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Discussion Starter #1
I'm working on a inline vortec which has no performance engine bearings available just stock size replacements -10, -20

I have a new GM service crank and am really in a pickle what to do to get bearing clearance - I really don't want to go -10 (first undersize) on a brand new crank.

Need an opinion from a crank specialist is it possible to grind .001?
 

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NO you can NOT grind .001. you can polish it off but no way to keep it round and not taper some. But you can not set up a crank in a crankgrinder and grind .001 off of it. it is too small of an amount. the GM crank will not even have the stroke set that close.
 

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NO you can NOT grind .001. you can polish it off but no way to keep it round and not taper some. But you can not set up a crank in a crankgrinder and grind .001 off of it. it is too small of an amount. the GM crank will not even have the stroke set that close.
This is very true for most production cranks, and many aftermarket cranks, but if the crankshaft was properly indicated in when it was ground, it is very possible for a good crank grinder with precise arnold gauges to grind off as little as .001" - I have had this done by our grinder several times when going to .010" on a crank that had no .009" or .011" shells available, when we got the crank back, the clearances were too tight, so he was able to put it back into the machine, indicated it in, and regrind just a thou off to put the clearance where we want it.

Like you said, it's very hard to try and polish more than a few tenths without creating a low spot in the middle of the journal.
 

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I'm working on a inline vortec which has no performance engine bearings available just stock size replacements -10, -20

I have a new GM service crank and am really in a pickle what to do to get bearing clearance - I really don't want to go -10 (first undersize) on a brand new crank.

Need an opinion from a crank specialist is it possible to grind .001?
What is the clearance at right now?

What will the motor be used for?
 

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Ask someone that knows how to run a crank grinder... can they set a crank up in their grinder and only take .001 off of the shaft??? I know a lot of people that run crank grinders, and the honest ones will tell you there is now way. but some will polish it to what you want.
 

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There is no way my crank grinder could remove .001" off the mains of a crank. When you figure the total length of the crankshaft, and realize you need to hit within a tenth or two no only on runout, but end to end, with all the journals perfect to begin with, etc, as well as have the crank PERFECTLY straight (very unlikely on most any crankshaft uless fresh out of the grinder) it starts to show how unlikely it is to achieve. Have a look at a .0015" feeler gauge, and think what it would take to set up a crank on a PERFECT grinder to remove 1/3 of the thickness of said feeler gauge per side of the crank. :?

Most any skilled crank grinder (operator) can do a good job of polishing .0005" to .001" off the crank journals with minimal taper on a factory cast iron crank. Aftermarket hardened forged and the factory GM tuftrided cranks, not so much. :smt062
 

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I used to grind cranks many years ago. I wouldn't be afraid to setup a freshly ground crank and take .001 off of the mains. But it would be hit or miss on the rods. Granted, I was running a well worn Storm 15A. On a nice, fresh machine it might be more feasible. I would rather take a little off with the polisher, which most guys seem to be afraid of. I kept a rotation of about 5 belts that were in various stages of "worn out". I never used a brand new belt on a crank. Had an old king pin on the bench that I "cut" new ones with before using them on a crank. The newer belts would take a little off. The most worn one wouldn't take .0001" off if you hit it for 5 minutes. But it sure made them shiny.
 

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Discussion Starter #10
I talked to the better of the local crank shops and they might be able to do 1 thou grind. More info soon. Thanks for the comments
 

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It is possible, but it will take a good crank grinder operator, and an even better machine. Find someone you trust, and ask them if they have a good enough machine to do it on.
 

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stock cranks as said by others,

are know to have some hardness thickness issues....
this can cause problems with the crank gut to "correct' the clearances needed....
oftentimes they will not stay round...but many well understood can polish the journal and not have issues with measurement....
...........it is all a matter of just how good the crank gut is...or is not.

it is also possible that your new bearings are not exactly as the original bearings were as factory installed...

there are many
related post topics with postings about clearances

align hone dimension could also be incorect ...
 

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Discussion Starter #14 (Edited)
You didn't answer our question about what the clearance is at now....
Tightest 0.0008 to loosest 0.0012

GM spec'ed the main clearance 0.0003 to 0.002

Looking to get 0.0018/0.002. We ran the opel last year at Bville last year with these clearances and the main bearing came out like new so we have a reference point.

When you use a bore gage they tend to dig in a bit. How much do most people take off the measurement ? I'm using 0.0002"
 

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I'm working on a inline vortec which has no performance engine bearings available just stock size replacements -10, -20

I have a new GM service crank and am really in a pickle what to do to get bearing clearance - I really don't want to go -10 (first undersize) on a brand new crank.

Need an opinion from a crank specialist is it possible to grind .001?
If your rods are on the low side take to the high side that should gain you an extra .0005
 

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Discussion Starter #16
The clearances posted are on the main line. The rods are actually a bit loose 0.0027 to 0.003. Any thanks for the feedback
 

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The clearances posted are on the main line. The rods are actually a bit loose 0.0027 to 0.003. Any thanks for the feedback
Open the main line up .0005
 

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Okay so for all the armchair crankgrinders I apologize, What Diff does it make if .001 is polished or ground off in this situation? And sure start in with your, "low spots and runout" it's fukking .001 and it's a stock crank. Put your editorial microscope away. He wants to take .001 of the crank. As a machinist your going to tell him, "no" and let the money walk fuk u
 

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a thousandth can be removed

just how accurate will depend on just how good and accurate it was previously

and how good the guy that is doing the new surface changes


whether he accomplishes it via grinding or polishing will depend on HIM.....

not every grank man is equal to another.
 

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Okay so for all the armchair crankgrinders I apologize, What Diff does it make if .001 is polished or ground off in this situation? And sure start in with your, "low spots and runout" it's fukking .001 and it's a stock crank. Put your editorial microscope away. He wants to take .001 of the crank. As a machinist your going to tell him, "no" and let the money walk fuk u
There's a huge difference between grinding and polishing a thou off a crank. Neither is really the right answer in this situation. It's almost impossible to polish a thou off a crank and keep it straight and round. As already said, it's a tedious task to grind a thou off, although the mains would be easier than the rods. The right answer is to either find some different bearings (different manufacturers are different thicknesses) or adjust the main housing bore. Heck, if it came down to it, I'd scrape half a thou of each shell and not lose any sleep over it.
As a machinist, I'm going to give him the best advice for the best outcome, regardless of the money. Your last comment was totally uncalled for.
 
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