The technical adventures of Dr_C

OK, thanks for enlightening me!
I take it the 550 still has the 32mm pin?

When studying some other pressed cranks, it seems like the main disadvantages to the Husaberg design are (in order of severity IMO):
1. too short press fit (the webs are only 20 mm thick at the location of the press fit) for the actual pin diameter. The press fit is very much "undersquared" in comparison to other designs.
2. too far between the main bearings, due to the CB
3. too small diameter of the pin, not so much for reducing the strength of the pin, but more for increasing the surface pressure to the web in the press fit. Perhaps more practically explained: When the crank is spreading, the pin remains "straight" but the holes in the webs are deformed.

I'm thinking (again!?): a thicker left web (not necessarily much heavier) will increase the length of the press fit, reduce the surface pressure to the hole in the web, and make the web hold the pin square. There is no room for such a solution on the right side. Instead the web will have to be hold into place by two bearings. I would prefer a pressed crank, because it will be possible to refurbish it, when/if the big end bearing wears out the pin, without having to manufacture a whole left side of the crank.

There are two options to the right hand side, both will make the alternator cover come some 20-30 mm further out (acceptable?). Either we put an additional bearing just outside the original bearing, in the flywheel compartment. Then the whole flywheel arrangement will be moved further out, and most likely otherwise unaffected. The other way is to let the flywheel/stator remain in the stock location, and build a new cover which holds a bearing at the very end of the crank. Any comments on this?

Oh, yes, one more thing!
Will anyone be interested enough to pay for this cure for a bike that old?

I believe that calls for a totally new alternator cover, as there will be quite some stresses on it from the bearing. One advantage with mounting the bearing in a cage/spacer between the casing and the cover, is that you can use the OEM flywheel/stator/cover. You can also use a larger bearing and design the cage/spacer to cope with the forces from the bearing.

I have my eyes on a pallet with crank forgings (in my region), which I'm developing these thoughts from.

Yes, to get the number up to, say 10 cranks, I believe that they need to be very easy to install (no other machining required). That's one of the reasons to fabricate a right hand side bearing cage as a spacer, and just bolt stock flywheel/stator/cover back on.

Rough cost estimate (based on 10 pieces):
crank webs - 3000 SEK (maybe guessed to low)
crank pin - 1000 SEK
bearing cage - 1000 SEK
That sum up to 500€, 410 AUD or 550 USD


There is absolutely no other gain for me personally but to get the pricing down for my own 2 sets and making other Husaberg-enthusiasts happy!

Going down the "New cases lane", will increase the work immensely and the market reduce to... very few.

I talked to the machinist today. He thought that crank with pin would sum up to 6-7000 SEK if doing a series of 10 pieces. Thats about 660€, 720 USD or 925 AUD, excluding the bearing cage. I'll have to check the pricing for that, when I've done the design. The main cost benefit with larger series seems to come from the hardening process. It was quite possible to do two different strokes. I'm assuming we are talking a 35mm pin for both 80mm and 70mm stroke?

@Bushie: I can try to make the crank as light as possible, but, I need to know how big "unbalance" we want the crank with pin assembly to be? Preferably expressed as "gram x mm". More practically expressed: how much weight on the crank pin (bearing+rod+weight) will balance the crank? Weight x 40 mm = X [gmm]. Same thing with the 70mm crank. Would it help with holes in the webs to put weight insert in, to be able to adjust the balance factor as needed?

bushmechanic said:

OK Dr_C ill check after work today if i have all the data to calculate the imbalance as a torque value ...

it gets tricky to replicate a traditional "balance factor" in this method though because we all have different rods and pistons. I at best I can express the "ideal" balancing moment as a torque value for the crank assemblies that I have measured up traditionally.

hmm damit! now my tight arsed logic says at $950 without a rod or bearing i think i would be very tempted to buy 2 oem cranks.

Click to expand...

Thanks, Bushie!
I suppose that tight arse of yours loves replacing mains on a regular basis and gets all cranked up (!) if a breakdown punches a hole in your cases? ;-) Making custom parts comes with a price tag. If anyone out there has a more price worthy solution on the manufacturing of webs and pin (requires knowledge about crank design and function), please let me know!

spanner said:

My thoughts on a custom design would be to make "one" and see if it worked.

I did post a drawing of a cost effective way of producing a flywheel and main pin,
will it work? I am not sure but that would be how I would go about it, as an experiment.

Click to expand...

If I produce a crank and fit it in my RST engine, we will not have test results until next August... And furthermore, what will the test result from that operation tell us? If the mains last for more than 20h in my engine, what does that correspond to in a "normal" operation?

I think I mentioned that my machinist have access to raw crank forgings. That means the crank web will be solid and require a minimum of machining.