crankshaft thoughts

JISupra88

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what are people doing about the low stock of available clean crankshafts for 7m motors? are people using cut and polished cranks for builds?

I picked up a running 7mge motor for cheap to use as a 7mgte replacement but might keep it to salvage the crank in case the one in my 7mgte bottom end is no good.

Is it safe to build a high horsepower car on a turned crank or is that asking for trouble
 

JustAnotherVictim

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I had my 7m(full counterbalanced) crank polished and balance at 10k rpm.
Not pushing huge power but the engine is very smooth even at high rpms.
If the engine is built right I wouldn't be too worried about the crank personally.
 

JDMMA70

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std journals is ideal, .010 under is fine, .020 under and I'd want to have the crank journals nitrided.
 

andrew_mx83

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My machine shop once told me not to go past .010 because it goes under the case hardening, and eliminates the undercut at each side of the journal.

That said I have run cranks at .020 in the past with no issues.
 

Enraged

A HG job took HOW long??
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I picked up a free 89+ shortblock a few weeks ago, haven't checked the crank condition yet though. I also got a 88 shortblock a few years ago for $200, with a nice 6M crank.

The plan is to use the 6M crank in the 89+ block, polish and balance the crank.

There seems to be lots of engines around for cheap, you just have to look. Ideally you'd want a BHG motor rather than a rodknock motor, but the crank can probably be refurbished either way.
 

JISupra88

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so I have a total of 3 cranks to use from: one in the 7mgte motor, one in the 7mge motor and one from a spare block

I guess I'll try to stay standard size bearings for everything if possible but I guess I'll won't mind if it's .010 under

Thanks everyone
 

JustAnotherVictim

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so I have a total of 3 cranks to use from: one in the 7mgte motor, one in the 7mge motor and one from a spare block

I guess I'll try to stay standard size bearings for everything if possible but I guess I'll won't mind if it's .010 under

Thanks everyone
Just make sure you size the gaps in the bearing while you're installing. If the crank surfaces aren't damaged material removal should be minimal.
I'm spacing on what the gauge material is called but most places should have it.
 
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Clip

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Just make sure you size the gaps in the bearing while you're installing. If the crank surfaces aren't damaged material removal should be minimal.
I'm spacing on what the gauge material is called but most places should have it.
Plastigage, typically found in three diameters. Make sure you get the right diameter for the clearances you're trying to measure.
 
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Z06gette

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I had mine polished and counter balanced. The first 6m crank I sent him that came with my ge short block would've gone over .020 so he said he wasn't comfortable with that. I pulled my other crank which was in much better shape and we got by at .010 again, counter balanced and micro polished.