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Thanks for all the suggestions. I am quite familiar with steel shims from my many years in shock absorber design and manufacture. If I were to go for steel, the parts would be etched, deburred and polished in the same way as shock absorber shims. At this scale, I am leaning more towards Mylar or...

I could of course use steel, but need to cut it to shape while keeping it perfectly flat. Etching perhaps?

Hi Jeff, I have not cast a cap in urethane yet. I have taken a hiatus from the radial engine for a while. I am still hoping to source some phenolic resin to do the job 'properly'. I can only find safety data sheets for the Epoxyseal 9000 - no dielectric properties. One significant discovery I...

I assume you meant to say compression is the ratio of (swept volume PLUS clearance volume) / clearance volume...

Thanks Gail! PTFE is on my list of possible materials. I was not sure whether it would be stable enough. I have used it in other applications and found that it 'creeps' over time. I expect it is constant load which leads to the creep and a reed valve never sees constant load.

What does anyone use to make model size reed valves? I need to make valves about twice the size of those found in Cox .049 engines, which I think are made in both steel and Mylar. The Cox valves operate slightly differently to conventional reeds - they are not fixed at any point, but are allowed...

And now it gets complicated ... Without getting into the detail of polar and non-polar resins, consider that automotive distributor caps are made from phenolic resin and are lacquered to protect them from water absorption.

Indeed, but I'd like to cast mine, so I need to mix the resin at the time of casting. It's made with formaldehyde, which might be an issue for the home workshop.

Not brilliant. The plastics used for extrusion are typically quite hygroscopic, which doesn't help. I made the "test" distributor cap for my radial from 'water clear' acrylic resin, poured into a mould. It works ok so far, but it's only been used for bench testing with no compression on the...

Yes, 10mm gap should be plenty. I assume the radial gap between the rotor contact and each plug lead contact will be less than 1mm. Regarding the coil charge time, you'll need a low resistance coil so that the current can build quickly.

Provided the gap between the rotor conductor and the active plug lead conductor is smaller than the gap between the rotor conductor and the adjacent plug lead conductors, by a factor greater than the difference between the gaps required to permit sparking in compressed Vs uncompressed cylinders...

Hi Ian and welcome. I also have a 3 1/2" loco "on pause" - for about 35 years! I must get back on to it some time.

No distortion issues, but I did take the precaution of leaving the main journals oversize and finishing them after welding.

I made the crank for my 15cc sidevalve boxer as a pressed assembly, using hard dowel pins for the big end journals. I'm the end, I had to lock the assembly together by TIG welding. There is a build thread on this site. I will be making a smaller, 10cc version of the engine. For that, I will be...

Hello Mick and welcome to the group. Do you have an idea of what sort of thing you'd like to build, or are you at the "looking for inspiration" stage? Pete.

I make head gaskets from annealed copper. I would echo the comments about having some surface roughness to 'bite' into the gasket. I am concerned that with only to bolts holding the head down, you may be fighting a losing battle. On drag racing motorcycle engines, I have previously made braces...

My Drummond Roundbed has simple push-in retainers for the change gears. To avoid dropping them in the swarf mountain under the lathe, I have simply glued a length of thread to them with hot glue, with enough slack to allow for all possible gear positions but not so much that it can get caught in...

It has been mentioned a couple of times that a rotating workpiece (i.e. drilling in the lathe) is less likely to produce a wandering hole. Can anyone suggest how this could be true? To my mind, the drill and workpiece rotate relative to each other - it doesn't matter which one is 'stationary' to...

Another potential issue is the spring force on the inlet valve of the pump. That force, divided by the active area of the valve, is an additional pressure which must be overcome to allow fuel to enter. For a fast pump, the spring force needs to be large enough to close the valve quickly. This...

Minh-thanh, the short answer is yes. The liquid had the same stress strain behaviour as you reduce pressure, so if you are able to pull a vacuum, you have reduced stress on the liquid by 1 atmosphere, or about 0.1 mPa and the liquid will exhibit strain accordingly. As above, the magnitude of...