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      Video: 2019 Yamaha YZ250F Features & Benefits 

2bitsamile

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About 2bitsamile

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  1. Will it be sold in USA? Traction c
  2. Rings have a small bevel/chamfered edge to prevent snagging on ports. Rings that are worn past service limit reduce that bevel , thus greatly increasing chance of ring snagging exhaust port and also accelerates cylinder wear. Rings can beyond service limit and still give good compression test result. A forged piston maybe good for 100-150-200 hrs but i doubt rings are in service limit after 50 hrs. I wouldn't let a cast piston go past 50hrs even if dimensionally in spec, as they may fracture. Rings are like $30(?) and 1 hr to replace. You don't even need to take the head off. It's beyond silly to leave rings in too long. Also, at least measure piston to cylinder clearance. Use new circlips and make sure circlip opening is at 6:00 or 12:00, not 3:00 or 9:00.....,,, Alex
  3. duplicate post
  4. w. 12t, chain was binding, i don't recommend
  5. measure bore in spec?
  6. Stator output must increase as rpm increases. It's possible with some poorly designed/defective regulator that voltage could drop with rpm, but the stator coil output will always increase with rpm. Perhaps the electrosport could pwr one of these: http://www.rockymountainatvmc.com/p/43/-/160/1195/-/-/213412/Vision-X-Solstice-LED-Light-Pod-Spot-10-Watt 800 Lumens, 0.75A and 9-60 Volt DC input. Just add a full-wave bridge rectifier, MOSFET series regulator, and small Li-ion battery to hold up the voltage at low rpms. In another post, Ricky Stator said they measured 20W at full rpm from the electrosport stator. Battery should stay charged if engine is at least 50% of time at mid to high rpm. Probably cheaper to skip the stator and just go with adequate size battery, LED lights, and no stator. Just fully charge the battery in your garage after every use. BTW, i'd mount the light on helmet. ....alex
  7. Shrub, I have a Moose brand stator w. "60W" lighting coil for '01 cr250, not yet installed. I recall an old post said it is also electrosport. If so, what is the problem? thanks,alex
  8. No problems with yamabond. Did the mod about 2 yrs and 80 hrs ago. I used the yamabond spec'ed for engine case half sealing (yamabond 4). I did file down a high spot where the case halves mate, as one case was a littler taller than the other (maybe 1/2 of a BCH?). It's been too long to remember powerband before the mod, but at the time i recall thinking low and especially mid definitely had more power. It didn't need as much clutching. I used to swap in the gnarly pipe in for trail riding but after mod the fatty was fine for trails. With mod, it maybe did loose a little top end. Loss was much less noticeable than going from the fatty to the gnarly pipe. Was a good trade-off for me as i hardly ever scream it. I've read reducing squish clearance increases MSV (mean squish velocity) and too high MSV can hurt top end. Machining the head to reduce the squish band's width might gain back the lost top end and still keep the good mid and low. I'm happy the way it is. if you don't like it, you can always go the other way later ....alex
  9. yes, you can measure squish with the 01 head presently installed on the engine and then cut 99 head to desired squish. Bring both heads to machinist and he will measure both heads and calculate the correct cut depth for desired squish on the 99 head and clean up nicks at same time. If you are changing anything else like base gasket, head gasket, or piston, measure the dimensions old vs new and include that in squish calculation. To increase low-mid rpm torque, you want to lower ports, increase compression, and advance timing. On my '01 250, instead of cutting head, i didn't install the base gasket, used Yamabond-2 case sealer instead. Result was 0.033" and .0034" (left and right squish min). I never get knock/ping with 92 octane 10% ethanol, and various pipes (stock, gnarly, fatty), even if gasoline 8 months old. The small squish prevents knock as the end gasses are so close to the head and piston that they can't get hot enough to ignite. There are several posts of others running mid 30s squish. It's ok as long piston not hitting head. I use a dental mirror with a built in LED to periodically look thru the exhaust port to look for contact marks on top of piston at the very edge. When checking squish, besure solder is tight against cylinder since that is where squish is min. Also be sure to squeeze solder on both sides simultaneously, as measurement will be higher if you only squeeze solder one side at a time. you can also get base and head gaskets of varying thickness. Or cut a base gasket your self from high temp vegetable-fiber based gasket material, can get it as thin as 0.007" from your local gasket supply shop. ...alex
  10. i switched to an aftermarket top triple clamp to move the bars fwd. the bars happened to be hard mount. i have a track on my property. it's mostly flat turns and hard packed to soft on top, depending on rain. there is a 360 degree circle that is constant radius, 3rd or 4th gear, depending on traction. for practice, i go round and round fast as i can, flat-track sliding stylee. after the swap to hard bar clamps, it felt like i had more feel and control of the bike. it was easier to control the slide and felt safer to go fast. bike also seemed faster thru the slalom section. steering felt faster and lighter. I guess moving the bars fwd could have also caused the improvement, since both mods were done at same time. front wheel at speed has significant gyroscopic force to overcome. The flex from rubber mounts means bars can be twisted a little before front wheel actually changes direction . imagine what your steering would feel like in the extreme case if rubber mounts were super soft rubber and you were going 70 mph dodging cactus in the desert. hard mounts have a direct connection between bars and front wheel = no slop or mushiness. try this: wedge your front wheel so it can't turn and twist bars to see how much flex rubber mounts add ...alex
  11. went to solid mounts on my 01 cr250. didn't notice extra vibes, using fat bar w/o crossbrace steering felt faster and lighter, won't go back to rubber mounts
  12. .0025 is plenty. i had .002 with my weisco, didn't see any scuffing. Weisco spec is .0015 min. Honda specs a larger min clearance as idiot proofing. BTW, i use feeler gauge method also, seems sufficiently accurate.
  13. I'd definitely remove clutch cover and kick starter gear + shaft 1st. I've seen a 2000 cr250 with kick start gear seized onto it's shaft and it would only let the crank move just a bit, as you describe. The kicker gear is always connected to the clutch basket gear and thus the crank. If kicker gear seizes onto it's shaft, it will lock up the crank. Bike will still roll if in neutral. Kicker gear seizes onto it's shaft when tranny oil gets low, like from a bad crank seal. ,,,,,alex
  14. Stock pipe is pretty good. Fatty definitely adds low and some mid. Fatty might be a tad stronger on top, but it's almost the same. This is all with the stock silencer. The shorty doesn't make a noticeable difference for me. YMMV as i have PWK, Boyeson ProSeries reeds, and 0.032" squish with otherwise stock engine.
  15. Unlike religion, politics, 2t-4t, Engines adhere to physics and metallurgy. The Wiseco guy posted a while ago that heat cycles do nothing for a new piston/rings. I'm pretty sure we can trust his expertise. Peeps are just repeating the same old heat cycle wives tale some self-proclaimed expert made up. I warm up rebuilt engine 3-5 minutes at light throttle, then 10 minutes 50% throttle to fully warm engine, then 75% to 100% throttle for another 20-40 mins to seat rings. Re-torque fasteners after cool down. Warm up is to thermally expand the cylinder to prevent cold siezure or scuffing , especially if piston-cylinder clearance is tight. The piston can heat up much faster and expand more than cylinder if too much throttle on a cold engine