Topic: Where's my 5th gear? SOLVED!!!

[flybox1]

OK...Thanks guys.
2nd round of mating surface cleaning tonight. 
Back together tomorrow night when I have an extra set of shop-hands.
I'll remember to get 5th referenced on the outer plate of the birdcage, too.

[70CB750]

Did  you find your 5th already?

[flybox1]

...well i sure hope so.  Cases apart, it shifts great.
Got the engine in the frame last night. 
I'll have a good chunk of the weekend to get the bike ridable.

[flybox1]

Yes.  I'm into the cases again.   Rode the rest of the summer with out 5th gear.  Pulled everything this weekend and , even though I've referenced hondamans book, I want to get your input.

I can shift thru the gears fine when on the bench and on the center stand.   I can get the bike running 5th gear when on the center stand....but under load, 5th is not there.

Please verify this clip and thrust washer are facing the proper direction.
Starting from the ground floor.
Thx.

[scottly]

Since we're starting from the ground floor, did the trans work properly before the rebuild?

[mystic_1]

Looks correct to me.

Is your C1 gear oriented properly?  It has a taller flange on one side than the other.  The taller flange should face away from the other gears, towards the end of the shaft.

[scottly]

Hey mystic, got any pics with a straight edge across the flanges?

[mystic_1]

Sorry, no I do not.

mystic_1

[flybox1]

Since we're starting from the ground floor, did the trans work properly before the rebuild?

No.  This motor came to me in completely disassembled.   A PO project started and shelved....
I see no visible signs of damage or abuse anywhere.

[flybox1]

I should add that the trans was not disassembled.   It came to me still in the lower case.  I did however remove it from the case  to clean it.  I did not pull it apart.
Other than this clip and thrust washer, I'm pretty sure the countershaft is correct.

[mystic_1]

Not sure if you already have this diagram but I thought it might be useful.

[flybox1]

Ohh.  That's great.I should print that out on the plotter at work tomorrow 

[mystic_1]

For reference that diagram is from the Clymer CB750 workshop manual printed in 1972.

mystic_1

[scottly]

Maybe the PO did some work on the trans, and set it back into the case???

[flybox1]

It's the main reason I decided to take it all out, separate it...and reassemble per HM's book.   
Just hoping to stumble.across something.....

[Don R]

If I was closer I'd bring one over and we could take it apart for reference. I have  a low mile rotating assy in a complete F2 crankcase and a seperate freshly backcut trans.  Good luck.

[mystic_1]

Since you can get it into 5th on the workbench, I'm guessing there isn't a gross assembly problem going on.  Possibly a bent or worn center shift fork?

mystic_1

[flybox1]

Check back a page or three.   I posted a video of me going thru the gears before the last reassembly.
Shift forks are straight.   Ends.within limits listed in hondamans book.

[flybox1]

[mystic_1]

Ah yes, my bad.  I've read back a bit and watched your vids.  You're right those shift forks look fine. 

The only other thing that jumps out at me is that your gears have way more play on the shafts than I think I'd feel comfortable with.

I have a spare tranny stashed away somewhere.  I could try to dig it out and take some measurements but it wouldnt be for another week or two at least, someone else may be able to get it done sooner for you.

mystic_1

[flybox1]

I'd appreciate the measurements.
The play, I'm assuming, is from the lack of those small.half circle needle.bearings keeping everything stable.  Please correct me.of I'm wrong.or if you need vid or images of something else....

[mystic_1]

I was more alarmed by how much your M4 shaft wobbles on the mainshaft in one of your vids, that seems looser than I remember it should be.

The weird thing here to me is that you report no noises when trying to engage 5th gear.  I'd expect some clatter or a grinding noise if M2 and M5 were trying to engage.

mystic_1

[HondaMan]

OK, I finally got to watch your video! Got a new computer. works much better...
The side-to-side and wobble on the far right 5th gear is at least twice as much as on  any F2 or K7/8 gearbox I have on hand now. They are all in the .5mm range, even in the K4 box I have.

Here's what I am wondering: if this engine case was cut a bit too far away on the bearing side of the 5th gear, it lets the gear slide away from the moving 4th when shifted. This is where I have seen Honda shim the far side of the 5th gear back toward the clutch side with thin(ner) shims. If they got lost once when the mainshaft was out, that may be part of the explanation? (I don't know the history of the tranny?)
Evidence of this is: that one chipped tooth, which shows approximately 1.5mm engagement before the clutch locked up, then chipped off the tooth when the clutch locked back up. If the 5th gear wobble on the inner bushing is sufficient to let it tilt non-parallel to the others (i.e., no longer at right angles to the shaft), then only 1 or 2 teeth get loaded.

Here's the original source of this issue in these later engines: when light oils got used, the cast-iron bushings (like the one inside this 5th gear) take a beating. After their Parkerizing wears off, they can have twice the nominal clearance inside, letting them tilt quite a lot. The "wobble" I see in your video surre points toward this being the issue here.

Most of the engines before the K4 had bronze bushings inside of most of the gears. I won't say "all" because I have seen mixed-metal trannies on occasion on apparently virgin engines, and I have seen bronze in F3 engines after seeing 100% cast-iron inside the F2 (which is one of the ones I now have). So, it's hard to know which way they were building them?

So...what to try next: I don't think I have any "junk" trannies, as most of mine are destined for engines I am building. I have a bottom end out in the shed, though, that might supply some parts? I think it is a K6 or might be a K7. I'm wondering about subbing in a different bushing on that 5th, to see if it tightens things up?

[flybox1]

@Mark,
My shim between M5 and the end bearing is .039".  I sourced another shim, and it too was .039"
When put together under the bearing, I ultimately could not get the mainshaft to sit properly in the lower case.
This pushed my end bearing just past the point where its ring could set in its groove.
 I'd need to find a shim approx . 01"- .020" (guessing) to be able to 'double up' and have it fit properly to take up some of the play.

New bushings for M5 are coming up as NLA  (23485-392-000)  There are quite a few F2/3 trannies on feebay.

@Mystic_1  ---   I have no chipped teeth on M2, and a full 5/6mm engagement into M5 for 5th gear.
Yes, and no chatter when trying to engage when on the road.  Crazy isnt it?! 

[flybox1]

If I was closer I'd bring one over and we could take it apart for reference. I have  a low mile rotating assy in a complete F2 crankcase and a seperate freshly backcut trans.  Good luck.

Don, that would be ideal    brandEn even mentioned to me the back-cut trans from cyclex, but because this bike doesnt slip out of gear even when I get after it, i cant justify the $200 cost to the bosslady.

I might however, play around with this if i dont come across anything in the next few days.  http://www.ebay.com/itm/371256866775

Anyone see any issues with this trans from the pictures?  It looks as clean as the one I currently have 
...and or it has a bronze M5 bushing that I can use instead of my current cast-iron bushing.