Has anybody ever made a crankshaft to replace the flywheels in HD engine? Just curious...

 

Strange question! The flywheels are part of the crankshaft. What do you have in mind?

 

The HD engines use two flywheels instead of a crankshaft, like an automotive type crankshaft as used in Triumphs, S&S X-Wedge engine, Ducatis, etc. I assume an automotive type crankshaft would be less expensive to produce, easier to balance perhaps?

 

Interesting point. As an engineer I have studied bike engine design over the years, with interest.

Single cylinder and V-twin engines need large flywheel mass to enable them to run smoothly, so there are good reasons why Harley and most other manufacturers over the decades have used the same construction. Harley currently uses two flywheel discs with an integral stub-shaft, joined together with the crank pin. It is a design that has worked since the dawn of time and is a good solution, very strong and economical to manufacture.

BSA used an automotive style crankshaft in some of their singles during the 60s and 70s, but it still required flywheel discs that were bolted on. The fact that it wasn't adopted widely through the industry suggests it was not seen as a superior solution! I haven't studied the Wedge, despite owning an S&S engine.

The beauty of the generic type of crankshaft Harley uses is that the engine has mostly roller or ball type bearings. They are very efficient and easily lubricated using a low pressure oiling system. Automotive crankshafts use plain bearings and require a high pressure system, although they are obviously also successful.

The winning feature IMHO is that with the forked rods roller bearings and flywheel design, a Harley crankcase is very narrow, compared with a plain bearing automotive style crank set-up. However I suspect the choice between the two designs is as much down to quirky preference than anything else!

 

Feuling has a different type of crankshaft that has a hitchiker rod set up instead of the hd knife and fork style. I think it is a solid crank with bolt on rod(s) but I only saw a picture. I don't know if they even have a pic on their web site.

 

I've heard of the Feuling set-up. It sounds like a similar set-up used on radial aircraft engines, which had a master rod, plus slaves attached to it. I can't see anything about it on their website.

The amount of flywheel an engine requires depends greatly on its design. The V-8 is an excellent solution, because of the 90 degrees between banks, as the way the cylinders interact reduces substantially the size of flywheel they need. A 90 degree V-twin also requires much less flywheel than any other configuration. As a rule the more cylinders in an engine the more practical the auto-style crankshaft becomes.

However Mercedes built straight-eight racing engines for many years that were built up like Harley engines, with entirely roller bearings! That's 17 in all. So there are many variations on crankshaft design out there.

 

The classic BMW boxer engine uses an automotive type crankshaft with offset cylinders, always wondered why the didn't use a forked rod arrangement like HD. Seems it would have been easier to balance and the resulting vibrations wold have been cancelled by the two reciprocating masses moving 180 degrees out of phase. The firing order could also be made to be 180 degrees with even power pulses.

 

There is a good reason for them being the way they are! The two pistons move towards each other in step, then away. To do that the engine needs opposing cranks. If the engine used a forked arrangement the pistons would follow each other to one side then the other. The engine couldn't be balanced! The cylinders would indeed fire at 180 degrees, but the next interval would be 540 degrees. With the current arrangement they fire at equal intervals of 360 degrees.

So a flat twin with forked rods wouldn't be easier to balance, quite the opposite! And it wouldn't have even power pulses.

Boxer engines were designed by a man of that name, although they are also described as being similar to a boxer punching his own fists together.

 

Yes, it does make sense now. Thanks for the insight!

 

Not so much for me anymore.

Yesterday I found out that my wife's 2010 Ultra Limited 28 months old with 28K on the clock has a loose flywheel - you can feel the give now that it's out of the case. It amazes me that the pressed fit relies on the rather small piece of keystock to maintain integrity. OK 2 flywheels are necessary, but why not press it on a spline or even a small weld to keep it together after assembled? As once it slips it gets replaced as a unit, are there times that the crank/flywheel assembly are disassembled for upgrades or is the most common upgrade the total replacement?

Fortunately we bought the extended service plan when we purchased the bike as I’m expecting that this failure will come on around $4-$5K to repair by the time it’s all said and done.

BTW, my wife rides it very mildly getting 45+/- MPG, and I’d guess that it rarely turns more than 3,200 RPM.