Looking for opinions are what to look for and where to go next. I have an RD350 I converted to LC a few years back that has seen about 5k miles. It's been running flawlessly the entire time, until it suddenly decided to waste the crank bearings two days ago. I haven't cracked the bottom end apart just yet, but the top end is in wonderful shape with visible crosshatch on the cylinder walls and everything measuring in spec. Ed Toomey rebuilt this crank three years ago, so I am really surprised this happened. There is no visible rust on the crank and no indication so far that coolant got to it. I didn't get to put a lot of miles on the bike this summer, so it sat more than it ran. Are there specific signs I should look for, besides rust, that would indicate coolant or moisture getting to the bearings? It has always passed regular pressure tests, so I never expected anything out of the ordinary. Anything else that would cause the bearing to let loose all of a sudden? Is this just one of those things that happens sometimes? I'm not wanting to pay another grand to have this crank rebuilt, so I am thinking of going with a Vitos crank. Seems like they are quality part.
i put a vitos in my hybrid, zero issues. no idea why it went on yours. on mine weights came loose 2x, and I rebuilt it both times myself. 1st crank i had in it got wiped out during a top end blowup back around 2011. so im on my 4th crank and its def been fine. but this is over 22 years of hard thrashing
Are you talking the main bearings or the lower rod bearings or both?
if its the main bearing, is it the drive side? if so, look at the interaction between the primary gear and the clutch
How does this even happen?
(https://www.dotheton.com/media/wasted-crank.428/full)
50+ year old metal fatigue. yikes
:eek: holy shit :confusing2:
https://vitosperformance.com/products/rd350-vito-s-performance-yamaha-crank-crankshaft-stock-size-oem-replacement-new?_pos=3&_psq=cranks&_psid=0a953f0ad&_ss=e
:thumbs:
Quote from: 85RZwade on August 28, 2026, 08:30:32 PM:eek: holy shit :confusing2:
It's wild. :lol: In all my years (I'm 55), even with 2t sleds, No one I know personally has seen anything like this. I was sure it wiped the bearing on the ignition side, so I went ahead and posted before I cracked open the bottom end.
ive seen a few sheared triple cranks and a broken daytona crank
I had that happen once also. :eek:
Sucks it happened to anyone else, but at least I'm not alone. Curious if there is simply a point where these cranks can't be rebuilt anymore and putting them through a press contributes to their demise. Not at all suggesting bad craftsmanship on the rebuild, but more that the process created fractures that led to what happened. My first reaction when I pulled it apart was that a bearing froze, but that didn't happen. The bike ran normally until it suddenly didn't.
The 400 Daytona crank is known to have not been hardened as much as the other 400's and those are the ones that break most often. I think it might just be old age and hard use doing it. Maybe also if the crank gets out of true it stresses it more in the middle. :umm:
I'd think more hardening would lead to more failures like seen here. You need ductility. Surface hardening is a factor in that break, or if it was, it's where the stress riser started.
Either way, this one was cycled out.
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...
Quote from: Dvsrd on August 29, 2026, 11:48:27 PMStock 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.
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.
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
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.
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.
Hopefully not a '77 RD400. There's no Vitos for that.
there def needs to be a 400 crank reproduced.
Quote from: m in sc on August 31, 2026, 11:22:02 AMthere 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.
well no one person is going to order 500. but they would def sell way, way more than that
Yeah, maybe everyone here should email vitos asking for 400 cranks lol.
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.
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.
Quote from: m in sc on September 07, 2026, 08:16:02 AMwell. 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.
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.
are there enough rod kits, bearings and seals available out there for rebuilding personal cranks that aren't trashed beyond repair?
Quote from: RDnuTZ on September 07, 2026, 09:25:01 AMare there enough rod kits, bearings and seals available out there for rebuilding personal cranks that aren't trashed beyond repair?
You can get the 4 main bearings from Yambits for about $100 a set plus shipping and tarriff. OEM is double that. The rod kits are about $100 each. No problem getting that stuff.
thanks, good to know :thumbs: Given that, it kinda makes the idea of commissioning someone like Vito's to build a minimum order of 500 with huge upfront cost less appealing.
I wonder if these guys would ever make a run of RD400 if contacted? They do a LOT of 250/350 new cranks. I even bought 2 of them and they look really well made- but haven't installed yet to rate them.
https://www.ebay.com/itm/364763626092
its cheaper to rebuild a 350 crank as well, if you can do it (i can) but honestly, not worth my time to save the 150 bucks, and no dealing w those stupid pressed in weights
Just thinking out loud but has anyone looked at a +10mm Banshee crank as a place to start. That's a 64mm stroke but I assume that they use the smaller diameter banshee/350 sized crank wheels and 115mm rods, so it would need 350 cases and a 1mm lift plate and a little crankcase shaving to squeeze the crank in, but it has to be an option.
You could always weld up the cases to take a 68mm CPI top end but that's getting into silly money. I also don't know if there's enough metal in the cases to be trenched for that long pf a stroke.
Just thinking out loud again. No. No. It's not time for my meds. I have been a good boy. Honestly...... :whistle: :toot:
to that point.. vitos could do tthe same w the 350 crank, just use offset rod pins you'd gsin some crankcase volume, hut it would be negligible