12.8cc two stroke. An early first attempt at an I.C.engine.

[Lathejack]

Around 25 years ago I designed and built this rotary induction valve engine. it is loosely based on the common small engines used in R.C. aircraft and other models.

The carb and silencer are O.S. and Ervine items, but I made everything else.

It has a one inch bore and stroke using an aluminium alloy piston with two cast iron rings located with tiny bronze pegs.

The head and cylinder barrel are both machined from a billet cast from diesel engine pistons, the cylinder barrel is fitted with a honed cast iron liner.

The crankcase is machined from solid aluminium alloy round bar. It is fitted with a long bronze bush which supports the hardened and pressed up crankshaft, and forms an air tight seal with a close running fit.

 

[Lathejack]

The 1/4 diameter floating gudgeon pin is retained by two bronze plugs. An unbushed aluminium alloy rod was made from flat bar.

The built up crank uses a 1/2 diameter hardened silver steel shaft. the crankpin is a shortened 1/4 diameter needle roller. The heafty crank web is mild steel.

 

[Lathejack]

The top of the cast iron liner has a wide lip. The long studs that secure the head and barrel pass through the lip of the liner slightly to ensure it does not rotate.

The barrel is a shrink fit on the liner which also ensures a good heat path for cooling. There is a single exhaust port and two wide, bridged transfer ports which allow the gudgeon pin plugs to pass safely over them.

The old piston material I used for the head and barrel was quite tough and sticky to machine, but it was early days and I had to use what I could find.

 

[Lathejack]

The crank case was machined from solid and uses long through studs to secure the head and barrel. The long crank bush can just be seen sticking out slightly.

The simple cylinder head is spigotted into the cylinder.

 

[Lathejack]

A few views of the loosely assembled engine, with a 50p coin to give an idea of its size, though that might not mean much to everybody.

It is a heavy lump, and so it is a good job it was not made with the intention of flying, as I am sure it would drop like a brick.

The Carb and silencer I used are a bit undersize. The engine still needs a bit of tweaking here and there to make it run properly.

The engine was made simply for the fun of making my own. A four stroke parallel twin, based on the Triumph motorcycle engine, is one I would like to design and make next.

 

[ixb1]

Hello.I have question.What were steps of hardening this hollow crankshaft?
You had any problems with his deformations?

 

[Lathejack]

Hello ixb1.

The 1/2 inch diameter silver steel bar I used for the crank main shaft was the oil hardening type, if I remember correctly. It is produced with a good precision ground finish, so was fully machined and threaded first, but with the outer bearing surface left as supplied except for polishing and a bit of lapping after hardening.

To harden it I simply gripped the threaded end, with a short extension, in the chuck of a pillar drill with a can of clean oil sat on the drill table below it. With the drill spindle rotating slowly and a blow torch flame on the shaft it was brought up to temperature evenly, and then quickly plunged into the oil to quench it.

After polishing and tempering it was found to have no distortion, so was lapped to the long crank bush with a good running but air tight fit.

Thanks for your interest.

 

[Swifty]

Lathejack, your heat treatment method is ideal for shafts. That method of quenching in oil by plunging the rod in end first is the best way to avoid distortion. If it was put in an oil bath sideways, you most likely would have ended up with a bent shaft as the cooling would have been one sided. Commercial heat treaters always wire up their long parts to hang vertically.

Paul.

 

[Lathejack]

Hi Paul.

Looking back all those years ago when that first engine was made, I did manage to get some things right first time. Even with the inlet port already cut into one side of the hollow shaft it remained straight after hardening, I hadn't thought much of it until ixb1 asked about it, a good question I thought.

I really should get back to making some more engines of that elegantly simple design, as used on comercial model aircraft type engines. I have been letting my home workshop activities get bogged down with other projects and full size engine work. With the bit more knowledge and better equipment I now have I should be able to make more refined versions, I hope!