JS1 1978 WATER COOLED BARREL

After reading the interesting posts with regards engine technology and various formulae I feel a bit inadequate in writing
this post but the way I did it worked in its day so I hope those like me will benefit, so here goes.

The construction of JS1 1978 water cooled 54x54 barrel started with an air cooled motor I built when Mick Bridges was riding
my bike, it proved quite successful so I used the same technique and information gained to build JS1. If my memory serves
me right I used a large fin thick spigot 125cc Bantam barrel.

First operation was to knock off all the fins then grind the transfere ducks away giving a flat surface to accept the new transfer boxes I had made, these boxes were fabricated from 20 gauge sheet steel complete with main transfer and auxilary ports.

Base plate being turned and transfer openings cut then brazed on to the barrel at the correct height then covered with old sacks and allowed to cool very slowly to prevent too much distortion.

Auxiliary ports then cut into the barrel first with a drill bit then filed to shape and the boxes were then brazed on and again covered with old sacks. I added some bronze to the top of the outer edge of exhaust port incase I wanted to increse the timings.

The part assembled barrel was then placed on the cases (which had already been modified as per usual). and stud positions marked and drilled (I had to do this because the extra large transfer ducts did not allow for standard positions). This done, an old standard Bantam piston was used to adjust approximate port timings for starters, these being EX87bbdc Trans 63bbdc Inlet 90btdc.
Top plate then added and brazed on and again covered with old socks, on this occasion I had a phone call at 7:30a.m. my neighbour telling me there was smoke coming from the shed, fortunately it was not on fire only the sacks smouldering.

The excess barrel from the top then turned off leaving a shoulder to accept a recess in the head which John had made. Four steel tubes then fitted and brazed to top and bottom plates. Before the jacket was fitted the exhaust port and inlet were opened out and polished, the barrel then bored and honed to 54mm and all port edges rounded off.

I had worked out the squish to be 30 thou but it came out as 45 thou, (so much for my maths).

Piston was standard TZ250 except skirt cleaned up to give 3 thou clearance, carburettor 1 and 1/16th TT main jet 560, needle 109, position 3rd notch down, slide No5, carb length 4 1/8th" overall track length 7 and 5/8ths, ignition timing 83 thou BTDC.

Cooling system was L.E radiator capacity 3 pts, thermo syphon self regulating, on average the water temp was around 80 deg, plug used NGK 8.5, 3plate 9spring clutch mixture 16.1 of R40.

The engine was completed 29th-3-1978 the first meeting Lydden 1-4-78 now I would like to quote from Johns notes.Gearing 14-54
practice missfire otherwise engine going well. 1st race would not start- duff plug-new N82G fitted. 2nd race (championship)
finished 2nd no problems except overgearing on slippery track.Power band 8000-10000 but will run on to 10500. As time went
by I changed the port timings slowly until I finally got to where I wanted to be.

The pipe we used came from an old 1976 long stroke but later changed which leads me nicely into the second part of Dereks
question. Exhaust formulae, I've tried various ones but the one I settled on was the Graham Bell paper easy to understand and
giving guidance and basically leaving it up to the individual to experiment,it worked for me,thats not to say everyone will agree
as I'm sure modern day i'deas prevail.

So there we are I had no access to computors nor dyno's but John did runup the bike on the rolls in the Ricards pollution lab and
again I quote"The program gave the following power at the back wheel, at 9100rpm 16.9bhp running on to 15.4 at 10,900rpm.

I have changed a few things with JS2, to date I have had some teething troubles but as the saying goes WE WILL OVERCOME.

Regards Les.

Hi Lez many Thanks for this, i found it very interesting.

could you tell us more about the brazing process - ref ex and trans - and any pictures of the new one? and did you weld the transfer boxes, before brazed them on and how did you limit the distortion,

I see you had a very specific cooling process.

kind regards Derek.