2018 YZ250F locked up

JP726
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JP726
Edited Date/Time 2/2/2020 3:52pm
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.

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xr70
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xr70 7/2/2018 5:40pm
7/2/2018 5:40pm
Are you rew limiter happy guy?
752dad
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752dad 7/2/2018 5:40pm
7/2/2018 5:40pm
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
dirtmike86
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dirtmike86 7/2/2018 5:51pm
7/2/2018 5:51pm
You cant come here talking about yamahas being broke. Only ktms.
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newmann
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newmann 7/2/2018 6:05pm
7/2/2018 6:05pm
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...


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BobPA
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BobPA 7/2/2018 6:27pm
7/2/2018 6:27pm
Sounds like a freak thing. Those Yamaha’s are pretty damn bullet proof.
JP726
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JP726 7/2/2018 6:29pm
7/2/2018 6:29pm
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.
PJRAUS
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PJRAUS 7/2/2018 7:10pm
7/2/2018 7:10pm
Man it sure looks expensive! Really disappointed for you!
Derek Harris 7/2/2018 7:46pm
7/2/2018 7:46pm
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 weekend...
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.

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

PJRAUS
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PJRAUS 7/3/2018 1:03am
7/3/2018 1:03am Edited Date/Time 7/3/2018 1:04am
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 weekend...
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.

Derek Harris wrote:
When yamaha updated the head in 16 it became fairly common for some people.

What is the cause though?
Texas Built
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Texas Built 7/3/2018 1:31am
7/3/2018 1:31am
Its a race bike. Things happen. But things happen a lot cheaper on 2 strokes.
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KG171
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KG171 7/3/2018 1:48am
7/3/2018 1:48am
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..
305FC250
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305FC250 7/3/2018 3:50am
7/3/2018 3:50am
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.
mx_phreek
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mx_phreek 7/3/2018 6:12am
7/3/2018 6:12am
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?
rmoto003
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rmoto003 7/3/2018 6:15am
7/3/2018 6:15am
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
miketherider 7/3/2018 6:20am
7/3/2018 6:20am
That's not good. Seems like a manufacturing defect with that few # of hours.

My condolences.

newmann
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newmann 7/3/2018 6:40am
7/3/2018 6:40am Edited Date/Time 7/3/2018 6:41am
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 insignificant percentage...
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.
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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Fresh
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Fresh 7/3/2018 6:49am
7/3/2018 6:49am
2018 yz250f here, 40 hrs put on it since January. 0 issues...
EZZA 95B
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EZZA 95B 7/3/2018 6:54am
7/3/2018 6:54am
Had 15 hours on a 2008 YZ 125... Obelix is standing on the shattered piston on my desk giving me the thumbs up.
752dad
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752dad 7/3/2018 6:58am
7/3/2018 6:58am Edited Date/Time 7/3/2018 7:00am
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 Japanese...
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...


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

KC
KG171
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KG171 7/3/2018 6:59am
7/3/2018 6:59am
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 weekend...
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.

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.
JP726
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JP726 7/3/2018 7:43am
7/3/2018 7:43am
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.
752dad
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752dad 7/3/2018 8:33am
7/3/2018 8:33am
Root cause?
Valve spring?
I bet Derek knows.

KC
cwtoyota
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cwtoyota 7/3/2018 10:08am
7/3/2018 10:08am
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...
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.
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.

murph783
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murph783 7/3/2018 10:13am
7/3/2018 10:13am
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 complete head...
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.
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
Flipsid33
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Flipsid33 7/3/2018 10:24am
7/3/2018 10:24am
I have a complete head off a 15. Valves, cams, 60 hours the bottom end went. $450 shipped.
JP726
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JP726 7/3/2018 10:52am
7/3/2018 10:52am
Flipsid33 Will the 15 head fit the 18? If so I’m very interested.
Forty
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Forty 7/3/2018 11:14am
7/3/2018 11:14am
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...
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.
makes sense.
newmann
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newmann 7/3/2018 12:42pm
7/3/2018 12:42pm Edited Date/Time 7/3/2018 12:46pm
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 Japanese...
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...


752dad wrote:
You don’t think the intake valves hitting the piston had anything to do with your failure?

KC
Intake valves hitting the piston, getting bent, stuck and breaking off before bouncing around going through the head and through the piston probably had a little to do with it as well. Happens quick at 13.5.

Vitards always spew shit over "but it was a first year bike, you should have expected it". But it's like the gift that keeps on giving.

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