05,650 piston diameter measurement

helithumper · Nov 20, 2013

Hey, Guys,

Winter has come and it's time for me to rebuild my engine. I'm trying to figure out what size piston I would need to order. Does Anybody know the actual diameter of a 650cc -I piston ( the smaller piston) eg. 99.95mm.

My liner is a little warped and I'm trying to see if a -I piston would fit and have the appropriate clearance or if I have to order a new liner as well.

Any help would be appreciated.

bushmechanic · Nov 27, 2013

hello pretty sure the sizes are listed in the workshop manual you can download it from the official berg site

regarding the liner, it is a problem often that the cases warp and force it out of round in a direction you would not associate with the piston forces

if that is the case I put it back in the cases put the cases in a press and straighten them back up, if it is still warped you could make up an ally jig to support the liner and also correct the warpage in a press

helithumper · Nov 28, 2013

Thanks for the reply bushie and welcome back :cheers:

I have the workshop manual and it does'nt mention the actual piston size, just cylinder size and the wear limit on the piston. I was just wondering if the pistons are actually 99.95mm new or are they maybe 99.93mm-99.94mm new.

as for trying to straighten the cylinder. Mine is tight on the piston skirt side of the piston, so maybe I'll try to put in in a press. How much pressure do you apply

Regards Dave

Taffy · Nov 28, 2013

I've had some success getting these round again. I got the first three right and then broke the next two. they were IMHO useless otherwise so it was a shot to nothing. my liner man chucks them off they are more than 0.1mm (.004") out of round.

I use the vice and press in the same direction that they are too small. seems weird but true.

they then go round. I simply wind on a little with the vice and then back a little.

be gentle!

Taffy

bushmechanic · Nov 28, 2013

Hi Dave

i use about 1-2 ton with the liner in the cases at a guess, its quite a lot but when supported there is no problem.. well so far

what i did was use an internal mic to measure how much deflection i put on the liner.. (approx 5mm at first but 10 is needed sometimes)

took it all apart and measured the out of round, if it needed more then I knew how much to deflect it next time

if you got a holesaw or treppaning tool and cut a hole in a series of 20mm structutal plywood blocks or even better some alloy plate about 120mm square you could pin or glue them and use those to put the liner in while squashing it... less chance of breakage that way.

IMHO though there really isn't much point measuring the liner if it isn't in the cases, to be more accurate they would have to be at operating temp

bushmechanic · Nov 29, 2013

helithumper said:
Thanks for the reply bushie and welcome back :cheers:

I have the workshop manual and it does'nt mention the actual piston size, just cylinder size and the wear limit on the piston. I was just wondering if the pistons are actually 99.95mm new or are they maybe 99.93mm-99.94mm new.

as for trying to straighten the cylinder. Mine is tight on the piston skirt side of the piston, so maybe I'll try to put in in a press. How much pressure do you apply

Regards Dave

ah its stamped on the pistons

my elko OEM "I" piston says 99.95 measured 99.93 at 200hrs

FWIW I have some data on a wosner piston tis a little bigger

KTM 560 piston wossner 8583- D

"A" size 99.96, 20mm pin

14.5mm deck height flat top 300gm piston weight

pin 60 gm

piston volume zero CR 13.74 :1 approx with the 80mm stroke crank.

05,650 piston diameter measurement

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