Hi, my 1994 KX 250 will not engage 4th gear - all the other gears are OK. When in the 4th postion there is a knocking noise like the dogs are not engaging. When I took it apart everything looked OK the only worn part was the mainshaft third gear shift fork could it be that?

Bearing gone in trans or a tooth missing off the cluster.

Hi,it sounds from what you are saying that you have got a inturnal falt with the gearbox,im affried the only way to make a propper diagnoses is to take it apart and look at the gear sincros there has to be worn bearings,or teeth on the gears,or the sellector,or something has just manidged to come loose.
I wish you all thhe best.

Normally, a knocking sound in a specific gear set indicates a broken gear tooth. When replacing a broken gear, replace the gear(s) it engages with as well. If you don't replace them you will have the pleasure of doing the repair job all over again when the weakened tooth on the existing gear(s) breaks off. Remember, whatever caused the problem in the first place put pressure on both the broken tooth and the gear it was engaged to at the time. Most likely is a tooth on a slider gear.

This is normal. A slider gear engages into rectangular slots in a drive gear. The slots allow the dogs easy engagement into gear. The knock you are hearing is the engaging dogs striking each end of the driven gear. Please rate my answer, thanks.

is it only 4th gear,are all other gears ok,is the shift loose or does the clutch pedal feel funny ,come back to me and i will get to the bottom of this for you.adrian,,,,,,

Thats a strange one.For some reason it may be just locked in 2 gears at one time.Lift the bike of the ground onto some sort of stand.Don,t start it.Take the plug out.Run the rear wheel backwards and forward.Clicking the gears at the same time.This might 'unlock' a wound up box.Being off the ground you can't hurt it.Just try different gears and in both directions.I hope this helps,because its a strange problem if all was ok beforehand.Thanks

Hi,

This might be because of the gear box problem. By any chance, did your car face flooding? In such cases, please drain the gear box and replace it with new gear fluids. Also, check if you go in low speeds, you might be able to engage it with ease. Please come back to me if you feel this doesnt solve your issue.

Regards,
Hari

Sounds somewhat like a bent shift fork not letting the slider gear dogs fully engage the gear. You probably have metal particles in the oil. Keep riding the bike and you will likely need major repairs. The metal particles are abrasive and thus destructive. Think of putting a teaspoon of fine sand into the gearbox. You can trash an engine pretty quick that way. I suggest you fix the gearbox now, before the top end gets too involved.

Please rate this answer. Thanks!

Selecter forks could be damaged, gear shift shaft bent, return spring faulty, clutch dragging maybe! Try rocking it backwards and forwards engine off and see if you can find that gear! Good Luck - The Yeti

Drain the tranny oil and check for any metal in the fluid. that is easier sorry