1st gear popping into N at 4000

I did a quick search of the forum to see if anybody else has this problem;

Bike runs great, and 99% of standing stop launches from a traffic light there is no problem. But If i leave Bike in 1st gear til 4000 RPM (or so), it pops into Neutral. this does not happen in 2nd, 3rd or 4th gear. Shifting is smooth and normal as far as I can tell. This gearbox i rebuilt just 1000 miles or so ago. Replaced all of the bearings, ratchet spring and the kick return spring.

Any Ideas? This is on my 750 commando...Been communting to work on it all week.

thanks, Tyler

If it pops out when you've kinda let the thrust off for leisurely snick to 2nd, I'd suspect a worn 1st gear cog and warn ya if that happens going slow in a lean like into a drive way it can remove engine drag you depended to to suddenly end up in hedge or worse. I'd suspect the rachet pawl spring if it was fussy going into gears but not coming out of engagement. I had two events the same day before I knew I had a worn 1st cog bush issue.
1st was going down steep tight bluff face road, wanting to be safe as possible, just stayed in 1st to coast 20 mph to keep cars ahead of me a full turn, while lightly leaned the rear cross a hand size 1" deep section of pavement missing, which I think nothing of ordinarily, but just then it relieved drag force on gear box and it let bike completely fly out from under me sideways, leaving me to run a few steps not to fall down while watching bike continue down the steep to slowly bump guard rail.

2nd was entering my drive way Gravel turn purposely leaning easy as can and marking I was at a secure 12 mph, tire hit a leaf filled rut 6" wide couple inches deep that unloaded drag on gear box which popped N which let rear slide out from under dumping bike on me, cracking pelvis and fracturing L5, but I was still pleased I'd fully protected the new $600 pain job.

Shifter dog ears can wear so not fully engaging gears, no way to know w/o going in completely. They tend to go away faster if bushes worn down.

Do not take the N surprise as just annoyance issue.

Good work saving the paint job.....priorities.

Well, at this point, its popping out only under harder accelerations, when I open her up and let the RPMs rise. Im thinking its probably past 4000 RPM, to nervous to looks really. But under normal accelerations from a stop, It wont happen. I tried to take my toe away from the gear lever to see if it was my foot accidentally tapping it down...But thats definitly not it. It almost seems like the vibrations from the higher RPMs are causing the "jump" to Neutral?

When the trans jumps out of 1st that generally means you need to install a shim between the kicker shaft and the inner cover to reduce the end play of the kicker shaft. Common Norton malady. Jim

reverse the selector forks.

In 35 years and 45000 miles I've repaired that condition twice on my bike by replacing the 1st gear layshaft bushing.

When the trans jumps out of 1st that generally means you need to install a shim between the kicker shaft and the inner cover to reduce the end play of the kicker shaft.

Click to expand...

Thanks for that - but what does end play do?

Common Norton malady.

Click to expand...

Unfortunately true.

I have a 74 Norton that did that also upon a hard throttle up condition and popped out. But stays engaged under normal driving. Now I know why these bushings were included as extra parts when I bought the bike 6 years ago. Previous owner never told me about it. Good Topic that may answered my minor problem with this bike.

hello tyler!

i posted this below on an other threat [member yello cad posted it], but same problem: jumping out of gears:

"hey yellow cad! as i know....when it jumps out of gear when you are going on load [in example driving up a hill or when you are hard speeding up] then [i had the problem with a bsa - the same gearbox technique] it is because the gear pinions [1st pinion layshaft to 1st pinion main in your case] are not parallel to each other.
Because they are heavy worn or there is too much play in the bushes/bearings of the shafts...."

i think when there is much float on the layshaft, then the gearing is a bit wobbly.
But i don`t think that gears will jump out - because the tooth of the pinions are with this axial float still true/parallel to each other.....

BUT: when the push of the 1st gear lay is in a bad contion: the pinion can twist not only axial ----the pinions aren`t parallel to each other.......and under load they are slipping - jumping out of gear!

so when the bearing of the shafts would be in a bad condition not only the first gear would jump out.

My guess:
the push on the 1st gear lay is to change or the 1st pinions lay and main [when the teeth aren`t parallel anymore] are to change.

try to accelerate hard up a hill in 1st gear for testing......i bet it will jump out earlier than at 4000rpm

as always ....my two cents!

have a nice day!
chris

maylar said:

In 35 years and 45000 miles I've repaired that condition twice on my bike by replacing the 1st gear layshaft bushing.

When the trans jumps out of 1st that generally means you need to install a shim between the kicker shaft and the inner cover to reduce the end play of the kicker shaft.

Click to expand...

Thanks for that - but what does end play do?

Common Norton malady.

Click to expand...

Unfortunately true.

Click to expand...

If the kicker shaft is allowed to move to the right because of excess end play then first speed gear is also able to move to the right. When first speed gear moves to the right it moves away from the gear next to it which is held in position by the shift fork. Then there is reduced engagement of the dogs so they tend to push apart.
It is an easy fix and something that should be checked on every gearbox rebuild. Jim

note to travelJerry, but slipping out of second gear is totally different than first gear.
Jim C says: "If the kicker shaft is allowed to move to the right because of excess end play then first speed gear is also able to move to the right. When first speed gear moves to the right it moves away from the gear next to it which is held in position by the shift fork. Then there is reduced engagement of the dogs so they tend to push apart.
It is an easy fix and something that should be checked on every gearbox rebuild. Jim"

Second gear slipping could be Bronze bushing wear or the layshaft bearing starting to go or a bad adjustment of the shifting index via the hair pin spring and or the sprung pin holding the shifter cam plate. Or a racing shift doeing off the engagment dags for that gear. ( You have to open it up) to know.

Hello all,

Ok, so this is great, alot of good information. Just hours after I posted this question yesterday, I was riding the Norton home. I have a 20 mile section of freeway that keeps you at 65 MPH the whole way. As I began to slow down for my exit, I grabbed the clutch lever to prepare for a downs shift, then, nothing.....Bike was stuck in 4th gear. The gear selection lever has is return spring, but nothing was ratcheting the cam. after I was rescued by a friend with a pickup truck, I took off the outer cover. The gearshift Pawl was 180 degrees out of position. That explains the emptiness when shifting, but upon closer observation I think I found that the gearshift pawl spring (the smaller gauge spring) may be in inside out. One of the legs of that spring has a small "dogleg" bent to it. And I guess there is a specific way it is suppose to lay in.
So this was my fault because i remember buying that new spring and installing it 2 months ago...but then I didnt know there was a wrong way to puit it in.

So since I now have the outer cover off, I may as well dig into the inner cover and check on the layshaft bearing???????? Regarding the original problem her of 1st gear popping out under hard acceleration.

Just to clarify, Its Item number 18 on this chart

http://www.oldbritts.com/nor_comm_71_6.html


Thankyou again all for the responses.

Tyler

For $2.44, you might also want to change number 15. My first gear was popping out under load and this fresh spring fixed it. I am not saying that this is your problem, I am just saying for $2.44......well, you get the idea.

Hi,

Once again this forum has been superb, just having a quick browse and saw this thread. The problem is exactly the same as my Commando has been suffering with for the last few months.
General solo riding , no problem
Hard Acceleration and 4000 rpm throws out of 1st gear only
Put under load and the problem gets worse, steep hill starts and it will jump out at 2000 rpm
Put a pillion and luggage on a hill and just use 2nd cos it won't hold 1st.

Doesn't jump out of any other gears.

So I'm off to try shimming, thanks again for posting all the replys

Shaggy

motoalchemist said:

I think I found that the gearshift pawl spring (the smaller gauge spring) may be in inside out. One of the legs of that spring has a small "dogleg" bent to it. And I guess there is a specific way it is suppose to lay in.

Click to expand...

The ratchet pawl spring's cranked leg must go at the bottom.

motoalchemist said:

So since I now have the outer cover off, I may as well dig into the inner cover and check on the layshaft bearing???????? Regarding the original problem her of 1st gear popping out under hard acceleration.

Just to clarify, Its Item number 18 on this chart

Click to expand...

No, it's the bearing at the opposite (drive side) end of the layshaft which needs to be inspected. If it is a metal caged 6203 ball bearing then it should be replaced with the upgrade roller bearing or the phenolic cage FAG 6203TB ball bearing.: http://www.doov.com/apps/nortoncompanio ... s&Itemid=8

While the gearbox is apart it's often a good idea to replace the layshaft 1st gear bush.


The layshaft end float may require shimming after a new layshaft bearing has been fitted: http://www.oldbritts.com/nor_comm_71_6.html - "Check end play on the layshaft and verify the gear clusters are properly assembled--"

So I took Friday off and decided I was going to fix my gearbox. I took the outer cover off and sure enough, the pawl spring for the shift lever was in upside down. I then measured my end play on the kick start shaft and had just over .050" play...way too much. So I took the inner gearbox cover off to install a shim as recommended by this forum. But then I noticed a crack in the started shaft, bummer. Also, my first gear bushing had migrated and was grinding into the inner bushing in the started shaft.
The nice thing about living here in San Francisco, I live 30 mins from a british bike parts mecca. $290.00 later and a couple of hours I got the gearbox back together, No endplay on starter shaft and 1st gear doesnt pop out at all, even at 5500 rpm.

Correctly installed Spring


Migrating 1st gear bushing


Back side of 1st gear


This is the old kick start shaft, inner view of bush and crack

This is the old start shaft pawl. all worn out . I find out there is a new updated pawl that has been hardend


The new harded Pawl..identified by the Letter mark "N" I think is what it was. you can just see it in this picture


Here is a picture of the new kick start shaft and its bushing. Instaed of shimming on the larger flange. I figured shimming here would give the same effect and also encapsulate the shim. I found and old circlip that was the proper thickness and diameter


Here is the new Start shaft installed with the inner cover back on. I did a dry fit first to check the endplay and make sure there was no binding. It worked perfect. It rotated freely and the endplay is just enough to know its not being squeeed by the cover...perfect.


Ther rest all put back together. no more popping out of gear


Here is the gap at the kickstart lever and outer case. Its nice and solid and has near 0 end play