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Collection, Preservation and Display of Old Lawn Mowers

ATCO & Suffolk help please

Hi folks, first post here so greetings


I have recently been given my Grandfathers mower that he bought new in London in 1962, the mower lay about till the 80's when I used to use it to cut my fathers lawn each week. 

The mower went into retirement again and I have recently been gifted it when dad had a clear out. 

The mower in question is an Atco 1761 / 2 / 3 - with a Suffolk 75cc engine (284968)


i am mechanically capable and have have a good understanding of these mowers and four stroke motors. I got the motor running after a carb clean, rebuild and clean of the points and plug lead, de-coke and freeing off the typical exhaust valve. however I need a couple of little hints to get me where we need to be!

1 - the mower is spitting oil out of the (damaged) filler/dipstick cap, I admit I am using too thin oil at the moment, but it seems excessive. This lead me to suspect the breather in the valve box is causing issue. I decided to pull the spring and drag all the bits out and clean em up, but in doing so I noticed the paper disc is past it's best, this is no dramas as I have a correct sized Fibre washer that'll fit. The issue I have is I took it to bits blind and am not sure what way it is meant to go back together! Any diagrams? 

2 - I stripped the deck to bits and cleaned it all up, sharpened it and adjusted everything, however I am not 100% I have put the drive for the blades back together in the right order, again, is there a diagram for this vintage of mower? (I can't find one)

i must ist remember to stop taking things to bits after a few too many beers!!







wristpin Wed, 26/04/2017

Take digital images as you go!

Breather valve - from the bottom up

Thin " paper" washer. 

Alloy body, two legs down through the washer and engaging in the base of the valve chest.

Paxolin disc - can't see it in your disassembled image.

Steel cap sitting on top of four legs 


Cutting cylinder bearings etc . An image of what you have will help.

EDIT Different engine but similar chassis - I think.…



ORB Wed, 26/04/2017

Thanks for the reply. That helps. So, paxilon disc?? Do I have to have one? Do you have an image of such so I can try to make one? 

Im sure I could get another motor easy enough but this is Grandpa's and I'd rather keep it this way!

Ive just been and lapped the valves and put it back together as such. No disc....

Is this what you meant?  I gather the paper washer I have substituted with a Fibre Washer is too thick? 

How can I bodge to get it to work? 


Thanks again

gtc Thu, 27/04/2017

And why do my images always rotate through 90 degrees??

That problem has Admin perplexed, too.



wristpin Thu, 27/04/2017

The thickness of the washer under the body of the valve will not affect its operation - just make it difficult to replace the spring. However the absence of the Paxolin disc means that the valve may as well not be there. When operating correctly the valve allows the crankcase air displaced by the downward movement of the piston to vent to atmosphere but when the piston rises the disk will seal against the body of the valve preventing air being drawn in and creating a small amount of negative pressure in the crankcase. This assists in keeping the engine oil tight. If yours is missing it will certainly account for some of your oil burning / expulsion issues - check that it's not "glued" to the inside of the steel cap. Also the paper washer under the valve body is reasonably compliant to aid sealing against the valve chest, whereas fibre washers are usually hard and unforgiving and may not make the best of seals. 

I use the term Paxolin because that's what it was referred to when I was learning many years ago but any lightweight oil and heat resistant substance should do as a substitute.


ORB Thu, 27/04/2017

Thanks again. 

No, that disc isn't anywhere to be seen. I've checked my bench, in the garage vacuum cleaner and in the dishwasher filter (don't tell her indoors)

ill have to create something. Can't think what to use though. Was thinking cutting a disc from a beer can but feel it'll be too thin? 

wristpin Thu, 27/04/2017

Not too thin but maybe too heavy. Possibly a bit of plastic packaging of some sort or even a bit of postcard soaked in varnish and dried hard.

ORB Thu, 27/04/2017

Cut a bit of plastic out of a sheet I had laying about. Built it up and I can blow through it from the bottom but suction is stopped (not fully but very noticeable) 


I will let you know if it's any different when I get it put back together. 

Then, next job find out what bearing is in the first motion shaft so I can find one...

wristpin Thu, 27/04/2017

Guessing either an RLs 4. 1/2" inner or an RLs5. 5/8" inner. If it's a self aligning bearing, RL4 or RL5. 

ORB Thu, 27/04/2017

Thanks Wristpin, I've just chucked the motor back together (albeit with the wrong oil) and it doesn't seem to be chucking oil out of the filler etc! 

I had to strip and clean the carb while I was at it as it'd only run on 1/2 choke. (Would you advise that one full turn on the air bleed screw and 3/4 on the main jet?) 

now to the bearing, I will strip it out later. Is there an easy way to tell what I need once I have it out? I assume measure it with micrometer? 


wristpin Thu, 27/04/2017

Oil : SAE30 lawnmower oil is what you need

Bearing: yes, measure it. May even have an ID number  engraved into the edge of the outer race.

Jets: just find the setting that works best, old machines develop individual characters  !

ORB Thu, 27/04/2017

So, bearing is out, seems ok to me. It's a self aligning bearing. 

I think the drive end needs stripping and putting back together properly!

wristpin Thu, 27/04/2017

Yes, it's a self aligning bearing. I can just read RL on the outer race but not the 4 or 5 that follows it. When it's all washed out and oiled do you still need a new one?

When stripping the clutch etc be careful - at the engine end there is a little countersunk screw R361 ( the book calls it a pin) . I seem to remember that it has a left hand thread, so tread carefully and test it before giving it full welly.

ORB Thu, 27/04/2017


Bearing seems ok (it's a 5) it's been in petrol now it's in some gearbox oil. 

clutch stripped and rebuilt. The screw was standard thread. Just need to put a new split pin in the mechanism, then rebuild the whole drive side.

then more than likely something else will give out!  

ORB Sun, 30/04/2017


the chains seem to be binding, any clues? It's like the gear is bent as it seems to be the same point? 

wristpin Sun, 30/04/2017

Option one. One or two seized links?  Flex each link and see if there's a tight one or two.

Option two. End of the cutting cylinder running out of true ( bent!) causing the chain to go tight.

ORB Sun, 30/04/2017

think I've sorted the the chain, it seems it had some burrs on the teeth that I've rounded with a file and also turned the chain so it's inverted and seems to be smoother. 

I however think I've done something in the rebuild with the cutter as I can't tighten the end nut without it binding. 


Above is the aforementioned nut.


i also haven't tightened the screw in the beating carrier and I'm wondering if I'm meant to apply lateral pressure to the Cylinder (pushing it towards the gear end) and then tighten? 

That screw above. 

I guess I need to strip it and rebuild it and take a little more care 



wristpin Mon, 01/05/2017

The lateral  location of the cylinder is controlled at the drive ( left) end. The bearing at that end is positively located by the holder clamping it against the chassis side plate. The cylinder shaft passes through the bearing  and is located either by a screw on sprocket or a nut. In your case, I believe, the sleeve nut M50 . If tightening that nut is causing the assembly to bind I suggest that you take a careful look at the Dropbox file  of the cutter unit that I posted earlier in this thread, and make sure that all the various washers, distance washers and spacers are assembled correctly.

At the other end the bearing is located against a shoulder on the shaft but floats in the carrier to accommodate minor inaccuracies between the cylinder and the chassis and facilitate its installation .When everything else is properly located and tightened up the pinch screw on the right hand carrier is tightened.

ORB Fri, 05/05/2017

So, the old bugger trims the lawn for the first time in many a year. Yes I cut it too short, but once I was away I wasn't stopping to adjust!

i sharpened the blade with an angle grinder and a flap wheel and then tidied it with a whet stone. It works well. 

The fuel tank is buggered (rotten) and porous, I've bodged it with liquid metal till I find another (tried to weld it but I kept blowing holes as there's little decent metal left) 


i mentioned to dad that I had it running but the motor needed work. He turned up with this lot;

Im sure I can solve the smoking from the exhaust with bits from these. I think it's been ran low on oil any burned the rings out, but I'll strip it one day and find out. Realistically will a compression test tell me much on these little motors?


gtc Sat, 06/05/2017

Good to see that it's running again.

(tried to weld it but I kept blowing holes as there's little decent metal left)

Just a safety note: Welding petrol tanks in general -- even those unused for years -- is considered a very dangerous operation. Even a small amount of residual petrol can cause an explosion when vaporized by the heat. The usual practice is to run water through them for a considerable time, first.

wristpin Sat, 06/05/2017

Soldering is a better bet for old steel tanks. As far as purging small mower tanks goes, a good flush out with boiling water is usually sufficient. If you have access to a steam cleaner - even better.

ORB Tue, 09/05/2017

Out of interest, what kind of compression should come from such an engine? 



52psi doesn't seem a lot - it's smoking a bit and I suspect the rings are shot??

wristpin Wed, 10/05/2017

As far as I know Suffolk never published any compression figure for that engine so really you can only compare your reading with a "known good engine". That said I consider compression readings on small single pot engines fairly meaningless; if it concerns you, you are better off buying or borrowing a leak down tester which will not only detect an issue but also point the cause - rings, valves or head gasket etc.

Just bear in mind that your engine may be over fifty years old and may never have had the head off in all that time, so before you jump to the conclusion that you have a ring issue I suggest treating the it to a "valve job". Reface the valves and , if necessary, re-cut the seats before lapping and setting the gaps will almost certainly improve the compression but wont do much for oil consumption. 

Alternatively, if it runs and does the job - leave it alone!