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Old 11-03-2016, 09:29 PM   #1
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Default Re-Using a crank during a rebuild

Hey all.
I'm in the planning stages of rebuilding my 4G63 (Evo 8). Unfortunately, the most common Evo forums are filled with a bunch of relatively poor knowledge members (the "my tuner tells me so and so" crowd). However, seeing as this is a relatively broad engine building question, I figured I'd ask here.

I am rebuilding the engine after a mildly blown head gasket (coolant consumption only, no fluid mixing/oil burning/smoke). The engine has high milage (150k) so I figured I may as well go ahead and rebuild it while I am paying for the labor.

So. The end goal is building the engine for longevity, and not ridiculous power. I've selected Manley H beams for rods, clevite bearings, ARP everything, and a set of 4032 Mahle pistons.

The block will be getting a hot tank, deck, bore, hone. The head will be reusing the original equipment, and will be decked and port matched.

The questions comes to mind of the crank.
What are the rules for reusing a crank? Can a crank almost always be reused (and last another 100k miles) with just machining considering there was not a catastrophic engine damage event?

Would it be advised to just go with a new OEM crank if building an engine to last another 100k miles? The OEM 4G63 crank is plenty strong for my future power levels/goals (350-400whp, well under 400wtq).

Thank you all in advance. I come back to my favorite forum for serious questions requiring intelligent responses.

As an aside, some of you would hate evolutionm.net... It is well within the rules to post 10+ classified threads, one each for different items, and bump them daily... Quite a **** community as well.
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Old 11-03-2016, 10:01 PM   #2
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As long as the crank is within spec I would not hesitate to reuse it. I would think since it was just a blown HG the crank should be more then fine.
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Old 11-03-2016, 10:04 PM   #3
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The best thing to do, would be to measure the crank journal diameter. Use a good quality micrometer, and compare to the service spec. For Miatas there is a specific table which has the specifications (3:30 in the Miata enthusiast manual if you want a reference). Along with that, if there is no obvious scoring/smearing of material (something you can feel with your fingernail), or cracks, you should be good to go.
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Old 11-03-2016, 10:32 PM   #4
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Great straight forward information guys. I would assume a crank to be one of the more resilient parts of the engine. The crank will get spec'd and examined thoroughly.

Here are a few photos of the basic port matching that has been going on while we are waiting for the parts to come in to send off to the machine shop:

Imgur: astral's Evo Port Matching
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Old 11-04-2016, 12:22 AM   #5
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As has been said. Inspect it for wear and spec. Check the runout and make sure it's straight. If that's all in it's good to go. If you want to go all out you can coat/treat/nitride/etc. but assuming everything is in spec I would have zero hesitation using a used crank.
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Old 11-04-2016, 03:22 PM   #6
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If you wanted to take the extra step, you can have the crank checked for cracks using a magnaflux or similar test. As long as the crank measures out within spec, you should be fine to re-use. If you are doing that much work to the block, you may want to ask about line-honing the mains and polishing the crank journals.
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