KR-1S.co.uk Forum

HI FELLAS IM DITCHING THE "B" PISTONS IN MY KR1 AND FITTING A PAIR OF MITAKI KR1S PISTONS BUT IM NOT REALLY SURE WHAT SIZE I SHOULD FIT.I`VE MEASURED THE PISTON CROWN FRONT TO BACK ABOVE THE TOP RING AND FRONT TO BACK AT THE PISTON SKIRT.USING THESE MEASUREMENTS WHAT READING SHOULD I USE TO BUY THE SIZES AVAILABLE???
WHEN MITAKI SHOW 4 SIZES AVAILABLE FOR THE KR1S WHERE ON THE PISTON ARE THEY MEASURING TO QUOTE THE SIZES AVAILABLE.
I`LL BE RUNNING THEM IN THE ORIGINAL BORES CANT AFFORD TO RECON TWO CYLINDERS THE CRANK REBUILD IS CLEANING ME OUT--HOPE IT DONT NEED WEB REPLACEMENT--GULP.
CHEERS
COL

WHAT!!!!! 21 VIEWS AND NO REPLIES--SURELY ONE OF THE THOUSANDS OF MEMBERS MUST HAVE FITTED MITAKI PISTONS TO THEIR KR1S BARRELS??
MAYBE I JUST CLOSE MY EYES AND PIC ANY SIZE AND JUST CRAM IT INTO THE BARREL AND WAIT FOR IT TO SEIZE--IS THAT HOW ITS DONE? I DONT THINK SO OR DO YOU ALL PAY SOMEONE ELSE TO DO YOUR ENGINE WORK SO THE QUESTION NEVER ARISES?

CMON ONE OF YOU MUST HAVE THIS INFO FOR ME PLEASE
COL

If you fit the mitaka pistons you must know that the crown of the mitaka is higher and that your squis wil be diverend.

Now my personal opinion DON'T FIT MITAKA'S , I HAVE FITTED THEM IN THE PAST MULITPLE TIMES AND HAD ALOT OF FAILURES DO TO BAD CASTING, CRACKS , ETC

spend a little more and buy wossners

Thanks Jarno boy this rebuild gets more expensive every day good job PJ ENGINEERING found no web damage on the ongoing crank rebuild.
Having trouble finding a Full gasket set for a Kr1 suppliers keep sending me sets for S MODELS WITH GASKETS MISSING AND GASKETS THE WRONG SHAPES.
I’ll get there in the end— 25 years in my garage and not ridden it yet(honest officer!!!)
Thanks again for the reply Jarno.
Col

Hey Jarno would the wossner pistons be a direct slot in as to are they the same crown height as the old Kr1 “B” pistons
Col

do they (woessner) have the ring-pin position under control these days ?

viewtopic.php?t=4648&highlight=one+seen+kind+damage

I know your issue in the past Jan but yes the do

Yes nosher


There a direct replacement with no extra work etc

Hi Jarno I have these piston measurements—can you advise which size Mitaki pistons I should fit?

Left piston front to back above top ring 55.52—————piston skirt front to back 55.92

Right piston front to back above top ring 55.56—————piston skirt front to back 55.91.

Any help much appreciated.

Col

If you want to know what size pistin you must fit in your cilinder you must messure your bore of the cilinder

For example if your bore is 56,00 mm you can fit a piston 55,94 mm
If your bore is 56,01mm you can fit a piston 55,95mm etc

You must have about 6 houndreds of mm play for the expansion of your piston when running the engine

This is for a standard engine , race engines sometimes have diverend clerance do to high octane fuel etc

I hope this is of any use

Cheers jarno,

Hey Jarno great reply thanks —-one more question—do I measure the bore at the top front to back or the skirt area front to back for piston size?

Cheers
Col

The bore is masured inside the cilinder ( you need to have a special tool to do this )
You mesure it above the ports and belowe the ports of your cilinder

Hope this helps you out

Hi Jarno yes I have been using a bore measuring tool and now with your useful input I feel safe that the pistons I order will be the right size and won’t give me an expensive seizup.
Many thanks
Col