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Offset machining UL flywheel crank pin hole?

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HK

Posts: 87

Joined: Sun Oct 28, 2001 1:01 am

Location: Sweden

Post Mon Oct 08, 2012 9:50 am

Offset machining UL flywheel crank pin hole?

Need advice regarding set up for machining UL flywheel crank pin holes offset, you know the old trick where the hole is machined offset outwards and a OHV large taper crank pin is used, to gain a few more cu-inches.
This modification is said to have been "common" in the early days but how did they set up the flywheels for machining?
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Dusty-Dave

Posts: 902

Joined: Tue Oct 12, 1999 12:01 am

Location: Ojo Caliente,NM,USA

Post Mon Oct 08, 2012 10:32 am

Re: Offset machining UL flywheel crank pin hole?

Normally set them up in a mill with either a fixture or bolted down side guides so that booth come out with the same offset. Some people bore both stacked then ream with the matched holes as the index. The most amazing I have ever seen was pictures of a New Zealand racer cutting the tapered rod holes out of a stacked pair of 741 Indian wheels with a holesaw. He offset the holesaw so that he could rotate the plugs with the rod tapers increasing the stroke then welded it back together.
Dusty
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Cotten

User avatar

Posts: 2685

Joined: Thu Sep 30, 1999 12:01 am

Location: Central Illinois, USA

Post Tue Oct 09, 2012 7:23 am

Re: Offset machining UL flywheel crank pin hole?

HK!

The simplest set-up is on a lathe faceplate, if you have access to a lathe large enough.
The taper is easily set at the toolpost.

A counterweight, bolted to the faceplate opposite of the wheel's mass, will reduce eccentric vibrations.

Good luck!

....Cotten
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RUBONE

Posts: 383

Joined: Fri Nov 30, 2007 7:24 pm

Post Wed Oct 10, 2012 8:38 am

Re: Offset machining UL flywheel crank pin hole?

Why not sell the UL wheels to someone who needs them instead of ruining them and buying a set of new made S&S or T&O flywheels in the stroke you desire?
Robbie
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Chris Haynes

Posts: 2648

Joined: Wed Jul 05, 2000 12:01 am

Location: Los Angeles, CA

Post Fri Oct 12, 2012 5:29 pm

Re: Offset machining UL flywheel crank pin hole?

RUBONE wrote:Why not sell the UL wheels to someone who needs them instead of ruining them and buying a set of new made S&S or T&O flywheels in the stroke you desire?
Robbie



Budget may have something to do with it. :mrgreen:
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HK

Posts: 87

Joined: Sun Oct 28, 2001 1:01 am

Location: Sweden

Post Mon Oct 15, 2012 1:22 pm

Re: Offset machining UL flywheel crank pin hole?

Dusty, boring the holes cylindrical and then ream the taper was quite smart I think! Definitely the easiest to do, no need for advanced fixtures and easy to index in the mill. Probably also quite OK to ream even that large taper in the cast iron wheel. Only need to find a large enough 12 degree reamer...
The holesaw trick sounds scary! I tried to weld a flywheel once with an instant crack as result, I got a feeling that it is more carbon than iron in old Harley flywheels... Perhaps better with Indian ones. Still, wouldn't dare to rev that stroker if myself was on board!

Cotten, your approach is closest to what I had in mind. I do have access to a large enough late and also a magnetic chuck, the best tool I have ever used in a lathe. No problem to get the flywheel up and index the existing crank pin hole, but how to translate the flywheel the right amount along the centerline? And then do the same with the other flywheel, with kept tolerances. I see the need for a high precision fixture with some sliding feature along the line of eccentricity! And a counterweight must be included as well, as you say, or the machine will wobble through the wall I guess.

Robbie, I agree fully regarding "destroying" old iron, and nowadays it's usually the other way around, much junk that was discarded a couple of years ago are now salvaged, often with considerable time efforts. In this case I am not the owner of the project and even though we have discussed substituting with new parts, it's to no avail, this engine will be built the "old way". It's a dream come true for the owner.

Chris, in this case its not even MY budget, I only have the pleasure of doing it! Talk about win-win situation, (I do all the winning!)!

Appreciate your replies!
Thanks,

Hans
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Dusty-Dave

Posts: 902

Joined: Tue Oct 12, 1999 12:01 am

Location: Ojo Caliente,NM,USA

Post Mon Oct 15, 2012 8:50 pm

Re: Offset machining UL flywheel crank pin hole?

The 741 Indian wheels were what Indian called Z metal. I've seen lots of discussions on what it really is but whatever it is, it welds and holds a hundred foot pounds of torque where the old Cast Iron would only stand 75 pounds of torque. Looked awfully Rube Goldberg to me but there are lots of 741s racing in New Zealand with that setup,
To setup an offset on a lathe I usually use a 4 jaw and line up the direction I want the offset with one jaw. Then I center the bore then loosen the opposite jaw then drive the part over and put a spacer on the jaw I didn't move then retighten the jaw I loosened. Usually have to back off the two side jaws some to get the part to slide,just be sure that you turn them the same amount and retighten the same amount of a turn on each. There is no way my 12" Atlas would handle that job! Just turning a Chief wheel centered on the lowest backgear usually causes me to re-level the bed.
Dusty
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Early Iron Motorcycles

Posts: 144

Joined: Thu Feb 27, 2003 1:01 am

Location: De Soto WI.

Post Tue Oct 16, 2012 7:19 am

Re: Offset machining UL flywheel crank pin hole?

Hans, Do you have a rotary advance table for your mill? if so put wheel on advance table pick up center of wheel (pinion & sprocket shaft holes) from center move up the amount of stroke for wheel and turn advance table the amount needed to pick up crank pin hole, after that move the amount needed to change to the stroke you want and cut crank pin hole with a tapered cutter, that's how we do it. Also if you can't get a tapered cutter you could bore the crank pin hole for a stright press in crank pin like we use on drag bikes.

Mark.

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