised everyone kept it professional
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Old 01-14-2009, 11:05 AM   #11
Manuel Azevedo
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Quote:
Originally Posted by C3Paul View Post
I am rebuilding an engine for my 1980 and while the block is in the machine shop I have the time to do some cleaning.
I have started cleaning the casting marks and rounding off all the sharp edges on my cast iron crankshaft before it gets balanced and reassembled.
How far do I go with cleaning and polishing?
Thank you, Paul
Click the image to open in full size.

Grinding any and all sharp edges will not hurt a thing but probaly will do nothing that you could ever measure. Only have a good crank shop polish the crank just before you install it. DO NOT and try polishing by hand!! Well it is your crank do what you want, but when you understand what can happen you probaly won,t do it. When any metal is cut or ground on it actually lays the metal over in the direction of the grind not unlike a cats tongue feels . The more it is polished and or the more wear the surface gets the shorter the hooks of the metal are. So polishing by hand (which almost always is done in both directions)or on a polishing stand running the wrong direction is a real problem. This is a must do for boats that have engines running in rev. rotation to polish the crank in the right direction or risk failure. Because of this a fresh grind is much more of a problem than an old crank is to polish. Also do not turn the crank backwards for the same reasons of the cats tongue effect of the metal as it can really hurt your bearings. The softer the metal the more all this is a problem. But your cast crank will have the least problems because a cast crank is one of the hardest cranks made. And steel cranks are the worst because of the softness of the metal, but that softness is what makes it seem stronger because it gives and the cast does not just like glass is hard but brittle.
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Old 01-14-2009, 11:38 AM   #12
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Why not make better use of your time by double checking all new and reusable parts along with any and all measurements and making sure everything is as clean as possible.
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Old 01-14-2009, 01:37 PM   #13
C3Paul
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OK I get it.
I will leave the crank alone.
It is interesting to find out that, I could do more harm than good
Thank you

Last edited by C3Paul; 01-14-2009 at 02:01 PM.
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Old 01-24-2009, 12:51 PM   #14
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Quote:
Originally Posted by Manuel Azevedo View Post
Grinding any and all sharp edges will not hurt a thing but probaly will do nothing that you could ever measure. Only have a good crank shop polish the crank just before you install it. DO NOT and try polishing by hand!! Well it is your crank do what you want, but when you understand what can happen you probaly won,t do it. When any metal is cut or ground on it actually lays the metal over in the direction of the grind not unlike a cats tongue feels . The more it is polished and or the more wear the surface gets the shorter the hooks of the metal are. So polishing by hand (which almost always is done in both directions)or on a polishing stand running the wrong direction is a real problem. This is a must do for boats that have engines running in rev. rotation to polish the crank in the right direction or risk failure. Because of this a fresh grind is much more of a problem than an old crank is to polish. Also do not turn the crank backwards for the same reasons of the cats tongue effect of the metal as it can really hurt your bearings. The softer the metal the more all this is a problem. But your cast crank will have the least problems because a cast crank is one of the hardest cranks made. And steel cranks are the worst because of the softness of the metal, but that softness is what makes it seem stronger because it gives and the cast does not just like glass is hard but brittle.
Manuel, an old thread for sure, but I have a question. When I degree the cam on a new motor I need to turn the crank both ways to dial in TDC. Am I damaging the bearings doing this?
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Old 01-24-2009, 01:12 PM   #15
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Manuel, an old thread for sure, but I have a question. When I degree the cam on a new motor I need to turn the crank both ways to dial in TDC. Am I damaging the bearings doing this?
Always turn the crank in the direction of rotation - never backwards.

When degreeing the cam, you want to keep the timing chain tight in the direction of rotation as well.

If you are "dialing in" TDC with a dial indicator on top of the piston (heads off) to set your degree wheel, you still want to turn the crank in the direction of rotation - Backing up may give false readings on your dial indicator as well.

Piston stops screwed into the spark plugs are not a great way to establish TDC IMO - Might as well just rely on your balancer marks.
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Old 01-24-2009, 02:02 PM   #16
tt 383
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Seems to be a waste of time for a cast piece and I think you should store that crank on end not on its side till you assemble.
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Old 01-24-2009, 04:35 PM   #17
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Manuel, an old thread for sure, but I have a question. When I degree the cam on a new motor I need to turn the crank both ways to dial in TDC. Am I damaging the bearings doing this?


If you follow how Capella suggests you will be just fine Good luck
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Old 01-24-2009, 05:04 PM   #18
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He wants to polish his shaft........Wide open on this one, I am surprised everyone kept it professional

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Old 11-24-2010, 05:27 PM   #19
blown 69
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Quote:
Originally Posted by C3Paul View Post
I am rebuilding an engine for my 1980 and while the block is in the machine shop I have the time to do some cleaning.
I have started cleaning the casting marks and rounding off all the sharp edges on my cast iron crankshaft before it gets balanced and reassembled.
How far do I go with cleaning and polishing?
Thank you, Paul
Click the image to open in full size.
dont let the rookies fool you! grind off the casting with 36 grit and die grinder! tiger wheels work good too! get rid of the sharp edges and then take to the balance shop ! have them shot peen then turn the crank! it will make you feel better!
check Ed Staffels book on budget smallblocks! you will learn a welth!
happy power to ya!
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Old 11-24-2010, 05:30 PM   #20
blown 69
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if you wann polish the journals urself! go to the machinest and ask him for used polish belts! he will probably give them 2 u! they work very well!
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Old 11-24-2010, 05:30 PM
 
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