Scotch All Round

[PaulR]

Nearly two hours of work filing through chain drilled holes then getting to size. 1/2" wide 3/8" thick. My fingers hurt.

[redhouseluv]

That's dedication looks very good!

[redhouseluv]

Another Scotch for you sir?

Paul, I thought you might like this given the design of your engine. It has a scotch yoke mechanism and some bearings supporting the piston rod - I've never seen anything similar before?

https://youtube.com/shorts/mCIXobkMN7A?feature=share

[PaulR]

Another Scotch for you sir?

Paul, I thought you might like this given the design of your engine. It has a scotch yoke mechanism and some bearings supporting the piston rod - I've never seen anything similar before?

https://youtube.com/shorts/mCIXobkMN7A?feature=share

Thanks for this, that's a novel way to support the rod. With a single cylinder there's often some support beyond the yoke (would be to the right in your video) but as I've got opposed pistons I don't really need any support. Your video shows something else interesting that I hadn't thought of: the large hex headed screw securing the yoke. I think I mentioned before, on the couple of Scotch yoke engines I've made in the past the yoke tends to rock a bit in the vertical plane and that screw would stop it, although it would introduce more friction. I'll see what happens it's a simple matter to switch to a screw later. Cheers!

PS Why isn't the engine running?! 

[PaulR]

The screws arrived but I had to take 1mm off the length (x16) as some of the threaded holes were a touch shallow. A bit of final fettling on the yoke and then the piston rod can be soldered in place.

[redhouseluv]

I looked at that hex head too and it seems newer than the rest of the engine, its actually a very thin bolt with a very thin washer behind it (see pic)

PS Why isn't the engine running?! 

Ha, yes, it's a new arrival and has been shelved with others on the backlog and marked 'in need of attention'  I don't want to get to side tracked from the job in hand.

[PaulR]

Thanks for the photo, yes it looks like an off the shelf bolt doesn't it? I'm guessing the thread has been turned away from the part nearest the head to provide the bearing surface.

You seem to have acquired a lot of engines!

I drilled the yoke for the piston rod and did a test assembly (the middle bit of the rod will obviously be sawn out after soldering!). I just need to shave a bit off the crankshaft (purposely left long just in case) to check everything settles in place then I can do the soldering and move on to the supports/air passages. Getting there.

[redhouseluv]

The engine is looking really good now, looking forward as you must be to see some manual motion, seeing all the component parts moving together!

You seem to have acquired a lot of engines!

shhh......the wife might hear! 

[PaulR]

A slight setback today; I tightened everything down on the valve side and found one of the spools was binding and not screwed quite far enough onto the rod. Took it apart and while screwing the piston on further the rod came adrift. I had a suspicion the solder wasn't great on that side so time to redo it. However, the rod was passed through as one piece for soldering last time then cut in the middle which ensured both sides were aligned. This time it took me ages fiddling around with clamps before I was reasonably sure that the rod was well lined up. Soldering went well but I was a bit over enthusiastic this time so there's quite a blob to file away (upper right connection to yoke in first photo).

Next I tightened the power side cylinders etc and found that the yoke and/or crank were just a bit too thick - I forgot I'd used nearest imperial stock rather than metric I'd designed for so I decided to take about 0.25mm off each side of each part. All seems ok now so I can finally solder/chop the piston rods, hopefully tomorrow.

[PaulR]

Found a little time to solder the other yoke/piston rod, cut out the middle and generally do some fiddling to get everything seated properly so it turns over by hand (with just a little tightness here and there). Here's a pic of it sitting on some chuck jaws. I'll decide tomorrow whether to hide the air passages in the yet-to-be-made supports or just hook up some pipes separately. The second pic shows where I was thinking of bringing the air up inside the support on the valve side (the yellow circle being the head of a hollow/grooved screw allowing air in) but lack of space would make it very fiddly to assemble. If the supports don't bring the air in then I'll probably put them under the outside cross-tubes which will probably look better.

[redhouseluv]

The second pic shows where I was thinking of bringing the air up inside the support on the valve side (the yellow circle being the head of a hollow/grooved screw allowing air in) but lack of space would make it very fiddly to assemble.

Agreed, I don't know how big the gap is, but doing screw up would be fiddly; time for that miniatutre right angled screwdriver! 

[PaulR]

The second pic shows where I was thinking of bringing the air up inside the support on the valve side (the yellow circle being the head of a hollow/grooved screw allowing air in) but lack of space would make it very fiddly to assemble.

Agreed, I don't know how big the gap is, but doing screw up would be fiddly; time for that miniatutre right angled screwdriver! 

I've already made some hex headed screws which are very satisfying to tighten with a ring spanner They'd still just about fit if the support was as originally intended but it would be very cluttered in there. I think I'm going for the alternative plan.

[PaulR]

Made two inlets from hex bar, one end threaded M3 to hold the valve chest in place the other turned down to 6mm to hook up the wobbly pipe (soft silicone, tends to balloon when under pressure LOL). After a few minutes of encouraging it past the high spots by hand and liberal application of oil the engine ran for a little while until the screw holding the button on the crank came loose. Once that was attended to and the timing reset, I tried again and before long it was running speedily. It doesn't want to run at very slow speed just yet but I'm sure that'll come, I really wanted to just see if the concept worked. Now I know it does I can decide on a stand and the plumbing as well as titivating up the parts.

Sorry about the unstylish method of clamping it my workbench in the meantime

<a href="https://www.youtube.com/watch?v=eSB-81r6-CM" target="_blank">http://www.youtube.com/watch?v=eSB-81r6-CM</a>

The inlets I made are way out of perpendicular when screwed in and I've noticed a few male threads I've made have been a bit off. Looking at the die holder I now know why - viewed on edge one side is thicker than the other and the die doesn't even sit flat. I was intending to make a simple tailstock die holder and this has moved it to the top of my list! Photo is blurry I'm afraid.

[redhouseluv]

Fabulous, what a great build Paul!

It'll be like my last build, it didn't run at low speed without more fettling and running in. You must be pleased, nothing better than to see something you've (designed) and built, burst into life!   

[crueby]

Congratulations!