2nd gear stutter.

[Bretty]

Hi All,

I would appreciate your thoughts and inputs on this...

So my bike has been running rough since it came out of storage over winter.  It's now had a 'no expense spared' service and check over to get it running smoothly without stuttering or misfiring. Now combustion-wise everything is running sweet!!!! but....

The bike is stuttering in 2nd gear. Like its jumping teeth?!  All other gears are fine and it changes gear no problem, but if I give it any throttle in 2nd it really stutters and the revs jump quite violently as it accelerates. No noises, clunks or whirring noises just a violent stutter.

I'm now pretty confident it has a mechanical gearbox fault  (assuming there are no electrics or sensors in the gearbox that would cut the engine intermittently)

What is likely to be the problem? and can I do any sort of diagnostics before taking the bike apart? It would be nice to have an idea of what I am looking for and parts I need to source before taking the bike apart.

I had the engine out before for a top end rebuild and am 50/50 if I just buy a replacement engine (£150) or do a gearbox rebuild? What do you think?

Cheers,

Brett

[darrsi]

I can't make the connection between the gearbox and a stutter?


Stuttering is more air/fuel or electrical.

[Bretty]

Maybe "stutter" is the wrong word. But it's the best way to describe it.

It's a stutter in power, not engine noise, infact I think there rev's jump up.
It's an instantaneous violent drop and pick up in DRIVE, the engine isn't cutting out but the power/drive is.

I've been investigating electrical faults, a misfire and even originally thought it was jumping teeth on the sprocket/chain at maximum torque.
A very violent drop in power which than instantly picked up, giving a significant drop and pick up on the front end.

I'm now fairly confident the problem is with second gear as all other gears are fine!

If there are a couple of teeth missing of the gear would that be it?!

[darrsi]

Throttle Position Sensor can make them run cranky lower down, you could give that a quick check and make sure everything is where it should be.

[Fazerider]

I'm surprised there aren't nasty noises if the gears themselves are damaged, but if that is the case it's not a long job to take the sump off. Not that that'll give you access to the cogs to change them, but there will be teeth lying at the bottom of the sump.
(If so, a new motor is the simplest solution unless you're keen on taking things to bits for the experience.)

[Bretty]

Done all that! Combustion-wise the bike runs sweet! In ALL gears... except 2nd!!!

First gear mental acceleration across full rev range
Third gear pulls like a train through the full rev range

Second gear power is intermittent! it's like it's jumping teeth.

[Fazerider]

Even simpler than looking in the sump: put the bike on the centrestand and engage 2nd gear, you should be able to feel a massive amount of slop at the rear wheel at certain positions if teeth are missing.

[Bretty]

I will need to turn the engine though to find the 'certain positions', No? will I be able to do that?

I might try putting the bike on the centre stand, run the engine, put the bike in second gear and see what happen when I slowly let the clutch out... I guess it could go bang.. I think I'll sleep on that idea. hmmm...

Thanks all for the help!

[limax2]

Two good suggestions from Fazerider. If you take the spark plugs out you  will be able to turn the engine over easier but still feel anything odd. Also running on the centre stand shouldn't do any more damage than running under load like you have been doing. Don't let the chain thrashing about worry you as that is normal with no load on it. Applying a bit of back brake should settle the chain and help indicate the problem if it is gear related.

[IamEEKY]

Hi Bretty,

Not sure if you are having the same issue as me, but I developed that exact problem a couple of months ago, ended up replacing the engine because it was my primary method of transport.   
Can you make it go up to around 6-7000 revs by lightly applying the throttle? and then anything after that it almost "jumps" out of gear? At first it felt like I had a massive clutch slip, and then it started getting very violent disengaging and re-engaging and then eventually i couldn't change into 2nd 

I've had the famous 2nd gear issue twice over the 3 years, first time a garage "fixed it" and then it came round again 2 years later. I looked into it and I was going to replace the selector forks, but i couldn't have the bike in pieces for several weeks   

just thought i'd say something 

Tom

[Bretty]

Hi Bretty,

Not sure if you are having the same issue as me, but I developed that exact problem a couple of months ago, ended up replacing the engine because it was my primary method of transport.   
Can you make it go up to around 6-7000 revs by lightly applying the throttle? and then anything after that it almost "jumps" out of gear? At first it felt like I had a massive clutch slip, and then it started getting very violent disengaging and re-engaging and then eventually i couldn't change into 2nd 
Tom

Exactly that!!! yes. I just picked up a knackered donor engine so I can replace the gear box.

Going to take a couple of days off work and get the engine out and replace the gearbox part.

Can I rebuild the bottom-end / gearbox without taking the top end off?

I understand you can replace the selector forks and drum through the sump and the gear shafts you have to split the case, but can I do that without taking the top-end off?

[Fazerider]

I understand you can replace the selector forks and drum through the sump and the gear shafts you have to split the case, but can I do that without taking the top-end off?

The cylinder head bolts go right through to the lower case, so the top end does have to come off before you can split the cases.

[darrsi]

Gear selector main spring!

[flakey]

sounds to me exactly like the 2nd gear cog and sixth gear cog (which make 2nd gear) are slipping on each other, I had the same issue on a gsxr750 and it needed 2nd gear cog,6th gear cog and new fork selectors, the 2 cogs are joined by 3 squares on the back of each cog back to back, under extreme load these are slipping then turning a third of a turn and joining back together again resulting in the most furousouis on off on power with no drop in revs, either needs a new gearbox or gearbox rebuild, my gsxr used to 'kick' like this 3 times in the 2nd gear rev range and gradually got worse, apparently it caused by dropping the clutch to wheelie and the gearbox doesnt like the instant load, cost me £540 for a gearbox rebuild which was as cheap as i could get.
kind regards

[Bretty]

Guys, your help is fantastic!!!

I picked up a 'donor' engine with a knackered top end over the weekend for £80. I've pretty much striped it to take out the gear shafts, selector forks and drum.

You're right, there are 2 bolts directly underneath pistons 2 and 3 so the head has to come off to split the case... This means all the cams have to come off also unless I want to break/rivet the cam chain. This repair is going to be a mission!!

Darrsi - What can I expect to see when I look at the gear selector main spring on my bike?

Flakey describes the symptoms exactly! I'm still not sure how I will diagnose the problem with my gearbox when it is in bits. I'm hoping it will be obvious or I can figure it out with a bit of head scratching. Else I'm just going to check for wear, shavings, cracks, play, bits missing? Or probably just switch all the parts over if the donor parts look in better nick.
 

[darrsi]

Not sure now if it's a similar problem now, but this is why i mentioned it.


http://foc-u.co.uk/index.php/topic,2913.msg23014.html#msg23014

[flakey]

first check the gear selector forks, each gear selector fork has a slightly raised lump on the end of each fork both sides, now 1 of your forks will have worn away those raised bits on 1 side of the fork-it will need replacing as it will be slightly bent and also you should be able to see where that particular fork was located in the gearbox and then to which gears it would move, the gears that would need replacment will have rounded off the edges of the square blocks on the back of each cog,

[flakey]

 here is a link to a picture of the selector fork showing the raised parts on the end of the fork,
 http://www.ebay.co.uk/itm/50713-Yamaha-FZS600-Fazer-1999-Gear-Selector-Forks-x-2-/301220011273?hash=item46221c9d09
 
here is a link to DANS Motorcycle gearbox repairs, scroll down the page till you see a picture with 'shifter drum' underneath, this picture clearly shows a shifter in position of a cog and shows the 3 x square blocks on the back of the cog, these block edges you will need to check for wear
 
http://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=7&cad=rja&uact=8&ved=0CEUQFjAGahUKEwiU7c6lprDHAhXCuhQKHQkaD6E&url=http%3A%2F%2Fwww.dansmc.com%2Fgearbox.htm&ei=1OvRVZQzwvVSibS8iAo&usg=AFQjCNGjOF9fY35faGBSR-He8t9kx9clSg&bvm=bv.99804247,d.bGQ