Has this ever been done before ?

[edholly]

After making an ML Midge some time ago - and then a Vee Twin based on the Midge - thought I'd make another but try something a bit different.

Last engine built was an Owen mate with a removable front nose, cap-screwed on. Now making a removable nose sure does simplify things, and the thought was to simplify it even more.

So ....

The nose is screwed on. As the direction of rotation will want to turn the nose clockwise from the pilot's seat - made the screw thread left handed instead of normal right handed. as you can see when screwed home it looks almost like it is one piece. This way it will want to tighten all the time.

The original Midge is alongside - this engine runs very sweetly. The new engine will have a few mods ... ball bearing inner, prop-shaft rotary induction, twin exhausts, bronze outer bush - hopefully will produce a bit more power than the standard Midge. Aim is to use it at next year's Oily Hand event at Cowra in a suitable model

Ed

So the question is - has anyone ever seen this done before in a model engine ?

 

[creast]

Hi Ed,
I haven't seen a screw threaded nose but there are plenty of designs around with 'bolt on' nose pieces.
Nice work!
Rich

 

[dave-in-england]

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The problem with having a screw thread directly on a bearing housing is that it will never line up exactly concentrically.

Would be Fine if the bearing housing is tightened and locktited permanently, and then afterwards the bore is finish turned to size,
but once you turn the thread even a little bit, all the concentricity is lost and the bearing will bind up on the drive shaft.

You would need to turn a small, close tolerance location spigot on the body, and a matching counter bore inside the front cap, to ensure concentricity
when re-assembled, but then all the hoped-for simplicity of the part would be lost.

Why not just make a long spigot on the cap and a very close fitting counter bore in the engine body, and press it in.
.

 

[edholly]

Rich, .... Thanks ...

Dave, .... The housing is not different to any bolt on one. All the bearings are a part of the removable part so the only loss of concentricity is if the mating surfaces were not square, which would be the same problem if a bolt on. The thread itself is tight enough when all the way home to locate the housing within the crankcase with the height exact.

I believe this system is the same mechanically as a bolt on, but simpler, a bit lighter and making for ease of machining the housing for the ball bearing as it is not buried down inside the crankcase ... Guess we'll find out when it is finished .... Photo is of the housing removed from the crankcase ( C/case thread can be seen face down) with the ball bearing just sitting on the outer edge not pressed in yet - it will have the shields removed before final assy.

Just wished I could get used to screwing it on to screw it off !

Ed

 

[dave-in-england]

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How about ....for something a little different ..making the crankcase with clear Perspex ?
So you can see it all working inside, would be a bit of a challenge !

May have to make it a little larger, and with thread inserts to hold the cylinder screws, but it would be fun to see working !

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