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Crankshaft polish

General engine tech -- Drag Racing to Circle Track

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BBOLINGER
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Crankshaft polish

Post by BBOLINGER »

Hey guys. First time posting-- but been reading here for a few years.

I just picked up my crank from local machine shop. The factory finish looked good and all journals mic'd out good, but a few of the mains had a little rougher finish than I wanted. To mu surprise, when I opened the packing from the machine shop with my "freshly" polished crank, there are belt marks al over the rod journals. And not just visually-- they can definitely be felt with a fingernail.

I immediately drove back to the shop and showed one of the head machinists, to which he replied "that's totally fine. I'd run that in a race motor." I was speechless. I'd NEVER run a crank that looks like this, let alone in a performance application. It looks ten times worse than what I started with. Who am I to question a guy who does it everyday, but it goes against everything I was ever taught. See the pic for reference.

Am I splitting hairs over nothing here?

Image
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PackardV8
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Re: Crankshaft polish

Post by PackardV8 »

So you paid to have it polished and think it's worse?

FWIW, the current micro-polishing machine systems aren't as pretty to the eye as the old hand-held belt finishes.
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lefty o
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Re: Crankshaft polish

Post by lefty o »

imo, if you can feel that its crap. as for who are you to question it, you are the guy paying!
rebelrouser
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Re: Crankshaft polish

Post by rebelrouser »

Will not claim to be a crankshaft machinist, but I told my automotive students for 26 years, if you can catch a finger nail on any polished surface of an engine, something is wrong and it needs to be addressed. I also told my students that if you chew your fingernails, you are losing a valuable precision instrument. I have been an automotive technician since 1974, and again if you can catch a fingernail on it, something is wrong.
rustbucket79
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Re: Crankshaft polish

Post by rustbucket79 »

Well from a functional point of view what you feel are low spots created from excessive belt pressure during the polishing process, and being low they won’t cause any issues. From a cosmetic point of view the job looks like crap. [-X

Any attempt to eliminate those marks will remove size from the journal.
Geoff2
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Re: Crankshaft polish

Post by Geoff2 »

Take it back & tell him to run it in HIS race motor, because it is not going in your motor.............
SupStk
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Re: Crankshaft polish

Post by SupStk »

If you can feel it there is something wrong. Mic the crank and see what you really have there. I can't imagine how much effort it would take with a polisher to do that. Wonder if they were trying to hide grinding lap lines?
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Re: Crankshaft polish

Post by mag2555 »

From the federal Mogal Bearing book in reguards to cast cranks .
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BBOLINGER
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Re: Crankshaft polish

Post by BBOLINGER »

Thanks for the replies. I was a so disgusted I haven’t even checked it with a mic yet. The crank finish looked very good before I brought it in and was round with no taper. Scared what I’ll find now.
MotionMachine
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Re: Crankshaft polish

Post by MotionMachine »

This is a result of threads in the belt coming loose on the edges and flailing around, scratching the surface. They should have stopped as soon as they saw it and snipped the thread off or changed belts. Take it somewhere else and have them polish it again with a well broken in belt, no material will be removed if it's broken in properly. At that point, the scratches will probably be highlighted and you can better assess if they are going to be an issue.
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Re: Crankshaft polish

Post by gunt »

OH the memories

as i have said many time , its the only reason we are tooling up , other wise we have to send all to the uk , I had heard of another shop 1hr away , and needed a crank polished and balanced real quick [ so no time to send to another country ] went up dropped it in , seams this guy has a name in the v8 community over here , the place was full of nice stuff . very cramped but rent is high , so whatever , all nice equipment , did up the crank while i did a few errens , paid went home , washed off the grease , instantly it was very obvious , the crank had far more mark's in it than when i dropped it in , so i rang the fool , and with out hesitation , he decided to educate me , [ you don't understand , the scratches from the polishing go around the journal not across and that's the way the oil flow its not a problem ] so i stated that it wouldn't even be acceptable in a diesel unit , i asked what grit he used and with great pride he declared he gives a quick run on 220 and then straight up to 400 , [ the crank was washed / spotless before it went up ] i told him that even the diesels are finishing in 2200 so where was he going and when i had access i even finished then off on leather straps .

problem is these guys charge you for the privilege of turning you items to scrap , they should be liable for all .

when i get around to finishing it , i have a shop / display room / i have a wall full of deliberately destroyed items by muppets with their contact details under each , and most of the time the public can pick the issue out , it helps me justify the additional cost as they have the option of using the machine shop they recommend or paying for the shipping to the uk , but up to that point they have never seen work close up from these people as they go on facebook
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Re: Crankshaft polish

Post by rebelyell »

If you can feel their polishing and it's fugly; they should be avoided.
1980RS
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Re: Crankshaft polish

Post by 1980RS »

BBOLINGER wrote: Sat Nov 21, 2020 6:39 pm Hey guys. First time posting-- but been reading here for a few years.

I just picked up my crank from local machine shop. The factory finish looked good and all journals mic'd out good, but a few of the mains had a little rougher finish than I wanted. To mu surprise, when I opened the packing from the machine shop with my "freshly" polished crank, there are belt marks al over the rod journals. And not just visually-- they can definitely be felt with a fingernail.

I immediately drove back to the shop and showed one of the head machinists, to which he replied "that's totally fine. I'd run that in a race motor." I was speechless. I'd NEVER run a crank that looks like this, let alone in a performance application. It looks ten times worse than what I started with. Who am I to question a guy who does it everyday, but it goes against everything I was ever taught. See the pic for reference.

Am I splitting hairs over nothing here?

Image
What the heck did he polish that with? 80 grit sand paper?, I would be asking for a full refund on that. Crap work right there.
smeg
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Re: Crankshaft polish

Post by smeg »

Boy that is an ordinary job, totally unacceptable.
We finish our cranks with a cork belt after an old 400 grit belt to get a nice smooth surface. Tell them you will be posting about their work quality on facebook if they don't fix it. Better yet, get some 600 grit tape and find someone with a lathe and fix it yourself.
BBOLINGER
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Re: Crankshaft polish

Post by BBOLINGER »

Ok, glad to hear I'm not crazy.

I have an old block with some decent bearings-- thought about dropping it in the saddles and having my son run the drill slow on the crank to rotate while I polish it myself. Am I asking for trouble? I've polished some daily driver stuff before, but not near the HP level I'll be at with this.
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