Crankshaft Polishing vs. Grinding - Team Camaro Tech
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post #1 of 6 (permalink) Old Feb 7th, 17, 06:48 PM Thread Starter
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Chad
 
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Crankshaft Polishing vs. Grinding

Pulled a crankshaft out of an older engine, and it has some scoring on the rod journals that go around the journal, not side to side. Most are light but one you can definitely catch one with a fingernail. Question is in regard to polishing versus grinding. What is the cutoff point?

If you had the crankshaft lightly polished to knock the burrs and/or high spots off the journal, would this not protect the bearing from further issue? Aside from the scoring holding a little oil, what would be the downside to using the crank at that point?

Just trying to understand why grinding might be a necessary option.

67 Black RS Coupe, 383, M21 & 10 Bolt Posi. Edelbrock E-Tech 170 Heads, 2204 Roller Cam, Air Gap Intake.
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post #2 of 6 (permalink) Old Feb 7th, 17, 06:55 PM
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Re: Crankshaft Polishing vs. Grinding

Chad, You need to mic these journals to determine if you are on the high or low side of limits. The journal could be egged. If the scoring will catch a nail or oil, it will catch trash.
Is the crank cast or steel? Depending on your usage, consider doing this one time and be done. Get a shop with mics to check.
You didn't say if this crank was std or cut.
Crank kits are cheap, depending on what you want. Another area to check is your rod big ends.

Don
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Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #3 of 6 (permalink) Old Feb 7th, 17, 07:35 PM Thread Starter
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Re: Crankshaft Polishing vs. Grinding

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Originally Posted by zdld17 View Post
Chad, You need to mic these journals to determine if you are on the high or low side of limits. The journal could be egged. If the scoring will catch a nail or oil, it will catch trash.
Is the crank cast or steel? Depending on your usage, consider doing this one time and be done. Get a shop with mics to check.
You didn't say if this crank was std or cut.
Crank kits are cheap, depending on what you want. Another area to check is your rod big ends.
Hey Don. Crank is standard cast. I pulled it out of an older engine that I have. I had it polished at the local machine shop, and the scoring is still on one of the journals. I was told that if the bearing can take the crank rotation without getting damaged, then it should be good to go and the scoring might just hold a little oil. I'm assuming that he mic'd the crank, but I'll have to stop back by and double check.

Not sure what I'm going to do with this engine, but of course, want it to be right. I figured if I bought a new crank, and had it balanced, that's another $400+, but if it would spin with no issues after polishing, then I'd go that route and save some $$$.

67 Black RS Coupe, 383, M21 & 10 Bolt Posi. Edelbrock E-Tech 170 Heads, 2204 Roller Cam, Air Gap Intake.
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post #4 of 6 (permalink) Old Feb 7th, 17, 07:56 PM
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Re: Crankshaft Polishing vs. Grinding

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Originally Posted by cv2065 View Post
Hey Don. Crank is standard cast. I pulled it out of an older engine that I have. I had it polished at the local machine shop, and the scoring is still on one of the journals. I was told that if the bearing can take the crank rotation without getting damaged, then it should be good to go and the scoring might just hold a little oil. I'm assuming that he mic'd the crank, but I'll have to stop back by and double check.

Not sure what I'm going to do with this engine, but of course, want it to be right. I figured if I bought a new crank, and had it balanced, that's another $400+, but if it would spin with no issues after polishing, then I'd go that route and save some $$$.
Since its cast , sounds like a grocery getter? If you bought an exchange reground, say 10/10, it comes with bearings and it shouldn't need balancing unless you have other plans. You may luck out and get a steel reground , never know, but shop or seller should back you up, provided you get a new oil pump. Just my thoughts here.

Don
TC # 349
Zdld17:69 Z/RS,306, NOR141111, 9N554XXX, 12A, X3G, 59/59,723, AFR 195,CCC282/290HR, TKO 600, BU1122B1E Owner since Dec 1968

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post #5 of 6 (permalink) Old Feb 8th, 17, 09:25 AM
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Re: Crankshaft Polishing vs. Grinding

I would be looking at the rod and bearing from that journal. If it has uneven wear then your going to need a grind and rod resize. You could possible get away with what you doing but is the savings worth the cost if it fails. If it fails you will spend the money anyway that your saving now....possibly/most likely more due to more damaged parts and tear down cost and cost to put it back together.

$500.00 saved now could be a $1000.00 spent later. I see it as take the chance and gamble or do it now. Crank shaft shop guy that said you will be fine has nothing to loose and your money to gain.

"If you can leave black marks on a straight from the time you exit a corner till the time you brake for the next turn.......
Then, you have enough horsepower."
-Mark Donahue
My 67 Camaro Time Line
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post #6 of 6 (permalink) Old Feb 8th, 17, 10:37 AM Thread Starter
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Re: Crankshaft Polishing vs. Grinding

Rod looks good. Bearing had the same scoring in the same location. I put the crank back in with a new bearing, torqued it to spec, then spun it a few times. Pulled the cap and bearing and it still looked new with no wear, so I'm assuming that the journal is not out of round? I'm dealing with the owner at the machine shop. Pretty decent guy with good local rep. After speaking to him again today, he said that he would not grind the crank, but I do see what you guys are saying. Definitely a little risk built in here.

67 Black RS Coupe, 383, M21 & 10 Bolt Posi. Edelbrock E-Tech 170 Heads, 2204 Roller Cam, Air Gap Intake.
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