Topic: 2nd gear issue

[ekpent]

 Congrats for tearing into it. If your looking to sell it will be worth more in top notch ready to ride condition.  Good Luck on it !

[Don R]

 When the case doesn't want to separate, remember that there's always one more bolt. Take a few good pics of the shift mechanism and read up on where sealer goes and where it doesn't.

[HondaMan]

I had this on my K0.  It started slow and got worse.  The second gear just would not stay in. all other gears and the clutch were ok.  I ended up riding it longer than I should - while building my K3F - going from 1 directly to 3 and up.  I believe the dogs were worn out.   The K0 is still boxed up, waiting to be rebuild, but I will be replacing gears with later ones.

You can also send them to FastByGast in Buffalo. Paul does an excellent job of fixing them up, I have had several done by him. You send the countershaft with the C2 and C5 gears and he squares off the dogs and slots, in perfect 120 degree fixturing.

Thanks for that info Hondoman.
Does he have a web page? 
I hope it's not the place in Grand Island, NY I found on google because a customer reported he's had his gears for 11 weeks and has been told it could be 6 more weeks.

Yep, that is where he is located. I've had nothing but good luck and stellar results with Paul.

[PeWe]

Good progress!
A complete good transmission does not cost much on eBay if needed.
Reason for the slippage and the result like fork and gears. (Worn dogs and mating surface it docks into.)

[750IV]

Good progress!
A complete good transmission does not cost much on eBay if needed.
Reason for the slippage and the result like fork and gears. (Worn dogs and mating surface it docks into.)

Yeah I've seen many ebay pages of trans parts but I'm hesitant because how do you know for sure you're getting anything better than what you already have? Pics and sometimes sellers don't always tell the actual condition.
Also I wonder why are there so many gears for sale on ebay?

[ekpent]

I'm sure a lot of the really hardcore 750 guys on here have a least an old engine or two hiding around their shops somewhere. Lots of them out there still getting parted out for a few dollars. So not rare by any means but is a gamble as to what you may buy off the internet without doing a hands on inspection or knowing the engine/parts history.

[PeWe]

I have bought 3 transmissions in good condition on eBay. Good photos show the status. Bad blurry photos no thanks.

My K6 got a low mile 1974 trans bought by a forum member, sent to a shop in NY for undercutting  back to him and shipped to me with other go faster engine parts.

I found a really good complete crank in Canada, photos showed good amber oily surfaces looking as really low milage without any scuff marks.
So I bought the rest from same engine still available, complete trans and kick shaft with gear.

My K2 has a K6 trans found in Germany, most likely imported from USA in containers of bike parts from scrap yards.

The forks with shaft, gear selector often to buy separate.

CycleX sell trans they have undercutted. But no meaning on a bike soon to be sold.

[750IV]

I have bought 3 transmissions in good condition on eBay. Good photos show the status. Bad blurry photos no thanks.

My K6 got a low mile 1974 trans bought by a forum member, sent to a shop in NY for undercutting  back to him and shipped to me with other go faster engine parts.

I found a really good complete crank in Canada, photos showed good amber oily surfaces looking as really low milage without any scuff marks.
So I bought the rest from same engine still available, complete trans and kick shaft with gear.

My K2 has a K6 trans found in Germany, most likely imported from USA in containers of bike parts from scrap yards.

The forks with shaft, gear selector often to buy separate.

CycleX sell trans they have undercutted. But no meaning on a bike soon to be sold.

Yes, the key words "Soon to be sold".
Although I want it to be right and shift as it should for the next owner. I split the cases today and here's what I found:
Pins on 5th gear look decent but slightly oval shaped at the ends.
Slots in 2nd gear don't look bad but slight marks between the slots from the ends of the pins rubbing.
Left fork doesn't appear bent and ends mic out to about .055" to .060". It does have a bad worn area where it's been rubbing on 5th gear. Does that mean it's bent?
As hard as this bangs in and out of 2nd I was expecting to find broken stuff but didn't. Every thing internal looks good, gears, bearings, etc. as you would expect a 16k mile trans to look like.
So does my description and the pics show that I need 5th gear and maybe 2nd and the left fork?

[750IV]

More pics

[750IV]

I just noticed something else. This thin whatever it is at the outer end of the fork drum is bent.

[bryanj]

Those dogs are badly rounded on one edge and combined with the slight taper on the holes would case jumping, the slector must be out of true to have that wear mark and to the best of my knowledge that bent plate would not cause your problem.
2 new(different) gears 1 selector, new circlips where removed and you ought to be good

[750IV]

I also found this. On the spindle that moves the forks the high point on the slot that moves the left fork has worn to where it's about 1/32" wider than the slots for the center and right fork. I think this prevents the 2/5 gears from total engagement but only by 1/32".

[bryanj]

Before you condem the selector drum compare it to another, its been so long since i did one i cant remember if the slots vary

[750IV]

Before you condem the selector drum compare it to another, its been so long since i did one i cant remember if the slots vary

The camera doesn't show it but there is actually wear on the high spot. It mic's out at .270" where the other two are both .300". Maybe that's not a big deal but on a dry run 5th gear lacks that much from fully engaging 2nd gear.

[bryanj]

Thats 3/4 of a mm so a vast amount in Honda tolerances, i know there was a modified drum early on but from memory that was just wider on the peak not taller, thats why i said compare to another one

[750IV]

I don't have one to compare it to.
The other two forks move only a few thou when on the high spot but the left fork moves .030".
There are plenty of gears, drums and forks on ebay but I hesitate because how do I know they're any better than what I have.
For as little as they sell for I doubt that any seller is going to mic slots (or even have the capability), show detailed close up pics, etc.

[ekpent]

 I have had at least 30 or more 1976 or earlier 750's over the years and only had one with a second gear issue and I knew it when I bought it.So my point being that it is a problem that can occur but I would not call it common problem affecting a huge number of bikes. Ask a seller questions and ask for better pics before you pull the trigger.
  Hopefully you find some good or new parts and can call your operation a one and done.

[750IV]

I have had at least 30 or more 1976 or earlier 750's over the years and only had one with a second gear issue and I knew it when I bought it.So my point being that it is a problem that can occur but I would not call it common problem affecting a huge number of bikes. Ask a seller questions and ask for better pics before you pull the trigger.
  Hopefully you find some good or new parts and can call your operation a one and done.

Thanks, that makes sense.
I just assumed from all the talk and knowledge of the issue that it was a common problem.

[PeWe]

I heard that 2nd and 4:th gear was a weak point and could jump. But I heard that 1979 from guys used to older CB750 like 1971-72.
4th more when accelerating, foot could touch the gear lever just enough to push gear into the false neutral beside. 
This is difficult to do with undercutted gear.

Maybe a slip on the road, bike dropped to left, gear lever hits the road, bending the fork?

My K6 did not get worn gears during 100.000km. I really ridden it hard but careful when gearing. Let gear take its time to dock, wot right after.

The undercutted trans went in just a few years ago 2016.
Good combo with the bigger bore of 1000cc.

[750IV]

It's possible the bike was dropped because I see some evidence on the dynamo cover.
So to cover all the bases I'm going to need a selector drum, at least the left fork if not all 3 and a 5th and 2nd gear.
I'm going to wade thru the multiple ebay pages to find a seller who I can trust to check out the condition of the pieces I need.

[scottly]

Although I want it to be right and shift as it should for the next owner. I split the cases today and here's what I found:
Pins on 5th gear look decent but slightly oval shaped at the ends.
Slots in 2nd gear don't look bad but slight marks between the slots from the ends of the pins rubbing.
Left fork doesn't appear bent and ends mic out to about .055" to .060". It does have a bad worn area where it's been rubbing on 5th gear. Does that mean it's bent?
As hard as this bangs in and out of 2nd I was expecting to find broken stuff but didn't. Every thing internal looks good, gears, bearings, etc. as you would expect a 16k mile trans to look like.
So does my description and the pics show that I need 5th gear and maybe 2nd and the left fork?

Your pics don't show the thrust side of the dogs (pins) where the wear that causes the trans to jump out of gear occurs, and this usually happens with much higher mileage bikes. Is there any evidence the bottom end has been apart before, such as rounded screw heads, silicon sealer, or pry marks in the cases?
What do you mean the ends of the fork mic out to .055"-.060"? Is the groove in the gear where the fork tips ride worn? The wear on the fork is not normal, but it's impossible to say if it's bent from your pics; slip the shaft into the fork and place a square on it.

[750IV]

Your pics don't show the thrust side of the dogs (pins) where the wear that causes the trans to jump out of gear occurs, and this usually happens with much higher mileage bikes. Is there any evidence the bottom end has been apart before, such as rounded screw heads, silicon sealer, or pry marks in the cases?
What do you mean the ends of the fork mic out to .055"-.060"? Is the groove in the gear where the fork tips ride worn? The wear on the fork is not normal, but it's impossible to say if it's bent from your pics; slip the shaft into the fork and place a square on it.
[/quote]
I see no evidence of the cases ever have been apart.
Sorry for the typo on the fork pad thickness. I meant to say they're all between .255" and .260". The left being .255".
The diameter of the pins/dogs that move the forks are left .271", center and right .278".
The slots in all three gears where the forks ride are .261".
With a square on the shaft the left fork is not bent.

[750IV]

Any comments on this one?
It's way more than what I need but most of the 7 pages of hits are for 77 and up.
Is it true that 69 to 74 are the same? Are 75 and 76 different?

https://www.ebay.com/itm/1974-69-74-Honda-CB750-OEM-Transmission-Drum-Shift-Gears-Forks-Lot/363317777350

[bryanj]

There are different widths of final drive bearings not sure if you can use the rest of a later box with earlier final shaft or not.
As to the ebay item the forks look perfect so the rest should be good as well

[PeWe]

The bearing look dirty or rusty?

K2-K6 should work.
Do not forget the thrust washer outside the bearing on the long shaft before primary drive hub is mounted on it.

Another alternative as 2 purchases.
There are others too.
Good if same seller can combine shipping.

There might be people on this forum close to you.

Forks with shift drum
https://www.ebay.com/itm/1976-Honda-CB750-SOHC-HM182-1B-Engine-transmission-shift-drum-and-forks-/232810422336?_trksid=p2349624.m46890.l49292


https://www.ebay.com/itm/1974-Honda-CB750-SOHC-HM573B-Engine-transmission-gears-set-/352206463569?_trksid=p2349624.m46890.l49292