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Building a FM 118 crankshaft?


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  #11  
Old 11-02-2013, 01:14:39 AM
beezerbill beezerbill is offline
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Default Re: Building a FM 118 crankshaft?

If you are planning to press the crank together, be sure that the steel you use has a high enough yield strength to accept the interference you plan on using for the press fit. Some of the bike cranks I have worked on have over 3 thou interference on a 30 mm crank pin - must be some pretty tough steel to not simply mash out of the way as the pin is forced in. Takes 20 to 30 tons to press these together.

I occasionally hear of a crank being welded together and was curious how everything was kept aligned. Two ways come to mind. One is to leave everything slightly oversized and then turn the crank to finished size after welding. The other trick I have heard of (but never done) is simply make everything to size, weld it, and then straighten it if it was an ordinary crank that got bent somehow.
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Old 11-02-2013, 10:20:45 AM
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Reed Engine Reed Engine is offline
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Default Re: Building a FM 118 crankshaft?

I'm using 2 1/4" then turning to size after welding. Pin is 1. 937, mail is 2.000.
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Old 11-02-2013, 01:22:48 PM
JSWithers JSWithers is offline
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Default Re: Building a FM 118 crankshaft?

Of course my dad isn't around anymore to ask questions and I don't know what size crank you're trying to build but dad used to have a machine shop and I know he made some crankshafts for a customer turning them out of 8-10" or bigger bar stock on the lathe. I remember watching him but don't remember much of the details.
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Old 11-02-2013, 04:32:44 PM
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Reed Engine Reed Engine is offline
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Default Re: Building a FM 118 crankshaft?

I believe they call that a billet crank. I've thought about that as well and cutting a blank out with a water jet and turning round. This third method is just a simple(r) way to go at it. (I think)

I'm going to try it, you never know I just might learn something. To be honest I already have.
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Old 11-03-2013, 10:50:10 AM
JSWithers JSWithers is offline
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Default Re: Building a FM 118 crankshaft?

A lot of the old engines with the nice polished crankshafts and connecting rods were machined like that from bar stock. That's a lot of material whittling.
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Old 11-03-2013, 11:52:29 AM
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Default Re: Building a FM 118 crankshaft?

So when you say you have a PATTERN...

Do you mean you have a CASTING PATTERN? Like... made of wood, from which the sand mold is made?

If it were in my hands, I'd just carry it around to my local foundaries (there's still a few around here) and tell 'em that I'd like 'em cast out of something sensible...

I haven't done it lately, but I've got friends at local shops that're always looking for small-run work to 'fill in the spaces' amidst production runs... and if timing isn't critical, they can do some pretty wonderful stuff for dirt cheap...
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Old 11-03-2013, 02:36:08 PM
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Default Re: Building a FM 118 crankshaft?

Yes, I own pattern. I have cast and machined over 70 118 crankshafts. It's not fisable to do that any more.
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Old 11-03-2013, 04:05:01 PM
Gary Reif Gary Reif is offline
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Default Re: Building a FM 118 crankshaft?

I used to work in a machine shop and we rebuilt all of the older FM cranks, of course at that time they were forged steel. We never had any trouble with them breaking. We used a preheat and post heat. We still had a little straightening to do. We had to watch for the cast cranks of course. Gary
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Old 11-03-2013, 04:38:24 PM
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Default Re: Building a FM 118 crankshaft?

I've seen way too many break after welding. Arrow cranks are something else, we do them all the time. I've been around this stuff for many years and I've never seen an OEM FM crank that was anything but grey cast. The ones we did were nodular ductal iron. I think Crow's were too but even Arrow cranks aren't a forging, they are cast steel. Not the FM cranks they had just the C series. Arrow gave me their FM 208 pattern but JenCast in Kansas lost it before I ever got it. Arrow had theirs cast at JenCast and Jack Swearingen machined them. He did most of mine too. He callede recently to tell me he's quit the machine shop and now owns a few oil wells.

I do agree, pre and post heat are important. We bury lots of things we weld in sand and let them cool slowly.
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Last edited by Reed Engine; 11-03-2013 at 05:04:16 PM.
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Old 11-04-2013, 12:06:17 AM
Gary Reif Gary Reif is offline
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Default Re: Building a FM 118 crankshaft?

Reed Engine we must be talking about two different types of cranks because we rebuilt ours with a wire welder and recut the flywheel ends on the lathe, and keyways with HSS cutters. I'm sure they weren't any kind of cast because the first cast iron one I rebuilt I couldn't cut so we quit rebuilding the Arrow cranks. Of course that was over 15 years ago and I don't know what's going on in that type of stuff now. The cranks we rebuilt were from the 40's 50's and 60's era engines. We also rebuilt a lot of C46, C66 and C96 Continentals (sp) before they became Arrow engines. Gary
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