March 26, 201115 yr Hi Gents, Just pulled the head off my 06 250 and was just about to fit the new Piston (I got from Chris) but noticed there is a cut-out missing on the side skirt compared to the old one... See the old piston on the right here (ignore the gudgeon pin holding them in the same direction for the photo)... The cut-out in the skirt lines up with the front transfer port (carb side) but I'm also concerned it's for con-rod clearance?... If not, why would Sherco cut the skirt out like that? Also the old piston is marked 05-11 / 10583 and the new one is marked 09-12 / 18744 .... both are "A" 72.75 ..if that makes any sense to anyone? I'm trying to get this bike back together today but I know it's very early hours for Chris...hence me putting this question up here. Best of balance. Neo
March 26, 201115 yr Both are "A" pistons so unless you are doing a hone job makes no difference. Stuff it in! Don't use that cutout any longer!
March 26, 201115 yr Typically that would be to delay the port closing to add more rev. Is it on the transfer port or the intake?
March 26, 201115 yr Looking at the exploded diagram it's the intake so it is a modification to add top end power.
March 26, 201115 yr Author Yes it's the port at the bottom of this photo (took some time back)... The effects of this are gonna be interesting Best of balance. Neo
March 26, 201115 yr Author Up and running. All she's done is idled so far, for 5 mins, but I can tell she's changed. She started first kick, without choke and only needed a small amount of choke for about 10 seconds before she'd idle (in the low hundreds RPM) on her own. She's idling perfectly. Only changing in note when the fan clicks in. The exhaust gasses smell differenced too ... much cleaner and no big pops so far. I'll use the throttle two or three times (letting her cool each time) tomorrow then let her carry over some flat grass later in the day. Do I sound like I'm in love? .... Well I can't wait to give her a good thrashing later this week!!! Thanks for your help guys Best of balance. Neo
March 26, 201115 yr Author new coated pistons are quieter! Hey Cope, Can you explain to me why this is? Best of balance. Neo
March 26, 201115 yr Yeah classic port configuration. Basically you shouldn't feel much or any difference at low RPM. At high RPM the column of mixture in the intake tract never goes to zero velocity so the reeds never close and closing the intake tract with the piston restricts the flow. That's why they use intake extenders, to add a longer column of air to act as a forced induction system. If I remember correctly back in the 70's this was Suzuki's big deal at the time on the RM's with a case/reed induction system where the intake fed the crankcase directly through a reed valve with no other valving. At the time most engines used no reeds and had a piston port intake. So yeah it'll run out of revs sooner then the cutout piston. Not important and probably safer if you're not an expert. Edited March 26, 201115 yr by Dan Williams
March 27, 201115 yr Hey Cope, Can you explain to me why this is? Best of balance. Neo Coating just acts as a damper. Eventually it will wear through.
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