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Collection, Preservation and Display of Old Lawn Mowers

First ever Restoration - Suffolk Super Colt - Lots of questions!

Hello all, I've been browsing the site more and more recently - mainly from search results while googling for information. After giving up cycling recently due to health problems i needed something to help pass the time and something to fettle with! I've always carried out servicing and repairs on my own cars and bikes, learning along the way and reading up about things i didn't know how to do, and like to think I’m mechanically competent. 

There has always been something about engines that has intrigued me, and so i decided to see if I could strip down and refurbish a lawnmower. One came up nearby on the bay, a 'Suffolk Colt' which was advertised as spares / repairs due to 'No Spark - suspected coil'. I figured it was worth a punt and would be a good learning experience even if i can't manage to get it running. Looking online, Colt's didn't seem to quite match the look of my mower, which led me to discover it's actually a 'Super Colt'.

What started off as a simple 'Let's find out why it's not sparking' quickly resulted into a complete strip down of the entire mower and lastly the engine!! Taking plenty of pictures along the way, and bagging up nuts and bolts with labels so as not to forget what went where, I've now stripped the entire thing down so that I'm left with the engine block, and an exhaust that is well and truly welded to the block - thankfully it doesn't appear damaged, just rusty, so It can stay where it is (frustratingly for my OCD).

I'm going to test the waters here to make sure I can upload pictures properly, and once I can, I'll post up a few pictures I've taken during the strip down. I've come across quite a few things I’d really appreciate some advice with so anyone interested in looking/reading can hopefully help me out - which I’m hoping will help others out in future who are thinking of tackling the same sort of project.

Here is a Picture of the mower after collecting it


RedLeader Fri, 08/11/2019

A few more pics before strip down...

First item added to the shopping list is a proper pull cord handle to replace the make shift one...

QUESTION - Is the small hole in the middle of the petrol tank cap supposed to be a breather hole? If so it's rusted over internally so will need clearing out.

Second item for the shopping list is a replacement Fuel tap and hose...

Next items on the shopping list are a new Spark plug - NGK B6S if I am correct? and also a proper spark plug Suppressor cap to replace what looks like a 'rusty picture hook'?! being used currently...

QUESTION - The 'L' shaped metal bracket on top of the engine cowling in the above picture - should that be angled over and used to cut the engine by shorting the plug electrode out? I've seen the slightly newer (I believe) engines having a smaller metal bracket like this with a plastic end cap  which cuts the engine? If this is what it is for, does anyone have a picture of how this bracket should be shaped normally?


Chris G Fri, 08/11/2019

The L shaped thing could be a home brew cut out, can't see that on the manuals, the more experienced of this model will be along I hope. - love the spark plug connector :-)

RedLeader Fri, 08/11/2019

Hi Chris, thanks for the welcome! Yes the spark plug connector is certainly an 'interesting' setup - possibly part of the reason for 'no spark' :)

Thanks for the link also - I've managed to have a good read through the manual for the Super Colt now, and it appears you are correct - the L shaped bracket is another 'interesting' modification for, I presume, stopping the engine. On page 7 of the manual it shows part number 5 as the Cut-out switch, which comes up through the spark plug cut-out in the cowling and has a rubber cap

So that's another thing I need to acquire - it looks like it must attach to one of the head bolts. I can only find one reference on google to that part number - an online shop in the Netherlands -

Hopefully I can source one a little closer to home!

Chris G Fri, 08/11/2019

I would look to make the cut out switch as close to the original as possible, it does not look that complicated, but I'm not a purest..

It would be a good idea to get as close to original spark plug connection and the right spark plug, clearly the cut out won't work with a modernish plastic cap as it won't earth out to cut out, also some are not specified for a suppressor type plug anyway.

Pull handles and fuel taps are easy to come buy, but your focus will be on getting that spark first.

wristpin Fri, 08/11/2019

The L shaped stop bracket is an original but not for that model and date: I think that it belongs to a similar engine on an Atco. The broken fuel tap is wrong , it would have been a plastic plunger tap. That machine would have points ignition so with a bit of luck the loss of spark is nothing worse than dirty points.

The cut out strip is a pattern part but follows the design of the original The original would have been fitted between the cylinder head and cowling and come up beside the plug but tended to get mangled up when removing the cowling so ended up on top under one of the exposed head bolts .

The tap is a pattern but is "right" for your machine.

The plug connector on the far right probably pre-dates your machine but second from the right, again a pattern, is about right.

wristpin Fri, 08/11/2019

Some thing about you images has been bugging me!

Although your machine has a Colt grass box I believe, from the construction of the handle bars and fuel tank, that it is the Atco branded version - hence the Atco L shaped cut out plate.  Essentially the same machine as the Suffolk but branded to appeal to traditional Atco customers at a premium price over its lesser sibling. Interestingly I have a manual for a much later Webb branded machine using the same pattern of handle bars.

Chris G Fri, 08/11/2019

Interesting...So you would deploy the "boot" to switch it off? 

If making the hand version, springy steel in the form of a 6" rule had  for a few quid off ebay would be developed for my answer, It should be strong enough to bend the L and springy enough not to fatigue and crack - well not for a good while anyway. Insulated atop with rubber cap of choice



hortimech Sat, 09/11/2019

Yes, it is a 12" Atco, apart from the grassbox, it has just been painted the wrong colour, it should be Atco green. The stop 'switch' is correct. I would image in the general scale of things, that they are fairly rare, after all it is just a Super Colt with different handles, but they cost quite a bit more than a Super Colt, so didn't sell in the same numbers.

RedLeader Sat, 09/11/2019

Thank you all so much for the information provided, as well as the images. So my Colt which I thought to be a Super Colt, is in fact an Atco model! Would it have been simply an Atco 12" Cylinder mower, or would it share the 'Super Colt' model name with the Suffolk equivalent?

That would explain why all the Super Colts that I had seen images off all seemed to have red handles/fuel tanks/engine cowlings, and yet there is no trace of any red underneath the current paintwork on my mower, just two different shades of green. Knowing it should be Atco green will certainly makes finding the correct paint easier. So on that basis, to try and maintain original colours, there would have been no red paint at all - except perhaps the cutting cylinder? The grass box would have been Atco branded and metal I presume?

And here's the engine cut out bracket in the flesh on an Acto Deluxe

Henno Sat, 09/11/2019

Hello & welcome, sorry to read you had to stop cycling, it is one of my passions too, spreading time between that, our Galgo (Spanish sight hound), mowers and well, humans and so on. :)

First thoughts regarding your catch: Nice mower to restore! The grassbox looks more from a Qualcast from the nineties with a sticker on it, shouldn't this mower come with a metal one?

Seen a couple of pictures now, the ony red should be the cylinder.


hortimech Sat, 09/11/2019

Yes, all Atco green, except for the cutting cylinder and engine block, the cylinder was red and the block was that strange sort of yellowy-grey colour.

 The grassbox was (on the ones I saw) a metal one (the same box as a Super Colt), again painted Atco green with an Atco by-appointment Decal

It was just known as the 12" Atco and retailed for approx £20-30 more than than Super Colt back in the late 70s - early 80s, this is probably why there are not a lot of them out there.


RedLeader Sat, 09/11/2019

Thanks for the welcome Henno - a Galgo - what a lovely dog! 

I'll probably look at selling the plastic grass box on if I can find a metal one that's structurally sound and can be refurbished in Atco green. For the engine, I've seen Hammerite Wild Thyme mentioned as being pretty close to the original colour on the 75cc engine block.

Hortimech - thanks very much for the info. So I'm looking at a manufacture date of late 70's early 90's then. After some googling I cannot find any other pictures online of this particular model, so if anyone knows of any, or comes across one, I'd really appreciate if you could post it or link to it on here. 


Henno Sat, 09/11/2019

Hi Redleader,

Galgo's are almost not dogs, they are mesmerising, but that's something for another club / forum :)

A picture I found:…


Be careful with the paint on the engine, you need engine-paint to withstand the heat. I usually use a silver engine paint. The green is a different matter. To get an exact match it is best practice to take a part that was not exposed to sunlight (underside of the cover) to a shop that mixes paint and can make cans for you. These shops usually have databases of mixtures and you will get a paint number which is very close. For example I got a number for green used on Atco Commodores, close to Daf trucks for the Bavaria Beer brewery here in the Netherlands. Strange, but there you go.

Regarding the grassbox:………


wristpin Sat, 09/11/2019

Been doing a bit of digging and delving in old Atco parts books and it appears that your machine was officially known as an Atco 12" Standard there was also a Suffolk based 14" Standard and a DeLuxe version of each; the DeLuxe versions having steel (? aluminium ) grass boxes and the handle bar design found on the more common 17 and 20" machines with an inverted U lower section clampted to a U top section by a rectangular fuel tank.

Back to your Standard it appears that it did have the Suffolk plastic grass box (see page 1:1:1 ) so all you need is an Atco decal to make it "right". Page 1:2:1 shows the steel (?aluminium) grass box.…

hortimech Sun, 10/11/2019

Not disbelieving what you are saying Wristpin, but I only saw a few of these (probably because of the price difference) and they all had the same steel grassbox that the Suffolks had, just painted Atco green. It may be that the larger versions (which I have never seen) did have an alloy grassbox but I am willing to bet they are rarer than hens teeth.

RedLeader Sun, 10/11/2019

Henno - thank you very much for the link to the picture - great to see how one should look and a very useful reference. Thanks also for the grassbox links too! The look of the metal grassbox certainly seems to fit better with the rest of the mower, in my eyes at least. However, Wristpin's link to the Atco document does indicate the plastic box was an option on that model, but Hortimech references only seeing metal boxes on these (thank you), so I'll hang fire and keep the plastic box for now.

Wristpin - Thank you very much for the Atco document, that's a big help and certainly clears a few things up and a useful reference!

wristpin Sun, 10/11/2019

However, Wristpin's link to the Atco document does indicate the plastic box was an option on that model, but Hortimech references only seeing metal boxes on these (thank you), so I'll hang fire and keep the plastic box for now.

Wristpin - Thank you very much for the Atco document, that's a big help and certainly clears a few things up and a useful reference!

I suspect that the type of box supplied may have been a "model year" thing or even "what stock they had available" at the time. As Hortimech points out, the 12" Atco branded machines were not exactly big sellers and to manufacture low numbers of metal boxes while also having big stocks of plastic ones , hardly made much sense.

RedLeader Sun, 10/11/2019

Well, seeing as the plastic box I have is sound other than the sticker and a few scratches / scrapes, I think I'll stick with it. It's the same colour as the underlying Atco green of the mower in the untouched parts underneath, which looks almost like a peppermint or pastel shade of green - different to a lot of pictures I've found of Atco machines so far at least. A few more pics

QUESTION - Would there have been an engine plate mounted on this front panel originally? Behind where the HT lead runs

A few dents and bumps on some of the panels which I can hopefully straighten out.

The front plastic rollers looking quite sorry for themselves, worn down and some have large cracks in them

These screws were quite badly rounded so after a lot of soaking in penetrating spray and a lot of downwards torque I managed to carefully remove them all - just! I would like to replace these when it comes to building the mower back up, if they/equivalents are available

Tut tut - paint on the plastic handles!

I'm sure electrical insulation tape wasn't on the parts list when I looked....

wristpin Sun, 10/11/2019

You may get a better idea of the original paint shade by removing one of the handle bar grips and seeing what’s underneath, or the inside of the chain and belt covers.

RedLeader Sun, 10/11/2019

Thanks - just checked and yes it's a different green under the handlebars, which doesn't match the grassbox - hopefully it's the original paint and hasn't been repainted incorrectly under there...

wristpin Sun, 10/11/2019

That green looks about right for what we would have seen on a new Atco back in the day. As the grass box is either Suffolk or Qualcast I would not expect it to match. Also, those days, plastic parts never exactly matched painted metal.

RedLeader Sun, 10/11/2019

That's good to know, thanks Wristpin. Any idea if there would have been an SIF engine plate on the cowling, detailing the engine as a 75G14, or would there have been an Atco equivalent plate instead?

wristpin Sun, 10/11/2019

Memory fails me on that but I have two cowlings that I know came from Atcos that have none of the slots that secured the metal ID plates but they could have had the later adhesive ones.

hortimech Sun, 10/11/2019

No, they didn't have the SIF plate, they didn't want to advertise that it wasn't an Atco engine, even though they were all part of the same group.


RedLeader Mon, 11/11/2019

OK thanks for confirming, so it will just be the logo stickers/transfers I will need to source after repainting. 

Strip down pictures...

The plastic grass shield has a few broken 'legs' so will I will see if I can either repair it or replace if not

RedLeader Mon, 11/11/2019

Apologies for the picture quality so far, I'm not sure what's going on with the camera focus so will need to investigate...

Things were very wet and oily behind the flywheel all around the points and coil - perhaps a weepy crankshaft oil seal?

There are 2 parallel score marks running through the magnet faces in the flywheel, as well as some light surface rust. Can anyone suggest what may have caused these? The metal poles surrounding the coil look ok with no visible damage, that's all I can think would have possibly made contact with the magnet faces, if the stator place wasn't fitted properly? Or a stone somehow getting trapped in there? Although I still can't really see how that would be possible...

wristpin Mon, 11/11/2019

Don’t worry about those scores. As you say possibly debris or even something magnetic picked up during careless servicing.

Change the oil seal now rather than have to go back to it . They wear and harden.

The size is 0.87 x 1.25 x .25 R21. Thank forum member Hillsider for me having that info to hand !

If you don’t have a favourite bearing, belt and seal supplier, try Simply Bearings. Excellent mail order service

RedLeader Mon, 11/11/2019

Great, thanks for the sizes and link Wristpin - I've heard of that site but never used them - I'll definitely get a couple of those seals ordered for the rebuild :)

I'll just remove the surface rust from the magnet faces and disregard the scores - a screwdriver still sticks to the magnets so they haven't lost any / much magnetism.


RedLeader Mon, 11/11/2019

QUESTIONI've discovered a crack in the end of the crankshaft where the flywheel nut screws on - is this likely to be a problem that means the crank needs replacing or is it nothing to really worry about??

wristpin Mon, 11/11/2019

How odd. If you look at the crank end on is there any sign that it extends to the end?

Is it just the image or is the threaded end slightly bent?

RedLeader Tue, 12/11/2019

I think it's just the picture making it look bent - maybe due to teh left hand threads adn the lines in the cardboard. Checking it front on it certainly looks straight. A couple more picture of the crack - doesn't seem to run very deep and doesn't show at the end of the threaded end at all

wristpin Tue, 12/11/2019

The “ distressing”  on the taper suggests that the engine may have run with a loose flywheel .  All rather strange.

RedLeader Wed, 13/11/2019

It does seem strange doesn't it. Well I'll continue with the strip down and check out the condition of the rest of the crankshaft.

Crankshaft Oil seal on the clutch side has some part numbers on it - POS 3078 IIP 12508727 5 , however I can't find any references to these numbers online.

And some sort of damage to the outer seal surface

The seal on the flywheel side doesn't have any numbers or markings at all, so not sure which of these, if either, are the original seal. Thankfully due to Wristpin's post with the correct sizes, I have found what I belive to be the correct replacement oil seals here:

I think I've discovered one possible reason that the flywheel side seal was letting oil through to the coil area (alongside usual wear) - the seal was not seated squarely in the housing

Both crankshaft oil seals removed

All looking pretty carboned up and gunky after removing the head - some sort of loose debris also

Spot the 'surprised' exhaust...

Cam timing marks circled for reference

Oil flicker on the end of the con rod

Chris G Wed, 13/11/2019

Weird stuff on the flywheel end with that lop sided seal and that crack...

That debris on the head looks like gasket material - did it have a head gasket fitted?

The exhaust connector pipe may have stripped its thread, hence the gunk?

RedLeader Wed, 13/11/2019

Good shout on the gasket material Chris - it's very similar texture to the exhaust pipe gasket which was all broken up. Not sure how it would have ended up in there - I don't think the head had been off at all and did have the gasket in place which looked fine other than being a bit squashed. If a previous owner had the spark plug out and was fiddling around or putting oil down through the plug hole for storage or something like that, I guess it could have got in then?

RedLeader Wed, 13/11/2019

QUESTION - Am I correct in thinking I will need to buy 3 x paper gaskets which fit between the block and the flywheel magneto backplate? 

wristpin Wed, 13/11/2019

In one of your images the main bearing looks pretty rough - is there any lift on the crank. If there is it may account for the scores between the stator and the flywheel. Also it looks as there is no friction material on one of the centrifugal clutch shoes.


RedLeader Thu, 14/11/2019

It's certainly looking like this mower has had a hard life, that's for sure. Regarding the main bearing picture, i'm not quite sure which one you are referring to, but I'll post up some more pictures of the engine strip down which will hopefully clarify things. I didn't notice any crank lift while stripping it down, but that would be a good culprit for those scores like you say.

Quite a prominent score which can easily be felt right in the middle of the big end bearing/cap and crank journal

A lot of scoring on the skirt of the piston, however a lot of used Suffolk pistons seem to have this appearance, so doesn't necessarily mean the piston has been catching the cylinder walls due to excess bearing movement does it?

As far as I can tell, the cylinder looks ok. The usual expected glazing on the upper section, compared with the lower area where the piston doesn't travel. 

Out come the valves and springs 

hillsider Thu, 14/11/2019

Hmm yes you certainly need to do something with those gaskets, I have a similar project running at the moment as a means of introducing my grandson to the world of machines and I have shown him the dark art of gasket making. Gasket paper is freely available via Amazon or even brown paper at a push can be used so long as you watch out for gasket thickness as it can alter shaft clearances etc.


wristpin Fri, 15/11/2019

An excellent set of gaskets , the young man is to be congratulated.

Brown paper, don’t forget the corn flakes box ( other cereals available etc) . Back in the day it was not unheard of to set point gaps using  “a bit of fag packet”.  

While on the subject of improvisation,  recently a strip of plastic cut from a 2 litre milk carton served as a non- magnetic gauge for setting the clearance between a BS ignition armature and the flywheel. 



RedLeader Fri, 15/11/2019

That's impressive knocking out that set of gaskets! Very well done to him. If you don't have any new genuine gaskets as references, how do you know what thickness of gasket material is required for each fo the different gaskets? I can see the head gasket thickness is imprinted on the underside of the head .062 but as for the valve chest, inlet manifold, carb bowl, flywheel backplate, sump gasket etc, were there any gasket thicknesses ever published for these anywhere?

I see you have 4 gaskets for the flywheel backplate to engine block gasket. The parts list for the engine lists 3 of these gaskets required, and as they seem hard to come by, I may get some material and have a go at these ones myself after watching some videos etc ;)

I'm certainly a fan of cereal, and go through quite a few boxes a month, so rather than recycling one of them, i might as well make myself a gasket or two - where this is the correct thickness required.

wristpin Fri, 15/11/2019

In the real world when repairing an old engine exhibiting as much wear as yours the thickness of the gaskets in fairly irrelevant . Consider what the gasket is designed to achieve. On your engine with just one exception it is just sealing  - to “ take up the slack”  between two rigid components that may have surface irregularities to achieve air or fluid tightness. The exception is those mag backplate gaskets which are used singularly or in combination to regulate crankshaft end float. Too little and the crank may be pre loaded  longitudinally and bind; too much , well within reason on an old SIF lump,  possibly not an issue!  I’ve never found a manufacturer’s figure for SIF end float so 5 to 10 thou when cold would seem about right.

RedLeader Fri, 15/11/2019

Thanks for the explanation about the gaskets Wristpin, appreciated. I've not had a huge amount of engine experience, only from servicing my own cars over the years, and never stripped and engine down this far before, so it's all a learning experience. How would I go about measuring the endfloat once I've reassembled the engine? I have a set of feeler gauges and a digital vernier caliper, but would I need a tool/gauge specifically for this purpose and how to you actually take the measurement?

Hillsider - would you mind posting the gasket thickness that you used for the mag backplate gaskets please?


wristpin Fri, 15/11/2019

Once you’ve got the engine apart you can run a quick check on end float. Slip the crank in and fit the mag back plate without any gasket . Gently pinch the bolts up and try pulling and pushing the crank. If you can feel end float, tighten the bolts a bit and try again . If you then feel end float it is  due to engine wear and the only way you can eliminate it is to add a shim to the crank** . If on the pinch up of the mag plate it starts to go tight , add sufficient gaskets that you can feel end float when it is fully tightened. Then measure what you have - probably easier done at the other end. 

** There’s so much other wear on your engine that excessive end float is possibly the least of its issues,    so fitting a shim is probably a council of perfection - hardly warranted under the circumstances.

Measuring - Very crudely slip a worm drive clip over the PTO end , push the crank right in, push the clip against the block, tighten the clip, pull the crank out and see what feeler gauges you can get between the clip and the block. Crude but probably sufficient for a worn SIF lump !  

RedLeader Fri, 15/11/2019

Thanks very much Wristpin. I've just tried this and with no gaskets in between, and the 4 bolts nipped up there is no end float at all and the crankshaft becomes tight to turn. Loosening the 4 bolts slightly, frees it up and introduces a tiny bit of end float but barely anything. I think with the gaskets fitted hopefully things will be ok in that regard, and I can look at addressing the other wear going on in the engine (everywhere!).

RedLeader Fri, 15/11/2019

The valves and followers cleaned up ok

The camshaft looks fine with no visible damage or wear - easier to see the cam timing mark in this picture

You can see in the above picture on the crankcase breather valve, one of the small alloy vertical legs has broken off ( I retrieved it from the crankcase breather chamber). As this is just for locating the breather in the hole that runs through to the crankcase, do you think it will be ok with just the one locating leg? There's probably no secure way of reattaching the leg back on, and the part itself if probably impossible to get hold of....

wristpin Fri, 15/11/2019

The valves look  to be in fair condition with nice wide margins, but the contact area on one of the valves appears to be very near the margin, possibly suggesting a possible seating issue. Also,  I don’t see any sign of the little “ mica / Paxolin” disc for the breather - hidden or missing?


PM sent re the broken breather body.

RedLeader Fri, 15/11/2019

Not sure if I need to replace the fibre(?) washer that the breather body sits on - it's in tact from what I can see but as I'm rebuilding would it be worth replacing this? If i could get an idea of original thickness, I'm sure I could make one from some suitable material. 

After cleaning up the valves, and testing their fit again in the valve guides, there is a bi of play mainly in teh exhaust side. How would I know if it's the valve steam, or the valve guide that is worn. Is it possible to obtain measurements for either of these 'as new' from anywhere? 

The exhaust seems well and truly welded to the engine, however as there is no damage to it and it's still structurally ok just with a degree of rust, it can stay put. I don't have any Stillsons or similar to attempt removal, and after a quick try with Molegrips, that thing isn't budging any time soon!

As Wristpin correctly spotted, the clutch is also missing it's friction pads on centrifugal shoes - both of them. Nothing left at all, just the copper coloured rivets (?)

Replacement friction material pads don't seem to be available, and it looks like there are 2 or 3 different clutch types available, so I'll keep an eye on on the bay and try to pick up either a pair of clutch shoes or an entire clutch mechanism with good shoe material left on it. This 'non-runner' due to suspected coil, was certainly an understatement........