Author Topic: Gearshift Drum Question (Read 728 times)

bigring · « **on:** May 20, 2014, 04:25:02 PM »

Hi,
thanks in advance for reading.....just about to button up my crank cases - my first bike, my first build, my first engine tear down and rebuild. I REALLY do not want to have to open it all back up after all the hard work I've put into it. I did a "dry run" and put the bottom crank case on to the top, made sure to get centre gearshift fork between the 2nd and 3rd gears on the main shaft. Once together I tried to turn the gearshift drum to see if I could get it to turn/shift - it moved maybe an 1/16th of a turn. Is something wrong with the shifting or does it all have to be buttoned up completely, with the shift mechanism installed before it will shift properly?

Cheers

fendersrule · « **Reply #1 on:** May 20, 2014, 04:46:26 PM »

You should always test the shifting by using the gear shift spindle rather than the screw on the drum for the best test. For 450s, it just involves putting on the bottom case and fastening a few bolts..

MCRider · « **Reply #2 on:** May 20, 2014, 05:56:15 PM »

750?
At best it feels clunky, as the gears are not turning to help you find the next combination. You might be able to do something, but I'd say it needs to be pert near buttoned up and as said use the shift shaft with the pedal on it. You'll need to be able to turn the drive sprocket to get thrugh all the gears. You gotta have all your sealer spread and ready, cause if you do get it right you don't want to take it apart again to put the sealer on. What's the point? PRactice I suppose.

bigring · « **Reply #3 on:** May 21, 2014, 05:42:18 AM »

I tried what you recommended Fender - assembled the gear shift mechanism - still didn't seem to want to go. Like MC said, maybe it needs to be all buttoned up first. I'm 100% positive I have the forks, drum, gears all positioned properly.

MCRider · « **Reply #4 on:** May 21, 2014, 06:33:31 AM »

Quote from: bigring on May 21, 2014, 05:42:18 AM

I tried what you recommended Fender - assembled the gear shift mechanism - still didn't seem to want to go. Like MC said, maybe it needs to be all buttoned up first. I'm 100% positive I have the forks, drum, gears all positioned properly.

You can shift it without the trans cover on it. Just support the shift shaft appropriately with your hand.

bigring · « **Reply #5 on:** May 21, 2014, 06:48:42 AM »

I might need two sets of hands

Tried it last night and it kept slipping. I have a buddy coming over tonight to assist - hopefully it goes well.

bigring · « **Reply #6 on:** May 22, 2014, 07:52:39 PM »

Got it all together, minus the cover . . . shifts ok, but it can't get into 5th. The gearshift (specifically the arm that fits onto the rollers at the end of the drum) doesn't want to slip in all the way or grab a hold of the pins while pushing or pulling out/into gear. Not sure if the spring on the shift arm is too weak - it appears ok. Maybe photos or video will better explain.

dave500 · « **Reply #7 on:** May 22, 2014, 09:31:16 PM »

youll have to spin the shafts back and forth as if the engine was running,itll end up not shifting as the dog wont find its slot.

fendersrule · « **Reply #8 on:** May 22, 2014, 09:48:12 PM »

Springs rarely go bad for these transmissions (so I hear).

"star wheels" or the "drum center piece" is one part that loves to wear itself down and groove itself.

Detent rollers are another that loves to grow slop around the rivet that creates weak shifting and slipping.

Burs along the labyrinth of the drum or bent pins can keep it from going fully into gear as well.

That is, if it's like a CB450 transmission, which is like almost every other one. Transmissions shouldn't be all that different from another.

bigring · « **Reply #9 on:** May 23, 2014, 06:47:05 AM »

Thanks Dave and Fender . . . that's what I thought. Going to have another try at it - will post results.

lucky · « **Reply #10 on:** May 23, 2014, 07:33:26 AM »

The most important fact has not been mentioned.
Did you have the clutch installed?

Just follow the workshop manual.

When the cases are together and everything is installed including the gears and shifting drum and shift mechanism, you should be able to turn the engine over by turning it by hand. If not you will need to take it all back apart.
The engine cases should have a coating of Gaskacinch (original sealer) or the copy cat Honda Bond or Yama Bond on each case half. After the sealer is dry then put the two case halves together.

If you pull it apart, then you have to remove all of the old sealer and start over.

Also you should be able to turn the engine over with the countershaft sprocket (front sprocket as the newbies call it), and shift through all of the gears up and back down then to neutral.

MCRider · « **Reply #11 on:** May 23, 2014, 08:06:13 AM »

Lucky: Points of order: It's Gasgacinch, not Gaskacinch. (and how do you know that's the original sealer? Seems odd Honda would do that)

CB750s do not have a countershaft sprocket. It has a third shaft, the final drive, and the sprocket is mounted on that. Not on the countershaft.

Awful hard to turn the engine with the final drive sprocket. You can turn the transmission though.

bigring · « **Reply #12 on:** May 23, 2014, 08:43:52 AM »

Thanks guys . . . cases are not together yet, just dry run at this point until I figure out this shifting issue. Good point about the clutch, however, I've been able to shift into every gear now. I've included photos of the issues I'm having:

shift mechanism installed

in neutral

roller mechanism stays put while in neutral

when a shift occurs it slips out

gear shift tooth doesn't catch on pins on drum and the stopper/spring combo don't want to push it into the drum like it should

I followed this video: [url=https://www.youtube.com/watch?v=qJd6NvhbCNA]https://www.youtube.com/watch?v=qJd6NvhbCNA to put the mechanism together

MCRider · « **Reply #13 on:** May 23, 2014, 09:03:19 AM »

Can't tell so far, but I must say. You have to have the neutral light switch installed before you go shifting it. The NLS acts as a guide to the drum and keeps it from drifting in and out. If its not there the drum will drift in and out and impede the shifting.

bigring · « **Reply #14 on:** May 23, 2014, 09:15:05 AM »

I didn't have it installed, and am wondering if it would have affected the shifting mechanism? I held the drum in place and was able to get into every gear....the issue is the shifty bits not meshing & working properly.

bigring · « **Reply #15 on:** May 23, 2014, 09:16:44 AM »

and sorry about the small photos - if you can click on them you can see the set that I took

MCRider · « **Reply #16 on:** May 23, 2014, 09:21:04 AM »

Quote from: bigring on May 23, 2014, 09:16:44 AM

and sorry about the small photos - if you can click on them you can see the set that I took

It needs to be in there before you can decide. I don't think you can hold the drum as firmly as the NLS does. And dry shifting a bang-box by hand is never going to be easy.

I knew to click on the pics. I didn't know if you just had the NLS out for ilustration, or if it was really out while you were shifting.

bigring · « **Reply #17 on:** May 23, 2014, 10:27:13 AM »

It worked!!

Who would have thunk it?!? Thanks MC - your suggestions very much appreciated!

MCRider · « **Reply #18 on:** May 23, 2014, 10:32:08 AM »

Quote from: bigring on May 23, 2014, 10:27:13 AM

It worked!!

Who would have thunk it?!? Thanks MC - your suggestions very much appreciated!

YW

Carry on.

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Author Topic: Gearshift Drum Question (Read 728 times)

fendersrule

fendersrule