A 15cc sidevalve opposed twin

[Peter Twissell]

Pistons are relatively straightforward.
I made a fixture from two scraps of aluminium stock, bored to form a pair of clamps to hold the pistons for the milling operations.

 

[a41capt]

Wow Pete, that’s an amazing bit of machine work Pard, and I’m sweating bullets when I have to tap 4-40, let alone anything as small as those tapped holes. How many set ups did that part require? BTW, I feel your pain. I’ve also spent hours on a part only to find that my overzealous twirling of hand wheels has ruined all the previous work…
John W

 

[Peter Twissell]

Thanks John. M1.6 is the same size as 10BA, for those more familiar with traditional model size threads.
I hold the tap in a pin chuck and turn it with finger grip only, no tommy bar.
It helps that the 2014 aluminium is nice and crisp. Tapping soft materials can be troublesome, copper being among the worst.
The timing gear housing was machined with just three setups.
First, I bored the hole through and the bearing bore in the lathe, then turned the register which fits into the main blocks, all at one setting.
Next, I bolted a scrap of aluminium plate to the rotary table and machined a register to fit the through hole. With the part bolted to the fixture, I machined all the features which are concentric with the main bore, then at the same setting, bored the offset hole for the camshaft to pass through.
Finally, I re-machined the fixture so I could mount the part by the offset bore and machine the features which are concentric to that.

My drawings for parts like this consist of 2 or 3 sheets. The first details the part as designed, while further sheets show the polar co-ordinates for all the blend radii, beginning and end of each orbital cut etc. All the information I need to make the part on the rotary table.

 

[Bentwings]

With the valve cages fitted, the ports are cut through the block and into the cage. The ports are counterbored for a small high temperature O ring which will seal against the manifold face. The M3 tapped hole below the ports will hold a clamp to retain both inlet and exhaust manifolds.
With the valves in place and open, there is a clear path for gas flow.

you’ve done a nice job so far. I’m a very long time madel plane builder and flyer oing back to early days of free flight then u control. Ultimately Rc and giant scal warbirs. My big Corsair flew for over 13 years. As with full scale I kept flight logs and maintenance logs and testing and research logs. My flight log book was over two inches thick. Most war birds flyers are detail nuts one of my sons internet friends has gone so far as to put scale foot prints on he wing walks and hand marks on the hand grip ports. I won 5 scale events which involve static judging and flying in scale appearing flight. So I had my 5 kill flags displayed. Early on I was a semi pro drag racer in both dragster and funny car. While not a money maker there was a positive balance in the check book . In both models and Rc I was known for running on “kill or the edge” I destroyed many early glow engines with loads of nitro and wild rpm often using custom tuned props. Misdeeds my own model fuel a long time ago as I had ready access to alcohol and nitromethane. So that out of the way I’ll try and give some tips. I also got into scale functioning exhaust and muffled tuned pipes. If you ar going to run alcohol and oil mix plan on plenty of compression I think I’d opt for various thickness gashead gasket. You can calculate compression ratio obviously fine adjustments in thickness of gasket might not be possible we used .001 differences for example but sheet like this is not available unless you make a special rolling press. Instead I’d mak a spacer that you can replace at will. Then having run glow for year and burning glow plugs up by the pound rather than having only a couple spares I think I might look at using two plugs per cylinder and running battery power on in flight. Engine out or one balky cylinder in big planes I’d invitation to bad things. Next exhaust. I’m not sure hat the electro….. I’d I’m thinking maybe 3D printed metal . That would be ok. Here is what I’d do as long as you are accomplished fusion user. I made fabricated p 51 exhausts out of thin stainless sheet TIG welded. I did presidium TIG welding so while very tedious did work. Later I neede to simplify and design for mfg. I modeled standard copper tube fittings then did weight calculation on cad. Then looked at trimming the fittings to minimums and both silver solder and braised the systems together using slip joints as necessary. You can trim fitting with aviation snips if you are carefull. Please , please don’t do the hack saw and vice as seen on so many videos. Copper gets pretty hot when welding or silver soldering simply chilling in water well remove a lot of scal and Anne at it at the same time don’t eve waste time with acid or rosin standard solder the exhaust temp will melt it . Be aware of pipe centerline length it has to do with tuning at least make it equal side to side you can alter fitting angle at will by cutting and welding or brazing I was able to trim about 65% of the weight by doing this. Because the brazing is so thin it really doesn’t count. Next I’d run dual plugs you may have to do a little rework but you can easily do this it loos like. Working in the auto machine shop I got to build a lot of engines from the ground up . I also worked at intl diesel that made Ford Diesel engines I ran the cylinder hone area. The blocks came in machined with .003” left in the bores for honing. There was rough gone to remove about .002 then the second stage was sizing that took them to about .001 with .001 or less for plateau hone and final size. This was exactly what we used in the auto shop. So try to do this even if you have to send the cyl out. Unless you want to try honing your self. Sun Ben is the great name in honing and I had good success with cyst. Support it’s a messy job if don’t have the right machin but it give perfectly straight bores with optimum finish. Your crank sounds nice. That’s standard construction I’m not real familiar with slide valves excep steamers the fit needs to be good there too. As for fuel klotz make good oil. I just did some research on steam oil as it’s not readily available here but castor oil is I just got a quart. It’s possible to use canola oil too. Castor is still used in modern piston engine breaking on new and rebuilt engingines amzoil has good synthetic. You might have to call support for recommendations. Keep up the nice work I’ll try and follow you .
byron

 

[Peter Twissell]

Hi Byron and thanks for all the tips.
I'm also involved with drag racing, as part of a small group running pre-unit Triumph motors. We are currently rebuilding a bike with two 500cc motors, which still holds a class land speed record. We intend to drag race it for a season, then attempt to beat it's standing record.

My 15cc engine is not intended to make a huge amount of power. It's going into an Acro-Wot, which can take anything from a 6cc two stroke to a 15cc four stroke. I'm not going for high nitro or tuned pipes. The electroformed pipes will be in copper.

 

[Peter Twissell]

The camshaft is quite simple, having only 3 lobes. The centre lobe operates both inlet valves and the other operate the exhaust valves.
The turned blank is set up in the dividing head and supported with a tailstock on the mill to generate the simple, flat flanked profiles.

 

[Peter Twissell]

With the cams machined, the part is returned to the lathe to finish the ends.
Despite its apparent simplicity, I still managed to make the first one wrong, with 16 degrees of 'underlap' instead of the intended overlap!

 

[Peter Twissell]

Parts made so far partially assembled.

 

[Drawfiler]

Peter
Back to the pipes, you could try Cerrobend inside commercial tube.

 

[Peter Twissell]

The electroforming thing has become a project now!
I'm keen to explore the possibilities of the process and I already have some ideas for other applications, including water jackets and radiators for water cooled engines.

 

[Majormallock]

Hi Byron and thanks for all the tips.
I'm also involved with drag racing, as part of a small group running pre-unit Triumph motors. We are currently rebuilding a bike with two 500cc motors, which still holds a class land speed record. We intend to drag race it for a season, then attempt to beat it's standing record.

My 15cc engine is not intended to make a huge amount of power. It's going into an Acro-Wot, which can take anything from a 6cc two stroke to a 15cc four stroke. I'm not going for high nitro or tuned pipes. The electroformed pipes will be in copper.

Hi, Peter, I am building a Forrest Edwards 5 cylinder radial and having trouble with the inlet tubes 9/32 thin wall brass. I have bought some cerrobend for a final attempt, but if that fails I was wondering if electroforming might work, reference the picture do you think it will work?

 

[Peter Twissell]

I haven't tried the electroforming process yet, but I have seen complex electroformed parts and I have read a lot about the process, so I am confident that it is possible.
Watch this space, I will detail my process, warts and all!

 

[Ken I]

Hi, Peter, I am building a Forrest Edwards 5 cylinder radial and having trouble with the inlet tubes 9/32 thin wall brass. I have bought some cerrobend for a final attempt, but if that fails I was wondering if electroforming might work, reference the picture do you think it will work?View attachment 132175

There are several tube bending tips and devices on the site - conduct a search.
Here's mine - note bending of 1/8" NOS lines.
Wire & Tube Bender
The ACAD plans are available as a Zip file here :-
https://www.homemodelenginemachinist.com/threads/wire-tube-bender.29079/
Regards, Ken

 

[Richard Hed]

Hi, Peter, I am building a Forrest Edwards 5 cylinder radial and having trouble with the inlet tubes 9/32 thin wall brass. I have bought some cerrobend for a final attempt, but if that fails I was wondering if electroforming might work, reference the picture do you think it will work?View attachment 132175

Can you tell us your process for bending the tubes?

 

[Majormallock]

Hi Richard. What i have tried so far is to anneal the tube, first of all by direct flame from my oxy/acc torch, then by 2 hour soak in my solid fuel fire. Air cooled, not quenched. I then made a tube bending small hand operated machine . Formers to clamp the straight part then bent found another half round former followed round by another former. In other word a small version of a standard none mandrel tube bender. All formers to exact 9/32 od. . Think I might have to upgrade to thicker wall copper, but I don't like to be beaten in the workshop, so next I have some cerrobend which I will try in the same bender. I am also in the process of buying some spring wire to make an internal support spring

 

[Richard Hed]

Hi Richard. What i have tried so far is to anneal the tube, first of all by direct flame from my oxy/acc torch, then by 2 hour soak in my solid fuel fire. Air cooled, not quenched. I then made a tube bending small hand operated machine . Formers to clamp the straight part then bent found another half round former followed round by another former. In other word a small version of a standard none mandrel tube bender. All formers to exact 9/32 od. . Think I might have to upgrade to thicker wall copper, but I don't like to be beaten in the workshop, so next I have some cerrobend which I will try in the same bender. I am also in the process of buying some spring wire to make an internal support spring

Did you fill the tubes with sand? Try that, then bend them. I know this works if it is carried out correctly.

 

[Majormallock]

Hi, no I didn't couldn't get fine enough sand , thats why I bought the cerrobend, but if you recommend, I will try it. Many thanks

 

[Richard Hed]

Hi, no I didn't couldn't get fine enough sand , thats why I bought the cerrobend, but if you recommend, I will try it. Many thanks

Absolutely try it. What is cerrobend?

 

[petertha]

I'm eagerly awaiting Peter's electroforming results because that would have so many other useful applications in model engineering. Keep us posted!

For those of you struggling with 'conventional' bends & are not opposed to aluminum, I've had good results with 3003 alloy aluminum tube which goes under a label 'Versatube' at N-Am FS aircraft distributers. There may be other suppliers of similar alloy, maybe under a different label? My radius was formed with conventional commercial tool & flared with home made tool, without the need for heat or filler which I was trying to avoid. I suspect as the radii decreases, this alloy too may have its limits. But its a very inexpensive material to try. Exhaust tubes would be a different matter of course, but thought I'd mention this.
https://www.aircraftspruce.ca/catalog/mepages/3003versatube.php?clickkey=17152

 

[Peter Twissell]

I now have a pair of 3D printed cores on which to form a pair of exhaust pipes.
I expect to be making my first attempts at electroforming in the coming week.

Re. Aluminium tube, I would not rule out using it for exhaust pipes on a glow ignition engine. Most model aircraft glow engines use cast alloy exhausts successfully.