Atom Minor Mark III - First IC Engine

PaulsGarageProjects · Mar 11, 2024

Hi all,

Here's my Atom Minor MK III that I built using plans and kit from Hemingway Kits. I also followed the accompanying book by Edgar T. Westbury. As my first build, I found it to be a good challenge, but not too difficult, and have learnt many new skills completing the project. The plans are all in imperial, which I converted to metric for each part before building with my metric lathe/mill.

After assembly, I spent about three evenings of tweaking to get it to run for the first time, but can now start it up pretty quickly. The trick seems to be jet screw 1/2 turn open, air shutter fully open, then prime a little before hand starting. Not quite sure on how best to adjust the engine speed once it's running, but I'm sure I'll get the hang of it!

Just need to decide on the next build now!

minh-thanh · Mar 11, 2024

Run well
Congratulations !

bluejets · Mar 12, 2024

Bigger flywheel will be an advantage.

Gedeon Spilett · Mar 13, 2024

nice to see one of these "sparkie" engine running...
its good to run with lot of oil in the petrol, up to 25%.
what kind of ignition you have, electronic module or HT coil and contact breaker as in the plan ?

PaulsGarageProjects · Mar 13, 2024

Gedeon Spilett said:
nice to see one of these "sparkie" engine running...
its good to run with lot of oil in the petrol, up to 25%.
what kind of ignition you have, electronic module or HT coil and contact breaker as in the plan ?

I've been running it on 1:4 petrol and SAE 50 oil. Tried it on methanol and castor oil but couldn't get it to start, or even make a pop.

I didn't like the look of the fiddly little rough casting for the contact breaker, so got a MiniMag MCL-1, with the hall effect sensor. Managed to shock myself with it when setting the timing - got a right belt off it!

Nerd1000 · Mar 19, 2024

PaulsGarageProjects said:
I've been running it on 1:4 petrol and SAE 50 oil. Tried it on methanol and castor oil but couldn't get it to start, or even make a pop.

I didn't like the look of the fiddly little rough casting for the contact breaker, so got a MiniMag MCL-1, with the hall effect sensor. Managed to shock myself with it when setting the timing - got a right belt off it!

Yikes that is a lot of oil in the fuel! Your plug must foul quickly. Do you need to use SAE 50? Modern air cooled 2T oil is SAE 30.

I've caught more ignition coil zaps than I care to mention. The most painful was from an old Lucas impulse magneto, my younger brother handed me the ignition lead and then cranked the engine before I realised what he was planning...

Jasonb · Mar 20, 2024

Don't know how you have mounted your hall sensor but the brackets that these older designs tended to use could be rotated around their mounting which advances or ******* the ignition timing and that would allow you to alter the engine speed.

PaulsGarageProjects · Mar 20, 2024

Jasonb said:
Don't know how you have mounted your hall sensor but the brackets that these older designs tended to use could be rotated around their mounting which advances or ******* the ignition timing and that would allow you to alter the engine speed.

I mounted the hall effect sensor on an aluminium ring, which has a slit and a screw to close it up. I'm going to add a small lever, so I can adjust it while the engine is running.

Jasonb · Mar 20, 2024

That should do it, I usually have an extended screw with knurled head.

This is a good example of how the ignition timing can affect a 2 or 4 stroke, just the odd adjustment to the carb is needed for smooth running

PaulsGarageProjects · Mar 20, 2024

Nerd1000 said:
Yikes that is a lot of oil in the fuel! Your plug must foul quickly. Do you need to use SAE 50? Modern air cooled 2T oil is SAE 30.

I've caught more ignition coil zaps than I care to mention. The most painful was from an old Lucas impulse magneto, my younger brother handed me the ignition lead and then cranked the engine before I realised what he was planning...

The engine has a cast iron piston and cylinder with no rings, might be why it requires so much oil? The instructions say:

"The fuel recommended for this engine is ordinary petrol, as used for motor vehicles, with the admixture of a fairly heavy oil, such as Castrol XL, in the ratio of one part oil to four of petrol".

I spent a fair bit of time looking for info on what fuel/oil to run it on, but couldn't find much that related to this particular engine. There was one chap who built one and ran it on SAE 50/petrol 1:4, so I just went with that.

I've tried it with petrol and Putoline Castor R 1:7, but this seemed too thick, and the engine would only idle pretty slowly. Think I need to try at 1:10 and see how it runs. Ideally, I'd run it on methanol, but haven't had any luck with that.

Any advice greatly appreciated!

PaulsGarageProjects · Mar 20, 2024

Jasonb said:
That should do it, I usually have an extended screw with knurled head.

This is a good example of how the ignition timing can affect a 2 or 4 stroke, just the odd adjustment to the carb is needed for smooth running

Wow, impressive how easily your engine starts! I'm going to have a play around with the ignition timing later on

Jasonb · Mar 20, 2024

That one is not mine but I have built a couple of Nicks's other engine designs. I keep asking him for a set of drawings for that one plus a few others.

Yes about 20% oil is right for a small 2-stroke like this much the same as you find in premixed fuel for glow (nitro) engines. I tend to use a good quality 2-stroke oil though Westbury did always suggest a fairly heavy oil to make sure it dropped out of suspension and lubricated the engine but just for display running when not under load you can go a bit lighter.

PaulsGarageProjects · Mar 20, 2024

Jasonb said:
That one is not mine but I have built a couple of Nicks's other engine designs. I keep asking him for a set of drawings for that one plus a few others.

Yes about 20% oil is right for a small 2-stroke like this much the same as you find in premixed fuel for glow (nitro) engines. I tend to use a good quality 2-stroke oil though Westbury did always suggest a fairly heavy oil to make sure it dropped out of suspension and lubricated the engine but just for display running when not under load you can go a bit lighter.

Many thanks for the info!

By the way, should I be able to run this engine on methanol/2 stroke oil? I bought some (supposedly) 99.9%, mixed 4:1 with 2 stroke oil, but couldn't get it to run at all.

Nerd1000 · Mar 20, 2024

PaulsGarageProjects said:
Many thanks for the info!

By the way, should I be able to run this engine on methanol/2 stroke oil? I bought some (supposedly) 99.9%, mixed 4:1 with 2 stroke oil, but couldn't get it to run at all.

Methanol will need a far richer air fuel mixture (6.5:1, rather than 14.7:1) than petrol, so one possible issue is that your carb simply can't provide enough fuel.

The other issue I've observed trying to run my Webster engine on alcohol is that alcohol has a higher boiling point than the 'light fraction' of petrol, making it hard for the engine to adequately vapourise the fuel when it is cold. The low compression ratio greatly aggrevates this. One option would be to mix some 'E85' or 'M85' by adding 15% petrol to your alcohol, then there will be some lighter stuff to help with starting.

Edit: just be warned that castor oil is insoluble in petrol, but soluble in alcohol. If you add too much petrol your castor may drop out of solution, I don't know exactly how much would cause this but the potential problems are obvious. So if mixing I'd keep the fuel in a glass jar for a while and make sure that the oil isn't separating before using it.

D and D · Sep 12, 2024

PaulsGarageProjects said:
The engine has a cast iron piston and cylinder with no rings, might be why it requires so much oil? The instructions say:

"The fuel recommended for this engine is ordinary petrol, as used for motor vehicles, with the admixture of a fairly heavy oil, such as Castrol XL, in the ratio of one part oil to four of petrol".

I spent a fair bit of time looking for info on what fuel/oil to run it on, but couldn't find much that related to this particular engine. There was one chap who built one and ran it on SAE 50/petrol 1:4, so I just went with that.

I've tried it with petrol and Putoline Castor R 1:7, but this seemed too thick, and the engine would only idle pretty slowly. Think I need to try at 1:10 and see how it runs. Ideally, I'd run it on methanol, but haven't had any luck with that.

Any advice greatly appreciated!

Hi

PaulsGarageProjects said:
The engine has a cast iron piston and cylinder with no rings, might be why it requires so much oil? The instructions say:

"The fuel recommended for this engine is ordinary petrol, as used for motor vehicles, with the admixture of a fairly heavy oil, such as Castrol XL, in the ratio of one part oil to four of petrol".

I spent a fair bit of time looking for info on what fuel/oil to run it on, but couldn't find much that related to this particular engine. There was one chap who built one and ran it on SAE 50/petrol 1:4, so I just went with that.

I've tried it with petrol and Putoline Castor R 1:7, but this seemed too thick, and the engine would only idle pretty slowly. Think I need to try at 1:10 and see how it runs. Ideally, I'd run it on methanol, but haven't had any luck with that.

Any advice greatly appreciated!

Hi Paul all those old engines with CI pistons use petrol (unleaded) with about 20%-30% oil I use a straight 60 weight oil (Aeroshell 120) IMO.
Lovely job by the way

bluejets · Sep 12, 2024

Nerd1000 said:
Edit: just be warned that castor oil is insoluble in petrol, but soluble in alcohol. If you add too much petrol your castor may drop out of solution, I don't know exactly how much would cause this but the potential problems are obvious. So if mixing I'd keep the fuel in a glass jar for a while and make sure that the oil isn't separating before using it.

Small percentage of acetone (10%) works as a catalyst and negates the problem.
I remember we would tune our 1/2a motors at home then have to retune at the field.
Reason turned out to be the methanol we bought from the Shell depo had 10% acetone for the blokes from speedway.
When we arrived at the field, we had to use the mix the organisers supplied which turned out to be zero acetone content.
Both used to be available at our local depo so that's what is in my stock now (100%)

Engine should run on methanol but as previously mentioned, will require around 4 times the amount of fuel @4:1 methanol/castor (castrol M).
Burn is a much softer affair and takes longer to ignite and burn so timing with spark would need to be advanced.
Also compression ratio much less than with petrol, and much less again if nitro is added.
Any nitro tends to make a measurable difference in 10% lots.(in place of methanol)

Old engines used cast piston/liners and required an amount of run-in.
They also lasted quite a while and turned out to be quite rev-ey little mothers.

Gedeon Spilett · Sep 12, 2024

very nice engine, congratulations !
I also did some years ago several little vintage 2 stroke engines, and yes, between 20-30% v/v of plain car oil in the petrol is "safe" , but I've ran engine with 12% for short demo in the garage, it also activate the smoke detector...

the same 20-30 % ratio is also recommended for piston with rings, as I see in a meeting of flying vintage model airplane, with lot of fabulous model engines running.

D and D · Sep 13, 2024

D and D said:
Hi

Hi Paul all those old engines with CI pistons use petrol (unleaded) with about 20%-30% oil I use a straight 60 weight oil (Aeroshell 120) IMO.
Lovely job by the way

Here is one running on Petrol with about 25% Aeroshell 120.

Atom Minor Mark III - First IC Engine

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