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Does anyone know how much slop is safe to have in these gearboxes? I checked the clutch basket and clutch components and everything looks perfect. There is not even a single spot worn in the basket and steel plates and clutch linings are good and fit very well without slop. The problem was there when I got it, it runs, and shifts perfect, but it has a Super Lot of backlash in the output shaft.
The original chain was worn when I got it at 5,500 miles so I replaced the chain, rubber cush drive, and installed 17/42 sprockets. It helped the cruising at 55 but the awful slack/play/backlash or whatever yall want to call it is still there. Every gear is the same. It's not in the chain, or the chain adjustment. The front sprocket fits the shaft like a glove but in any gear I can turn the shaft with two fingers without any resistance over a quarter turn each way before it stops. On the stand with chain removed the shaft will turn over a quarter turn each direction before it hits the end of the slack. It doesn't matter which gear it is in, the slack is there.
Does anyone know how much slop is tolerable before facing a failure on the road? It has so much slop somewhere inside the engine case that it actually breaks traction temporarily in 1'st or 2'nd if I'm turning in to my uphill drive and have to release the throttle to avoid a bump and give it slight throttle again. That's how much slack is in there somewhere.. it'll absolutely slug that rear when the throttle has to be released to slow then even with the slightest twist of the throttle it'll slam again off the backlash. But none of this is from the chain or rear cush drive.. all that is brand new. It is somewhere in the engine/transmission case itself.
*Edit. I should also say that that when parked in gear, any gear, I can roll it back and forth freely a couple feet each way before the it reaches the end of the slack each way. The front sprocket and shaft are moving the whole time until it reaches the end of the slack inside the case each direction.
I've only ridden it about 300 miles since I got it because I'm worried this may not be right and it may fail. My other bikes in the past did not have this feeling, but I've never had a Yamaha 250 so I don't know if it's normal, semi normal, or just isn't right.
Without knowing that motor directly, first check that the front sprocket nut and spline drive is ok. After that, I would remove the clutch cover and put it in gear and attempt to replicate the problem by moving the rear wheel or moving the bike. Watch for something slipping, my guess is that it is not inside the gearbox but is on the primary drive side.
'81 XV750, clip ons, 18" rear wheel, lowered 920 forks with twin discs and 1.5" spring spacers, 1100 brake master cylinder with CNC billet cap, -3 braided brake lines, lowered instruments and headlight, CNC billet mirror mounts, small billet turn signals with running lights, Koso tach/ speedo, stainless 2 into 1 stepped headers with reverse cone muffler, starter heat shield, 4 guage starter cables, rear exhaust heat shield, 4" round open air filter with billet CNC mount, TM38 flat slide Mikuni carbs, XV700 ported heads, BT-C05 cams, colder BP8ES NGK plugs, stiffened swingarm, polished engine side covers, polished rear peg mounts with carbon cover panels, single horn relocated, Sparto tail light with 3D printed lens, BSA tank kneepads, one off carbon fiber cafe seat with brown cover, fork gaiters, KDX200 rear shock, single tach/speedo with carbon fiber dash, red LED under tank and seat lights, black pearl paint with silver accents.
That's weird. I have owned a new XV250 Star and a used 89 Route 66...Neither has any of the slack that you described (meaning I can't roll it a foot or so either way while in gear). Don't sound good. You might want to ride or trailer it by a Yamaha dealership and "pick their brain". It doesn't mean they have to do the work to fix it. Keep us in the loop with what you find and good luck.
Last edited by Tom Boyte on Fri Apr 21, 2017 9:31 am, edited 1 time in total.
There will always be quite a bit of "slack" or "backlash" when turning the output shaft on these bikes as the dogs and dog engagement slots in the gears have quite a bit of clearance in them. All my 250 boxes seemingly have a lot compared to other bikes. Not the nicest or smoothest setup.
Engine Specs:___________________________________Bike Specs:
HE 285cc_______________________________________FZR250 twin disc front end
52.4mm ceramic/teflon coated flat top pistons_________GSX600F handle bars
Wiseco TTR125 intake/exhaust valves_______________Relocated rear shocks
TTR125 valve springs_____________________________17/40 sprocket
Ported heads, 3 angle seat cuts_____________________XV700 Tacho
SRV250 cams on custom needle roller bearings________Metzler Lazertech tires
Twin Mikuni BDS26 carbs__________________________Custom 2-1 exhaust
Lightened rotor__________________________________Harley sportster muffler
XT250 clutch pack
Ah the dog ears. Makes sense. I work on vehicles but never cracked a bike case in half before. I was dreading the thought of going deeper in to investigate. Other than the slack it seems to be a really good dependable bike. I'm second owner, I got it from a lady who bought it to learn on then it sat in her garage quite a while after she bought a harley. She only put 5,500 miles on the little 250 but it was used on open road and interstate with factory 16/45 sprockets. So I was worried something may've been over spun when she told me she forced it to do 77 on I-40 to keep moving with traffic. I removed those sprockets right away and changed them to 17/42 before taking it out on the hwy. I still won't take it out on an interstate myself even with these sprockets because it still revs pretty hard above 60. I'm used to a 84 Shadow with overdrive so I baby this thing
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