YZ450f gearbox issues :(

4/12/2021 8:18am Edited Date/Time 8/9/2022 3:32pm
Hi guys,

I have a 2020 YZ450f I bought brand new which has just over 40 hours on it. The other week it started making a what can only be described as chain slapping sound when putting it in second gear and felt like the clutch was slipping.

I changed the clutch with no luck, if you go 1st to third and so on it's perfect with no sound.

So now I'm putting it down to something inside the gear box. I know it's going to have to come apart regardless but is there any known faults with these?

Thanks.
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DynoDan22
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4/12/2021 9:10am
Yamaha's have been know to have tranny issues. Sounds like you need to split the cases and inspect all of the gear dogs and shift forks carefully. I wouldn't recommend continuing to ride it as it could cause further damage. Let us know what you find. I really wish Yamaha would update the material and heat treatment of their trans components as I've seen way too many early failures over the past few years.
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soggy
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4/12/2021 9:18am
Sounds like a possibly chipped gear or dog
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BeachMX
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4/12/2021 7:02pm
It's the shift forks/gears. It's slipping out of gear. I have a 2020 YZ250f, and had the same exact problem at 70hrs. Had to replace 4 gears and 2 shift dogs, running me about 600.00 bucks just in parts. I did all the work myself.





2
BeachMX
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4/12/2021 7:12pm
DynoDan22 wrote:
Yamaha's have been know to have tranny issues. Sounds like you need to split the cases and inspect all of the gear dogs and shift forks...
Yamaha's have been know to have tranny issues. Sounds like you need to split the cases and inspect all of the gear dogs and shift forks carefully. I wouldn't recommend continuing to ride it as it could cause further damage. Let us know what you find. I really wish Yamaha would update the material and heat treatment of their trans components as I've seen way too many early failures over the past few years.
I called Yamaha about it, and they acted like they didn't know what I was talking about. It's a known issue that they fixed for the 21's, but us with 19-20's are screwed..

I'm a slow vet guy too... no jamming it in gear/always use the clutch/never even see the limiter.

The Shop

Rider 5280
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4/12/2021 7:41pm Edited Date/Time 4/13/2021 9:41pm
Dang, I hate seeing this!

Is there any way to know by S/N if your bike is in the "fixed group?"

If I need to replace gears, I am going to have the transmission isotropic superfinished (ISF) and cryogenically treated before reassembly. I did this on an old Honda CRF450R- really nice mod.
DynoDan22
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4/12/2021 8:29pm
BeachMX: I've had a few friends smoke transmissions in their Yamahas and the dealers were of little help. It's not just the fourstroke either. I've repaired a fair amount of YZ250's with rounded gear dogs. I replaced all mating gears/forks/shift drum and they would still fail around 70-80hrs. These were mostly vets as well. The rule of thumb is after you hit two false-neutrals, it's time to split the cases and replace. I really wish Yamaha would bite the bullet and admit they need to update their materials and processing.
4/13/2021 3:37am
Thanks for the reply's everyone, I have spoken to 2 dealers today who both said there's know issues which "Yamaha wont admit to" and it's likely a bent shift fork or chipped cog but wont know until it's stripped.

I'm going to pull the engine out this week and take it to them so will update with what we find !

Thanks.
Skerby
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4/13/2021 7:17am
I've seen more 'slow vet guys' blow up transmissions than any other group. They are all wear items anyways though, and probably just luck of the draw.

1
BeachMX
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4/13/2021 8:50am
Rider 5280 wrote:
Dang, I hate seeing this! Is there any way to know by S/N if your bike is in the "fixed group?" If I need to replace...
Dang, I hate seeing this!

Is there any way to know by S/N if your bike is in the "fixed group?"

If I need to replace gears, I am going to have the transmission isotropic superfinished (ISF) and cryogenically treated before reassembly. I did this on an old Honda CRF450R- really nice mod.
Yeah sucks.. I am not sure on the S/N.

I looked up that isotropic finish... nice looking stuff. What does something like that run?
BeachMX
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4/13/2021 8:55am
Skerby wrote:
I've seen more 'slow vet guys' blow up transmissions than any other group. They are all wear items anyways though, and probably just luck of the...
I've seen more 'slow vet guys' blow up transmissions than any other group. They are all wear items anyways though, and probably just luck of the draw.

Who knows.. I know that I'm not hard on my bike, especially compared to some who I ride with and have no issues.

I heard a fast kid at my local track blew through his tranny in 9 hours! Same bike as mine. That to me seems crazy no matter how hard you are on the bike.
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Skerby
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4/13/2021 9:59am
Im just bummed to hear that this is happening to people. Im currently transitioning to 'slow vet guy' and I bought a 21 yzf for the purpose.

Put around 300 hours on a YZ250 trans as a faster younger guy, it finally started eating the dogs up and I replaced everything.
3
Rider 5280
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4/13/2021 10:52am Edited Date/Time 4/13/2021 11:58am
Rider 5280 wrote:
Dang, I hate seeing this! Is there any way to know by S/N if your bike is in the "fixed group?" If I need to replace...
Dang, I hate seeing this!

Is there any way to know by S/N if your bike is in the "fixed group?"

If I need to replace gears, I am going to have the transmission isotropic superfinished (ISF) and cryogenically treated before reassembly. I did this on an old Honda CRF450R- really nice mod.
BeachMX wrote:
Yeah sucks.. I am not sure on the S/N.

I looked up that isotropic finish... nice looking stuff. What does something like that run?
The isotropic superfinish cost me ~ $300 from Yoshimura. I sent them EVERYTHING in the lower end, minus bearing, and let them determine which parts could be treated. Definitely the shifting was improved. "Buttery" is how would describe it - easy shifting, very positive engagement, things just work better with minimal actuation force.

If this gear problem happens to me, I'll also be cryogenically treating the parts to improve strength and durability (in addition to the ISF). I plan to use these guys:
https://www.cryogenicsuperfinish.com/

I BOUGHT MY 2020 YZ450F BECAUSE THEY'RE BUILT LIKE A TANK ... FINGERS CROSSED ... PLEASE STAND BEHIND US YAMAHA!!!
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seth505
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4/13/2021 12:24pm
DynoDan22 wrote:
BeachMX: I've had a few friends smoke transmissions in their Yamahas and the dealers were of little help. It's not just the fourstroke either. I've repaired...
BeachMX: I've had a few friends smoke transmissions in their Yamahas and the dealers were of little help. It's not just the fourstroke either. I've repaired a fair amount of YZ250's with rounded gear dogs. I replaced all mating gears/forks/shift drum and they would still fail around 70-80hrs. These were mostly vets as well. The rule of thumb is after you hit two false-neutrals, it's time to split the cases and replace. I really wish Yamaha would bite the bullet and admit they need to update their materials and processing.
Yup, my old yz 250 broke gears at 70 hours.
captmoto
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4/13/2021 12:28pm
Paging Foreman52.
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WEAL
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4/14/2021 3:13am
To avoid jumping out of gear you need an undercut at the dogs - this will pull the pinions together when power is applied. Unfortunately those gears are cast and don´t have any undercut at all. The only thing that could help you for a little while is a stronger detend spring but it will cost you more wear on the forks. Its a crappy cheap design - not only Yamaha but Honda and Kawa as well. I have replaced so many gears in the bikes of my riding buddies that I lost count long ago.
We are now remachining all those gears on the milling machine and do an undercut to re-use them. 5 degr gives you enough holding ability to avoid jumping out of gear.
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rjg
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4/14/2021 4:54am
DynoDan22 wrote:
Yamaha's have been know to have tranny issues. Sounds like you need to split the cases and inspect all of the gear dogs and shift forks...
Yamaha's have been know to have tranny issues. Sounds like you need to split the cases and inspect all of the gear dogs and shift forks carefully. I wouldn't recommend continuing to ride it as it could cause further damage. Let us know what you find. I really wish Yamaha would update the material and heat treatment of their trans components as I've seen way too many early failures over the past few years.
BeachMX wrote:
I called Yamaha about it, and they acted like they didn't know what I was talking about. It's a known issue that they fixed for the...
I called Yamaha about it, and they acted like they didn't know what I was talking about. It's a known issue that they fixed for the 21's, but us with 19-20's are screwed..

I'm a slow vet guy too... no jamming it in gear/always use the clutch/never even see the limiter.
Don't let up on them. Yamaha always plays the innocent/dumb role. They will bend if you keep applying pressure. I have seen it before, then they will admit/acknowledged their failures. Its a phobia that they have, not just them, most Japanese mfg
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4/30/2021 4:23am
Update:

second gear cog and forth gear cog worn, shift fork worn..

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DynoDan22
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4/30/2021 7:36am
Wow. Yamaha has to buck up and acknowledge that they have a problem. Keep on them and work with the dealership. Just an FYI, replace the shift drum as well. The thrust generated from worn dogs will notch the shift drum slightly. Whenever I rebuild a Yami transmission, I always replace the shift drum.
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DuroTools
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5/3/2021 5:52pm
WEAL wrote:
To avoid jumping out of gear you need an undercut at the dogs - this will pull the pinions together when power is applied. Unfortunately those...
To avoid jumping out of gear you need an undercut at the dogs - this will pull the pinions together when power is applied. Unfortunately those gears are cast and don´t have any undercut at all. The only thing that could help you for a little while is a stronger detend spring but it will cost you more wear on the forks. Its a crappy cheap design - not only Yamaha but Honda and Kawa as well. I have replaced so many gears in the bikes of my riding buddies that I lost count long ago.
We are now remachining all those gears on the milling machine and do an undercut to re-use them. 5 degr gives you enough holding ability to avoid jumping out of gear.
Good info, that makes sense to me, wish you were in the USA and willing to help out paying customers? any way you can include more info and pics on this?
7/14/2022 8:05am Edited Date/Time 7/14/2022 8:09am
2019 yz 450 with 246 hours. 3 piston changes and 3 cam chains and on 2 nd bottom end. Everything looked good when replaced with new parts, I still ride with original clutch plates. Gearbox holding up excellent, I believe this is because I use the clutch when shifting gears, and making sure I don't lug bike and drop clutch at high revs when exiting corners, I rather go down a gear. That said, I know of 5 yz 450's and two yz 250 f's dropping 4 th gear. I know of two guys who had undercut 4th gear ,replaced the shift fork and never had issues again. I understand that the yz's have a weak gearbox, 4 th gear seams to be the biggest culprit. Undercutting looks to be the solution, or use the clutch when shifting to save money and lots of headaches.
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WEAL
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7/14/2022 10:37am
Well - I opened the engine of my buddies 21 HQV 450 as he had a problem with the gearbox after 125 hours. Turns out, KTM has no undercut any more like a couple years ago! So now we have to undercut KTM gears as well...
captmoto
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7/14/2022 3:41pm
WEAL wrote:
Well - I opened the engine of my buddies 21 HQV 450 as he had a problem with the gearbox after 125 hours. Turns out, KTM...
Well - I opened the engine of my buddies 21 HQV 450 as he had a problem with the gearbox after 125 hours. Turns out, KTM has no undercut any more like a couple years ago! So now we have to undercut KTM gears as well...
Was your buddies problem related to no undercut? 125 hours is a lot in 2 years. I'm sure there's going to be issues.
Rider 5280
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7/14/2022 3:59pm
Albie_Nel wrote:
2019 yz 450 with 246 hours. 3 piston changes and 3 cam chains and on 2 nd bottom end. Everything looked good when replaced with new...
2019 yz 450 with 246 hours. 3 piston changes and 3 cam chains and on 2 nd bottom end. Everything looked good when replaced with new parts, I still ride with original clutch plates. Gearbox holding up excellent, I believe this is because I use the clutch when shifting gears, and making sure I don't lug bike and drop clutch at high revs when exiting corners, I rather go down a gear. That said, I know of 5 yz 450's and two yz 250 f's dropping 4 th gear. I know of two guys who had undercut 4th gear ,replaced the shift fork and never had issues again. I understand that the yz's have a weak gearbox, 4 th gear seams to be the biggest culprit. Undercutting looks to be the solution, or use the clutch when shifting to save money and lots of headaches.
Who are the "good guys" to send gears to for the undercut machining?

If I knew this, I'd likely order some gears now and have them ready (+ isotopic superfinish (ISF) them).
WEAL
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7/15/2022 1:58am
WEAL wrote:
Well - I opened the engine of my buddies 21 HQV 450 as he had a problem with the gearbox after 125 hours. Turns out, KTM...
Well - I opened the engine of my buddies 21 HQV 450 as he had a problem with the gearbox after 125 hours. Turns out, KTM has no undercut any more like a couple years ago! So now we have to undercut KTM gears as well...
captmoto wrote:
Was your buddies problem related to no undercut? 125 hours is a lot in 2 years. I'm sure there's going to be issues.
Definitely an undercut would have avoided the problem. The shifter fork of 5/6th gear is worn away almost half - this indicates that the gear pinion wanted to jump the dogs and all that kept it engaged was the fork. The dogs edges are rounded on both pinions - never had these wear patterns on the older KTM tranny.
Maybe KTM reacted to all the bike magazine idiots testing the bikes that complained year after year that a KTM is not as quick shifting as the japanese bikes. Now you got quick shifting but lost the safety of knowing the gear will never jump out just when you accelerate for that mighty step-up which is known as "do or die"Blink
Yeti831
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7/16/2022 5:00pm
Imo, I’d have shop do the undercut that others have mentioned and get it REM’d and cryo treated while the guys are out.
1
7/19/2022 11:28am
I had cyro treat and micro polish my 2021 yz450f.. My bike did exactly what the original post stated with 3 hours. 2nd and 4th gear had to be replaced and fork shift 1 and 2.
Rider 5280
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8/4/2022 8:21am
I had cyro treat and micro polish my 2021 yz450f.. My bike did exactly what the original post stated with 3 hours. 2nd and 4th gear...
I had cyro treat and micro polish my 2021 yz450f.. My bike did exactly what the original post stated with 3 hours. 2nd and 4th gear had to be replaced and fork shift 1 and 2.
Dayuuuum ,,,

I would have bet a lot of $$$ that you would never have a single issue for the life of the motorcycle with the cryo and micro polish. Ever.

Do you think racing/full-power shifting contributed? Your profile pic looks faster than I will ever be ... by a looooong shot.

8/4/2022 12:05pm
I had cyro treat and micro polish my 2021 yz450f.. My bike did exactly what the original post stated with 3 hours. 2nd and 4th gear...
I had cyro treat and micro polish my 2021 yz450f.. My bike did exactly what the original post stated with 3 hours. 2nd and 4th gear had to be replaced and fork shift 1 and 2.
Rider 5280 wrote:
Dayuuuum ,,, I would have bet a lot of $$$ that you would never have a single issue for the life of the motorcycle with the...
Dayuuuum ,,,

I would have bet a lot of $$$ that you would never have a single issue for the life of the motorcycle with the cryo and micro polish. Ever.

Do you think racing/full-power shifting contributed? Your profile pic looks faster than I will ever be ... by a looooong shot.

And that’s exactly why I did it! lol. Super bummed.

And 100%.

. I tried giving the jap bike a chance and it’s almost like the transmission just isn’t built for the micro polish, maybe just the cyro treatment.

I think by doing the micropolish it took off little pieces (I’m talking just deburring the corners and such for less friction) but the bike actually needs it with all the power and stress.

Hate me for this but I had a 19 450SXF before this bike and did 129 hard hours and never had to replace anything in the bottom end besides the rod at 100. So having these problems with the YZ just made me get another KTM lol.. very unfortunate but also not the only one with this issue.
1
stone881
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8/5/2022 10:09am
I had cyro treat and micro polish my 2021 yz450f.. My bike did exactly what the original post stated with 3 hours. 2nd and 4th gear...
I had cyro treat and micro polish my 2021 yz450f.. My bike did exactly what the original post stated with 3 hours. 2nd and 4th gear had to be replaced and fork shift 1 and 2.
Rider 5280 wrote:
Dayuuuum ,,, I would have bet a lot of $$$ that you would never have a single issue for the life of the motorcycle with the...
Dayuuuum ,,,

I would have bet a lot of $$$ that you would never have a single issue for the life of the motorcycle with the cryo and micro polish. Ever.

Do you think racing/full-power shifting contributed? Your profile pic looks faster than I will ever be ... by a looooong shot.

And that’s exactly why I did it! lol. Super bummed. And 100%. . I tried giving the jap bike a chance and it’s almost like the...
And that’s exactly why I did it! lol. Super bummed.

And 100%.

. I tried giving the jap bike a chance and it’s almost like the transmission just isn’t built for the micro polish, maybe just the cyro treatment.

I think by doing the micropolish it took off little pieces (I’m talking just deburring the corners and such for less friction) but the bike actually needs it with all the power and stress.

Hate me for this but I had a 19 450SXF before this bike and did 129 hard hours and never had to replace anything in the bottom end besides the rod at 100. So having these problems with the YZ just made me get another KTM lol.. very unfortunate but also not the only one with this issue.
The KTM haters will hang you for this post! Didn't you know that Austrian bikes are the only one's allowed to have failures??
NITRODOG
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8/9/2022 3:32pm
I had cyro treat and micro polish my 2021 yz450f.. My bike did exactly what the original post stated with 3 hours. 2nd and 4th gear...
I had cyro treat and micro polish my 2021 yz450f.. My bike did exactly what the original post stated with 3 hours. 2nd and 4th gear had to be replaced and fork shift 1 and 2.
This.....Smile

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