GSX250 build

[pete]

Top stuff Greg... I see what Sci's saying though!

Looks like engine removal will involve valve cover off to give clearance to get the head off... which will give clearance for the cylinders to come off... which will give clearance for the bottom end to come out... is that right?

I guess as a racing motor you would expect to pull the top end off a bit more often than a road bike anyway...

[GregT]

Actually I was extremely annoyed to discover that i couldn't QUITE get the frame off the motor without pulling the cam cover...And yes, cover has plenty of room to come off for valve adjustment.

I'd sighted down the sides of the motor when bending up the side rails and was pretty sure i'd left enough room.

At least i don't have to pull the head off....

[pete]

Ah how silly of me... I missed the fact there are no rails under the engine!

[hugo151]

Maybe...but TIG introduces more distortion too. I like the lower temps of bronze welding. My eyes have never changed fast enough to be good at electric welding and at my age they're never going to...

I'm aiming for around the 100kg mark with oil and battery - a couple of my 350 Aermacchis have come in just under this so it's achievable.

With the relatively soft tube i use, a large fillet in manganese bronze gives me a structure which doesn't crack easily. Better tube and Nickel bronze would be nice but price up T45 or 4130 here in NZ....

Scored a TZ seat at the weekend and discussed the front fairing today with the 'glass guy. Honda NSR250 sitting there in stock so that will do.

Bought the alloy plate for the triple clamps - and a sheet of 16g soft as I plan to make a tank too

I'll put up some more pics tomorrow.

100kg will be a big ask ! on account of the engine weighing 50kg on its own. i dare say by loosing starter motor,big batterie, ballance shaft, stator etc may save another 10kg . i've got my gsx 250 cafe racer down to 138kg dry but with a 4kg batterie & centre stand. i'm interested what you're doing with the cams.love the frame as well,i've heard of this bucket class racing before that you have down under, i think its a realy good idea.

[GregT]

Yeah, the engine is a little porker...But in my defence, my GPZ500 racebike - long since retired to the barn - weighed 143kg half wet. It had the balance shaft, a braced stock frame, GSXR 17in wheels and big brakes...and the motor was 72kg dry....
The frame on this one is very light...and the wheels which none of you except Dave have seen yet are VERY light...

Picked up the cams yesterday. So when I run out of gas for the frame build as i undoubtedly will over Xmas, I can start on the motor build...

[pete]

Wheels are very light? Hmmm... I ride regularly with a Katana that has very light wheels... it is non-stock and his aim is under 200kg's for it with fuel and I think he's currently at around 204kg or so... the material his wheels are made from is not period correct

[hugo151]

theres alot of things that are well over engineered on this bike making it heavy, although it was probably designed as a 400 as well, for example 6 x m8 bolts to hold the front disc, about 30 x m6 bolts to hold the clutch & alternator covers on, i can't believe how heavy the clocks, carbs & chain are, does a 30hp bike need a chain that big ?

[GregT]

Two steps forward, one back....What frame builders don't want to talk about - distortion...
I've spent some time removing an approx 1 degree twist which was apparent after finishing the front welds incl coil mounts,a front tank mount plate and the front fairing mount. As pic now.

To say the least, it's bleedin' stiff...But I'm happy with the alignment now and will carry on with the swingarm. Unfortunately I've used rather a lot of gas so I'll probably only be able to tack the arm up until Southern Gases reopen in Jan. Plenty to go on with though..

As there was some interest I fired up the electronic scales - thanks Dave.

frame as it stands with pivot bolt 8.725kg There's about 1kg of seat frame and footrest subframes to go on. Arm should come out about 2.5kg.

Bits coming out of the motor Balance shaft 1.745kg, starter motor 1.134kg, alternator rotor and starter clutch 2.434kg.
Total 5.313 kg - plus the stator of course.

Wheels - same style as T8er's 750 project, alloy rims, wire spoke.Both wheels with bearings but bare - front 3.23kg, rear 4.80kg

[Triplenut]

Weights to 3 decimal places ... Flash ...

Very light weights.

I may be showing my ignorance, but will removing the balance shaft require further balancing of crank and other components to stop it shaking to bits?
Or is the balance shaft simply a nicety for the road.

Cheers
Dave

[GregT]

Weights - well some grocer probably charges to 3 decimal places, eh Dave...At least i didn't have a thumb on the scales.

Logically, a 180 twin with balance shaft should still have a balance factor in the 55 - 60% range with the balance shaft there to take out the rocking couple. Given they're only 125cc cylinders I'm hoping apparent vibration won't be significant....I can't be bothered setting up and measuring the std balance factor anyway. Gotta be better than the 650 Benelli I built which as std shook everything off. That had 83% balance factor from the factory. Reduced it to 70% and it was all good...
We'll see - and you may be one of the first to find out, Dave.....

[Triplenut]

you know how to make a girl feel special!

[GregT]

Another one of the many small jobs done. Steering head bearing carriers machined up - from an offcut of 5083 plate - and pressed in.

Should be apparent there's no photoshop work being done...you're seeing lumpy welds and all....

If i get keen i may make the swingarm bearing carriers today.

[nikosg]

This build is fascinating keep up the good work!

[GregT]

Thanks - in a lot of ways building from scratch is easier than a restoration - with the strange (to me) imperative for originality...Or the more common cafe conversion where the std frame enforces choices...ie. shift one thing and two others are affected...

I can look at it and say, where is the BEST place to put that...no compromises. Pure racebike where the only judgement that will be made is whether it looks "period"....and how it goes of course,lol...

[kiwimacchi]

book a ride

Hey Greg, have lost 5kg recently and by Methven might be down to a svelte small elephant weight. Dont tee Dave up yet!! PS Sorry the ST engine held you up.