Wasted crank bearings

[irk_miller]

Stock alternator? Ported engine/ chambers?
The heavy stock rotor combined with higher rpm would cause more problematic crank dynamics, from what I understand.
TZ's had much lighter rotors...

Highly modified- ported, shaved, chambers, etc.  If my internet research has any amount of accuracy, i was seizing the center bearings.  After inspection, the top end is uneffected.  The outside bearings spin smoothly and freely as they did with installation.  However, the inner bearings show some resistance which suggests to me that with heat they could have been seizing up.  It's been converted to water cooled and I didn't get to ride much this summer, so I am back to the original theory that maybe some water inclusion on the bearings caused them to start to seize.  Would make sense for the way the crank twisted itself apart, at least. There was also a god-awful sound right before it went, like the sound of really rough bearings.  I at first thought I lost a clutch.

[1976RD400C]

When mine broke the motor just suddenly changed pitch and the power dropped off. It had a very light HPI rotor, modified ports, big reeds, 34mm carbs, chambers. Wound out in 3rd gear at 9500 rpm. I kept going poking along, using very little throttle, for 5 miles to get home.

[bitzz]

I find the "big rotor" pulls the cheeks out of phase, it doesn't break cranks... and the biggest advantage of the TZ rotor is it's diameter, not mass.
... but then I only deal with the 3J7, that has  a superior crank

[mnein]

Maybe this is not relevant, but I had a Polaris 500 (twin) sled that broke its crank in half religiously every 8000 miles, did it twice and I had a friend with the same sled same thing. No bearing damage evident so it just seemed a metal fatigue thing, stock motors.

[m in sc]

yeah, you get certain harmonics going and add on fatigue and bam. unusual on a 250/350 crank or rz, but ive seen a few 400s.

[2steve]

Hopefully not a '77 RD400. There's no Vitos for that.

[m in sc]

there def needs to be a 400 crank reproduced.

[Aaron Russell]

there def needs to be a 400 crank reproduced.

I have emailed Vitos when I was building my motor, Vitos said they would like to make stuff for the 400s but they needed at least 500 units made which might be tough to sell.

[m in sc]

well no one person is going to order 500. but they would def sell way, way more than that

[Aaron Russell]

Yeah, maybe everyone here should email vitos asking for 400 cranks lol.

[irk_miller]

You're looking at somewhere in the neighborhood of $60k - $70k to produce the 400 crank depending on the tooling, mold and die costs. You're looking at $50k or more there alone. Assembly jigs are going to run you around $5k, plus the cost of engineering, CAD and QC.  They would have to sell 200 just to cover the cost to start producing them.

[m in sc]

well. thats the cost of doing business. I deal with it every day on a much larger scale.  But it would def pay off, easily.

[irk_miller]

well. thats the cost of doing business. I deal with it every day on a much larger scale.  But it would def pay off, easily.

I know that world, as well.  Taking on that large of a production cost and 18 months from engineering to market warrants some level of guarantee that you will at least come out even. Suggesting 500 units is commendable considering they are likely trying to keep the cost low to the customer. Motorcycles are the smallest division for Vito's and 350s benefit from 10X units built compared to the 400. I'm in no way arguing about a demand for 400 parts, but profitability in producing them is still a risk.

[m in sc]

I dont see it as a risk as much as possibly a longer term payoff. but, you say there were more 350s built. But not in the uk/Germany. they ran the 400s up to 1980.  so 5 years on the 350 platform, 5 years on the 400 platform (globally)

I know, for a fact, the rd400 webco reproductions sold out in less than a year, and that was 500 pcs.  a lot more people need fresh cranks than fancy cyl heads.

[RDnuTZ]

are there enough rod kits, bearings and seals available out there for rebuilding personal cranks that aren't trashed beyond repair?