Hello, I'm new to the forum

[KdlH]

Hello.

I'm new to the forum, I live in the UK. I have just bought a 1995 Yamaha Moto 4 350.

Generally the condition isn't too bad (I paid very little for it!), it looks quite original and all the plastics are quite good. The bad bits are no brakes, the rear axle bearings are shot and the transmission won't shift through the gears properly.

I'm not planning on a full rebuild but I would like to sort it out a bit. The transmission is my main concern. If anyone has any ideas on what might be the cause I would be grateful. I can explain what's happening in more detail if required.

Thanks everyone,

Kester

 

Edited December 20, 2024 by KdlH
Edited title

[Mech]

Hi. Welcome along.

You'd better explain in more detail how the shift's working (or not).

I take it you're used to bike shifters ? Know about using the throttle to get them to change nicely etc.. ? Rocking the bike to get it to go in or out of a gear sometimes, (especially if the engine's not running) ?

[KdlH]

Hi Mech,

I rode a 1987 Kawasaki klf300 growing up. I assume the yamaha will shift similar? 

While rocking it, the first shift up from neutral most times doesn't find a gear, second shift does and then the next shift might find "neutral" (the light doesn't light).  

Thanks for the help.

[Mech]

Well rocking the bike as a way to get the gear's to change isn't the most reliable. It's a bit hit and miss which way the bike needs pushing to get the last shift fully done, and the next gear attempted, and sometimes you need to push hard enough to get the engine to turn over. To test a suspect shift fault I always jack the bike up and turn the wheels, or run the engine. If you rocked the bike enough and kept on trying it, and sometimes shifting down a bit, pushing, then trying the shift again, it should eventually shift through all the gears.

If it really can't get each gear after a lot of turning the wheels, and sometimes turning them quite forcefully if needed to turn the gearbox input shaft, then it's perhaps got teeth missing off several gears, or, the shift ratchet mechanism isn't working properly. The ratchet mechanism is I think on the left side on that bike, under that cover.. If there is bad damage in the gears, the oil will have metal, either dust, flakes or even chunks. The dust and flakes might be obvious if you use a wire to dip a bit of oil out of the oil filler, or, take the oil filter out and inspect it.

You could also test carefully to ascertain which gears it is and isn't getting, then figure out whether it's the shift mechanism or the gear teeth that have the fault. The fact that each cog us used for two different ratios will be how you tell if it's cog/tooth broken. If you check and tell me which gears you can get and which you can't get, I'll look at the exploded parts diagrams and figure if it's a gear or not.

If you haven't got a service manual yet, Babbits parts have exploded diagrams of the gears and the shift mechanism.

[KdlH]

Thanks Mech.

I will check it out some more and report back.

The engine does run but with the combination of absolutely no brakes, the rear axle bearings being completely destroyed and not knowing the condition of the oil/filter, I didn't want to drive it too much to keep trying to shift it.

I haven't got a service manual yet. Thanks for the info on the Babbits parts diagrams, they will be very useful.

 

[Mech]

You should be able to get all the gears if you jack it up and turn the rear wheels enough.

When you are looking at the parts diagrams you'll find they generally have the gears, and the gear shift mechanisms on separate pages. The fault will be in one page or the other. It's unlikely to have problems with shifting as well as the actual drive.

The shift mechanism is a ratchet mechanism to let the shift lever return to center between shifts, a start shaped washer that helps it move fully into gear once you've moved it over half way to the next gear, and another short lever and swash plate and ball bearings that disengage the clutch as you shift gears. The problem if it has one in the shift mechanism will be with the ratchet (lever, spring or pins the lever engages with), or spring loaded star washer part. The clutch operating part you can ignore in the diagrams. The pins the ratchet engages with may be shown in the gear section because they are on the end of the shift barrel which is normally in with the gears.

Edited December 23, 2024 by Mech

[KdlH]

Hi Mech,

Thank you.

I'll start a new thread with what I've found.