2018 YZ250F locked up

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7/2/2018 4:45 PM

Anyone else had an issue with their ‘18 YZ250F dropping a valve? I have 13 hours on a stock motor and this happened this past weekend. Any input would be appreciated. Trying to determine if this is a common issue or just a freak incident with this few hours. Photo
Photo

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7/2/2018 5:40 PM

Are you rew limiter happy guy?

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Born in Prague,living in LA,so if you don't like my spelling,blow me!

21 CRF450R
16 Yamaha YXZ 1000R
17 Yamaha MT-10 FZ-10 165 Hp RWP
06 CRF450X street legal supermoto
96 CR250R smoker
2012 CR500AF
2003 KLX110 mod




7/2/2018 5:40 PM

Definitely a freak deal, we have 80 hours on our 2016. One valve moved .002” that’s all. All moto no woods and more limiter than I like.

KC

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7/2/2018 5:45 PM

what map are you running? what gas?

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7/2/2018 5:51 PM

You cant come here talking about yamahas being broke. Only ktms.

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7/2/2018 6:05 PM

I see the 2018 model holds up about as well as the 2001 did. Remember the recall on the 2006 models? You would think the Japanese would have learned a thing or two over the past two decades...

Photo

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7/2/2018 6:27 PM

Sounds like a freak thing. Those Yamaha’s are pretty damn bullet proof.

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Tomac and/or Anderson for 2020.....

7/2/2018 6:29 PM

I’m not a rev limiter guy at all, quite the opposite. I’ve been running like half VP T4 and half 93 with stock mapping.

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7/2/2018 7:10 PM

Man it sure looks expensive! Really disappointed for you!

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2020 YZ450F
2006 YZ125
2013 YZ 250F special edition
2017 YZ 250
2015 YZ 250f soecial edition
2019 KTM 85 big wheel
1979 YZ 250

7/2/2018 7:46 PM

JP726 wrote:

Anyone else had an issue with their ‘18 YZ250F dropping a valve? I have 13 hours on a stock motor and this happened this past ...more

When yamaha updated the head in 16 it became fairly common for some people.

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7/3/2018 1:03 AM
Edited Date/Time: 7/3/2018 1:04 AM

JP726 wrote:

Anyone else had an issue with their ‘18 YZ250F dropping a valve? I have 13 hours on a stock motor and this happened this past ...more

Derek Harris wrote:

When yamaha updated the head in 16 it became fairly common for some people.

What is the cause though?

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2020 YZ450F
2006 YZ125
2013 YZ 250F special edition
2017 YZ 250
2015 YZ 250f soecial edition
2019 KTM 85 big wheel
1979 YZ 250

7/3/2018 1:31 AM

Its a race bike. Things happen. But things happen a lot cheaper on 2 strokes.

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7/3/2018 1:48 AM

I have an almost stock 17 with about 90 hours which ran well all the time, also have an 18 with the gytr kit and it already happened twice in 16 hours tho.. Photo

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7/3/2018 2:46 AM

Have not seen this, in for more info!

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2020 YZ450F
2018 KTM 450SXF FE
2016 YZ250F 2008 CRF450R
2015 YZ250F 2008 CRF250R
2001 CR250R
2010 YZ250 2012 CRF150R
2009 YZ125 2010 KX109.5
SSR Motorsports Dealer YCF Motorcycles
TAGMX Suspension & Graphics! www.tagmxsuspension.com https://www.liquidskinzdesign.com/



7/3/2018 3:50 AM

No issues with mine at 24 hours (knock on wood) and I like to ride mine hard. I know these posts represent a tiny insignificant percentage of total bikes sold but I'm still a bit worried now.

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7/3/2018 6:12 AM

xr70 wrote:

Are you rew limiter happy guy?

Isn't that the purpose of a rev limiter to stop it from revving to high and doing damage?

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7/3/2018 6:15 AM

mx_phreek wrote:

Isn't that the purpose of a rev limiter to stop it from revving to high and doing damage?

Nah bro, they only put the rev limiter there cuz it sounds cool. Ur supposed to ride the bike in 5th gear at like 3000 rpm

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7/3/2018 6:20 AM

That's not good. Seems like a manufacturing defect with that few # of hours.

My condolences.

Photo

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7/3/2018 6:40 AM
Edited Date/Time: 7/3/2018 6:41 AM

305FC250 wrote:

No issues with mine at 24 hours (knock on wood) and I like to ride mine hard. I know these posts represent a tiny ...more

Tiny insignificant percentage?laughing Not when it's your percentage.

Same story keeps playing out since 2001. I would say that you could also add in frames breaking with amazing regularity on the aluminum ones, but my steely also had a motor mount break off.

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7/3/2018 6:49 AM

2018 yz250f here, 40 hrs put on it since January. 0 issues...

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7/3/2018 6:54 AM

Had 15 hours on a 2008 YZ 125... Obelix is standing on the shattered piston on my desk giving me the thumbs up.

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7/3/2018 6:58 AM
Edited Date/Time: 7/3/2018 7:00 AM

newmann wrote:

I see the 2018 model holds up about as well as the 2001 did. Remember the recall on the 2006 models? You would think the ...more

You don’t think the intake valves hitting the piston had anything to do with your failure?

KC

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7/3/2018 6:59 AM

JP726 wrote:

Anyone else had an issue with their ‘18 YZ250F dropping a valve? I have 13 hours on a stock motor and this happened this past ...more

Derek Harris wrote:

When yamaha updated the head in 16 it became fairly common for some people.

PJRAUS wrote:

What is the cause though?

I believe when giving a snap of gas in the air (not keeping it wide open all the way, just 0,5 sec and closing the gas back down), the back wheel will spin really fast causing a big force to go into the engine. Because of that the cam chain Will flex a little bit causing the timing of the valves to be a bit off. When that happens the piston will give the valves a little “Kiss” , after a certain amount of times a valve will break.

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7/3/2018 7:43 AM

Thanks for the replies guys. Looks like I’m in the market for a new head. Anyone have any suggestions on where to get a complete head with valves. I’m aware of the GYTR but that would be a last resort.

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7/3/2018 8:33 AM

Root cause?
Valve spring?
I bet Derek knows.

KC

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7/3/2018 10:08 AM

Derek Harris wrote:

When yamaha updated the head in 16 it became fairly common for some people.

PJRAUS wrote:

What is the cause though?

KG171 wrote:

I believe when giving a snap of gas in the air (not keeping it wide open all the way, just 0,5 sec and closing the gas back ...more

I think you're right about the valves kissing the piston, as evident by the markings in the valve relief cuts.

I don't think you're correct about the free-rev in the air. If that were the case, the same would be true when free-revving the bike on the starting gate before a moto. The wheel adds inertia, so the engine will actually rev slower in the air (in gear) than in neutral, or with the clutch pulled in. It's like running a very a "heavy" flywheel.

Mechanical over-rev is certainly a possibility, but you would have to downshift and dump the clutch coming down a hill, or on the landing of a fast jump. Usually on these bikes, the compression ratio is high enough to skid the rear wheel when you downshift, so mechanical over-rev is not much of a concern for most riders.

It can happen if you have the throttle wide open when you downshift and dump the clutch at speed. You'll go right past the rev limiter that way and likely end up with a mess similar to this. Road racers are more likely to have this problem, but it could happen on an MX track.

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7/3/2018 10:13 AM

JP726 wrote:

Thanks for the replies guys. Looks like I’m in the market for a new head. Anyone have any suggestions on where to get a ...more

I remember seeing one in the bazaar recently for like $500 bucks. I think they’re at least semi common, with people swapping them out for the gytr set up

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RPM Performance
CT
783

7/3/2018 10:24 AM

I have a complete head off a 15. Valves, cams, 60 hours the bottom end went. $450 shipped.

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7/3/2018 10:52 AM

Flipsid33 Will the 15 head fit the 18? If so I’m very interested.

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7/3/2018 11:14 AM

Derek Harris wrote:

When yamaha updated the head in 16 it became fairly common for some people.

PJRAUS wrote:

What is the cause though?

KG171 wrote:

I believe when giving a snap of gas in the air (not keeping it wide open all the way, just 0,5 sec and closing the gas back ...more

makes sense.

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