diy gearbox repair b400

[Velthuis]

Hi all,

My B400 is slipping out of the 2nd gear, needs probably a new shifting fork and gear assembly.
Is it difficult to change the gears and forks with the engine removed from the bike? How to do this step by step?

The repair manual doesn't describe this part at all.

Do I need other components apart from the forks, gears and seals?

Thanks in advance!

[greg737]

This is an interesting post for me. 

Because these motorcycles are 20 years old now the chances are pretty good that they will have passed through the hands of an owner (or maybe 2 owners) who did not have much mechanical understanding or sympathy.  So many sport and supersport bikes that go up for sale have been previously owned/ridden by guys who thought that "clutchless up-shifting" was a really cool, good idea and the "dogs" on the transmission's fixed-sliding output shaft gear that engages the free-rotating 2nd gear ratio end up getting rounded off.

I've just begun the process of exploring and diagnosing the overall engine condition/health of a 1993 Bandit that I bought off Craigslist in October of this year.  So far my 20 year old bike hasn't exhibited any of the 2nd gear problems that clutchless-slamshifting causes.

Of course, any gear in the transmission could be damaged by this treatment but based on the typical behavior of ignorant posers on sportbikes it's usually 2nd gear due to the "boy-racer" stoplight to stoplight pretend Moto-GP mentality.

As I understand it the only way to replace the dogs that engage to select 2nd gear is to completely disassemble the engine and remove the transmission's output shaft.  I'm guessing that the dogs on both the free-rotating 2nd gear and on the fixed-sliding gear that is involved in selecting for the 2nd, 4th and 6th gear ratios are damaged and will have to be removed and replaced.

I guess the silver lining to your stormcloud is that just about any other engine component that might need to be serviced or replaced (like the cam chain and the cam chain guides) will be easily accessible as you dig through the engine to reach the gearbox.

Good luck, let us know what you find and learn about the situation.

Greg

[Velthuis]

Hi!

I know the previous owner and i don't think that this bike has been abused in the past. The output power was limited to 25kw for insurance reasons. I've replaced the carbs of this bike to enable the full 37kw output power. I've ridden this bike for 3000km's without any problems, it runs smooth and doesn't consume any oil.
However,  since the bike has 40000km's on the speedo and it's age is passing 22 years I think we speak about normal wear.

The question is how to fix the 2nd gear. Parts can be easily obtained but I can't find a work instruction. Hopefully the gears can be exchanged without removing the cilinders, head and timingchain......

[greg737]

Hopefully the gears can be exchanged without removing the cilinders, head and timingchain......

In my copy of the Suzuki GSF400 Bandit Service Manual, on page 3-3, there is a listing of all the components that can be removed while the engine is still in place (i.e. still installed in the bike's frame).  You won't find the transmission's gears anywhere on that list so you must continue onward to the next page of the Service Manual.

After the listing of easily removed items (page 3-3) the Service Manual begins describing the process of removing the engine from the frame and then it goes step-by-step through the actual disassembly of the engine. 

The Service Manual's description of engine disassembly continues in this logical, step-by-step manner, beginning on page 3-4 and continuing until the engine has been completely disassembled on page 3-20.  If you look through these pages you'll see that the gearbox components are the very last items that are accessible during the disassembly process.

So it appears to me that you will have to perform a complete engine removal and disassembly in order to gain access the gearbox components.

But, as I said before, the necessity of completely disassembling the engine to reach the gearbox components will afford you an opportunity to address any other maintenance issues the bike might have like worn piston rings or worn valve guides or a cam chain that doesn't pass the length measurement test or worn cam chain tensioning guides, etc.

[Velthuis]

Hi!

That would be an absolute pitty. Cam chain length has been measured 2 months ago, ok. No oil consumption, compression is ok on all four cilinders.

Removing the engine from the frame is not an issue, a complete disassembly of the engine is a real brain breaker to me,

[greg737]

I guess you could continue to do some more research and trouble-shooting and testing to find out if there might be some other cause that would make your transmission jump out of 2nd gear (something other than actual damage to the "dogs" on the gears themselves).  Does the transmission always jump out of 2nd or does it only happen occasionally?

Perhaps there's an adjustment that could be made to the bike's shifting mechanism.  Maybe when you try to shift into 2nd gear the shift lever isn't rotating the shifting drum far enough, or maybe you're just not being firm enough with your foot when you shift it into 2nd.

[bdouvill]

@Velthuis,

Not sure this thread is still valid: did you do anything to your bike?

I am currently in the middle of the process of replacing the output shaft ball bearing and I can tell that you can open the crankcase of a GSF 400 without removing the cylinder head, the camshafts and the timing chain. You can separate the 2 parts of the crankcase as per the manual said, the crankshaft will stay in place as well as the timing chain. Obviously, you cannot measure the length of the timing chain this way...

I hope this helps.
Regards.

[bdouvill]

A quick pic of my upside down B400 engine with crankcase opened and crankshaft + timing chain still in place:



Note that the output shaft of the gearbox is obviously not in place ;-)

[Chris H]

I know this reply is old but a few things you need to be careful if stripping the engine this way up.

Remember simply removing the outer case pins will not allow the case to be split,
you will have to remove the flywheel then remove a three pin plate behind it then remove the clutch to take the lock plate from behind that.

When you split the case be aware that there's an o,ring (as seen in the picture) and on top of this ( not shown) is a copper cup washer, these should be fitted from the other side (as you would work with no cylinder on) so are easy to miss place.
This is the main oil feed so needs to be spot on.

Remember on rebuild the correct sealant must be used to join the case, do not use cheap blue silicon it will leak and this must be applied perfectly as to seal BUT not seal the small oil feed cut outs and oil jets.

If you have fair mechanical ability its not too bad a job, hardest part is the flywheel and really needs a proper tool made up to hold it.

[Velthuis]

@Velthuis,

Not sure this thread is still valid: did you do anything to your bike?

I am currently in the middle of the process of replacing the output shaft ball bearing and I can tell that you can open the crankcase of a GSF 400 without removing the cylinder head, the camshafts and the timing chain. You can separate the 2 parts of the crankcase as per the manual said, the crankshaft will stay in place as well as the timing chain. Obviously, you cannot measure the length of the timing chain this way...

I hope this helps.
Regards.

Sorry for my late response, unfortunately (or happily) I didn't opened the block yet. I've bought a nearly as new Bandit 400 for spare parts, block has 6000 miles on it.

Great to see that you've managed it to replace the parts without splitting. Can be handy in future.