Sneak peek at my crankshaft project

[mrriggs]

Oct 1, 2013 21:40:47 GMT -5 plattey said:

Is this going into your big bore engine?

Yep, this is for the big bore motor.

Is it going to be a stock 360 phase or the 270?

I'm actually going to make it a 315.

The idea started when I looked at the Ausralian 270 crank pin and thought to myself, "I could make one of those." The problem with that design is that you need to cannibalize a second crank to get a splined crank web. That splined shaft is the weakest part of the crank, so why add a second one? A big straight pin is stronger, doesn't require parts from a second crank, and can be phased for any conceivable firing order. With that kind of freedom, why not try something a little different?

[kopcicle]

with the 144mm rods and 74mm stroke the "offset" is 76 degrees for one piston to be at rest and the other at max acceleration .
just fyi Brett ..

315/45 would give the same firing "cycle" as my common crank pin 45 degree V-Twins


~kop

[mrriggs]

Oct 22, 2013 18:06:19 GMT -5 kopcicle said:

with the 144mm rods and 74mm stroke the "offset" is 76 degrees for one piston to be at rest and the other at max acceleration .

Max velocity, not max acceleration. I understand the Phil Irving concept but all that does is make improvements in one segment of the cycle while hurting others. The net result is the same.

This chart shows the instantaneous torque of the two combos.



The improvement from the re-phase can be seen immediately after the 360° mark. The burning mixture is only having to accelerate one piston so the output is much higher. However, look at the trend just before the the 360° mark. There is a large dip on the re-phase motor since there is only the inertia of one piston pushing against the burning fuel mixture. When you integrate the trends you find that the mean torque values are the same. No matter how you rearrange it, the same work is required to move the pistons up and down.

315/45 would give the same firing "cycle" as my common crank pin 45 degree V-Twins

I wondered if anyone would catch that. Yep, It'll say, "potato."

[xsleo]

Ah So your building a Sportster out of your XS.
Leo

[mrriggs]

Nov 14, 2013 16:25:03 GMT -5 xsleo said:

Ah So your building a Sportster out of your XS.
Leo

Nah, if I wanted a Sportster then it would be a hell of a lot cheaper to just buy a Sportster.

I liked the sound of my 277° motor but didn't like the buzzy vibes. The 360° has more pleasing vibes but sounds bland. I'm hoping to split the difference and get the best of both. Of course, it could end up worse than both but you never know until you try.

[mrriggs]

I had a bit of a setback when I cracked the pins while trying to heat treat them. Started over with 4130 instead of 1045. The chromoly pins should have the same strength as the heat treated 1045 pins, but not require heat treating.

I'm just about back to where I was before and [hopefully] will be assembling a crank soon.

[crazypj22]

Did you ever get new pins sorted out?

[mrriggs]

I got one pin done but haven't had time to build up a crank yet. There is always something more important that needs my attention. I may be losing my shop so this could be one project that never gets done.

[mrriggs]

This project is not dead yet. I just finished balancing the crank webs. Had to drill the counterweights and press in tungsten slugs.

[mrriggs]

I assembled and trued the center section a few weeks ago.



Unfortunately, I made an error in measurement [or calculation] when determining the width of the flanges on either side of the sprocket, and the crank assembly is 1mm too short at this point. I had to order a couple 1.5mm connecting rod thrust washers to use on the inside of each rod. That should put the rods and outer webs where they need to be.

While I was waiting for the backordered washers, I started on the ignition system. Sure, I could have simply made a new 315° reluctor for my HEI ignition but I've already been-there-done-that. This project is about pushing it to the next level so I designed a digital ignition that will work with the odd firing order. In fact, it will work with ANY firing order! With two DIP switches it can be set for 360°, 270°, 277°, or 315°. All done without changing the pickup or reluctor.