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GN 250 - Touring Project

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smegballs
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PostPosted: 23:23 - 27 Apr 2014    Post subject: GN 250 - Touring Project Reply with quote

Here it is as I got it. Picked it up for 450 with 3 months T&T.

http://i.imgur.com/TjxKNvs.jpg

I plan to ride it to portugal later this year (the long way thru france) so want to get everything tip-top to have the best chances of surviving the trip.

Done so far:

Oil, filter and plug changed.
MX bars installed.
Rear rack installed.
Voltmeter installed.

Stuff to do:

Install 11mm master cylinder.
Stainless steel brake piston + seals.
Change wheel bearings.
Install gayters.
Change fork oil.
Upgrade lighting.

I'll post up pics for the more unusual stuff as well as the maths involved for stuff like sizing master cylinders, so people have a something to refer to for future projects.
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TUG
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PostPosted: 04:26 - 28 Apr 2014    Post subject: Reply with quote

I have some fork gators you can have, I probably won't be riding in winter or poor weather conditions so I have no need for them.

If you want some pics let me know or look at my thread.
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smegballs
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PostPosted: 07:36 - 28 Apr 2014    Post subject: Reply with quote

I've actually got the giaters already, just need to get them fitted. Thanks for the offer though. Thumbs Up

Already coming to the thing of, well if the forks are coming off.... might as well change the oil at the same time. Then if the oil is being changed might as well do the seals too...

Fork cap is a ridiculous contraption, not threaded, rather held in with a circlip....
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TUG
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PostPosted: 07:51 - 28 Apr 2014    Post subject: Reply with quote

smegballs wrote:
I've actually got the giaters already, just need to get them fitted. Thanks for the offer though. Thumbs Up

Already coming to the thing of, well if the forks are coming off.... might as well change the oil at the same time. Then if the oil is being changed might as well do the seals too...

Fork cap is a ridiculous contraption, not threaded, rather held in with a circlip....


Oh one of those? have you already done them? Doing them on your own can be a right pain but if you do it just right you can do it quickly. I have a set of these which I bought about 6 years ago, they are one of the best things I have ever bought for working on bikes. They make getting at ring clips and o rings and even cleaning up brake seal seats extremely easy.

If there seems to be a bit of corrosion then a bit of wire wool and wd-40 will help but it is really fiddly on your own.
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smegballs
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PostPosted: 08:04 - 28 Apr 2014    Post subject: Reply with quote

Yeah one is pretty rusty, one not so bad. So already I've started soaking them in oil to try and loosed them up. It does look pretty fiddly, I might knock up some kind of extractor device to help compress the spring, like a G-clamp jubileed to the fork leg or something. I plan on keeping the bike, long term, so a custom made extraction device would be a fun project. Probably get something that slips under the top yoke, then you wind down a long bolt to compress the spring.
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TUG
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PostPosted: 08:32 - 28 Apr 2014    Post subject: Reply with quote

They shouldn't be too stiff, if they are then a bit of wood and a hammer to help ease it up. Is it a brass piston like top and you push it down a few mm to reveal a spring clip in a recess? If so I remember when I changed the fork legs on a yamaha Aerox with the same set up. I left the forks in place, pushed down on them with the handle of a hammer and used the 90 degree spike tool I linked to you to pull the spring out.

I hope this helps you out a little, your best bet is to disturb the rust with shocks like mentioned so the oil penetrates better then quickly getting the spring out.
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hmmmnz
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PostPosted: 08:33 - 28 Apr 2014    Post subject: Reply with quote

i think every kiwi biker has had one of those as a learner bike,
they may be slow, ugly, handle like poo and slow but they are reliable, i bet if you just did the valve clearances, and changed the oil and filter, you could head off tomorrow and have no dramas,
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smegballs
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PostPosted: 08:53 - 28 Apr 2014    Post subject: Reply with quote

Good to know!

This one only has 14,000 miles so I'm hoping that 1500 mile oil changes will keep it ticking over happily for a long while to come. According to the UMG these things will reliably run up to around 40k before they start getting terminal issues.
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PostPosted: 08:57 - 28 Apr 2014    Post subject: Reply with quote

I have a strange love of these things, must have had about 5 of em by now, built most into flat track or cafe racer style bikes and one as a bobber which I built out of bits and cost me 85 including a years tax and ticket!

they are great on fuel, do 60mph comfortably, personally I think they handle quite good (had pegs down many times) but they don't stop!

top bodgemaster tip, you can remove the rear baffle from the exhaust with a chisel, makes it sound good but not offensive. also possible to move rear mudguard back and up to make it a bit flat tracker looking
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smegballs
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PostPosted: 09:10 - 28 Apr 2014    Post subject: Reply with quote

That's what I'm going for.

A portugese has done a rather nice job on his:

http://motrizadas.blogspot.co.uk/2013/05/project-gn-250-by-paulo-gomes.html

http://4.bp.blogspot.com/-1JxWJrkjHig/UznBgD9wExI/AAAAAAAAAlw/nnbxnksmqHE/s1600/IMG_1548.JPG

Remove all the cruiserness!! Cool

Stopping wise I've ordered a new 11mm master cylinder which should improve braking no end. I did the maths on the calipers, more to follow, and the stock 14mm master cylinder is massively oversized for this application.
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slowlydoesit
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PostPosted: 09:14 - 28 Apr 2014    Post subject: Reply with quote

smegballs wrote:
That's what I'm going for.
A portugese has done a rather nice job on his

That's amazing. If you can get it looking anything like that you'll have a smashing bike.
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Teflon-Mike
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PostPosted: 11:45 - 28 Apr 2014    Post subject: Reply with quote

GN 250 - Touring Project? Planning a continental over-land expedition; GN250 would not be the first bike to spring to my mind as the tool for the job....
Go on then, explain your thinking; this is probably more interesting than the mechanics.
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smegballs
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PostPosted: 14:18 - 28 Apr 2014    Post subject: Reply with quote

Well I wanted something cheap to go touring on, so I was looking at C90s and Yamaha Townmate 80s. Both of these seemed to be running around 400-600 quid depending on condition, insurance was 170 for both of these. Fuel economy was the primary consideration here.

So then I widened my search a little to four stroke 125's as well, insurance was 200 for all the ones I looked at, Yam SR, Honda City Fly etc etc.

Then up on the local gumtree sprouted this GN for 450 with three months tax and test. Everything looked in order and insurance was still only 200, I've no doubt it will fly thru the MOT in July. Should still do 70/80 mpg at a 50mph cruise so altho not the 100+ mpg of the stup-thrus still will only cost a shade over 100 quid to ride down to portugal where I'll stay for a few months before coming back.

Consider that last summer I was touring portugal on a bike that derived it's power from my legs the modest progress afforded by the GN will be quite alright. It should be reliable, simple to fix and a not a massive theft magnet.


Moar pichers:

http://i.imgur.com/cpSGsYk.jpg
http://i.imgur.com/jNQ9GAO.jpg
http://i.imgur.com/G5nnUQx.jpg

That weird pink thing on the left bar is my GPS speedo mount. I use an old blackberry as a GPS Speedo. It is a clear pencil case and a pair of zip ties..... Cost less than 2 quid.

Third pic is the voltmeter I installed. I took the tacho off, uncrimped the housing, put a drop of machine oil on the coil spring and installed the voltmeter onto the clock face before sealing it all up again.

So much nicer to ride with the flat bars. I can pretend the cruisery rear end doesn't exist for now. I've been pondering making a new seat from scratch. As I lack the tooling to make a sheet metal one, I reckon some hardwood fly would be sufficiently strong.
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mattsprattuk
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PostPosted: 14:28 - 28 Apr 2014    Post subject: Reply with quote

This is the most civilized bike you've ever owned.

http://1.bp.blogspot.com/-wGd2NtdnflY/UQ5C3j9bXOI/AAAAAAAAI9U/ErAkjFd5KBY/s1600/citizen-kane-clapping.jpg
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hmmmnz
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PostPosted: 15:21 - 28 Apr 2014    Post subject: Reply with quote

Teflon-Mike wrote:
GN 250 - Touring Project? Planning a continental over-land expedition; GN250 would not be the first bike to spring to my mind as the tool for the job....
Go on then, explain your thinking; this is probably more interesting than the mechanics.


seen mondo enduro??
they do round the world by the longest possible route, on the aircooled dr350's which are just the big brothers to those motors,
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pepperami
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PostPosted: 19:22 - 28 Apr 2014    Post subject: Re: GN 250 - Touring Project Reply with quote

smegballs wrote:

I plan to ride it to portugal later this year (the long way thru france) .



DO IIIITT!!!

If you do ,I would be mightily impressed Thumbs Up
Pah! who needs a rocket-ship? Smile
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Brolly Dolly



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PostPosted: 22:24 - 28 Apr 2014    Post subject: Reply with quote

Haha that portugese bike looks just like a couple of my old ones but with a bigger budget.

they have done the same trick and reused the rear mudguard mounted higher and looks like a cut down standard pipe too (I wouldn't recomend it it will run like shit and be loud as fuck)
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smegballs
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PostPosted: 14:09 - 02 May 2014    Post subject: Reply with quote

Welp, my shiny new stainless brake piston and seals arrived today, new master cylinder came earlier in the week. Even got a new stainless nipple, red rubber grease hasn't arrived tho so I'll have to wait Sad
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smegballs
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PostPosted: 21:00 - 03 May 2014    Post subject: Reply with quote

RRG arrived today so got the front brake rebuilt.

http://i.imgur.com/Qv8vBLgl.jpg

Parts ready for action, including 11mm R125 master cylinder.

http://i.imgur.com/NU25EsYl.jpg
Manky piston.
http://i.imgur.com/RYX1FUSl.jpg
Treacle type substance.
http://i.imgur.com/940RCvcl.jpg
Nice sludge filled caliper.
http://i.imgur.com/Nbbh0XAl.jpg
Old piston next to shiny stainless one.
http://i.imgur.com/vy67ioHl.jpg
Place caliper on a baking tray and bake at 120 degrees for 15 mins.
http://i.imgur.com/yExEHASl.jpg
http://i.imgur.com/TG5vXG1l.jpghttp://i.imgur.com/aYfaPall.jpg
Quite a lot of pitting on the original piston after I cleaning it up, I'm pretty glad I just manned up and bought the stainless one when I got the new seals.

Got the whole lot back together with lots of nice red rubber grease. It's the first time I've used RRG and it is awesome stuff! The piston slid right into the caliper with just a little thumb pressure.

Brakes are awesome now, easy 2-finger stopper with barely any effort. The lever does come all the way back to the bar though, when static and squeezing with my whole hand. In practice though the wheel would look at (I'm guessing) 1/2 and 2/3's of the lever travel, it doesn't take much to haul the bike right up! Is this an MOT failure? Even tho the lever can touch the bar with excessive force, in riding use the braking power is very much improved! Now just to address the fork dive!
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i.p.phrealy
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PostPosted: 21:53 - 03 May 2014    Post subject: Reply with quote

that Portuguese one looks like it has longer rear shocks on it, as well as moving the rear mudguard.

can you not use the seat base you have and just custom cut some foam?
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slowlydoesit
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PostPosted: 22:00 - 03 May 2014    Post subject: Reply with quote

smegballs wrote:
Place caliper on a baking tray and bake at 120 degrees for 15 mins.

Glad your brake rebuild has gone better than mine! What was the idea behind baking the caliper? I'm intrigued.
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smegballs
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PostPosted: 22:19 - 03 May 2014    Post subject: Reply with quote

Simply to dry it, I washed it in the sink and the near boiling water from my hot tap did a good job of flushing out that crud. Obviously needs to be 100% dry before use and I didn't want to wait...[/code]
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BenR
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PostPosted: 06:36 - 04 May 2014    Post subject: Reply with quote

smegballs wrote:
The lever does come all the way back to the bar though, when static and squeezing with my whole hand. In practice though the wheel would look at (I'm guessing) 1/2 and 2/3's of the lever travel, it doesn't take much to haul the bike right up! Is this an MOT failure? Even tho the lever can touch the bar with excessive force, in riding use the braking power is very much improved! Now just to address the fork dive!



An old trick you could try is to cable tie the brake lever & leave it overnight. Any air in the fluid line should come out at the top. Thumbs Up
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pepperami
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PostPosted: 09:03 - 04 May 2014    Post subject: Reply with quote

Well Mr Smegballs!
I am enjoying this thread Thumbs Up
MOAR NOW!.

If you make this bike road-worthy and don't tour on it, we will come round your house Evil or Very Mad Laughing
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Teflon-Mike
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PostPosted: 10:36 - 04 May 2014    Post subject: Reply with quote

smegballs wrote:
The lever does come all the way back to the bar though, when static and squeezing with my whole hand.

BenR wrote:
An old trick you could try is to cable tie the brake lever & leave it overnight.

That's if it still has any air in the lines; yes, good trick.

This ere' brake be a bit of a hybrid though, with Yamaha R125 master cylinder and Suzuki GN250 caliper.

Smegs;
1/ Whats the new master cyl sizing compared to original?
2/ Is the new Master cyl, gen Yamaha Spares?
3/ Whats the lever on it?

Thoughts occuring to me, after eliminating air in the pipes;
1/ New master may be slightly under-sized compared to original, hence takes more travel to get same piston pressure; in which case may be a mis-match you cant solve other than by a different substitution.

2/ If copy cyl or lever... then it MIGHT be possible to shim the actuation cam on the heel of the lever so that it moves lever at 'rest' further from the bar.

I have done this a few times as I have big hands; using M6 washers on the end of the master-cyl piston; on one cyl I had to file a little metal off the back of the lever so that it would return fully, but with a little jiggling with file and washers you can get quite a significant difference in lever angle vs take up point.

But do it fucking carefully, if you try! If you have no clerance on the end of the master cyl piston you can end up 'jacking up' never fully relieving pressure on the caliper, so every time you brake it tightens up.
Could be worth a mess, though.

As for MOT Fail for touching bars; they test brake efficiency, Rollers put force on wheel, tester pulls in brake, and it has to stop the rollers. Provided it does that before lever touches bar, should pass... but dont rely on a static lock test as your guide, rollers are putting a lot more force on the brake than you pushing against it.

Snowie's 'Pup' brake lever is similar; she has tiny hands, so her brake lever heel-cam has been filed to bring the 'take up' point closer to the bar, so she can get her fingers around it at 'rest'.. was also re-shaped a tad to increase the take up rate to compensate a bit, but even with stanless braided line, I can get the lever to touch the grip if I pull it hard enough... though wheel's well locked well before, and MOT efficieny test'passed' long before.

smegballs wrote:
Now just to address the fork dive!


Have you got round to replacing fork seals yet?

smegballs wrote:
well if the forks are coming off.... might as well change the oil at the same time. Then if the oil is being changed might as well do the seals too...


Did you measure the fork-spring free-length? Cos they could have gone soft with age; new ones would stiffen it up a bit, if you can get them, and old trick is to use 2p pieces on the top under the fork cap to shim them up to add pre-load, again, stiffening up the initial rate a bit.( & one chap I knew, used to use Diesel Truck engine valve springs to 'extend' dirt-bike fork springs.)

New oil, often makes a workd of difference and makes damping 'smooth' again; but if oil fork oil REALLY shitty, then can have gone 'thick' or previouse owner could have stuck anything in there, really, like engine oil! And new fork oil of correct grade have much lower effective weight. Found a few people find overhauled forks rather 'soft' when rebuilt to book, for this sort of reason. However, one weight 'up' from book, is usually quite helpful.

But a bit of 'dive' is just a feature of old bikes and lightweights I think... you just have to be a bit more 'predictive' and easy on the anchors and not load them up too quick... technique over technology.
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