Drive problem with my Atco 1460/1
Just had my first test drive with the above machine sine rebuilding the engine and fitting the new carb etc.
Everything seems to be working fine and it produced a pretty good cut without any blade adjustment. The only problem was that the drive would disengage at random moments. Just to be clear I mean the red thing on the end of the roller axle. There doesn't seem to be much to it so could it just be worn? Is this a common problem on old mowers?
One thing, when I first started working on the mower the red thing was completely seized onto the axle and needed lots of penetrating oil and persuasion to free it off.
It reads as though the “ red thing” - roller drive engagement dog - is either not fully engaging with the sprocket or due to wear on its teeth and the corresponding slots in the sprocket , it’s “ camming” out of engagement. The teeth are usually made with some undercut so that they are pulled into engagement under load.
A couple of decent images of the dog’s teeth and the slots in the sprocket, may reveal all.
Ok, here are a couple of photos of the sprocket and the ratchet.
They don't look too worn to my inexpert eye.
As you say, neither the teeth on the dog nor the slots in the sprocket are disastrously worn, but careful light cleaning up with a fine tooth file may be useful. Consider that the sprocket J297 drives the dog J292 which has an internal hex recess ( visible in your image) that engages the male hex on the internally splined sleeve J300 which drives the rear roller shaft. The relatively light spring J296 keeps the dog in engaged with both the sprocket and the hex on the splined sleeve. The hard work of keeping the dog engaged, is performed by the profile of the its teeth, and the sprocket’s slots, drawing the dog into engagement .
Which is a long winded way of saying that the intermittent loss of drive is due to the dog loosing engagement from either, or both, the sprocket or the hex on the splined sleeve. Cure. Careful re-profiling of the dog’s teeth and possibly inserting a washer or two to increase the spring’s pressure.
Thanks for your thoughts and the picture. I agree that the most worn part is the internal hex of J292. The odd thing is that once it jumps out of drive it stays disengaged until I wiggle it back. I also agree that the spring seems particularly weak. I will try as you suggest and pack it out with some washers or somilar.
“The odd thing is that once it jumps out of drive it stays disengaged until I wiggle it back. “
Well, to some extent that’s how it’s supposed to happen, but only when you pull and twist the red knob out to intentionally disengage the roller drive. I believe that the answer to your self activating disengagement lies with tweaking the self servo effect between the dog and sprocket.