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we'll be sure to get right on this after the Supercross series has commenced. thank ya 'now.
A few years ago (maybe more or less) Yamaha announced they were going to be built 50% recycled metals/materials. There was a lot of negative opinions about it here on Vital. Not trying to compare above transmission problems. Would like to reread it.
once again the communication has been broken down.
ahem, we got Anaheim 2 this weekend. let us focus on that.
Yamaha gearboxes are made with chocolate
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He truly is a shitty (media) guy. A friend, who helped create his entire empire, speaks about a safety issue (that goes way beyond pro moto) and instead of facilitating/probing when Phil says he would like to go deeper, he deflects the entire topic and throws in an ad to boot.
Dont buy Yzf’s. 2 strokes or 4 strokes, all yz-f’s do it.
1. Do you need to replace the YZ250 mainshaft and countershaft with YZ450F shafts when performing this retrofit?
2. Do you need to replace the YZ250 shifting cam with the YZ450F cam?
3. Do you need to replace the stock YZ250 shifting forks with YZ450F forks?
4. Are any YZ250 crankcase modifications required to accept the wider YZ450F gears?
5. Can you elaborate in detail on how the stock rigidly staked YZ250 shifting forks are changed to a slide-over-pin design per your modification? The rigidly staked YZ250 forks are an abysmal engineering oversight, allowing the pin/fork combined assembly to be weakly supported in the loose crankcase pocket while sliding into the tight opposing crankcase pocket. Ideally, your modification would employ longer pins which allowed for equally strong support in each of the opposing crankcase pockets while the modified fork slides over the now stationary pins.
Yamaha has a history of weak tranny's and great engines dating back to the '70's.
Here you go, here's a thread about the event that hasn't happened yet: https://www.vitalmx.com/forums/moto-related/a2-doors-open#comment-6069396
You can go contribute to that conversation and leave the guys that ride moto to talk about moto-related things.
Have owned 9 YZ250 2 strokes going way back. Like you, would ride 100 or so hours then flip them. Only one that gave me issues was the '97. 3rd wheel gear busted a tooth about 60 hours in. Yamaha had an issue back then but never made it public. Replacement part and mating gears were beefed up significantly. Zero issues with my '98, '00 or any future ones I owned.
I didn’t see it that way. The “blu crew” comment seemed sarcastic to me. Steve was the one who said that it was a blown tranny on the review pod and then asked Phil to come on when he didn’t want to knowing what was on his mind. He was just trying to keep things moving, at that point Phil had made his point. Just my $0.02
Yamaha’s just aren’t what they used to be. Quality has gone downhill rapidly, heads, frames, now transmission.
Speaking of weak trannys ^
Yep.
I did, and it's been a hell of an improvement.
Had the gear box problems at 50Hrs instead of 40
Somebody who remembers!
I remember my friend's father working on his 1975 DT-250 where the transmission wasn't working. I asked him what was wrong and he said "it's a common problem on these DTs...". That was over 45 years ago!
I'm 100% on board with the bad transmission in the 1975 DT-250 being related to Phil's transmission breaking in his 2024 YZ 250f during a Supercross race.
1) Yes, both shafts have to be replaced and the YZ450F main shaft must be modified to work with the 250 clutch.
2) No, I use the two stroke cam & ratchet mechanism.
3) Two of the forks have to be replaced with the four stroke parts (Left & Center).
4) The left case needs precise machine work and two special bearings to accept the new gears and shafts.
5) Abysmal... I totally agree and made pretty much the exact changes you described to that system.
I use pins from a 2005 - 2021 YZ125 engine and set them up to span the width of the cases.
A small rubber o-ring in each case bore can prevent the pins from rattling axially. Many gearboxes have a spring inside the hollow pins.
These pins make the transmission a lot easier to assemble. Just that change without changing gears and shafts is a major upgrade.
The YZ250 and early model YZ450F shift forks are not actually staked, they have spring tension pins (roll pins) that can be driven out using a punch. I use a 10mm hone in the shift fork bores to allow a sliding fit on the YZ125 pins. If the bore is honed oversize or if it has a lot of taper, it will rock and bind instead of sliding across the pin.
You end up getting wider gears with four dogs on all of them instead of three. The "4th gear pinion" also gets a wider bearing surface on the main shaft, so it is less likely to seize or gall under high pressure.
Several years ago when I started exploring solutions I thought I would make a kit by modifying some new OE parts and machining shift forks. I still have some prototype 4340 shift forks and the fixtures to make them on the CNC, but I've been busy with so many other things in my shop. The old photo has an unfinished early prototype on a 450F main shaft next to the equivalent two stroke fork and gear. The large boss eventually got machined down to become a cam-pin and I milled the corners off of the stiffening ribs to reduce weight. I may revisit this stuff in the future.
If I was you I would stop speaking. Every time you open your mouth a turd comes out.
Pit Row
Helpful post and thanks for your response.
Can you provide more detail on the YZ450F mainshaft modification required for the YZ clutch?
Can you provide manufacturer and part numbers of the required special bearings?
Can you provide more detail on the required left crankcase mod? And are you able to modify customer cases in your own shop?
Thanks again from a fellow YZ gearbox sufferer.
Yes, please we need a dedicated thread in the tech section about this!
cwtoyota bringing the goods as usual 👍🏻
I got about 120 hours out of my last YZ250 before 3rd started getting weird.
I instinctively use the clutch with every shift and run 850ml of Bel Ray Gear Saver. I could imagine it not lasting nearly as long if I were rough on it.
No problem.
Per UGOTBIT 's suggestion I'll start this thread in the tech section...
(I hate to hijack a perfectly good thread for our dumb old two strokes)
https://www.vitalmx.com/forums/tech-helprace-shop/yz250-gearbox-upgrades-broken-3rd-or-4th-gears-two-stroke
Seems like a lot to unpack, after listening to Phil. I'm a big fan of Phil and I know he keeps it real. That being said, it's kind of all over the place with who is at fault. It sounds like it's essentially a stock gearbox, maybe tumbled or whatever but not outsourced or strengthened like some other teams do. So that's been the same stock gearbox since 21 on the 250F. Like ML said if those Club bikes are pumping out serious hp, is Yamaha at fault, if it's not able to handle an engine modded to the moon? We do know that YZFs are pretty reliable, stock. But they mod easily and they quickly reach their limit on a few areas (cam chain, rod, gearbox etc.) Phil sort of made it seem like there was no budget to get the tranny sent out. He also said the team being "under-staffed" and maybe the intervals are running longer. To me, that would be more on the team. But then he mentioned more than just his team (that run YZFs) are having issues. Kind of confusing. Also I thought of how Marchbanks is probably the biggest 250 rider. His bike hauls him easily and he hasn't had issues, which is weird. I'm sure Phil wanted to say more but didn't. I'm not saying he's wrong it's just a lot in play. I'm not sure I can just say it's as easy as Yamahas are unreliable, when I factor in everything that was said.
they need an xtrac transmission from england
Seeing as there are about a million YZ250's out there, you would think someone would have done one.
Most companies like Xtrac in the UK wont make things unless they have a demand.
When Dixon Yamaha went to Cosworth, the deal would have been sweetened by the fact that Cosworth had a retail arm to sell the parts on, when he came to us at Ilmor, there was no way to recoup any money from it , so it would all have been at his cost.
I also know he went to a beefed up 3 speed box on his 250's as well, and they were decent.
I know there are people getting CR500 gears made, but its not a fast process to spec and get made, on the latest bikes.
I've considered doing CR and KX 500 gears in the past, but the promise of very low volume keeps me focused on other projects.
It would be very easy to sink a ton of time and money into fixtures, tooling and processes that aren't justified the volume.
The YZ250 engine hasn't had a major design change in 25 years while the four stroke changes every three to five years. There must be a million of the two strokes...
I guess if all the yamaha teams made the investment it would happen. i remember hearing PC Kawi had x trac components since the Kawi/suzuki shared project in 2004.
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