Fairbanks 80HP 3 cylinder model

[vcutajar]

Good progress Chuck.  I am following and learning as you move forward.

Vince

[b.lindsey]

The crankcase looks good Chuck and leaving that little bit of extra stock is a good lesson for all of us to remember. The crankshaft is also coming along nicely. Looking forward to your continued progress on this one for sure.

Bill

[peatoluser]

Will enjoy following this build as well, but I do have a question
was hot rolled bar chosen for a reason to make the cranks or was it just a conveniently lying around?

regards

peter

[swilliams]

This is an interesting project Chuck

I'll be following along

Steve

[cfellows]

Will enjoy following this build as well, but I do have a question
was hot rolled bar chosen for a reason to make the cranks or was it just a conveniently lying around?

regards

peter

Hi Peter, I just happened to have a short length of the hot rolled of the right size on hand, so that's what I used.  I have heard that hot rolled steel is less likely to have internal stresses than cold finished steel, but it probably wouldn't make much difference on a piece this small. 

If this first crankshaft doesn't work out, my second attempt will be turned from solid starting with a 1-1/4" diameter piece of 12L14 round rod.  I used 12L14 for my V8 crankshaft and it's very easy to machine and mill.

Chuck

[Bearcar1]

Wow Chuck, your off to a good start. I somehow missed the beginning and had to back and catch up. I like how you are building up the crankshaft like that. I too have popcorn and am in the wings watching intently as this one progresses. I can almost hear that full scale engine thumping merrily along, ahhh, sweet music. 


BC1
Jim

[cfellows]

Wow Chuck, your off to a good start. I somehow missed the beginning and had to back and catch up. I like how you are building up the crankshaft like that. I to have popcorn and am in the wings watching intently as this one progresses. I can almost hear that full scale engine thumping merrily along, ahhh, sweet music. 

BC1
Jim

Thanks, Jim!  Picking up from where I left off yesterday, I decided to bore the mains journals in the lathe.  While positioning of the holes exactly isn't particularly important, getting them parallel to the connecting rod journals is critical.  So, I mounted them in the 4 jaw chuck and used a DTI to center and position them as close as I could get, probably within .005" or better.



After center drilling, I drilled a 3/16" hole through both webs, then enlarged the hole with a 1/4" carbide end mill.  Figured this would straighten out an wandering by the 3/16" bit.



Next I enlarged the holes with a letter N bit followed by a 5/16" reamer.  I also turned some clearance on the outside of the webs, leaving a small circular piece on each side to contact the crankcase.  Here's the three pieces slid loosely on a length of 5/16" drill rod.



I mounted the crankcase in the milling vise and indicated it to the centerline for the crankshaft.  I'm using a 5/16" ball end mill to cut the crankshaft main journals into the crankcase top.



Here's the upper crankcase with the crankshaft mains milled in.



And here we have the crankshaft parts sitting in the crankcase...



Next I have to figure out how to hold the webs at the proper angle while the loctite hardens.  One of the possibilities I've considered is using set screws through the bottom of the webs against flats in the crankshaft main.  Not sure I would even need loctite if I did that.  Anybody have any thoughts?

Chuck

[peatoluser]

thanks for the reply George. never really considered that internal stresses could bend the crank . I shall have to keep that in mind if I ever turn a crank from solid.
with regards to assembling the cranks, with my triple , because the crank pins and shaft were the same size , I rested  the shaft on some blocks and  2 of the crank pins on smaller ones, the difference in height being half the crank throw. well, at least that's what my rudimentary trig. told me. once the loctite was set , done the same with 3rd crankpin and one of the already set ones. With different sizes of pins and crank, I suppose its just a case of altering the packing.  Hope this helps somewhat.

regards

peter

[steamer]

Chuck

Pete is on to it!....if you mount your block to the mill table, and then set the first crank to TDC..and loctite it place while in the block using the block as a jig.   Now if you move that crank to 30 from vertical, you can get the next crank horizontal....and loctite it there...ect....there are other ways...leave the first one vertical, and then tram the next one to 30 degrees below horizontal.    You could make a 30 degree angle plate and attach it to the side of the crank in order to tram off of it?....


Just some thoughts.....

Dave

[Don1966]

If the crank throws are 120 degrees apart, why not use you three jaw chuck to line up the throws, the jaws are 120 degrees apart, saves making a jig.

Don

[steamer]

Good point Don!   I only suggested the block as it could align the mains....but there are other ways to do that.

Dave

[cfellows]

Thanks for the suggestions, guys.  All good ones.  Hadn't considered the three jaw chuck.  Might be a possibility.  I would like to use the block for a jig as Dave had suggested.  Probably going to wind up doing piece at a time.  Gonna put the crank on the back burner for now.  I drilled the holes for the cylinder barrels and will likely do the cylinders and heads next.  Kind of trying to keep my options open as long as I can.



Chuck

[b.lindsey]

My engine will be somewhat smaller with a 3/4" x 7/8" bore and stroke. 

Chuck, it looks like from your drawing and the appearance of the crank webs that the bore is 7/8" and the stroke is 3/4"  I was looking at the crank positioning question and if I draw it up with a 7/8" stroke and fit it into the 1" x 1/2" stock you used, they don't look like your picture. Could be my brain isn't awake yet though.

BIll

[b.lindsey]

Using the crankcase it would seems that if you can accurately set one of the crankwebs vertically, then a ..09375" spacer block under each of the other two crankpins (based on a 7/8" stroke) would get the 120 degree spacing you need.

See the attached PDF

Edited to correct dimensions and pdf file

[cfellows]

Hey Bill,

Thanks for the input.  The cylinder bore will be 3/4" and the stroke is 7/8".  Here's a partial drawing of the crankshaft.



What may be confusing is that the holes in the crankcase are 7/8".  The bottom portion of the cylinder will have a tongue that sits down inside that hole.

Chuck