Author Topic: DR/GN/SP400/ 370  (Read 5595 times)

cloggy

  • Guest
Re: DR/GN/SP400/ 370
« Reply #15 on: December 29, 2007, 04:37:27 PM »
Well for XRs with similarly weak clutches they say go for the best 10/40 mineral. But don't ask me. I'm not at your level. Joy did my cam 20 years ago. He may have a spec for a full on race cam.
Let me know if you ever discover an oversize  piston match. My motor's all midrange. great for B roads, which is pretty much all that exist here [W Herefordshire].

cloggy

  • Guest
Re: DR/GN/SP400/ 370
« Reply #16 on: December 29, 2007, 04:45:27 PM »
Oh yeh
Powroll [the Honda singles engine people]did a whole bunch of tests on aircooled stuff and found better wear rates with mineral oils. It's all on their website  http://www.powroll.com/tech_specs_OIL.htm

#88

  • Guest
Re: DR/GN/SP400/ 370
« Reply #17 on: January 06, 2008, 10:20:36 PM »
Happy New Year
 made a start to the spare motor,stripped the spare 370 motor right down doesn't look too bad for a 20 odd year old lump,cleaned up the crankcases and painted them,going to replace the main bearings then check the gearbox and rebuild the bottom end.fit a heavy duty clutch then some porting of the head then a cheecky valve job and try and find a piston for the job.still trying to find a piston if I go 91mm using the 400 barrel that makes it 424cc.
    cheers the noo Brian #88   

guest207

  • Guest
Re: DR/GN/SP400/ 370
« Reply #18 on: January 13, 2008, 10:48:55 AM »
many years ago a mate of mine managed to get his SP370 out to approx 490cc running a big carb, using what piston I dont know but it was quite lively.

camdoctor

  • Guest
Re: DR/GN/SP400/ 370
« Reply #19 on: January 16, 2008, 08:12:41 AM »
Hi there,
I'm Hans from Munich (so please pardon my english ::)) and join the forum to get some info for my GN400-classic-racer project. Of course I let take part everyone here to (nearly..) all of my knowledge.. ;)
I do some hobby-racing with a slightly modified XT500 with the Grab the Flag, where "no japanese four-valves" are allowed. The GN is for my brother in law, who won't ever sit on a Yamaha...

First I try to build up a reliable engine with 400ccm, and later perhaps will downbore it to 350ccm, or upstroke/-bore it a bit, to be competitive in the 500-class.
I found out, the GN-engine is very nice made, many things are solved much more elegant than in the  yamaha XT/SR500 engines. Advantages for racing are the close gear ratios and the lower weigth.
Also the valve-gear seems to be less sensible. I ordered stage2 megacycle cam, and after having calculated the valve spring force, I will choose the right ones from Schrick, as I made good experiences with his products, unlike with R&D-springs.
For the first trials I will use a Mikuni TM36(I've got a spare one) and later an old 38mm Mik. flat slide out of a DR600. Exhaust will be a megaphone with reverse cone (mostly no noise limit).

Info: XT/SR500-Pistons have a 2,5mm lower compression heigth, equal pin diameter, but exhaust valve pocket is not in symmetry axis and must be reworked. There are many aftermarket pistons with different compression ratios from woessner(athena), wiseco,  J.E. and others.
I don't know much about the british racing scene, except what I read on the http://www.bmzrc.org.uk/


Cheers,
Hans

andy230

  • Posts: 1322
Re: DR/GN/SP400/ 370
« Reply #20 on: January 16, 2008, 02:18:47 PM »
hi

sounds like interesting projects are afoot! 

Hans, what were your problems with R&D??
Anyone got a preferance?

andy

camdoctor

  • Guest
Re: DR/GN/SP400/ 370
« Reply #21 on: January 16, 2008, 05:54:04 PM »
Hi andy,
SR500 with hi-lift (more than 13mm) cams make lots of problems with broken R&D-springs.
Best would be, to change them after each racing weekend. Schrick springs last several seasons.

Cheers
Hans
« Last Edit: January 16, 2008, 05:56:23 PM by camdoctor »

#88

  • Guest
Re: DR/GN/SP400/ 370
« Reply #22 on: January 18, 2008, 04:26:12 PM »
Hi Hans
  If you find a piston suitible for the 400 could you let me know,I was looking for a 91mm piston which should be around 420cc's
 cheers the noo Brian #88

camdoctor

  • Guest
Re: DR/GN/SP400/ 370
« Reply #23 on: January 18, 2008, 07:26:43 PM »
Hi Brian,
I only could find a forged Athena-piston with 90mm, for XT500, which is ~2-3mm lower in compression heigth.

Cheers
Hans

andy230

  • Posts: 1322
Re: DR/GN/SP400/ 370
« Reply #24 on: January 22, 2008, 12:52:30 PM »
seen www.kedo.com for XT and associated pistons??
dunno if its any use....
a

camdoctor

  • Guest
Re: DR/GN/SP400/ 370
« Reply #25 on: January 24, 2008, 08:07:15 AM »
You are right, KEDO has 91mm-Pistons, but not for XT500. With original sleeve 90mm maximum bore.
They offer 91mm pistons for the TRX850. I don't know any measures of it.
There are very modern 91mm pistons for KTM 450 in the wiseco-list I would like to try, but they are very short.
Please compare a XT500-Piston with one of a Honda CRF450:
http://www.nefo.med.uni-muenchen.de/~hiha/bilder/kolben_alt_modern/kolben1.jpg
Weigth difference is 150g...

Cheers
Hans

stugn400

  • Guest
Re: DR/GN/SP400/ 370
« Reply #26 on: January 25, 2008, 07:00:54 AM »
Not sure if this has already been mentioned, but.....

The GN400 Yahoo user group had a posting a year or so back about a chap who raced GN400's. He extensively modified the bike (chassis and engine) and, if memory serves me correctly, was talking about speeds of around 120mph!!!

Photo,s too- so I guess he was genuine (certainly sounded like he knew what he was talking about).

stu

camdoctor

  • Guest
Re: DR/GN/SP400/ 370
« Reply #27 on: January 25, 2008, 09:34:28 AM »
Thanks for the tip, I think I will join that group.

Cheers
Hans

#88

  • Guest
Re: DR/GN/SP400/ 370
« Reply #28 on: January 28, 2008, 07:16:35 PM »
Evening all
 was up the shed at the weekend and got the spare head ported including tapering the inlet valve guide.Cleaned the valves up on the lathe and carried out a wee bit machining of the valves.Head is ready to be skimmed once a piston is sourced,measured the liner and think it would be safer to go 90mm which would leave some meat on the liner.Was also up at my local bike tuners YPE who is Scotlands leading engine tuner,recently over the last few years Stuart the owner has been building motors for top moto x teams and showed him the piston out the SP he laughed and said the last time he saw a piston like that was in a Jaguar.He is going to try and match something up ,possibly a Rotax or KTM.Will keep you all posted.
   cheers the noo Brian

#88

  • Guest
Re: DR/GN/SP400/ 370
« Reply #29 on: February 04, 2008, 07:22:11 PM »
Hi there
  Had a wee bit bother with the the rear wheel/chain line up,the wheel has to go.Got another wheel from a TZR 125 to try.The front brakes all bled up and feels great.There is a couple of photos of my bike under members current projects.Its at the top with #88 on it,the numbers are offset for a reason so when I race with another club/circuit all I do is put a 1 or a 2 infront of 88.My spare engine is coming on new mains,SP 400 gearbox and a SP 400 clutch.removed all the kickstart gears shafts as I bump start the bike and was told that you can get bother with the gears and they cause damage to the crankcases,so I'll make a plug for the casing on the lathe.
  cheers the noo Brian #88