3rd gear problems

[Conrad]

Hi,

I need some advice regarding the bike I recently bought. The speedo doesn't work at present, so its difficult to tell what the true mileage is, but it stopped working on 38000km. It selects 3rd gear, but drops back down to 2nd the moment power is applied.Is this more likely to be a damaged/worn shift fork or the dogs on the 3rd gear itself?

Currently the motor is running and doesn't smoke, but since I will have to tear it down to repair the gearbox, I wanted to find out what parts I should replace while its apart.

I realise that I won't know what is still serviceable and what needs replacing until I strip the engine. What I'm trying to establish is what other parts commonly wear on these bikes eg should I change the timing chain and tensioner?

Does anyone have a good source for piston rings as I would like to replace these when I fix the box, but couldn't find them on ebay.

Thanks
Conrad

[banner001]

timing chain will need changing if its loose, when you remove the tensioner listen for the clicks as the ratchet extends. i cant remember the number of possible "clicks" but if its well over half way extended consider changing the chain, possibly the guides as well. the tensioner is pretty simple, it either will or wont work so if it rachets fine then just give it a clean.

if you replace the piston rings you will need to hone the bores to remove the shine.

you will probably need to re-do the valve clearances so get a selection of shims.

the valve springs might need changing, and a valve lap/valve seat repair might be needed depending on leakage.

the big end bearings might need changing, estimate on some oil jets being blocked beyond repair, your gonna need a load of seals/gaskets/circlips and o-rings as well.

if it was me i would also replace the clutch friction plates, possibly the steels, and definitely the springs...this will make the clutch like new.

check with a fine tooth comb all the gear teeth for damage, as well as the dogs and the locating holes, either/both might cause the gear to jump out. selector forks are probably ok, from experience damage to these usually makes it hard to get into gear...but possibly think about replacing all 3 as well and the selector drum.

think that about it for now, gonna watch F1 highlights...

[Conrad]

Wow thanks for the detailed reply!

It reconfirms what I was thinking, namely a valve lap job, hone the cylinders and fit in new rings.

Changing the clutch makes sense while I'm there, but I'm a little concerned by your comments on the oil passages. Is this a common problem on these bikes? I also note that you said these would be un-repairable, won't that lead to oil starvation and running a bearing?

Does anyone know a good supplier for the piston rings, as I haven't been able to find these via ebay?

Thanks again

[banner001]

the oil jets...basically if you think that you have had a dog fail, or its been wearing metal away then that swarf is gonna go somewhere, now the oil filter should remove it, but you always get some tiny fragments of metal and clutch friction disk material going through the filter, especially if its not been changed recently, and sometimes these can clog an oil jet...its more something to look for.

a good sonication in acetone/trike should dislodge any dirt you cant see...

[Conrad]

Thanks for the feedback, ill try and get the block cleaned when its apart.