Topic: Won't shift out of second up or down

[Greenducky55]

My cb750 k1 engine has been fine up until now I have about 500 miles on her since I rebuild the crank and did the 836 kit. I have rearsets and have checked the linkage adjustment. Bike clicks into first fine goes into 2nd fine but once I'm in 2nd I can't get it into 3rd unless I get it at just the right rpm but sometimes it won't even do that. Goes into 4th great and 5th great. Shifting down goes into 2nd fine but will not go into first even if I where to push it hard. Once I do get it into 1st it goes into neutral fine. And dose not matter if engine is running or clutch in or out. Maybe a shift fork? Not too sure haven't split cases or anything yet. When I do I believe I can do so without pulling the pistons correct? Thanks for any help.

[HondaMan]

You may have the "worn dogs" issue on the C2-C5 gearset. Also, the pre-K4 engines had a shift drum that tended to wear on the nub that pushes the fork back & forth between 1-2 gears, which then makes it real stiff. When this happens, sometimes the screw on the end of the shift drum comes loose from the effort, which can lead to bigger troubles like a bent fork, later.

If you rebuilt the engine, a few questions:
1. Did you also install new O-rings at: the countershaft bearing oil feed to the tranny, the 3 that seal the oil pump to the bottom of the engine, and the 2 that seal the oil hose to the side of the engine? These all need replacement by now, and will 'suck air' or leak pressure if they are old and shrunk. If you split the cases, also replace the 18x3 O-rings at the front oil journal and the Neutral Switch.

2. What kind of oil are you using? If you use the [in]famous "V-Twin Motorcycle Oils" out there, they will almost lock your gearbox like it has sand in it. They have WAY too much detergent in them for these bikes: use a low-detergent, 20w50 or 15w50 oil only in the Big Four.

[scottly]

I have rearsets and have checked the linkage adjustment.

Since you brought it up, how about showing a pic or two of your linkage, from the side?

[Greenducky55]

I replaced the oil pump o rings and the one between the case. I did not replace the neutral switch or for the oil feed due to stripped screws and having no luck at the time trying to pull them. I use castrol actevo same as I use in all my dirtbikes it's not the v twin stuff. Ill check to see if that screw has backed out tonight and try to replace those o rings and go from there. Thanks for your help.

[gregripko]

Check oil level... Too much oil causes my shifting to stiffen up

[lucky]

I agree with Scottly.
Take all that rear set linkage off and see if it shifts right.
Make sure the linkage is not limiting the travel.

[70CB750]

You may have the "worn dogs" issue on the C2-C5 gearset. Also, the pre-K4 engines had a shift drum that tended to wear on the nub that pushes the fork back & forth between 1-2 gears, which then makes it real stiff. When this happens, sometimes the screw on the end of the shift drum comes loose from the effort, which can lead to bigger troubles like a bent fork, later.

C2-C5 on the schema is # 13?

[Greenducky55]

Main reason I doubt it is the linkage is I have been riding the bike for quite a few miles with no issues. And all other years shift easy it literally ends up locked in no tight oil level is good.

[scottly]

You may have the "worn dogs" issue on the C2-C5 gearset.

Worn dogs cause jumping out of gear under load issues, not engagement issues, at least in my experience.
Ducky, I've seen some improperly set up rear-set linkages before, on both brakes and shifters. A picture is worth a thousand words...

[phil71]

you don't say if you can go smoothly thru the gears with no load. Put the bike on the center stand. Gently rock the back wheel while operating the shift linkage. If you get all gears easily, you may have a clutch problem.

[HondaMan]

You may have the "worn dogs" issue on the C2-C5 gearset. Also, the pre-K4 engines had a shift drum that tended to wear on the nub that pushes the fork back & forth between 1-2 gears, which then makes it real stiff. When this happens, sometimes the screw on the end of the shift drum comes loose from the effort, which can lead to bigger troubles like a bent fork, later.

C2-C5 on the schema is # 13?

Yes, #13 and the companion, #7. The worn dogs will make the holes in #7 slanted on their inside edges, too. When this is bad enough, the 2-N-1 downshift also becomes very stiff, often from a bent L shift fork or damaged L groove on the shift drum, because the dogs are dragging across the face of #7's web. That's where the stiffness comes from.

[Greenducky55]

I'm guessing its pretty safe to say that if my cogs or drum are worn the ones from my f2 motor won't work

[Greenducky55]

I think I have found the problem. The screw did come loose causing the inner plate to bend and the shift mechanism to fall of of te disc as well. Luckly I got some extras.

[Greenducky55]

Replaced the thin disk cleaned the threads put a little locktite in her and put her all back togeather works great! Thanks hondaman for he help and everyone else

[HondaMan]

Good job!
Enjoy the season.