Can anyone recommend a reputable repair center to recondition a Mach Z crankshaft here in Michigan.

check out this page
www.snobuds.com
i think yo will find someone there under repairs.

Check out your local D00 dealer you can get a remanfactured crank at a resonable price.

Try Advanced Racing Technologies in Saginaw, MI
They are the people that have that turbo crank, you know the one with all the holes drilled into it. Suppose to give you 8hp on stock sled. That's were all the dealers send them to around here.

benoint performance does something like that its to get more fuel up there on mod sleds there getting more than 8

Folgers your right, a mod sled will have more hp from the crank. They told me 17hp if its totaly a modded sled. They just went over 150 mph asphalt in 1/4 mile with this crank.