classic motorcycle forum

Assume you have checked that you have no supressed/high impedance ignition components?......also will assume you are aware they double magneto voltage and cause failure even in rebuilt mags?......but symptoms sound a bit like a faulty spark plug.

The owner is a millenial.......and if he says "cool" one more time ,he will be walking funny,with Jap parts inserted.

Ive looked at all the options ,main problem is the case is  not very strong..........same as the rest of it.......Anyhoo,Im thinking the cheapest option is to make a new outer race,and skim the case bore just enough to round it up........fortunately the 22mm mainshaft is good......looks like it was replaced....................the rebuild with INA bearings is probably the best,but  too costly........The main bearing is somewhat similar to a WLA part,similar dimensions ,and I could use WLA cages ,but the JAP alloy cage is still good........................I suggested to the owner to rebuild the whole motor with new WLA parts,including flywheels,rods, shafts ,bearings..........but cost is an issue ..... and its only a sidevalve................the conrods are also problematic,but the owner wants the JAP system retained..........in fact the outer forked rod is completely wrong since day one,and machining out the centre rod space has made part of it paper thin ,and its cracked.......every non racing JAP ive ever worked on had serious issues with poor quality and bad design.

I have a JAP 750 to rebuild,and I m wondering about the drive side  mainbearing........the shaft is OK,but the outer race is chewed,and been turning in the case..............My old fallback of using INA races and rollers has hit a snag....SKF.......seems Skf have taken over INA,and prices are now astronomical,as in 2.FN.DR!...........inner race +caged roller +outer race..(need to be trimmed) is over $200.............but big advantage is it all fits in the case.......which case IMHO is a bit weak to be enlarging bearing bores.........However ,a 62/22 ball is 50mm od,needs about 4 mm enlargement,say 2mm  cut from the housing.(original bore is oval ,and needs skimming anyway,at 46-47mm........but a 62/22 is 22mmID,fits the shaft ,and costs around $20 depending on brand............one other option considered is tapered rollers with 22mm bore /44 mm OD,but obviously needs two opposed bearings ......not impossible,.....but.

About the same time as the Arblaster patent ,Ricardo &Co patented and licensed a simplification of the Barr and Stroud system ,do ing away with skew gears altogether and using a link driven by a single eccentric and lever,achieved the same rotary motion of the sleeve and applicable to inline multicylinder engines ........engines were built by Peter Brotherhood &Co ,and by Mirrlees ,Bickerton  and Day..............The Mirrlees engines were quite common once .as they were a WD contract item genset .....and built in hundreds.................incidentally ,the Day mentioned was Charles Day,who invented the crankcase compression two stroke .

Is the springbox saveable?...What about the endcaps?...........the rod is easily replaced ,remaking the plunger unit ,a fair job of fabrication and machining.

There was a B&S powered bike for sale about 10 years ago,IIRC,it was locally made ,and for sale on either ebay or just bikes.I think it was a 350,and the price was very high for what it was.

Heat does sound right....on  along downhill with throttle closed,no air or fuel to cool carb..................a lot of early SV s had the carby on a long intake pipe......maybe a good reason why,although it seems the pipe is needed to clear a magdyno.