There is a diagram of the chain drives of an ATCO 14-20 4 stroke in the parts and manuals section of this site, but you have to subscribe to get access to it. The manual is a protected PDF so I can't just post the diagram here. However I believe photos of ATCO chain drives have been posted here before - if you do a search you should find what you need. You will probably find it better just to subscribe to the mower manuals section, and download the whole manual. That way you will have access to download any of the mower manuals for a year.
Hi wirraway, and a warm welcome to the forum. Here is a pic of the chain set-up previously posted by Peterm...Click HERE I agree with Grumpy's advice, a parts list and manual will come in handy in future; Click HERE for instructions on how to access the Parts Lists and Manuals area. Once again, wirraway,
Please do not PM me asking for support. Please post your questions in the appropriate forums, as the replies it may receive may help all members, not just the individual member. Kindest Regards, Darryl
In the bottom right of the "Quick Reply" window you should see a button for "switch to full reply screen". Press that. In the new window you should see a button for "File Manager". Press that, then browse to your pic and follow the instructions to post it. Max picture size is not all that huge, and you need to format it in one of the approved styles (jpeg etc.)
The feature does not seem to be working right now, hopefully it will be working again soon.
The peterm picture was a 1950s ATCO. The diagram below (Fig 9 from the manual) is a later (handlebar) ATCO. It may be more like yours - but the differences are not all that great anyway (chain tensioner, clutch on one sprocket, etc.)
Item 2 is the chain tensioner - its only job is to take up the slack on the return (non-tension) side of the primary chain drive (the one from the engine to everything else). A sprocket on the tensioner would not change anything. I can't imagine why it would have two sprockets, since there is only one primary chain, unless you twist the link between two sprockets to tension the chain. Sounds like we need to see a picture.
OK, that really is different. I'm guessing that the double sprocket directly driven by the engine sprocket is just an idler, it isn't connected to anything. That makes it possible to change the drive ratio from the engine to the reel, and everything that comes after it. I've seen some complaints here from ATCO owners who didn't like the mower's forward speed, so maybe this was a design change from ATCO - or maybe a cobbled job done by a former owner.
I recognise that this is an old thread but I have obtained a diagram for the 4S20 chain drive - I have a 1958 version - and thought that it would be useful putting it up here.
Thanks Sir Chook, and welcome to Outdoorking. I don't recall seeing that model ATCO, I'm used to them having the kick-start at the flywheel end of the engine.
No worries and thanks. The 1950's 4 strokes generally all have the kick start on the inboard side. The 4S20 is not a common machine - the one I have was bought from a bowling club by the previous owner. I believe that once ATCO went to recoil starters the kick start disappeared altogether. The machine that I bought had not been used for over 30 years and after a minor clean up runs like a dream.
Getting back to wirraway's question, from Sir Chook's diagram it does look as if the double sprocket 9A was just an idler, introduced as a design change to gear down the drive so that the mower's forward speed was reduced. It looks as if ATCO spaced the tiny sprocket on the engine/clutch drive shaft further out, to accomodate that idler. It also appears that wirraway had put the idler on its pivot shaft backwards (larger sprocket on the inside, when it should have been on the outside), which would have defeated its purpose altogether.
![[Linked Image]](https://www.outdoorking-forum.com.au/forum/uploads/usergals/2011/05/full-2772-1069-atco_sprockets.jpg)
![[Linked Image]](https://www.outdoorking-forum.com.au/forum/uploads/usergals/2011/05/full-5001-1040-4s20_diagram.jpg)
and thanks. The 1950's 4 strokes generally all have the kick start on the inboard side. The 4S20 is not a common machine - the one I have was bought from a bowling club by the previous owner. I believe that once ATCO went to recoil starters the kick start disappeared altogether. The machine that I bought had not been used for over 30 years and after a minor clean up runs like a dream.
