wont shift into 4th gear, yz85

Alright my kid has proved me wrong. He's been telling me his nearly new yz85 wont shift into 4th. Im like it will shift just go whaaa whaa whaa whaa... and hit the jump. Well he's jumping out of of his seat trying to shift, just a little guy so im thinking it's his boots, right. Until the other day we're doing holeshots and again he's complaining it wont shift into 4th. So dad says watch ill show you and i come back and admjt, ya it doesnt go into 4th under load. So what am i looking at hear, any easy advice.

Here are some of my questions. Would the wrong weight of trans oil cause hard shifting under load? Should a yz85 be able to shift without the clutch being pulled, would you have to ease off the throttle on the yz85. Could tbe 4th gear in the transmission have a rough spot. Since the bike has 15hrs total, and hardly ever in 4th, does the shifting get smoother with time?

I use 80wt in my oil. Yes you can shift without the clutch and easing of the throttle but I personally don't recommend it. You end up with bent shift forks (which may have happened to your bike. Thats probably why its not shifting into 4th) but some would say otherwise.

That oil is way too heavy, the yz85 takes 10W-30 oil that's safe for wet clutches. It only takes a half quart so get the right oil and see if it helps.

The yz85 will shift up or down without the clutch I have one myself, I usually use the clutch but it could be done.

You could take off the clutch cover and watch the shift drum while someone shifts it through the gears. See what happens when you get to fourth, if it isn't a problem with the drum or shifter assembly then you will have to split the cases to inspect, not a bad job on these 85's as they are pretty simple

80wt it perfect for the bike. Ive never heard anyone using 10w30 in their transmission but if it works for you great.

Btw I use bel ray gearsaver 80wt. Thats whats recommended for my bike.

Do you use the 80 weight in the yz85 or yz250? I could see using it in a cr250.

10W-30 motor oil JASO certified for wet clutches is what the YZ85 calls for in the service manual. 80 weight is way too thick for these transmissions as the tolerances are designed for 10w-30

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I'm not sure what oil the owner is using, but using the too thick if oil will make shifting tougher. Go and try it yourself and you will see

Thanks for the replies. I put fresh 10w-40 Yamaha oil in the bike with same results. Also moved the shifter down one notch and gave the clutch lever more pull to insure engaging. We rode today at a practice track, and it still wont shift under full power. I guess it shifts fine if he's not wide open. It was giving him fits running at a large 4th gear jump, so he told me he was shifting into 4th right out of the turn before the revs were up. Oh, also sometimes when he comes out of a turn wot 2nd to 3rd, it's hard for him to get into 3rd.

I'd still look at the shifter mechanism behind the clutch, if all looks good there then you have to split the cases unfortunately.

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