Cutting a crank .10/.10...is it that bad?

[Verticaljump1]

I'm building a 4G64, took the crank to the shop, rod journals are already .005" undersized and the main journals are at the bear minimum for a polish. Shop tells me to cut .10/.10. Everyone has the balls to come out and say it's a dumb idea (no disrespect to them), but does anyone know why this wouldn't be a good idea? I thought you had a good coat of nitriding left even after a .10/.10 cut? Please let me know, thanks...

 

[blackGSX2g]

Exactly how deep the coating goes is debatable my many. Regardless of that, Mitsubishi cranks are non-serviceable and must be replaced if damaged. With that being said, you will find people on here that have had both good and bad experiences with under-cut cranks. I prefer not to risk it, but obviously others have with mixed results; though many of the poor results may be attributed to improper machining and clearancing during the build.

 

[Verticaljump1]

Thanks bro.

 

[94awdcoupe]

I am 100% possitive the nitride layer is lost during the first undercut. This makes the layer less than .005 thick. The crank will be like a 7 bolt at that point, as far as journal durability.

The factory 1g manual says not to cut the crank or the hardness layer will be lost. The 2g manual says you can cut the crank.

 

[TSIfreek]

As long as the crank is cut correctly and polished corectly I highly dought you will have a problem. There are many 4g63 engine builders that do this to 90% of there cranks. If your going to be at 600+ hp I would get a new crank.

 

[bryanwheat]

I would cut the mains, but i wouldn't even think about cutting the rods, just because you are investing money in it, won't hurt to put a little more in and make it right.

 

[sho_tyme_psi]

As long as the crank is cut correctly and polished corectly I highly dought you will have a problem. There are many 4g63 engine builders that do this to 90% of there cranks. If your going to be at 600+ hp I would get a new crank.

+1 Agree

 

[steel_3d]

As far as I can tell the real issue is not the nitriding or lack thereof. That only really affects the surface hardness of the journal, which resists wear. Unless an expert metallurgist can tell us otherwise, I believe that has little effect on the overall structural integrity of the crank. I wouldn't be too worried about journal wear with a clean assembly and correct tolerances. Another thing to help journal wear would be to buy Calico coated bearings from SBR, they're pretty much the same price as conventional bearings. It can be a bit of a wait though.

I think the real issue is the fillet area that gets scored and not smoothed, and possibly the thrust surface that gets ruined by a bad grinding job. The first will create stress risers that will make the crank prone to cracking, and the second will kill your thrust bearing.

It's possible that the well known shops can cut a crank properly. But I don't have much faith in that since I've seen well known shops screw up much simpler machine work. If on the other hand the fillets and thrust are perfect (which I'm not sure you can reliably check), then there's no reason a cut crank shouldn't live a long and happy life.

 

[StreetThisDSM]

Just make sure you check all of your clearances w/ plasti gauge, or something similar. I think you'll be fine.

 

[Suparata]

Mitsu cranks are induction hardened NOT coated therefore removing .005" off the surface can be done without a problem. As a matter of fact, if the job is done right, you will end up with a better than a lot of "untouched" cranks since you can have control on sizes, fillets and so on. There is one thing however that should be done which is removing the 4 ball bearings that plug the oil passages in the crank. There is so much dirt in there and it is a great place for foreign particles to end up in. How many shops are willing to do that? None that I know of. Well almost none.

 

[dnhieu]

i did a bunch of research awhile back and found that the nitrate coating penitrates .020 deep. so if your cutting off .010 then you are okay. this is what SB racing takes off when they sell there remanufactured cranks.

 

[92awddsm]

My 10/10 crank lasted several thousand miles. It would still be in my engine but a piece of casting flash came lose in the front oil passagage an destroyed my #2 main journal. I would be more afraid of running a stock crank than running a machined crank. Everyone should also realize that are cranks are forged steel, not cast so nitrided or not, they are harder(and more brittle) than most other manufacturers. Machining does not compromise the strength of the crank.

 

[steel_3d]

http://www.teamnabr.com/ubb/ultimatebb.php?ubb=get_topic;f=6;t=004929 May 22 post shows the hardness at various depths. Basically by cutting it .010" under you've still got 90% of your surface hardness.

So again the key is whether the shop cutting the crank can do a good job on the fillets and not mess up the thrust surface.