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About corksil

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  1. corksil

    Need to find street tires for 95 YZ80

    I decided on 14" tires for now. Already ordered the parts and am in the process of relacing stock front and rear stock yz80 hubs to the same 1.60 x 14" rear rims with new spokes and nipples. All the spokes and nipples that came on the the bike were rusted to shit and both front and rear original rims were cracked. Now I need to figure out which of these two tires will be a better profile once mounted on the 1.60 x 14" wheels I'm building. The tires I'm going to use are the michelin pilot sport SC *cough* scooter *cough* tire. They are available in 120/70 R14 and 160/60 R14.
  2. corksil

    Need to find street tires for 95 YZ80

    Hey, I'm setting up a yz80 for a kid on a kart track. It has a 1.40x17" front rim and a 1.60x14" rear rim on it. It seems that when ppl convert a dirtbike for street/supermoto use -- they typically ditch the 21"/19" original wheels and replace them with 17 inchers. I'm assuming that the large 21" front wheel is more unsprung mass, raises the center of gravity, and it's diameter is excessive for street use because a typical commute does not involve riding over logs, boulders, roots etc. Also assuming that the rear 19" wheel is swapped out in exchange for a smaller wheel to give increased acceleration in addition to the reasons listed above. Smaller rear wheel takes less engine work to get moving and gearing can be adjusted to retain the stock acceleration/speeds etc from the original 19" wheel. Swapping rims also allows the bike builder to use wider tires, which have a larger contact patch and therefore more available traction. Now ----- assuming I'm on the right track, would there be any disadvantage to my swapping the 1.40x17" yz80 front wheel out for a 1.60x14"? I've counted spokes and measured and it seems like I can disassemble the front rim/hub/spokes and lace it back together with a new "rear" spoke kit (14 inch) using a "rear" hoop/wheel/rim that is 14" instead of the oem 17". That way I could run the same 120/70R-14 michelen radial tires in the front and rear. What would be the disadvantage to doing this?
  3. Hello, I found a seized 1995 YZ80 yamaha two-stroke on CL and rebuilt the engine. The bike was sitting for a long time and the front tire has cracks and the rear tire is toasted. Can anyone provide a link to street tires for this bike? Planning on using it as a mini-supermoto on a kart track. Original tire sizes are... 70/100-17 40m front 90/100-14 49m rear Dual-sport tires may be a better option because if this bike is ever ridden in grass or mud -- I don't think street tires would provide ANY traction whatsoever. Please help, and thank you for reading my post.
  4. Alright... Following up. Yesterday I got the engine 90% reassembled and this morning I hope to get it back on the bike and get the machine fired up and rideable. It needs new front fork seals and I'm hoping the eBay Chinese knockoff carb is not going to be a problem. Off to the garage for now.. Hopefully i come back soon with good news.
  5. New crank arrived. New piston. New rod, pressed together into crank. I typed the last post on my phone and thought it got deleted -- now I log in on the computer and it looked like it was posted despite the error message. Wondering if I'm making a mistake by trying to get this bike running with the chinese carb from previous owner. In the next few days I'll get the cases reassembled and get the engine back on the bike. My old seized crank is now a core for a stoker crank. Still researching best rod and stroke before I figure out who can do the work and mail it off. If anyone has a flywheel bolt, let me know. Best price I have found for a replacement is 12 bucks which is rude. It's a nut which weighs a tenth of a gram -- it shouldn't cost that much to replace. I mangled it with a hammer getting the crank out of the engine case, so it needs replacement. Thanks guys, I can post some pics if anyone is interested -- but it's kind of a hassle if no one cares to see the pics. Ultimate plan for the bike is a 112cc bored/stroked set up for oversized rider. Street tires, wider rim in front, big brakes in the front with stiff fork spring and clip-on bars. I've sourced some .65kg front springs, and am pricing out a .65kg rear shock spring. Pure hooliganism.
  6. Following up.. I split the cases and inspected everything with a service manual and caliper/micrometer checking all the tolerances and service limits. The crank definitely needs replacement, along with the con-rod and bottom end bearing. I see on eBay pre-assembled cranks so that will be the solution. The cases seem fine apart from a bit of scoring around the crank but it looks like the gaskets will still seal the two halves together so it's a non-issue. The clutch plates measured at 3.05mm which is within the service limit of 2.70mm so I don't need a clutch yet. The piston was barely past the service limit but it was scored along the side skirts so I'll need a piston. All the gears look alright. Water pump seems fine. Radiator is a bit mangled but it holds pressure so it's fine for now. Main thing left to figure out is whether or not the no-name Chinese carb that was on the bike is going to work or not. Would be nice to replace it with the appropriate mikuni vm26ss OEM carb but I haven't found one for sale yet. Am I forgetting anything? About ready to order parts and I don't want to get stuck waiting again if I forget to order something crucial. Thanks guys!
  7. Thanks for the insight. Sometimes I feel as if I'm figuring all of this out as I go, but I've got a shop manual and I'm good with tools so I will continue proceeding in the best way forward that I can figure out. Tomorrow I hope to check the piston clearance but things are more or less stalled until I get that puller and split the cases to inspect the crankshaft and big-end of the connecting rod.
  8. I don't think this yz80 has a power valve. I'm not sure what a power valve actually is, but the bore of the cylinder has 2 exhaust ports/holes in the sidewall of the bore and five smaller intake ports/holes in the sidewall of the bore. I've located service manuals for the 1994 and 1996 zy80, but haven't found one for the 1995 which I am working on. Both manuals say "CAUTION: Do Not Rebore The Cylinder." This makes me think it is indeed a plated cylinder as you said. All of the service limit specs are identical between the 1994 and 1996 manuals with the exception of "Piston ring side clearance." For the 1994 the spec is 0.030-0.070mm and for the 1996 the spec is 0.030-0.065mm. Doesn't seem like a big deal because the variation between the two numbers is so tiny and I don't have the tools to measure thousandths of a milimeter. UP UNTIL THIS POINT -- Everything is "within spec" according to the manual. The cylinder doesn't appear to be warped or out of round, the piston is at the large end of the acceptable "range" but it is within spec, the wrist pin is within spec, no heat discoloration on any of the parts I have inspected so far, and no gouges or pitting in the cylinder walls. The piston skirt measured to be within range, and the next thing for me to calculate is piston clearance after I triple check everything I have already measured. Once the puller arrives I can split the cases and see what the big end of the connecting rod and the crankshaft look like. It is my understanding that the crankshaft has two halves which are pressed together with the rod and big-end bearings between them. Is this something I could disassemble myself? I obviously need to replace the big-end rod bearing at the very least. I'll also need to replace the rod if the big-end is gouged or scratched or has heat discoloration. Hopefully the crank is salvageable. Thanks and I appreciate any and all help.
  9. Thanks for the advice. I ordered a puller to get the rest of the engine apart. Planning on splitting the cases and inspecting the condition of all transmission gears before ordering any parts. I've got the cylinder off and I've been running a feeler gauge all up and down the inside of the bore feeling for oval-shaped, out-of-round spots or anything that doesn't seem correct and I haven't come to any conclusions yet. The piston slides up and down in the cylinder with not much resistance throughout the entire stroke. The main rod bearing is not completely seized but difficult to turn, and there's all kinds of copper-colored shavings inside the engine case.. probably from a failed main bearing. Once the puller arrives I'll get the rest of it apart and assess any damage to the crankshaft journal. Where are the experienced engine builders around here? If I decide to bore the cylinder slightly to bring it back to a perfect round shape I believe I will need to chamfer the edges of the ports but I don't really know. This is my first two-stroke engine project and I'm learning as I go. Thanks!
  10. Alright, I pulled the VIN/serial number off the frame near the triple clamp and the info I pulled up says the machine is a... 1995 YZ80G1 originally 'white' color. Engine casting marks match the 4ES-00 listing on the this page. I mic'd the piston at 47mm exactly and the bore in the cylinder was 47.85mm if I remember correctly. From my research this means the bike has never been bored before and this is probably an original piston. Pulled the engine out and started taking it apart, now I am stymied. Appears I need some sort of puller to get the stator/flywheel off. Time for more research. From my limited understanding, the biggest I can go with this build is 112cc, with high compression and race gas. I'll check back later. If you folks want pics, I'll start taking them.
  11. Hey guys, I found a used and abused yamaha two stroke mini-bike to rebuild as a cheap form of practical transportation on back roads. It's not running, and feels as if it has compression but the clutch is not working and this thing is beat to all hell. This bike has been abused and molested in every way imaginable. When I was kicking it over, it had spark -- and looks to have some nameless aftermarket carb on it. I don't know if it's been bored out or anything about it really. Anyways, I've started stripping it down and taking it apart and trying to figure out what I'll need to get it running again. Will probably end up stripping it down to a bare frame and then rebuilding from there. First question --- how do I identify the motor/frame/chassis/year? The frame has been "repainted" twice by previous owners but I think I can make out the serial number stamped in the frame near the triple clamp. Please help and if this is posted in the wrong section please move the thread. Thanks and if anyone is interested I can take pictures and document the whole project.