GSX250 build

[Guest]

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

 

[Guest]

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!:dancing:

 

[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...

 

[Guest]

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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.

 

[GregT]

So I've got to make the riding position the same as the macchi do I ?......

Yeah, you on it for Methven is a possibility.

A bigger holdup at present is not having access to a big lathe until Lloyd comes back from holiday...

 

[fast pom]

Hi Greg only just found your build thread, Must say looks a real cracker look forward to seeing it in the flesh, If you are looking for a rider my youngest is only about 45Kgs wet and if he rides it like he dose his Dirt bike ?, Hmmm hold on he is faster than me on the dirt don't want the little bugger doing the same on the track so scrap that. Cheers Dave

 

[GregT]

How old is he dave ? One of the reasons for building this is the 125 2 stroke/250 4 stroke limit on young riders up to i think 16....

i figured to finish it, race it with "guests" aboard and sell it.....gotta be a better buy than an old RS125...

Having said that, it looks like there's a queue forming to ride it - and Kev's at the front lol.

 

[fast pom]

Only just turned 13 not showing any interest in riding on the track so my wallet is safe for a little while.

 

[Triplenut]

Have just been speaking with the club president over a bottle and bourbon, he has agreed to a new min weight limit for the class.... rider must now be a min of 95kg :-\\\ ...and slow...... and a ginga.... ahaha

 

[fast pom]

Bugger!!! i am all of the above but Gray and balding

 

[GregT]

And while you lot are enjoying the silly season, an old bugger slogs onward..

Bottom end together. cases cleaned, paintstripped, TEN helicoils inserted...probably par for the course for one of these.
Bearings all good, still on the tight side actually...Camchain good. Don't know this motor's history but I'd say quite low mileage. Gearbox fine..

The shells for the balance shaft I've put in just so i don't lose them, lol...
The oil galleries for the shaft, I've tapped 3/8 UNC and will pick up a couple of socket head grubscrews along with the shopping list of ZP capscrews for the covers...This will be an all capscrew motor except for the case bolts, easy and cheap.

Next, build up the clutch and oil pump etc.

Then, mock up the pistons and the barrel, check head gasket thickness and see if the barrel has to be machined to achieve the approx .035in squish clearance i want

 

[GregT]

Squish is fine - around .038in with the gaskets i have.

Clutch good, oil pump in, shift mechanism in - and working, always a bonus...

i realised i was coming to a point where i was going to have to pause so made up a manual camchain tensioner...another weight saving,lol...

Need to get a heap of fasteners - and it's the practise day for the NZ GP friday so I'm into town....

Probably do the balance of the head porting on the weekend unless i score a free pass to the GP. I've built a lot of GSXR's and seen the pics of Ray's headwork. I'm quite surprised at the 250 head, no filling of the bottom of the ports needed IMO - and what little enlargement I plan will be done at the top. They're already quite a lot higher at the carb flange than later GSXR's - a surprisingly good shape IMO.

 

[GregT]

Some progress to report....some negative. the pair of Mikuni 29 smoothbores I wanted to use won't fit. Frame too narrow...just.
So alternatives were found - a pair of 30mm Mk1 Amal concentrics. I'll make up a pair of slightly curved manifiolds for them - they'll angle inwards slightly.

Positive - i got onto the swingarm. Worked out the dimensions and angles i needed to bend the arms. Used a jig I have here to holesaw the crosstube position accurately in both legs.
Pic shows how I do it - the axle hole is 15mm and there's a stepped register in the top of the pillar. Bolt it on there, clamp it to the jig and both arms are the same...Crude but effective.

 

[GregT]

Once the legs are finished - the 3 X 15mm holes drilled get filed into slots on each arm and everything gets deburred - it's jig it up for welding.

Usually any arms i make are short enough that the box jig in the pic can be used with through bolts for axle location and pivot tube....This one is just too long to go in the jig so it's sitting on top. Not as rough as it appears as the jig is dead flat and true...

So it's tack everything up including a cross tube. Low on gas as i expected but the suppliers reopen on Monday.

Once fully welded, the bearing carriers will go in the ends of the crosstube. I use 15mm bore double row angular contact ballraces...not a common answer to the swingarm bearing problem but i like them. They'll take a small amount of misalignment without problems...

I align the bearing carriers with cones in the open ends when they're welded in place so any prior distortion of the crosstube is irrelevant.

At the NZ GP last weekend I had a talk to an old friend/customer I hadn't seen for years who was running a genuine Harris in the Post Classic GP. It looks as though I've got most of my mini copy pretty right....Except for one thing - he can't get the cam cover off with the engine in the frame but I can...