DR/GN/SP400/ 370

[andy230]

Hey Brian

Looking good...  Who do you race with??  And whats your front end-

I've got a KR1S 41mm front end on my supermono project, but I dont know if it'll be up to much...  Lets get it running first!

andy

[camdoctor]

Hi Brian,
really looking good.
 For the class I want to race USD-Forks, multi-piston-brakes, slicks and 17"-wheels are not allowed, so the GN will look a bit more like a "classic"-racer.
What engine-mods will you do? Only bigbore, ore stroking too?

Cheers,
Hans
 

[#88]

Hi Andy the front end is of an aprillia RS 125,I used the steering stem/inserts fron the original Hejira
yokes,RS 125 front wheel and disc and a Fireblade Caliper with CBR600 master cylinder.I race at East Fortune In East Lothian,about 20miles east of Edinburgh with the Melville club.I race it in the Junior Forgotten Era class.Hans for the first couple of meetings I will run the 370 motor that I got with the bike but when I get the 400 motor built will use that,hopefully will find out soon what piston I am going to use,may need to change the liner,will get a cam. reground aswell.Dont think I'll be stroking the motor unless I get a wealthy sponsor .Away up the shed to see if I can get a smart wee race can to fit as the old mega is a bit too noisy.
 cheers the noo Brian #88 

[#88]

Evening all
   got a rear wheel from ebay from a TZR 125r fits a treat and the chain lines up perfectly.Hans hows the bike coming on?any joy with a piston yet?decided to go for a 90mm as it leaves a bit meat on the liner.Andy do you still live in the weege or have you moved doon south.hows the bike coming on?Waiting on a rear disc from ebay then get the bike up an running a hopefully ready for practice on the 16th of March.
  cheers the noo Brian #88

[camdoctor]

Hi #88
I found some modern 90mm-pistons on the Woessner-pages: KLX400 '03-'07, 20mm pin, and DR-Z400 '00-'07, both are also available as "Hi-Compression"-types. But no idea about heigth and other measures. Maybe you have to use a stroked crank or a longer Rod. I would like to try one of them, if I only could find somenone making the crank-weldings for me...
There are also 90mm-ATV-Pistons. As I could see, they are mostly a bit longer, but also no measures.
http://www.woessner-kolben.de

I'm still waiting for the Megacycle-cams, it will need time until middle of March.

Most cahssis-modifications belong to my brother in law, and he has a to do lots of work in the moment. I'm only the motor-guy ..

Cheers,
Hans

[andy230]

Andy do you still live in the weege or have you moved doon south.hows the bike coming on?Waiting on a rear disc from ebay then get the bike up an running a hopefully ready for practice on the 16th of March.
  cheers the noo Brian #88

Hi Brian,

Nope, I ran away to London about 6 years ago now...  Its ok, but starting to do my nut a bit, thinking about reloacation at *some* point...

The bike's coming on slowly, am getting some help from a club member Rog to make up some shims to go under the valve springs to give correct installed height...  I have a feeleing maybe the head's been machined for different srings at some point??  A pain, but should be ok.  There are a few pics here-->

www.team-thumper.blogspot.com

The motors now out the chassis again, head off to get it built up and then once its down the combustion chamber is (hopefully) not going to see daylight for a while...

cheers

a

[#88]

Got the bike fired up for the first time this year,sounds fruity.Going to use last years 370 motor
but in the middle of building a 400.Hans I may have found a piston that might just do the job,its
from a tractor(Harley),if you go on the Wiseco site and go on the Harley catalogue it is the big bore kit for the 883 to take it out to 1200.They do a piston that is just shy of 90mm and is a high comp.
I have measured the pistons as my friend has bought a kit for his bike and I measured them.The gudgeon pin is 20mm and the crown height(pin to crown) is just over 21mm which is roughly the same as the suzuki one.I will go down next week and compare both pistons and let you know how I get on.I have put a couple of pictures in the Gallery section,the bike now has a tz fairing and the word Tattie on the fairing.
   Cheers the noo Brian #88

[Jez F]

Have been looking for piston as well. Try googling 'Pistal' they do pistons for 2 valve bevel Ducati's,  90mm bore 20mm gudgeon pin, not sure whether the pin to crown height would be ok but might be worth a look.They also do a 92mm version. There is also a Guzzi with a 90mm bore but they use a 22mm pin.

 Jez

[themoudie]

Aye Brian#88,

The Tattie 's looking good and I hope you have a good season at East Fortune. Maybe down for some of the meetings and will be trying to get down for the Bob Mac as usual. Just hope the precipitation leaves us alone this year. Last years Bob Mac was not much different from what we have now, except it was rain for 36 hours instead of the white stuff!

My regards, Bill.

[camdoctor]

@#88
Hi Brian,
I would search for a more modern piston, especially one with low crown and very low heigth. The Pistals look like what I'm looking for      Thanks to Jez F 
Next thing: I will do some crank-welding research for stroking the original crankshaft. Here in Germany I couldn't find anybody who did such, and would tell me something about that. (350ccm-conversion is dead momentarily)

Brian, your Tattie looks really nice. But for the class I am racing, such brakes are prohibitet
Nice frame, did you write something about it?
Only thing I wonder is the tiny diameter and extreme length of the ext.pipe. Have wou been on the dyno with it already?

Last week I tried the fit of the head-carb combo in the GN-frame. For your info: I'll use the 38mm Mikuni flatslide out of a DR600 with a 24mm spacer between head and carb-socket(?). It fits great, I'm really eased about that.

Gruss
Hans

[#88]

Hi Hans
  Not had the bike on a dyno yet still got a couple of things to finish off,found that the fuel taps
where leaking so will have to source new ones.Will probably do the first meeting at East Fortune in April and if all goes well will get it on the dyno.Bill hope you get down to East Fortune sometime this year come over for a bleather,if you are going to the Bob Mac I'll be there as I help with the scruitineering.
 cheers the noo Brian #88

[Jez F]

A couple of possible piston alternatives that I'm looking into, Ducati Monster 900, 92mm dia, getting to the limit on the liner according to a mate who has built a few racing engines in his time and modern Triumph twin, 90mm dia but a 4 valver, might be worth a thought.
Cheers Jez

[cloggy]

Since piston materials are matched to their use, putting a piston in that's designed for a watercooled engine may pose problems for an air cooled motor.
At the very least one would have to run greater clearences, and with a very short slipper piston you could end up with piston rattle  before you'd even run the thing in, not that I'm an authority.
Air cooled trail bike engines recommended  piston clearances are greater than equivalent road motors [though I don't think Suzuki bothered with different clearances for the GN motors] due to fording streams and having the barrel shrink onto the piston.
The Yam XT 600 piston has a much shorter skirt than the Suzy

[cloggy]

Since the standard Suzuki rod is nothing special anyone know a better replacement?

[camdoctor]

Hi there,
there is no need for a different rod. The only advantage would be a replaceable small end bushing.
Japanese rods are made of very good steels, and if nobody had polished them without shot peening, they will last nearly forever.
@cloggy
you are right, clearings in air cooled cylinders with very short slippers could be a big problem. And I know what can happen, if a worn short piston hast to much clearance:
http://www.nefo.med.uni-muenchen.de/~hiha/bilder/schrott/kolbenschrott-001.jpg
http://www.nefo.med.uni-muenchen.de/~hiha/bilder/schrott/kolbenschrott-003.jpg

Gruss
Hans