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Building a FM 118 crankshaft?

Reed Engine

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Last Subscription Date
07/10/2019
I own a pattern and I've even machined a few castings myself but I can't afford to do them in any kind of a production run any more. I was looking at the thread on smoke and flames showing them build a crankshaft for a ship engine in pieces.

http://www.shipsnostalgia.com/guides/William_Doxford_and_Sons#Introduction

This got me to thinking why not? So, I'm having some journals cut out in a water jet and ordered some cold roll. I'm going to build a few and see how they do.

Has anyone here ever tried this before? Any input would be appreciated.

I will take pictures along the way and will show the final product.
 

dalmatiangirl61

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Last Subscription Date
07/10/2019
A lot of motorcycle cranks are built this way, of course with multi cylinders getting every pin indexed just right is the trick. A single cylinder should be pretty easy:shrug:. Are new cranks, or reground cranks hard enough to find to justify this?
 

Reed Engine

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Last Subscription Date
07/10/2019
As I tried to say, I have made them before. 70+ of them. To my knowledge I made the last ones. It's not fisable any more. Welding them is disaster, they will break. I think I would trust this more than a regrind for sure. We just never weld and grind a FM crank. Others might, we don't and am not considering starting.
 

J.B. Castagnos

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01/01/2006
If I were going through this much trouble I would order better than cold roll, 4140 or one of the alloys, someone on here will probably have recommendations. If you order ground and polished and the correct reamers it would be an easy to machine job. Tack the throws together, bore and ream, press together. I would leave the rod pin and the main shafts long, machine a few thousandths off the ends for and inch or so so it lines up before the press fit starts, press it through and cut the excess off. Make a snug fit dowel to hold the main holes in line while pressing.
 

Reed Engine

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Last Subscription Date
07/10/2019
JB, wish I could spend some time with you. Sounds like you have some good ideas. I do plan on machining the journals at the same time but was planning on welding the assembly together. 4140 would be nice, I'll think about that for later if the first one works out. Cold roll would be better than the stock FM crank though. (My cranks were nodular ductal) Wish I knew more about reaming? I don't. I plan on making a light press so they go in straight with big counter boring so the weld penetrates deep and also gets it down out of the way.

It did cross my mind to put the main shaft in in one piece and after welding the outside cut out the middle. Similar to your dowel suggestion.

Do you care to tell me more about what you refer to as reaming? I have various Sunnen hones, would that work?
 
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J.B. Castagnos

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01/01/2006
You can buy reamers in standard sizes, an undersize like you would need would be expensive. Sometimes a metric size will be close. You drill or bore the hole to within a few thousandths and ream it to size, correct size hole, good finish, no measuring. The Sunnen hones should work, I have an old Sunnen pin honer that I use to get an accurate bore with a nice finish. Welding wouldn't hurt but I would try to get a good press fit. If you press the main shaft through in one piece I would make it oversize at the throw, turn the rest down so you don't have to press all the way. Turn two beveled grooves for the weld area. Cold rolled doesn't machine real well, usually kind of gummy.
 

Reed Engine

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Last Subscription Date
07/10/2019
Leaded steel does make a nice finish. I do alright with cold roll if I spin it fast.

This will be a learning experience but that's what I like.
 

Thob

Registered
I have thought about this for some time but haven't had the time to try it myself. It seems to me that it would work - cold rolled steel should be much stronger than cast iron, shouldn't it? As long as you can weld it up without distorting too much, it should work. My book has the FM 118 crank pin diameter at 1.936 to 1.937; that should make it easy to start with 2" stock and grind it down after you've finished welding. How big are the mains (under the taper roller bearings)?
I had originally thought of turning the ends of the rod down to 1 1/2" and only have to bore a hole that big in the flat pieces, but that would prevent your idea of starting with one piece for the main shaft and cutting it in two after welding. That's a great idea!
If you've got some scrap laying around, I'd make a "learner" crank out of that, weld it up see how it works - i.e. how much runout does it have after your "done"? Unfortunately, I don't have a bunch of 2" round and 1" plate to play with myself.

The other thing to check is how much space you have between the main shaft and the rod bearing journal. If I looked at the right info, a 6" stroke would have a 3" offset (main to rod). With 2" material, that would give you 1" between the two. Some cranks have a lot less stroke and the rod and the main overlap, which makes it hard to build one up by welding pieces together.

Are you planning on welding on the counter weights or cutting the side pieces out of a large piece of stock? Which brings up another question - what about balance? I know a single cylinder engine isn't going to be perfectly balanced (without countershafts), but you need to get the weight close enough that you don't wind up with a terrible jumping engine.
How thick are the side pieces? I assume you have an existing crank to measure.

---------- Post added at 07:27 PM ---------- Previous post was at 07:25 PM ----------

Leaded steel is horrible to weld. I think 4140 is a kind of chrome alloy steel (cromoly).
 

Elden DuRand

In Memory Of
Age
78
Last Subscription Date
12/22/2017
Not an expert and I haven't made any big crankshafts but I've used two methods to make the ones I've done.

Method 1: Waterjet cut a blank then turn it in a lathe. This is time-consuming but I've had good results. The 30-60 replica engine is an example of a crank like this.

Mdthod 2: Cut out and machine the crank cheeks and pins then press the whole works together. I don't like welding them because of the distortion (and I'm not a very good welder). Examples of this kind of cranks are The Homebrew Engine and The Homebrew Hvid.

Go to my webpage to see details.
 

beezerbill

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Last Subscription Date
01/10/2019
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.
 

Reed Engine

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Last Subscription Date
07/10/2019
I'm using 2 1/4" then turning to size after welding. Pin is 1. 937, mail is 2.000.
 

JSWithers

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Age
63
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.
 

Reed Engine

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Last Subscription Date
07/10/2019
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.
 

JSWithers

Registered
Age
63
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.
 

dkamp

eMail NOT Working
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...
 

Reed Engine

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Last Subscription Date
07/10/2019
Yes, I own pattern. I have cast and machined over 70 118 crankshafts. It's not fisable to do that any more.
 

Gary Reif

Registered
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
 

Reed Engine

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Last Subscription Date
07/10/2019
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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Gary Reif

Registered
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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