Removing the gearbox from a GN250

Hi,
I have broken one of the dogs in the gearbox on my GN250 so I have set
out to remove the gearbox

I have drained the oil and taken the engine out and I am about to
remove the top end.

Can I do this without dismantling the top end?

I have removed the spark plug and the four bolts which seem to hold it
all together. What else do I need to do before the top end can come
off? What kind of persuasion does it need? What special tools do I
need? And what else should I look out for in my quest to remove the
gearbox?

Also does anyone have a workshop manual for a GN250? I have been going
off the diagrams on motofiches.com.

kenahs

 

kenahs is of the opinion:

Holy crap, you're daring. I'd be obtaining a manual by any means necessary
before trying anything of that nature. You'll get all sorts of truly useful
information out of the manual -- torque settings, the order in which to pull
certain critical bits apart, and putting it all back together properly
again.

No useful info on the GN250 specifically, though -- rode one for a half-day
on my L's course, that was enough for me.

- Matt

 

Before you pull it all apart, how do you know you have broken a dog?

Hammo

 

In aus.motorcycles on 30 Aug 2004 22:09:38 -0700

Unless the GN is really really different to what I think it is... there
is no "gearbox".

There's a bottom end, containing a crank, and sharing the oil and the
crankcase, are the gears.

Unlike a car (or a Guzzi...) which has a separate set of castings
containing the gears, most bikes have them in the same castings as the
crank. Some have cassette gearboxes where you can open a plate in the
side of the case and pull the gears out,but the GN ain't that posh!

So yeah, to get to the gears, you have to tear the thing all the way
down, have to take the head and barrel off, then split the cases and
extract the gearbits.

I suggest you try and source a workshop manual, might be something at
www.haynes.co.uk which you can source through Repco.

Zebee

 

Ahh, have joy, have fun, oh what a task you have taken upon.

Anyhoo. Yep, you need to remove the top end. If you've undone the head bolts
you'll find that you might need to give the head a bit of a tap with a
mallet or some description to actually get it to part from the block. After
that you'll have a piston and a conrod floating about the place. Look
through the haynes manual, take all the side plates off, and you should
begin to be able to start splitting the cases to get into the gear box. It's
a pretty full on job, so I'd highly reccomend getting the Haynes manual, as
well as the proper tools to do it. Things like a torque wrench and also
circlip pliers, other odds and end that you might need.

Glad it's you and not me ....

Cam

 

I thought he'd removed that already! But yes, not much will happen without
the cams being out etc.

Cam

 

I found it floating around in the engine when I took the clutch cover
off, took it into the suzuki shop and they told me what it was. Said I
should pull the motor apart and bring the gears in and they could see
which one was broken.

 

That's right.

Haynes don't do a manual

 

kenahs is of the opinion:

You'll learn a lot more with a manual...

That's because people keep pulling them apart and losing the bits! <grin>

I'm actually a bit surprised you can't find someone with a donk for it --
they were a fairly popular steed in their day, from what I've heard.

- Matt

 

kenahs is of the opinion:

The factory would do a manual, and there's always Clymer. Take a ring
around a few second-hand and technical bookshops, you might find one
somewhere.

And one thing to note about your "educational experience" -- if you ever do
plan on putting it back together, it'll cost you a moderate fortune in
gaskets. And don't even *think* about skimping on them -- a pool of oil at
your feet at every set of lights awaits you if you don't replace *every*
*single* *one* of them.

- Matt

 

I figure I got nothing to lose, to get someone to repair it will cost
more than its worth. Might make a good learning experience.

Worst case scenario I will get a second hand engine and stick that
back in. Anyone know where I can get another engine? None of the
wreckers I have called have got a complete one.

 

You better get someone to cast an independent eye over that logic.

Nev..
'03 ZX12R

 

In their day?

[looks down nose over glasses]

Hammo

 

Take lots of photos and notes so you can put it back together again. I
suggest a manual would be a good investment. There is usually a screw
hiddne behind the clutch basket, and you will probably need a
flywheel puller to get the flywheel off the crank. When it is
reassmebled, turn it over by hand a few times to make sure you have th
ecam timing right, and that the valves and piston don't interfere with
each other. You may want to change the rings if they are worn, while
it is apart

Suzuki online fiche (but not this model
http://www.ronayers.com/fiche/getdesc.cfm?man=su
IIRC the DR250 has the same motor
Geoff

 

further to the previous post
http://home.zonnet.nl/jjkeevel/motorfiets/index.htm
has info on the GN400 - they are similar
Geoff

 

And i just remembered:
http://www.motofiches.com/sites/TYRBUW/default.asp?cs=&mk=SUZUKI&cc=250&ml=GN250
has the GN fiche (and lots of others on that site)
geoff