Engines > Your Own Design
Scotch All Round
PaulR:
Ordered a 2.5mm tap and some sacrificial screws to hold the supports together for soldering (the parts aren't wide enough for csk heads or thick enough for recessed cap screws). Did some more running in today and it's gradually running on less and less air.
PaulR:
I decided to sack off the supports as I couldn't get the uprights satisfactorily aligned; they're not the easiest shape to clamp for soldering with the very limited gear I have and there's not room to fit the head of a countersunk screw to screw them together. Instead I made two simple blocky supports with the same recesses at the top and screwed into the base from below. I just want to fit some rubber feet to the (rough) wooden base then I think I'm about done with this engine.
I'd not seen an engine with Scotch Yokes controlling valves and pistons before and the arrangement for this engine was lurking around my brain over a decade ago so I'm quite pleased that it works (after a fashion!). I've also learned quite a few things while building it, but here's a quick post mortem on the build itself:
* A combination of design issues and sub-optimal accuracy means it's too leaky. It'll run fine at 25 psi, and tick over with intermittent stops around 20psi but doesn't want to run at lower pressure. I intended to fit fibre washers on the screws that hold the cylinders and valve cylinders against the frame but there just isn't room.
* The design of the air inlets with a single screw holding them to the frame means there's a tendency for them to work loose by vibration or being knocked when turning over the flywheel by hand. It would probably have been better to put the inlets directly into the valve chambers from below which would have made it easy to add some plumbing for a single air inlet (although the supports would probably have to be taller).
* There's a small but noticeable tight spot at TDC on one side, I think it's down to having to re-affix the piston-yoke rods (twice!) which means that they're not perfectly aligned.
* There's no facility to oil the bearings and they're not easy to get at to splash some oil on!
* The buttons that drive the yokes would probably be better if they were like screws, extending beyond the yoke so the head would stop it rocking.
* The yokes would be better in brass to reduce friction against the crank and crank disk.
* I should have turned some parts from solid to improve accuracy rather than taking the quick route and screwing together simple pieces.
http://www.youtube.com/watch?v=HT8hbelAV1w
Sanjay F:
Well, you're done, you have a working engine, of your own design, sat nicely on a wooden plinth and puffing away.......I guess the only question which remains to be asked is........what's next! :D
PaulR:
--- Quote from: redhouseluv on May 04, 2025, 02:35:59 pm ---I guess the only question which remains to be asked is........what's next! :D
--- End quote ---
Well I spent most of the day buffing up the parts a bit and sanding/priming the base for a bit of paint. Next build I'm thinking will be another simple oscillating engine with a bit of a twist or maybe the 'scraps' engine with lever operated valve. Thinking!
PaulR:
After stripping down and reassembling I just couldn't get this going again >:( At one end the movement seemed definitely too tight, at the other a bit tight, so I decided on some drastic action. First I opened out the holes holding the inboard cylinder covers and reduced the size of the registers slightly. Next I scrapped the air inlets on the inside of the frame; these made it difficult to attach the tubes and I could see rust beginning to form in the small holes/grooves - having the air tubes coming in from above meant a tendency for droplets of condensation to enter the engine. The tiny holes and grooves also seemed to be choking the air supply.
I made some threaded holes on the front of the valve chests which allowed the tubes to run 'uphill' a bit, avoiding condensation build up. This and the extra space between the frames meant I could also fit fibre washers all round to minimise leaks. The net result is it runs much better although I think it'll take a lot of running to get it turning over very slowly.
I had a smidgeon of hammer effect paint left in a can so, despite it being 'straight to metal', I thought I'd try to use it on the primed wooden base. The first couple of coats were good but the third coat just refuses to dry so I'll have to re-do it with something else. Here are a couple of photos of the 'new look' (excuse the misaligned supports, it was only loosely fastened down!).
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version