KR-1S.co.uk Forum

on one of my cylinders, the woesnner piston had broken of the bridge between the 2 ports, so I did the same to the other cylindre to have them matched.

I thought TSI would shoot me for doing that , but he said it was bether that way than that silly port

What I wouldn't do, is lower the skirt at the back of the cylindre. Gives less support to the piston when it rocks at BDC. Unless you plan to change piston's more often

reduced the back skirt 7mm to match the kr1 barrel that had already been fettled ,ime guessing this is to open up the inlet tract from the reeds.


and removed the hump in the bottom of the exhaust to match the other barrel ,gaskets on order and cheers martin for the temp sender and thermostat,
had a quick measure up of the barrel heights ,i may need to skim the kr1s barrel .15mm , ive got a kr1 left and kr1s right on the engine on the bench and measured the squish at .8 and .9 in several places ,so i can compare to barrel heights and if i use the same pattern gaskets (i can remember turning the head gasket over ,i think the tool maker was australian,to keep the kips free) so questions tonight ,do i need to skim the head .15mm (i could lap that in on my granit surface plate on wet n dry) and going to do some searching as after i shotblasted the barrels ,on the kr1 barrel i found engraved Whitby ss400 tb81 or t881,be good if i can find any history

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a guess for the function of the extra lower boost port may have been to promote circulation/mixing that might have aided lubrication/cooling of the gudgeon/piston...
...as the older pistons also had ports in the piston (behind the pin) which would have allowed cross connection of this lower boost to the transfers
so this might happen on the intake/upward stroke of the piston.

both disappeared in later models

that makes sence ,ive never seen any original kr1 pistons

on the topic of the lower port, taken vertibram from
A. G. Bell, Two-Stroke Performance Tuning 2nd edition, Haynes, 1999, pg 52

"... When staggered porting is employed, it is usual for mid-range and maximum power to increase, due to the longer transfer periods improving cylinder filling, particulary at high rpm. Much of the mid-range power gain, I feel, is due to the cylinder being scavenged better. With the new type of transfer porting, a pocket of exhaust gas can be left unscavenged high up in the cylinder at lower engine speeds. Opening the boost port early would tend to get this pocket of stagnant gas moving, because it's flow stream is still directed upwards at 45 to 60 degrees. Some fuel charge is possibly lost out of the exhaust but, because this pocket of exhaust gas is purgesd out of the cylinder, there is less dilution of the remaining fuel/air mixture. Consequently combustion will be faster and more complete, raising the hp output."

what i get from that in laymens terms is that at lower engine speeds (i'm assuming in the range of 4-7k ish) which the kr1/kr1s use being road going bikes, it helps to move the exhaust gasses out of the cylinder quickly however at high speeds, such as on a race only bike this would not be needed.

made a bit of progress and had a shift around in the shed,one of my mates gave me a unused shotblast cabinet for my 40th thats half the size of my home made tardise one,and finally managed to scale some gaskets .

love the bottle of newcastle brown fred

good evening ,barrels n head back on and new small ends , cut a .3 gasket for right 90.6 high barrel and .4 gasket for left 90.5 barrel ,checked squish at .7mm so hopeing i havent gone too low as the other gasket paper i had would`nt add up, and chucked the new links on just to see cheers lee,so spent £140 on barrels,15 on bolts 20 on links n 20 on thermostat n sender

realy want to crack on with the cones i copied ,lets get rolling this weekend

good progress today ,them carb t airbox rubbers always seem a pain to me(bit of hot water and rotate them to get seated allways with the airbox open) cheers spannerman for the throttle cable ,tommoro ile be gutting my standard expansion chambers and maybe make a jig for the new homemade exhausts to aid repeatability on the next ones ,booked in to run the hill at prescott hill climb as well in a month or so ,should be fun ,ile be shit scared of being infront of a audience tho
http://www.prescottbikefestival.co.uk/
ive never been so am look it up on the tube now

Tell you what Fred, that's like looking down onto my bike, only yours is a whole lot cleaner & neater

Are you keeping the wheels white? I do like white wheels

yep white wheels ,black everything that could be powdercoated,zinl plated fixings n stainless, and plain kwak green with no stickers to keep people guessing ish

Good work Fred =D>

Looking good there fred.
I'd be a bit nervous about that .7 squish myself though. I don't think even MJ runs them that close on his race bike. If memory serves me correctly, anything closer than .76 is risking the piston crowns kissing the head at high revs (even on a race bike that's rebuilt regularly). I may be mistaken of course (wouldn't be the first time ).

i'll look out for you at prestcott hill climb(hope your clutch can stand it it's bloody steep and sharp in places).if mine is up and running i'll bring it along [-o< .not up the hill i'll be running it in.(excuses,excuses)

nice one fred can't wait to hear it running cheers.