Pops out of first gear

Tangozulu · Mar 3, 2016

When I really twist the wick on my '71 Commando, at approximately 5K RPM it pops out of first gear. Under less than full throttle, no problem. This does not happen in any other gear. So, what specific transmission part is presumably worn to cause this problem?

comnoz · Mar 3, 2016

Tangozulu said:
When I really twist the wick on my '71 Commando, at approximately 5K RPM it pops out of first gear. Under less than full throttle, no problem. This does not happen in any other gear. So, what specific transmission part is presumably worn to cause this problem?

That generally means there is too much endplay in the kickstart shaft. If you can move the kickstart shaft in and out more than about .020" then you need to install a shim on the kickstart shaft inside of the inner cover. I would shim it down to about .010".
The other possibility would be a damaged first layshaft gear but the shim usually takes care of it. Jim

worntorn · Mar 4, 2016

Is the clutch dragging at all?
When I first put my Commando on the road the clutch was dragging a bit to the point neutral was difficult but not impossible to find. First gear would only partly engage sometimes and when the happened it would pop out of first gear on full throttle acceleration, like your bike does. At the time I didn't realize that first was only partially engaging because of the clutch drag.
I assumed it was a worn gearbox problem of some sort, however on this bike, when the clutch drag was cured the popping out of gear problem went away completely ( 12 years ago) and has never returned.

Glen

pete.v · Mar 4, 2016

I think there is more than one way to lead a horse to water.

For me it was changing the detent spring and plunger.

04-0034, 04-0442
14 and 15 seen here,
http://www.oldbritts.com/1972_g6.html

brxpb · Mar 4, 2016

worntorn said:
Is the clutch dragging at all?
When I first put my Commando on the road the clutch was dragging a bit to the point neutral was difficult but not impossible to find. First gear would only partly engage sometimes and when the happened it would pop out of first gear on full throttle acceleration, like your bike does. At the time I didn't realize that first was only partially engaging because of the clutch drag.
I assumed it was a worn gearbox problem of some sort, however on this bike, when the clutch drag was cured the popping out of gear problem went away completely ( 12 years ago) and has never returned.

Glen

+1.

Had exactly same problem as Worntorn, led to some underpants filling moments from time to time!

Madnorton · Mar 4, 2016

Clutch adjustment could be just masking a problem, it should still go into gear even with a dragging clutch and lead to a stall in this case - strip it and investigate, if it has seen many miles you might as well refurbish it whilst apart. Slamming in the clutch in the event of a failure in the gearbox may not save you.

comnoz · Mar 4, 2016

pete.v said:
I think there is more than one way to lead a horse to water.

For me it was changing the detent spring and plunger.

04-0034, 04-0442
14 and 15 seen here,
http://www.oldbritts.com/1972_g6.html

Of course if the detent spring is shot it should be replaced.

Many time replacing the detent spring is just a bandage for the real problem which is lack of engagement depth for the cogs on the side of the gear. If the cogs are only engaged a little bit, then applying high power and lots of revs will cause the gears to push themselves apart and force the selector drum to rotate -so it pops out of gear.
If there is adequate engagement depth of the cogs then there will be no force trying to push the gears apart.
Shimming the kickstart shaft increases the engagement depth of the cogs. Jim

CanukNortonNut · Mar 4, 2016

comnoz said:
pete.v said:

I think there is more than one way to lead a horse to water.

For me it was changing the detent spring and plunger.

04-0034, 04-0442
14 and 15 seen here,
http://www.oldbritts.com/1972_g6.html

Click to expand...

Of course if the detent spring is shot it should be replaced.

Many time replacing the detent spring is just a bandage for the real problem which is lack of engagement depth for the cogs on the side of the gear. If the cogs are only engaged a little bit, then applying high power and lots of revs will cause the gears to push themselves apart and force the selector drum to rotate -so it pops out of gear.
If there is adequate engagement depth of the cogs then there will be no force trying to push the gears apart.
Shimming the kickstart shaft increases the engagement depth of the cogs. Jim

+1 on all that Jim stated.
I would check the layshaft first gear bushing as well if you open it up. I have found some broken into bits with chunks missing. The four holes in this L/S 1 gear should be sharp and round. I have one that has some real notches where the dogs engage = badly worn.
Cheers,
Thomas
CNN

Torontonian · Mar 4, 2016

Don't much ever recall hitting 5000 in first. I always shift into 2nd. well before that to enjoy the torque of things.

Stillreel · Mar 6, 2016

I had the same problem. Popped out of first and occasionally 2nd under load. Put in a set of new bushings: problem solved.

Easy job BTW.

BC

Tangozulu · Mar 8, 2016

worntorn said:
Is the clutch dragging at all?
When I first put my Commando on the road the clutch was dragging a bit to the point neutral was difficult but not impossible to find. First gear would only partly engage sometimes and when the happened it would pop out of first gear on full throttle acceleration, like your bike does. At the time I didn't realize that first was only partially engaging because of the clutch drag.
I assumed it was a worn gearbox problem of some sort, however on this bike, when the clutch drag was cured the popping out of gear problem went away completely ( 12 years ago) and has never returned.

Glen

New Barnett clutch with less than 2K miles on it running in ATF. Works great, neutral uber-easy to find. that's not it.

Tangozulu · Mar 8, 2016

Good input, especially from Jim and Thomas. End-play on the kick starter does not seem excessive at all, but I will put a dial indicator on it. The lay-shaft issue as well as the detent spring sound like possibilities. looks like I need to take it apart. Inner drive seal is leaking badly anyhow. Thanks guys,

Pops out of first gear

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