Skip to main content
Collection, Preservation and Display of Old Lawn Mowers

How to dismantle a JP Super 16 inch model (manual not petrol)

Enter a word or two to search the forum section and click the Search Forum button.


I'm a newcomer although not a member - yet - but wondered if I could tap into your knowledge database.  I've just bought a JP Super 16 inch model and am about to attempt an overhaul rather than just a tidy up.  The machine is intact with no damage and seems to have been looked after apart from a missing grassbox and three missing machine screws securing the shear blade.  Needless to say the 5 screws present are pretty well seized but I'll deal with that later when (hopefully) the dismantling is complete.

I'm not sure exactly how the 2 alloy side plates may be removed.  As far as I can see it looks like some of the cross tubes are interference fit and some are both interference fit and secured with nuts eg the tube/bar on which the cutters spin.

Related to this - exactly what function do the cotters perform.  I'd initially assumed that these would have been driven in from the rear (taper fit) and that they'd pass through the cross tubes to lock them in place but this doesn't seem to be the case.  The nut on each doesn't seem to serve any function. Do these cotters need to be extracted before the cross tubes are freed?

I don't want to "bash away" in the hope of freeing the tubes but I'm pretty sure that the side plates will free off with heat- provided any hidden fasteners are out of the way.

Any advice/suggestions most welcome.

Many thanks in anticipation.




worzel Sun, 02/01/2022



An update.  After some headscratching I've worked out how the cotters work- and have managed to free them off.  So the obvious next stage would be to remove the side plates but I'd welcome ideas on methods that work.  One idea I had was to use threaded studding and metal blocks- by placing the blocks at suitable intervals and then winding out the nuts on the studding (the plates would have a hole each end thru which the studding would pass) then an even pressure could be exerted on the side plates.  At the same time a blowlamp or similar would heat up the alloy plates.  

A pity that JP didn't use solid cross tubes.  With less of an interference fit these cross tubes could have been fitted slightly looser and something like "Bearing Fit" by Loctite would have secured them with the collets.  Dismantling would then be a lot easier as with heat the bearing fit loses its grip.

Anyway- any views on my idea of using studding?







Henry Ellis Tue, 04/01/2022

Hi John,

Assuming you have removed the front axle and the cylinder cutter and have unscrewed the four 1/4" BSF nuts a few turns and tapped the four cotter pins inwards, proceed as follows:

Insert a screw jack between the two side frames close to the front cross tube with a piece of wood at each end;

A wedge is needed top and bottom between the side frame and and the back plate (next to the brass rings) to force the side frame apart (I use two large screwdrivers);

A two-legged hub puller around the rear with the centre screw bearing onto the rear "axle".

Take up an even tension on all four positions and now apply heat to the aluminium surrounding the cross tubes and increase the tension gently and evenly, then more heat and more tension until things start to move.

A bit crude but it does work but be patient ! I have successfully done lots of these by this method.

The left side frame (with the drive chain) is the 'fixed side frame' so the cross tubes stay in place therefore the right side frame is the 'removable side frame'.

Be careful with the hand wheel on the left - the casing here is a weak point.

The cotter pins can only be removed after the side frame is removed, they work by being pulled against the cross tube by tightening the nut.

Re-reading your query maybe you have not taken the cutter out ? If not, unscrew both large and small disc covers and unscrew the flanged brass nut with a box spanner or socket (5/16" BSF) and knock the socket inwards until the axle moves out of the cutter and continue with a suitable drift until you can pull the axle all the way out.






Henry Ellis Tue, 04/01/2022

Assuming you have removed the cutting cylinder and front axle complete and have unscrewed the four 1/4" BSF nuts and tapped them inwards, proceed as follows:

Insert a screw jack between the side frames with a piece of wood at each end,

Insert a wedge top and bottom between the right side frame and the back plate (I use a pair of large screwdrivers),

Put a two-legged bearing puller around the rear end with the centre screw onto the "axle",

Take up a firm tension all round and apply heat to the aluminium surrounding the cross tubes and gently and evenly increase the tension and at the same time drive the screwdriver blades to force the side frame off until the  frame starts to move.

The right side frame is known as the 'removable.side frame' the other side has the cross tubes firmly secured.

A bit crude perhaps but it does work - I have successfully dismantled lots of Supers by this method.

Hope this helps and can you tell me the serial number of the mower which is stamped on the front of the left side frame - I can then date the mower for you.



worzel Wed, 05/01/2022

HI Henry


Apologies for the delay this end in replying to your very kind input.  Your method sounds pretty good to me- similar to my idea?  Past experience with alloy block car engines has taught me not to use brute force- unless you desire a lot of tears.

I'll upload a few pictures in the next few days so you can see my idea in action- when a friend has made the items I need.


PS Belated Happy New Year!



worzel Wed, 19/01/2022

Hi Henry

Can report that I've (eventually) removed the side plate.  However I reckon that this is not the first time since manufacture that it has been dismantled as I don't imagine the manufacturer would have fitted one of the cotters upside down,.

So the problem I have now is whether or not it was correctly assembled as if it wasn't and I simply re-assemble things I may be just repeating errors.

The first problem- the 3 rear rollers.  Before dismantling I noticed that there seemed to be a lot of lateral play between the rollers.  I can see two thrust washers (one at each outer edge) but what is considered the correct amount of free play laterally in the rollers.  I'd have thought there wouldn't be very much play but in my case the free play is around 3/8 inches.  Is this too much?

Second- and I'm not sure this is a problem.  With the 3 rollers removed if one of the "output" shafts is turned by hand the opposite side turns in the reverse direction.  This is similar to what happens on a rear drive car (one without a limited slip diff) with the back wheels raised.  If one side is rotated the opposite side usually turns in the reverse direction- but this is usually caused by oil drag.  On a car this "opposing" rotation can be stopped merely by holding the other side still and in any case both sides can be manually rotated in the same direction.  On this lawnmower this can't be done- if I turn one side the opposite side will, only rotate in the reverse direction.

I'm trying to figure out how this would work with the machine fully assembled. if the right hand roller is rotating one way and its opposite number is trying to turn the other way- or am I missing the obvious?

Lastly- and again I'll apologise in advance if I'm asking something to which the answer is pretty obvious but- if I manually turn the large rear gear by hand I notice that the front gear (the one on the rotor) doesn't turn even though the chain is connected to both yet I remember that before dismantling the rotor turned when pushing the machine (but it didn't seem very positively connected to the rear rollers.  Again, am I overlooking something?

I don't want to do any reassembly if I need to correct any of these areas.

Any advice/comments much welcomed.

Many thanks




worzel Thu, 20/01/2022

Hi Henry


Not sure if this was already posted- if so my apologies.

Have answered one of my questions- the one about the rear outer rollers rotating in opposite directions.  I should have realised that only one roller drives the rotor blades so in effect the opposite roller freewheels.

Apologies for that one, however the other two questions still remain so if either you or your fellow readers have any ideas on these I'd welcome your suggestions.

Regards and thanks



worzel Mon, 31/01/2022

Hi Henry


Just an update.  Re- my previous post I'm going to assume that there should be minimal lateral movement on the rear rollers as if too much the ratchet(s) would not fully engage with the centre roller.  I don't think that this machine was correctly re-assembled in the past- possibly what happened was that it didn't work properly after some diy and was just stored.  It's actually in pretty decent condition- oiled greased etc with no rust on the cross tubes/drive gear etc so seems to have been looked after in the past.  I'd post a picture but for some reason the "add images" icon isn't being highlighted at the moment.