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Collection, Preservation and Display of Old Lawn Mowers

1929 Atco Standard Parts & help needed

Hi all,

I am here looking for some basic help that i could not see in the ATCO User book.

I am looking to replace the old spark plug in my 1929 atco 30" J.A.P 500cc but could not find a plug number on old plug due to old age or in the ATCO User manual.

I am also looking for a timing sprocket for the same engine(crankshaft end) as i noticed the other day that there is a tooth missing from my one.

If anyone can help with this it would be a great help.…


Superexcellent Tue, 25/09/2012

I have one of these mowers. I have not yet got it running but a NGK A6 should be suitable. They are an 18mm 1/2" reach plug with a wide heat range.

The engine is a standard 500cc JAP engine so it may be possible to find a timing gear. Which one has the missing tooth, is it the crankshaft pinion or one of the camshaft pinions?

Widow Maker Wed, 26/09/2012

Hi there,

I meant to edit my post as i made an error in it.

There is missing a tooth is the timing sprocket on the crank shaft (NOT TIMING GEAR).

Other wise it runs well and has been used last year to cut a football pitch while there mower was in for repair.

But thank you for the info on the plug, i looked through the manual but could not see a plug part number in there, The old plug is at end of life sometimes it will start other times it fails to start i have put another plug in there but it does not like the plug much very hard to start and run poor until warmed up..


Widow Maker Sun, 16/06/2013

I have since found a suitable spark plug for this engine a champion D21 it has a good heat range and is very good in oily conditions.

So far it has been fine i have mowed the locale football club pitch the other day while there modern day mower was broken. They was stunned to see how well it cut and rolled there pitch flat with very little effort. How ever it is still in need of a timing sproket as there is a tooth missing from my one, i have for now welded a piece on to it and shaped it to match the others but it does need a replacment one soon.

hillsider Sun, 16/06/2013

It is good to hear that you have got your machine working and have given it some excercise cutting the local football field. Re the damaged sprocket it is good that you were able to effect a repair that some may view as a bodge but personally I feel that a good engineering repair such as the one that you have completed will keep the engine running until such time as you can find a replacement however long that may be. Thinking about the hunt for a replacement sprocket have you tried Meetens Engines I see that there website lists JAP spares among the makes that they cover. There may well be other folk who could be worth a call but the one quoted is the one that I know of.

wristpin Sun, 16/06/2013

Good that you've found a suitable Champion as from my experience in my Dennis  the NGK A6 does not stay the course. I have a selection of ancient Champion Com 8s, Lodges and KLGs all of which run fine but put an A6 in it and it will start and run until I stop it and then never again! Don't ask me why unless a post on the VHGMC forum a while back is relevant. This post said that older plugs had "glazed" centre electrode insulators while modern ones did not and this allowed the insulator to become contaminated and fail to insulate.

As for your sprocket repair, as Hillsider says, full marks - it will probably last "for ever". I'm sure that he won't mind if I say that we both belong to an era when repairing things was a necessity as we learnt our trades well before the days of twice daily deliveries from factors, mail order and eBay!

Meetens is certainly a possibility for a new sprocket but failing them it may be worth posting on the Old British Bike Forum as there were plenty of JAPs on old British bikes and there was probably some commonality between bike and industrial applications.

Widow Maker Mon, 24/06/2013

Thanks for the reply i have emailed them but they have replied with a no support email for my engine. How ever i am now in my new work shop with my shiny new lache. I am going to have a go at making a new sprocket to match the one i have. I have good friend that has a machine for taking measurments from any item and putting it into a software form so i can then put it on to my new lache and turn most of it the rest i will do on my mill if it works out well i could make a few spare ones for others who find them self in the same place as me.


Widow Maker Mon, 24/06/2013

Yes when fitting a new plug run it up on your old plug first until it is at normal running temp then remove old plug mind yourself it will be hot. put new plug in and run it up again use to cut lawn so it gives the new plug a good coating of carbon. This is the way i do a plug change as you say the older plugs was glazed this gave them the protection they needed for a cold start when then get wet & oily.


The green spark plug company knows there stuff if you get stuck with a plug just email there support link on there site with the mower/engine detail and they will mail you back with the correct plug or one very close to the one that was in there when the mower was new. This is what i did and so far i have not had any plug issues with the choice they gave me.

Widow Maker Tue, 01/12/2020

The last show I did last year I managed to loose the brass Handel from the oil turn off on the fuel tank. This how ever did give me the chance to remove the tap and drain down the oil tank so glad I did there was a lot of dirt in bottom of the tank. I've now turned a new Handel copied from the fuel tap.