Normally people will shave the M47 crank nose when building an M42 stroker to fit the crank sprocket. Can the crank sprocket be milled to fit over the M47 crank nose instead? any effects by going this route? thanks in advance.
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M47 crankshaft question
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There used to be a ton of info on metric mechanics site about this crank but it seems they took it all down. Is the diameter of the crank different or is the key just in the wrong location? Maybe there isnt enough material to modify the sprocket? There must be a reason that everyone does it that way but I don't know what it issigpic
1991 318is x 2 .
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Here's a couple of pics I took yesterday of both cranks side by dide. M42 left, M47 right. The M47 crank nose is a little bigger. I talked to a guy who did a stroker build, and said he had to mill off 0.6mm off the M47 nose to fit the M42 crank sproket.
Sent from my SAMSUNG-SM-N910A using Tapatalk'91 318i (Alpine) - daily
'88 325ix (Zinno) - drive here and there!
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Boring the sprocket to fit would be easy but as said cutting existing key deeper or cutting a new keyway in a hardened sprocket is going to be a pain with a broach or shaper/slotter. So I asume the difference in location of the key don't matter? If you were really brave you could just mill .6mm off the top of the key instead... sketchy .sigpic
1991 318is x 2 .
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Sub'd for responses. I'd love to know more about this for future ideas.My Garage
2001 Z3 2.5i Steel Gray/Black (Lexi)
1988 325ix Diamond Schwartz/Black (Izzy)
1989 325i Cirrus Blue/Houndstooth (Stitch)
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Originally posted by AndrewBird View PostIf it is infact .6mm off the diameter, all you would need to remove is .3mm off the key, which is only .012", not much at all. This would work.
Sent from my SAMSUNG-SM-N910A using Tapatalk'91 318i (Alpine) - daily
'88 325ix (Zinno) - drive here and there!
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Originally posted by fresh_TD View PostIt's more the just the key way..the nose of the m47 crank is bigger then the nose on the m42 crank
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Originally posted by AndrewBird View PostRight. So modify the sprocket to have a larger hole, then shave the key down so it still fits. No need to modify the crank.
Sent from my SAMSUNG-SM-N910A using Tapatalk'91 318i (Alpine) - daily
'88 325ix (Zinno) - drive here and there!
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Originally posted by AndrewBird View PostIf it is infact .6mm off the diameter, all you would need to remove is .3mm off the key, which is only .012", not much at all. This would work.sigpic
1991 318is x 2 .
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Originally posted by Fsnow View PostOh yeah, woops. If it is that simple why in the hell would anyone machine the crank? I'd say go for it then
Sent from my SAMSUNG-SM-N910A using Tapatalk'91 318i (Alpine) - daily
'88 325ix (Zinno) - drive here and there!
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