The technical adventures of Dr_C

The 550s have cast crank

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Is this so?

Dr_C said:

I was thinking (believe it or not) about if it was possible to make a tougher crank (one fat web to the left and two bearings to the right) and still be able to use OEM flywheel, stator (SEM or Kokusan) and cover. Would that be a solution that would help more people besides myself? I was just figuring if doing this effort it would be nice if I could satisfy somebody else on the planet at the same time. Your thoughts, please!

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yes! it would help everyone with 650 cases .. particularly after 2018 when ktm is supposed to stop supplying parts

Dr_C said:

Are the 550:s also chewing mains? I thought perhaps the shorter stroke (70mm?) was easing the stresses, but maybe higher rpm gets the revenge?

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John Priors (ORANGEBERG) huge thread on main bearing failure identified the 550 as the bike with the most failures in Australia, and the 628 as the least likely to go, there was a 550 local to me that ate 3 sets of mains in rapid succession.

the main difference between the 628 is that the 550 crank and rod is 5kgs, the 628 crank+rod is about 4.5kgs with a heavier rod and pin so a lot less mass in the crank itself.

even though the 550 has a shorter stroke the crank webs of both cranks are the same OD though so as finn explained the spreading forces are higher on the 550 crank due to smaller pin, higher mass moment of inertia and higher rpm.

I read somewhere too that the 550 crank is cast but im not sure about that looking at it.

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?

Mr Ballard has tried the outrigger bearing solution.
I would think it would be effective.

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.

all sounds very good Dr_C

yes the 550 still has the 32mm pin

im interested in buying a crank or 2, what kind of price figure are we looking at very roughly speaking?

the oem crank is still available and i can get a new one for approx 500 USD complete and assembled and when running slightly bigger roller mains or spherical rollers im yet to see a problem with mains in my MST engines. even in the stock engine there was no problem, even though I broke 2 rear hubs and 2 geaboxes i the first year

edit: some thoughts on demand/practicality of a super crank:

if looking to sell a reasonable number of them I think would be most attractive if it was able to fit in the stock cases without modification.

there is a Billet 4030 crank for the KTM RFS engines available, same critical dimensions but said to be much stiffer just becasue of the material and construction.

its more work but given our OEM parts are set to stop in a few years perhaps there would be more interest in a complete engine of similar output and under 30kgs made mostly from various current OEM parts that can fit inside the husaberg frames, this would attract people from desert, super motard, super mono and sidercarX who got to know and love the 650.

ideally it would only involve making specific cases but ive not checked everything over 100% LOL

I believe that calls for a totally new alternator cover, as there will be quite some stresses on it from the bearing.

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Not so sure the stress would be extreme on the cover as the further out from
the big end the less the leverage on the bearing would be.
Most of the stress I think would be on the drive side and by the looks of JBS cover on that side would take care of that.

yes these were done with spherical rollers inboard and something out on the end
to stop the shaft moving around

all degrees of freedom are then contained and flex minimised

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.

Great initiative! I'm assuming that stroke is fixed for the 10-set run, and therefore the case selection as well? (And which cases then if so? 644?)

I had best get myself an earlier berg quick smart. You are a legend mad scientist crack head like this other mad ******* I know in the Southern Hemisphere. I'm not worthy :bow: :bow: :bow:

Tourist you need an offset ground pin on this crank and make a Franken-motor ha ha

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?

35mm pin for 70mm stroke yes. (I assume this means a custom rod. Which would be warranted for the task.)

(Thought: Maybe a 570 rod could be used? 72mm stroke. Doubtful that it would work with the cases, right?)

When would commitment be required?

I probably need a new crank in the fall, if you can get them for reasonable price I would be interested in one.

Dr_C said:

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,

@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?

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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.

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.

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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!

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.

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.

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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.