Page 2 of 11 FirstFirst 1234 ... LastLast
Results 16 to 30 of 160

Thread: Yamaha NXC125 20,000km

  1. #16
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    They also sell hi-torque starter motors

  2. #17
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    The parts arrived today which isn't bad service. I paid for them with PayPal on the 29 August. They were very nicely packaged in seperate boxes and I must say the bits look the part. The cylinder has a chrome bore and the piston is a very nice looking forged item. It has two base gaskets of different thickness for altering the compression. The crank looks OK and has Japanese NTN bearings and seems to be reasonably well finished. The only piece I'm not 100% on the looks is the conrod which seems pretty short and "looks" cheap and possibly nasty. Markings on the rod would suggest it's from a Chinese clone Check the photos out. Anyway it's full steam ahead stripping down the scooter to fit the bits.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	PIC_1840.JPG 
Views:	64 
Size:	90.5 KB 
ID:	246430   Click image for larger version. 

Name:	PIC_1839.JPG 
Views:	64 
Size:	91.5 KB 
ID:	246429   Click image for larger version. 

Name:	PIC_1837.JPG 
Views:	63 
Size:	88.8 KB 
ID:	246427   Click image for larger version. 

Name:	PIC_1838.JPG 
Views:	62 
Size:	89.1 KB 
ID:	246428  

  3. #18
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    I've got the engine assembly on the bench with the cylinder and head off. I found the cam chain was loose when I was disassembling it and after a bit of investigation found the tensioner wasn't extending under it's own steam. I pulled the spring out and prodded the ram out further with an allen key. It seems OK it just won't extend freely with just the spring tension. The head looks good with the valves being nice colours and even and consistent so I won't be doing anything to the head. The cylinder on the other hand has obvious signs of wear. The bore itself is chrome and has absolutely no signs of being used. The piston though has brown stains below the rings indicating blowby. If I was keeping that cylinder it would need new rings. This would be the cause of the lack of power I've been noticing. With everything disconnected the problem with the bearings is really obvious. When the crank is turned it is really easy to feel that the bearings are a bit stiff and badly brinelled as they are quite rough to turn. Just have to borrow a rotor puller and I should have it all apart tomorrow night and maybe even start on reassembly with the new parts. Once I've run it a bit I'm gonna put it on the dyno to tune up the transmission by playing with the roller weights. It'll be interesting to see what changes to the power at the back wheel it makes at various road speeds.

  4. #19
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    More progress and a lesson learned.
    Pulled the alternator rotor off and the crank got all smooth to turn. As it happens the stator has a lot more poles than I thought and the notchy feel is from the magnets moving over the poles. The crank is primo. All the noise must have been from the cam chain. I'm not totally convinced as the fresh oil that's done less than 100km has shiny flakes in it. The crank bearings all spin smoothly though.
    The new cylinder is 72mm high and the old is 73mm high. The 2 base gaskets are totally different thicknesses. One is more or less stock and the other is 2+mm. I'll be checking and may even make some alloy shims to adjust the height. If the assembled height is less than the original I might need to replace the slightly worn camchain.

  5. #20
    Join Date
    3rd May 2005 - 07:22
    Bike
    2005 Custom Moped
    Location
    where the sun sets
    Posts
    434
    Short conrod like you say.
    Must have a lot of angle on the rod with the bigger stroke

    I run my china scooter with the cover off the variator and clutch so my mate can observe the workings and the timings of clutch springs and variator weights
    He has to lay on the ground to see anything

  6. #21
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    the scooter is back together. I used the thin base gasket so the compression is up there. There is a possibility the piston is just kissing the head now that it is all torqued down, it was pretty close when I measured it earlier. The piston is flat around the perimeter where the bore is larger. I thought about relieving the edge of the combustion chamber and opening it out a bit, but in the end just bolted it together. The starter spins it over OK but you can definitely feel the extra effort needed if kicking it over. With the extra capacity I figured I'd put the original weight rollers back in. Even so it gets off the line way faster than the 125 ever did. At about 30-40kmh it really gets going and is doing 80kmh way quicker than before. Having a larger capacity with the original valves/ports and cam will help the bottom end but whether it is restricted higher up I don't know yet. It isn't a high revver so maybe it'll be fine.
    It's got me thinking about taking it out bigger now.

  7. #22
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    Done a few miles now and starting to use a lot more throttle and revs. It has felt a bit weak over about 90k so time for a bit of a tweak. Changed the oil after riding home and took the opportunity to check the carb. The carb looks like it takes the small round head Keihin jets but actually the jet has a slightly smaller diameter thread. It was a 105 and trying a couple of different drills it was between 1.0mm and 1.1mm so seemed to conform to the drill size jet numbering scheme. I've drilled it out to 1.1 or 110 jet size. Giving it full throttle now results in way more go. It's got a definite bark to it now which is kind of funny considering it's a "125" scooter and has standard air filter and exhaust pipe.

  8. #23
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    Couple of 1000K later and the noises were back. I ordered a new cam chain from Powersports in the USA and gaskets and rings for the original 125cc cylinder. Small change over $50 including freight so bloody good price. I pulled the motor completely apart and as before can find nothing wrong that would account for the noise, though the piston has been kissing the head. I got all the bits today and reassembled the engine with the thicker base gasket supplied with the big bore kit. This should give it about .8mm clearance piston to head. I've reused the head gasket but sprayed it with copper gasket stuff. The crank had a lot of end float and a barely discernable freeplay when dummy assembled. The bearings showed signs of turning in the housing and the housings had marks as well. I've put it together with Loctite 641 locating the bearings in the housings. Suddenly there is no more end float. It's still a bit noisy but heaps better. I've only given it a good thrash round the block so far but it seems to be going good. The noise could be coming from the alternator rotor area but I didn't notice anything when it was apart. I'll have another look once the rotor puller($22) arrives from Haldanes. I've found a listing on Ebay for some taller final gearing and have ordered some 14/38 gears, currently 12/40. The gears in the scooter are completely different ratios to what the Americans seem to have but it all looks to be similar design so hopefully they'll fit. With them fitted it'll be about 10% higher geared which should be good on the motorway. Check out "jiangwayne" for all sorts of goodies for scooters.

  9. #24
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    Ordered on 3/1, payment from account 5/1, on the doorstep 9/1. Service doesn't get much better than that. $81.37 including freight. I'll be fitting them this weekend.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	SAM_0403 (640x480).jpg 
Views:	64 
Size:	257.9 KB 
ID:	254825  

  10. #25
    Join Date
    31st August 2005 - 12:00
    Bike
    2018 GSXS1000
    Location
    Temple View
    Posts
    5,042
    Blog Entries
    1

    Unhappy

    bloody yamahas....high quality..

  11. #26
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    I don't know what the noise is but it isn't getting any worse and doesn't seem to be hurting performance. I gave it a bit of a run this morning and it went to 110Kmh pretty quick. The motor is definitely a bit softer with the lower compression so I will carefully measure the clearance next time and make a solid base gasket the exact right thickness to leave the minimum squish clearance, allowing for rod stretch and stuff. Though, the next time it's apart I can see it getting stretched to 200cc with a new cylinder, and head.

    The cam timing is a bit out as well. Without slotting things it wasn't possible to get it exactly right. It was timed better with the old cam chain but the tensioner was nearly fully extended with the old one. Should really put a DTI on it and really see where things are. Silly really, the last time I degreed cams it was on an 1100 turbo and a Moriwaki 1100 before that. Now I'm thinking of degreeing "a" cam in a 125 scooter. I must be getting REALLY old.

  12. #27
    Join Date
    12th January 2012 - 09:37
    Bike
    Gilera DNA180
    Location
    Christchurch
    Posts
    28
    good posts, like seeing someones progress like this!

  13. #28
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    Got the new gears fitted. Managed to press the gear off the old shaft and onto the new one using a big vice at my mates engineering workshop. There was a good selection of steel pieces with holes in the middle etc so easy as. Only been for one ride and not on the motorway. The NW motorway is all screwed up at the mo' so I'm keeping away. Just tootling along it seems about the same. Open the throttle and it gets going more or less the same. When taking off from an intersection from a dead stop it may be just a little slower but as soon as it's moving at say 15-20K it's all the same. I only had it up to 90Kmh and again it may have been doing a few less revs. I was accelerating so the CVT could/would/should have been pulled back increasing the revs to compensate for the higher gearing. It's good enough to take to work next week and I think it'll be good on the motorway, as long as the motor will pull it and the CVT adjust for it. Coming home on Fri it was full throttle at 90Kmh into a pretty stiff headwind.

  14. #29
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    4,194
    I've been for a ride down the NW m'way to Gt Nth Road and back. On the flat with a little tail wind it pegged the speedo without too much effort. The needle went to about 112Kmh but the scooter went a bit faster. It holds 100K quite nicely and isn't revving so hard and will accelerate to 110K nicely. Coming back it was into the headwind and would only do about 100Kmh full throttle but it held 90Kmh without too much drama. The gears seem to be a good modification. It's quite noticeable that the clutch gets a little bit more of a workout taking off. I never noticed at what speed it disengages when slowing down before but it disconnects at about 25Kmh now which I'm sure is higher than previously. It's only any sort of a problem in stop/start traffic, which isn't a problem because I never stop/start with traffic as I'm on a scooter.
    I have the standard weight 9g rollers in the variator and I'm thinking I'll try some 8.5g rollers I have. I've been giving a bit of thought to how the variator works with engine revs and speed and load. The lighter rollers will mean the motor will rev a bit higher to counteract the ratio change brought about by me asking the motor to make more power which will move the rear pulley against the sheave effectively lowering the gear ratio. The lighter rollers will raise the revs at all speeds except when the variator is at it's highest speed position. Once the scooter speed is obtained where the variator is maxed out and the engine doesn't have the power to work the sheave against the force from the rollers, the rollers don't make any difference and it'll be down to engine revs and gear ratios. I wish there was a way of checking the variator and seeing when it topped out. It would need to be checked loaded and unloaded. I do have access to a dyno but it doesn't have a brake. Still, it might be useful to lock the variator in the high speed position and do some runs to see where the motor is making it's power and then do some runs with everything back to normal.
    To think, I bought a 4-stroke scooter so I wouldn't be tempted to mess with it. Now I'm thinking of trading to a 180cc 2-stroke or something similar. I could really make one of them fly.

  15. #30
    Join Date
    26th April 2008 - 00:01
    Bike
    KTM 950SM, '78 X7, FZ750, GN250
    Location
    Wellington
    Posts
    706
    Good read. Do it! Stupid 4 strokes with those valve things

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •