30cc Flat Four (Puma)

[doubletop]

Roger

Thanks. The intake/exhaust configuration is something that I had not considered. I think making it a twin carburetor design would be a step too far.

So given the current design of a single carb and manifold you think either option would be acceptable? If thats the case then going the 1,2,3,4 route would mean two camshafts with the same configuration and the two sets of cams set 180deg out.

Which is as Malcolm's original design.



The two camshafts will then be set up with the left hand camshaft leading the right by 90deg, which is 180deg on the crank. That keeps it simple.

I think that will be correct but I will check my assumptions

Pete

[doubletop]

Well that didn't take me long to find out I was wrong. I was trying to reconcile why the cam layout for the left hand (1,3) cylinders would be the same as Malcolms Bobcat design when the crank for the two adjacent cylinders on the Puma are 180deg apart.

Back to the start with the crank diagram and my proposed firing orders were incorrect (* indicates firing cylinder)



So now it is 1,2,4,3 or 1,3,4,2 either way adjacent cylinders will fire one after the other.

I'll eventually get my head around all this and get the cam shafts assembled.

Pete

[Brian Rupnow]

Four cylinder automobile engines are timed 1-3-4-2. There must have been some logic behind this. Rotary engines has sequential firing order.

[doubletop]

Four cylinder automobile engines are timed 1-3-4-2. There must have been some logic behind this. Rotary engines has sequential firing order.

And thats from a VW man, also flat 4's, so let's go that that way.

Thanks Brian.

Pete

[Bluechip]

Ditto for Subaru it seems ..

https://www.bing.com/images/search?q=subaru+firing+order&qs=HS&form=QBILPG&sp=1&sc=8-0&cvid=20ABD881D899438ABC41129F89FFB1D9

D.

[Ian S C]

Lycoming and Continental 4 cylinder  aero engines are 1342.
Ian S C

[Admiral_dk]

Lycoming and Continental 4 cylinder  aero engines are 1342.

Yes - but they have a normal flat-four crankshaft layout - this one is VERY different, or as stated earlier - it is a V4 that has been flattened from 90 to 180 degrees without changing the crank.
This completely excludes any normal firing order !!!!.... and it also results in an engine that should vibrate quite a bit more - that said, it is also a much easier crank to make ....

I still expect it to give you great satisfaction when it runs 

Best wishes

Per

[doubletop]

Thanks for all your input, 1,3,4,2 it is.

I've now sorted the cam assembly and glad I took the time to get my head around it and model in CAD. Only 1/2 an hour ago I realised that the table of angles for the rotatry table setup had one of the inlets lead the exhaust rather than lagging. (Of course they don't when running but as the start point of assembly is an exhaust cam the  table is rotated clockwise and the inlet is 102.5 degree behind it.)



The table and the assembly now reconcile

Pete

[doubletop]

Camshafts assembled and installed

[youtube1]https://youtu.be/QgefE1PddUI[/youtube1]

[youtube1]https://youtu.be/kC5fpwutvds[/youtube1]

Tommorrow I'll do the pistons. I'm not expecting them to be too much of a problem.

I'll admit it now, I'm going to cheat. My Bobcat and Lynx took ages to get running. When Brian did his flat twin, based on Malcolms design, he got it going just about his first try. I put it down to him using O rings.  I'm convinced the compression on my engines has improved just by them sitting on the shelf. I believe the, once new, rings have normalised over time improving their fit.

So, I'm going to try 1x20 metric O rings as they will go straight into the ring grooves. I can then always go back to rings, I have them already.

Pete

[Vixen]

I'll admit it now, I'm going to cheat. My Bobcat and Lynx took ages to get running. When Brian did his flat twin, based on Malcolms design, he got it going just about his first try. I put it down to him using O rings.  I'm convinced the compression on my engines has improved just by them sitting on the shelf. I believe the, once new, rings have normalised over time improving their fit.

So, I'm going to try 1x20 metric O rings as they will go straight into the ring grooves. I can then always go back to rings, I have them already.

Pete

I know O rings are commonly used on the pistons of steam engines but are not that common in i/c engines. Which O ring materials and hardness works best? Do you use nitrile or viton or PTFE O rings or something else?

What works best? What does the team think?

Mike

[Jasonb]

The last couple of IC engines that I have made were both fitted with single Vitron rings. Though both are relatively slow runners.

[Allen Smithee]

Four cylinder automobile engines are timed 1-3-4-2. There must have been some logic behind this.

Think of it as 3-4-2-1, which is "inner-outer-inner-outer" torque pulses on the crank. This is less likely to set up torsional resonances in the crankshaft (at least that's what it says in an automotive engineering textbook on my bookshelf).

AS

[fumopuc]

I'll admit it now, I'm going to cheat. My Bobcat and Lynx took ages to get running. When Brian did his flat twin, based on Malcolms design, he got it going just about his first try. I put it down to him using O rings.  I'm convinced the compression on my engines has improved just by them sitting on the shelf. I believe the, once new, rings have normalised over time improving their fit.

So, I'm going to try 1x20 metric O rings as they will go straight into the ring grooves. I can then always go back to rings, I have them already.

Pete

I know O rings are commonly used on the pistons of steam engines but are not that common in i/c engines. Which O ring materials and hardness works best? Do you use nitrile or viton or PTFE O rings or something else?

What works best? What does the team think?

Mike

Hi Mike,
my Hoglet engine is running with Viton O-rings, one at each cylinder, since the first fire up.
I could not believe that it will work, but so far without any issues.

[Vixen]

Hi Mike,
my Hoglet engine is running with Viton O-rings, one at each cylinder, since the first fire up.
I could not believe that it will work, but so far without any issues.

The last couple of IC engines that I have made were both fitted with single Vitron rings. Though both are relatively slow runners.

Thanks guys,

That's two positive votes for Viton O ring piston rings.

The next important question is the dimensions of the piston groove. Should the depth of the groove equal the width and equal the O ring cross section? Or should the groove be shallower to squeeze the O ring?

Mike

[Jasonb]

Shallower than the ring section but also wider so it can take on a slight oval shape, I use Model Engineers Handbook for the groove sizes as they are less than you will find quoted on the ring makers sites which will give a good seal but far too much drag. reeves paper catalogue also has a similar model specific chart.