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Collection, Preservation and Display of Old Lawn Mowers

atco royale B24 cylinder not spinning

Hi all

hope you can help with a few questions, i have an Atco B24 1981 that has worked well for the past couple of years i've owned it but has picked up a fault with the cylinder intermittently stopping spinning during cutting.  I also then wrongly adjusted the cylinder with the adjustment screws and it stopped spinning completly (it wasn't jammed against the bottom blade and could still spin freely just not powered). After readjusting the cylinder adjustment screws  i now have it working but still with the original fault and dont understand how those adjustment screws are connected with the dog clutch assembly inside (if they are)



christians Tue, 08/07/2014

thanks for any thoughts!



hortimech Tue, 08/07/2014

When you say that the cylinder stops spinning, does the rear roller drive stop as well?

If it does, this could be a problem with the main plate clutch and you should inspect this, usually culprit is the rollpin inside that breaks.

if not, then the problem is probably to with the ratchet drive on the end the cutting cylinder, you will need to strip this down to examine it properly, but a usual clue is a rattling sound coming from inside the chain guard.




christians Tue, 08/07/2014

cheers for the reply, the rear roller continues working when the cylinder stops, and yes it does make knocking/rattling noise from inside the chain guard.

So i opened up the chain guard and the dog clutch was 5mm open even though the mower was in the cutting position. So i changed the blade adjustment screws and after a while experimenting got the dog clutch closed and the cylinder spinning properly but it still has the intermittent problem, what else could i look for?

thanks for any thoughts


hortimech Tue, 08/07/2014

You are going to have to strip the cutter dog clutch down and examine it. setting the cutters should have no effect on the cutter clutch, after all, the two bolts either end of the cylinder move the bottom block and only the bottom block.


wristpin Tue, 08/07/2014

Have the feeling that you may be confusing the cylinder to bottom blade adjustment with the cylinder clutch adjustment.

As Hortimec says, the nip between the cylinder blades and the bottom blade is adjusted using the two screws at either end of the cylinder. The bottom pair tighten and the top slacken and they must be used in unison, Those screws bear on cast steel rocking arms and if too much pressure is applied the arms snap like the proverbial carrots!

To adjust the cylinder, arm yourself with some inch wide strips of 80/90 gsm copy paper, Slacken the two bottom screws say 1/8 turn and take up the top ones the same amount. This should result in the cylinder spinning free of the bottom blade . Then reverse the process until the rotating blades just touch the bottom blade and use a strip of paper to check the nip. if the cylinder blades and bottom blade are in reasonable condition it should be possible to cut paper cleanly along the full length of the cylinder. If not, you may need to consider having the cylinder reground and the bottom blade refaced. When you have the adjustment right just tighten the two top screws a fraction of a turn to lock the adjustment.

Cylinder clutch. If this has been run out of adjustment for some time and is now jumping out of drive the chances are that the ratchet teeth on the double drive sprocket and the engagement collar (sliding dog) are irreversibly worn and will need to be renewed - expensive! There are two types of ratchet set up but if you have an H60 engine I would guess that you have the later type'. Sprocket F016L20312 and Collar F016L20314. Confirmation of this is that your machine will have UNF threads where as the earlier machine were BSF.

Adjustment of this clutch is done by adjusting the pivoting lever that moves the engagement collar in and out of mesh with the double sprocket and is controlled by the small push/pull lever sticking out of the side plate just behind the chain case.

Basically with the drive engaged the forks of the lever that moves the engagement collar should be just clear of collar when it is fully meshed with the double gear and when disengaged the collar and gear should not be touching.



christians Fri, 11/07/2014

thanks wristpin,

its not confusion between the two adjustments its more stupidity on my side! the reason adjusting the cylinder screws adjusted the cylinder clutch was because i had the mower lay on its side and there seems to be about an eighth of an inch play allowing gravity to move the cylinder in and out of drive!

now i take it there should be a little play because of the spring being there (acting like a safety maybe?) but an eighth of an inch is a lot and the parts you showed me look condition wise not too different from the ones on my mower so could there be other parts or reason why there is so much movement?

thanks for any thoughts and please let me know if i've not been clear enough.

wristpin Fri, 11/07/2014

I may be missing something but  I can't follow how adjusting the cylinder cut can effect the clutch regardless of the orientation of the mower!

Anyway , with the machine on the flat first check that the cylinder has no end float - that is , you can't move it left to right and visa versa. If that's ok pull the clutch knob (to the rear of the chain case)) out to disengage the drive . That should move the sliding dog clear of the double sprocket. Now move the knob to the engaged position and the sliding dog should be fully engaged with the sprocket. You may have to rotate the cylinder a few degrees to allow it to drop in. 

Now with the sliding dog fully engaged with the sprocket check that there is some clearance between it and the forks of the actuating lever. If the sliding dog is not fully engaged with the sprocket  of it appears to be engaged but you have no clearance between it and the forks you will need to undo the nut at the rear end of the  actuating lever a turn at a time until you have created about 2/3 mm of clearance. Having done that disengage the clutch and check that the teeth of the sliding dog are clear of the sprocket.

If the teeth on the faces of the sprocket and dog are in good condition the cylinder will drive ok. If it's been run out of adjustment and they have been jumping and wearing  the problem will only get worse as under load they will cam out.

I've seen all sorts of bodges in attempts to over come worn teeth on the cheap but if you want the machine to work as it should renewal of the dog and sprocket is the only answer.