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Collection, Preservation and Display of Old Lawn Mowers

24inch HD and Royale similarities

I am a new member of the club and have joined after buying a 24in ATCO with a roller-seat. It is one off my bucket-list as we had a 20" HD ATCO for as long as I can remember at home and from the late 1960s I was allowed to cut the grass - something that probably would not be allowed in these safety-conscious days ! However, I always thought of the ATCOs  with the roller-seat attachments as being far superior and used to look at the adverts showing them with not a little envy. I now also have my fathers's 20" HD fitted with a newer MAG engine  - as well another 20" HD  left to him by an old friend which was in pretty poor condition and which I would like to restore at some point.

Anyway - back to the point of this post. I am having a lot of trouble actually identifying these various machines as well as the engines and fittings. I seem not to be able to find a single source of info about ATCOs from the late 1950s to the early 70's. Perhaps this period falls between the vintage or "old" lawnmower categories and the newer and somewhat less interesting varieties. Does anyone know of such a directory which can be used to identify a mower ?

In particular I am trying to work out the differences between the 24" HD series and the Royale. One reason I am interested is that I have what I think is a 24" HD BSF model which has a slipping cutter clutch. I have temporarily "glued" the dog-toothed parts together but want to sort out a proper fix at some point. What I was wondering is whether it is possible to replace enough of the parts on the 24"HD with Royale pieces  to effectively alter the cutter clutch to the newer system - for which parts are still available. Or is there a source of parts for the older models that someone can direct me to ?

Thanks in advance for any help regarding these various questions.

wristpin Mon, 02/05/2016

Hello and welcome to the forum.

A single source of information is, I think, going to be difficult, but it's quite possible that we can piece together the parts books to cover what you need.

Th HD machines would have been BSF  and then changed to UNF threads with certain other alterations as you have found with the cutter dog clutch. These changes continued into the Royale models which also acquired altered controls etc to comply with the  Operator Presence Control  legislation.  My guess is that the original style sprocket and dog parts are unlikely to be found but you could try Jon Cruse at the Hailsham Mower Centre.

I've no knowledge of anyone attempting a conversion from the original dog clutch to the later type  but I'm fairly certain that it would involve at the least some modification to the cutting cylinder, if not a complete new one.

I'll sort out and post some parts lists later.


This may help you to identify what parts were changed when they switched from BSF to UNF…




Woodwind Tue, 03/05/2016

Thanks for that, Wristpin.  I had downloaded a copy of the parts lists from an earlier post of yours and have been using it to try to sort out the differences between the various machines. As far as I can tell, the cutter assemblies seem to be the same (apart from some small parts such as washers), and this was part of the reason I wondered if one could try to modify the BSF model to a later version.

My mower has the words TWENTY FOUR written under the ATCO logo on the fuel tank. A friend up the road has a similar version but without the twenty four and I assume this was the unified version before the Royale was introduced - which had the double lines on the clutch cover etc. (Or have I got that one totally wrong ?)

If the conversion is not possible, is there anyone who repairs cutter clutches out there ? Also - has anyone got a spare foot-brake for sale as I have had some close shaves when traveling at speed and my wife's beloved flower borders suddenly appear on the horizon.


hortimech Tue, 03/05/2016

As Wristpin has pointed out, if your cylinder clutch is the earlier type (and note that there was more than one earlier type) and you want to change it to the later type, you will need to change the cutting cylinder. You can easily identify what type of cutter clutch you have, remove everything from the drive end of the cylinder, if the cylinder has an external thread, it is the earlier type, if it is the later type, there is a threaded hole in the end of the shaft.

As for the brake, it sounds like someone has fitted a second hand seat assembly to the machine. When bought new, the seat was an option and the brake was part of the seat kit.

If you can supply a picture of the chain drive, it will be easy to tell the type of cutter clutch and if it is a later type, parts should be possibly easy to obtain, this is because the machine is still in production, only it is now made by Allett.




wristpin Tue, 03/05/2016

I've never made a study of the decals and stripes but the only change that affects your problem is the change from  BSF to UNF .  The fact that the BSF and UNF cutting cylinders have different part numbers  suggests that they are different  and I'm fairly sure that they are because of the differences in the method of securing the sprocket and freewheel mechanism.

I've seen several failed attempts to grind new teeth into the mating faces of the dog clutch components but never a successful one!

Before you rush to fit a foot brake , we used to see more than a few rollers with the rubber stripped due to over enthusiastic application of the brake.

Woodwind Tue, 03/05/2016

Thanks Hortimech. In fact it is clear now that it is the older type which means I have to change the cylinder. I have spoken to Allett and Mowerworld and, as you mentioned, all the parts are avail as new. The only drawback is cost, with a new 24in Allett/Royale cylinder costing well over £300. I  might be better off getting a second hand Royale and starting from there.  At the end of the day I like the idea of having a BSF version of the old mower - makes it feel more authentic for some obscure reason. 

If it was easy it wouldn't be as much fun I suppose !


Woodwind Tue, 03/05/2016

I was wondering about the rubber, Wristpin. It has also struck me as being a wearing surface that might give up at some point. I suppose an emergency turn might be the alternative - or an anchor slung out over the stern in a complete emergency.