Need info on 2nd gear problem

[bikertucker]

1975 CB750  K5, slips out of 2nd gear when upshifting. Down shifting rock solid. This is the bike my
elderly friend owned. Slipped out of 2nd and third. Engine was opened and parts scattered thru out
independent shop for 2 years in four crates. Collected parts from shop owner plus extra transmission
parts. Assembled it all, 3rd now ok, still slips out of 2nd. My elderly friend is 83 and decided to
sell off bike collection. I bought this 750. I'm about to remove the engine, break the cases and try again.
Shifting forks measured in spec. All gears looked good, as did shifting drum. I've read undercutting
the gears engaging 2nd will do the trick. Some say you can under cut by hand, others say have a shop
do it. I'm open to any suggestions or (be sure to check this, information)
Second note: In pile of transmission parts when my first assembly was compleded. Found a washer
about 40mm in dia. that only fits on the end of the shifting drum. (portion that is inside the engine)
This washer is not shown in the Honda parts listing, so I did not install it. It even shows a wear
pattern that matchs being on the end of the shifting drum. Did I make a mistake by not installing
this washer, or is it simply a washer that dropped in one of the four boxes the parts were stored in.
Did some searching on youtube, not much luck.
I'll be out of touch for a week or so, if you reply and I don't reply right away thats my reason.
Hoping to collect info while gone and ask questions, and reply when return.
Any help would be great, Thanks

[bikertucker]

Just returned, no replies?? Guess it's time to move on

[TOOLS1]

I'm not sure about the washer, but there is a thrust washer on the shaft behind the shift drum. As, for undercut gears, get with Cycle-X. They have an exchange program.
TOOLS

[shinyribs]

I have read where some guys have undercut them by hand using dremels and files. And they held up. I have never undercut cut any by hand, but the cheapest price I have found was $400 for the service. I plan to cut mine by hand after I devise some sort of jig. I couldn't be that hard.

[bikertucker]

Thanks for the replies guys. From what I gather what is not installed is the thrust washer behind
the shifting drum. I have Clymer and Chilton's repair manuals plus access to the Honda parts
list with diagrams. I have not been able to find any referance or diagram listing this washer.
Basic question.. what is function of this thrust washer? My imagination thinks it moves the
entire shift drum outward, thrusting the gears further into each other. With end result being 2nd
gear now works. I know this could all be wishful thinking. Just looking for some education before
I tear it all down again. I will contact Cycle-X. The exchange program caught my attention.

Thanks

Tim

[bikertucker]

Ended up dealing with Cycle X. At first was just going to have them undercut 2nd since thats the only
gear Im having problems with. After thinking on it some more decided to have them look at everything
so I'll not have to break cases again in the future.  Ken said.... sounds good to him.
On the way back to me are undercut, 2nd, 3rd ,4th gears. One replacement fork, and replacement
shifting drum. Ken also stated one main shaft bearing got his DO NOT LIKE judgement, so he replaced
that also. Total cost $329.00  So if all is very wonderful when it's all back together, Im a happy guy

[Lucky 1]

Undercutting the gears in not going to suddenly make the gear box work.

Like you said the parts were scattered all over. Who knows what part or parts are missing or incorrctly installed. Shifting forks get bent by people banging down on the shift lever with a big boot.

So the shifting fork may be in spec but can be BENT.

You need to have someone put it together that knows what they are doing.
It sure wont be any dealership now.

Have Cycle-x put it together for you. Send them all the parts  for both shafts and see if they tell you if any parts are missing. Tell them what year the gear box is.

When people take things apart, and throw the parts all over the shop they get what they deserve.
It is not your fault.

[shinyribs]

Or....refer to the pics in the FSM. It'll take some staring at and some head scratching,but with enough time and patience I am confident you can get your gear box all sorted out

I like to tell myself:" Assembly line workers learned to do this,so can I..."

[bikertucker]

I did send all of the gear box to Ken at Cycle X, for the very reasons you stated.  Everything is back
in place just waiting for a couple of o-rings to show up in the mail before I button it back up.
Everything worked smoothly before, so high hopes all will be well. Part of the project is so (I) become
the guy who knows what they are doing. I know.... (BRAVE WORDS) but I've been successful on
different bikes and different projects. Just trying my luck one more time.

I've found pulling up the local Honda shop parts list and parts diagram on line has worked well
in the past for sorting out which way, what sequence , what part questions.

In the past ten years this is about the 10th project bike. In each case a good forum like this one
is the only way I've been successful. Without guys like you I would still be trying to oil my
ignition points gap.

Thanks

Tim

[bikertucker]

Well, just got all buttoned up and took the first ride today. Thanks to Ken at cycle X, I now have a
five speed transmission again. My problem child 2nd gear is rock solid as well as all the other gears.
Just need to order a couple of o ring seals for the oil lines and all should be well.

Thanks Guys

Tim

[Lucky 1]

I think you were very wise to have an expert work on
this since there were so many unknowns.
It seems like you are happy with your results.

[bikertucker]

Like I told Ken, It's great being able to forget my old shifting pattern of 1,3,4,5.
Now it's time to pull the wheels for new tires, bearings, sprocket, chain and
buff,buff,buff.