piston/cyl running clearance

pappa_golf

do we have any 2 stroke bikers , or rebuilders on this forum?


an old Kawasaki ke125 ,(aircooled rotary disk) needing a rebore , no original stock pistons available , and more worrying is the fact that all the old 2 t reborers have now retired ,


in a very old workshop manual for genuine Kawasaki pistons on a new barrel it was suggested 0.025-0.035 mm however I keep getting told 2.5 thou (inches) by the "young" generation" that have probably never seen a 2t disk valve engine!


new pistons are of dubious quality , catch 22 time?


a friend (who I trust) who deals in pre 1st world war stuff , cant come up with a figure but suggests ereing on the larger size of the Kawasaki book and going for something like 0.045 ,due to unknown quality , and suck it


anyone had ant small 2T,s bored recently?

AdrianC

2.5 thou is 0.06mm - so a bit looser than the bit looser than the workshop manual's loosest recommendation. Or 2.5x the tightest recommendation...

Pre-WW1 stuff is going to be much looser than modern, because of variable machining accuracy and poorer materials.

cb1979

I would contact Service exchange parts in Kegworth, they are expert Motorcycle in engineering services, they will be able to advise you and maybe able to supply a suitable piston

pappa_golf

thanks , piston has been located , very few available now , only chinease imports , major players deleted from stock

DoaM

0.025 mm is just under 1 thou. 0.035 mm is about 1.4 thou.

With the cylinder I'd aim for nearer minimum clearance initially ... it's easier to increase the clearance if necessary (widen the cylinder bore by further boring) than it is to reduce it.

pappa_golf

ok , now received the correct info via another forum https://www.manualslib.com/manual/860082/Kawasaki-Ke125.html?page=107#manual


0.066 - 0.072 mm


or


0.0026-0.0028 inch

mark1959

So 2.5 thou is right then. [0.0025 inch].
I wish they still made 2 strokes, as one old fella said to me..............."you can't go wrong with a load of holes"

pappa_golf

alas , this one had a "eating disorder" and decided it did not liker the odd 6 mm nut or bolt! there is a rotating disc on the end of the crank (like a cd) with a cuttout to allow fuel/air , the carb is behind the r/hand alloy panel , the disk spinning at about 9k sliced up the object , digested it and shattered the crankcases and destroyed the crankshaft


all rebuilt now , and should be making smoke within a day or 2

DoaM

Huge photo is huge ... please remove the IMG tags and leave simply a link.

Richard53

Even at an advanced age, and not having owned or ridden a 2-stroke since the 1980s, I still love the smell and the sound. I have been known to go considerably out of my way to follow a stroker which was pushing out the old fumes.


It takes me back to my GT250A and RD350YPVS days.