First gear not engaging

[pstock1]

Good Morning. I have a 1952 Model 18 with a Burman GB box. The issue is 1st gear will not engage. All the other gears engage absolutely fine, the clutch is nice and free in these gears with no drag and they all engage smoothly and quietly.

First will engage with the engine off and if the bike is rocked forward and back it feels like it should. However with the bike running and the clutch pulled in the gear lever will feel as if it has clicked into position, but then on releasing the clutch there is a graunching/grinding with the gear not engaging so there is no drive.

The other oddity is when attempting to engage first the clutch feels as if it is dragging slightly, although it is freely engaging and disengaging for the other gears.

The gearbox shafts have no noticeable excess wear or play. Any advice gratefully received.

[pstock1]

Ok, further investigation has shown further symptoms. 2nd,3rd and 4th all work as they should, the clutch is free and smooth. When dropping down into 1st on the move it works under deceleration as in the bike slows, and the gear engages smoothly, however when I try to accelerate it still grinds as if not engaged.
Any suggestions or similar experiences to this?

[clive]

One of the gears in the GB box engages by pegs slotting into holes in the adjacent gear on the shaft. Cannot remember if this is the first gear but if the pegs were worn it would fit the symptoms. When engaged on the move it would slow the engine as the unworn edge would be under pressure, as soon as you accelerate the worn edge would be under pressure and could be coming out of engagement. If it is not that I would suspect wear in the selector arm.

The problem with engaging first when stationary may be clutch rod adjustment or more likely the plates not disengaging fully. Ensure the pressure plate lifts the same all the way round by using a reference mark and rotating the clutch basket all the way round whilst the lever is pulled using the kickstart. If this does not work suspect wear on the inner tangs of the clutch basket. These are quite difficult to clean up to ensure the plates are fully releasing, so much so that I have fitted the earlier CP box clutch with the ears on the clutch plates rather than slots. The slots are in the clutch basket and can easily be cleaned up with a file. When the bike is on the move the slight sticking of the plates will not affect engagement of the other gears.

[Mick D]

Hi

Has this happened all of a sudden or has it become worse with time? Have you done anything to the gearbox recently?

It sounds like you have excess wear in the selection mechanism, this could be burred and worn drive dogs, worn selector forks, wear in the cam shaft and pins or more likely a combination of all of these. Worn bushes that allow excess end float of the main and lay shafts are another area that can give these symptoms.

It's time to strip the gearbox and have a look before more damage occurs.

Dragging clutch will make selection noisy / clunky but won't stop the gears fully engaging when riding.

Regards Mick

[1608]

As already stated probably wear in the selector This wear ( particularly on Burman boxes) can be exacerbated if a too thicker gasket is fitted to the outer cover. This happened to me and I discovered this cause from another source. This theory can be tested if you can detect too much end float when pulling the gear shift lever in and out when in situ. There should hardly be any play detected. There is also a small top-hat bush on the inside cover which also governs the end float.

[pstock1]

Good morning and thank you for all your reply's so far. The bike has been a rebuild project having been bought complete but in large lumps rather than a basket case.
The problem has made itself immediately apparent after recommissioning the bike and attempting to road test.

I do have a spare gearbox (untested and missing the outer cover) so it may be time to have a good look at both and see if one good one can be made out of the two.

I'll check for play later today.