Dinkus - A Side-Crank Rotary Valve Engine

[PaulR]

Time for the next bar stock monstrosity!

This will be a simple single-acting engine, with a rotary valve at the outboard end of the cylinder. The valve will be turned by offset cranks at each end with matching disks/pins on the end of the crankshaft. The mass of the four crank disks will hopefully be enough to do the job of a flywheel.

This afternoon I got the cylinder and valve blocks to size, and made the bores for the piston and the valve. Also made the air inlet because I found a piece of scrap brass the right size while looking for something else I made a separate threaded tube to connect it, so it'll fit flat to the surface without any leaks.

Here are the bits with some piston and valve placeholders. Pretty boring to look at but there we go. 

[PaulR]

Drilled and threaded the holes for the air inlet passages - really need to shorten that plug a bit though (the long brass rod) Also faced the valve to length and drilled the longitudinal passage. Next will be the passage that transfers air to/from the cylinder, the flats on the valve and the holes for some long screws to hold the valve block to the cylinder. Oh yeah, need to turn a spigot on the valve block as well.

[PaulR]

Turned the spigot on the valve block (need to sharpen that tool!), drilled the second passage and plugged the first one. Despite putting some thin shims between the jaws and the part I found that they'd marked the edge of the valve hole so I'll need to tidy that up 

In case anyone is interested in how the air gets in and out... first photo view of the two passages in the valve bore. Second photo, the open and plugged passages into the cylinder.

[PaulR]

Made the holes and threaded those in the cylinder block ready to attach the valve block, here held by two temporary screws. One of the holes is a bit out of position; I'm pretty sure I marked it up and punched it accurately but the old pillar drill has a mind of its own  -  this strike rate of 1 in 4 having an issue is typical. Thanks to the orange man-baby my chances of affording a new one are receding further, I'll probably end up with a brace and bit by candlelight at this rate. 

[PaulR]

Made a bit of progress. Looks more like an early 20th century ice cream cart than an engine.

[Sanjay F]

Minature traction engine, with the front wheels missing? 

Looks great, coming along nicely 

[PaulR]

Minature traction engine, with the front wheels missing? 

Looks great, coming along nicely 

Cheers Sanjay.

Made the first of the two side rods this afternoon....

[PaulR]

Made the fiddly end bits for the second rod as well.

[PaulR]

A little more done today. One day I'll make some of those nice piston rod/con rod joints that mesh together...

[Sanjay F]

A little more done today. One day I'll make some of those nice piston rod/con rod joints that mesh together...

In a 100 years time when your engines are on the Antiques Roadshow, collectors and the experts alike need to be able to recognise them as a 'One of Paul's engines' - I wouldn't go changing anything, they are unique and great the way they are 

[PaulR]

In a 100 years time when your engines are on the Antiques Roadshow, collectors and the experts alike need to be able to recognise them as a 'One of Paul's engines' - I wouldn't go changing anything, they are unique and great the way they are

Thanks for this 

Just a short session today but enough to complete the simplistic big end. Not much room for error but as ever one of the holes went a little adrift. It's only cosmetic and nothing a one-eyed man on a galloping horse would notice 

[PaulR]

Made the parts for the simple crankshaft. The drill press managed to keep its **** together for a change so all the holes were in the right place! Fixed the 3mm journal in place with Loctite,  once that's set I'll get the main shaft to length and fix that in the same way. Hopefully Loctite will prove strong enough but if not I guess I could make some tiny pins or silver solder it.

[PaulR]

Chopped out the middle bit, seems to fit ok, next up, bearings of some sort.

[Sanjay F]

Are you building a miniature steam powered drag racer? This I gotta see! 

[PaulR]

Haha, it does look a bit like that at present but it'll look much less exciting in a bit 

Due to lack of forethought and materials on hand I'm going to fit sealed ball races as I've got some left over from the Stirling engine. The ones I'll be using have an 8mm OD and are 3mm thick so I need to make a flat bottomed hole to accommodate them. To do that I need a small boring bar so I just winged it and ground one from HSS and have to say it works rather well. Here's the hole it made in on some scrap steel that I bored out to fit a 12mm dia race as a test.

[PaulR]

Stock of some material is getting low so I had to rummage around to find some pieces for the bearings - if only I'd designed them to be of 5/8" x 1/4" steel instead of 16mm x 5mm, life would have been a lot easier! Never mind, I found just two remnants of 5mm thick bars from a suspension file drawer which were just long enough. After a bit of sawing, I glued them together and turned two sides to get the correct dimensions. I'll glue them back together and drill the oversize holes for the shaft then separate them and bore out to fit the ball races.

Also made a little lump to lift the engine and get enough clearance for the big end.

[PaulR]

Got the pair mounted and centred in the 4 jaw and drilled a 4.5mm through hole. As the shaft is 4mm I figured just a bit extra would do as the bearing race is only 3mm deep in a 5mm thick piece of steel. Used the tool I ground yesterday to counterbore the hole. It came out pretty good but the bearing projects very slightly (about 0.25mm) - I think some backlash came into play as I was constantly winding the tool around to measure the hole. Not a major problem anyway as I've allowed 0.5mm gap between the standard and the crank disk. The sealed bearing fits just right, no free play and no force needed to get it seated; I'll probably Loctite it in place in the end. Next to remount it and do the other side.

[Sanjay F]

Looks very neat and you've made lightening speed progress! 

[Michael S.]

Good progress Paul. 👍

[PaulR]

Thanks both 

Unfortunately bearing #2 didn't go to plan, the recess came out way too big, the ball race was jiggling about all over the place :'( Never mind, I've plugged the hole so I can face it flat and try again tomorrow!

[PaulR]

Things went much better after a good nights sleep. The second bearing fits snugly, both are now held in place with Loctite and I turned down the plug on the back. Everything looks nice and square but I might use a bit of JB Weld to fill that little hole and any other tiny gaps around the plug. No idea what sort of steel this is but it's pretty soft to machine although I need to remove the silvery coating.

[PaulR]

Milled the recesses for the standards and decided to modify the base and cylinder support block so the thing has a slightly less 'wall of metal' appearance' 

[PaulR]

That's about all the parts, just need to do the valve flats. I wanted to get the crank disks as near identical as I could so I made them from a single stub of steel, making the shaft hole and the crank pin holes in the lathe then sawing in two and turning each one after fitting the grub screws (I'm developing an aversion to 2.5mm socket grubscrews, as it's hard to exert enough force to properly tighten them and the key  ends up getting worn - I've shortened the one I have on the grinder about half a dozen times today!).

Waiting for some long screws to arrive in the next few days, should then be ready to assemble properly but I get the feeling this is going to be a fiddly little thing to get running....


 

[Sanjay F]

Looking like an engine! 

[PaulR]

Filed the flats and this time remembered to score a line on the end of the shaft to indicate the orientation of the flats to help when setting the timing. Filed some chamfers on top of the standards to make them a little less brutalist and made the four pins for the side rods. Oh, also made a top quality wooden base 

Just waiting on some long screws to fasten the valve block in place (as I don't fancy turning an inch length of hex down to 3mm dia!) and then it might just be ready for a spin.

[Michael S.]

The individual parts look good  , but when will the engine run?

[PaulR]

The individual parts look good  , but when will the engine run?

Maybe that should just be 'will the engine run?'  We should find out in a few days.

[PaulR]

I've had little time to devote to this over recent days but finally got all the pieces together. However, there's quite a bit of binding and it's really difficult to turn over by hand without a flywheel! I resorted to removing one crank disk at a time and replacing it with a temporary flywheel. It's possible to turn it over when one side or the other is connected but not both  I can see this is going to take some time to sort out let alone trying to get the timing right. Ho hum.

[Jasonb]

With this design any slight difference in link rod lengths or throw of the cranks at either end will likely lock things up. As a temporary measure, you could make a new rod end for one side that has a bit of an oversize hole. Not really the way to do it but it would show if the basic design is going to be a runner.

[PaulR]

With this design any slight difference in link rod lengths or throw of the cranks at either end will likely lock things up.

Yes, I thought that might be the case which is why I made the disks in pairs although the front and back pair could be slightly different. As far as I can see the rods are pretty much equal but there's bound to be some small difference. I'll persevere for a while 

[Charles Lamont]

With the ends screwed onto the rods, you would be very lucky if they were the same length. Really they could do with a simple jig. Drill and ream one end of each, then locate them on a fixed pin to make the holes at other end. However it is no big deal to open the holes to give a bit of leeway. Locomotive coupling rods have to have a bit of clearance to allow for uneveness of the road. 

[PaulR]

With the ends screwed onto the rods, you would be very lucky if they were the same length. Really they could do with a simple jig. Drill and ream one end of each, then locate them on a fixed pin to make the holes at other end. However it is no big deal to open the holes to give a bit of leeway. Locomotive coupling rods have to have a bit of clearance to allow for uneveness of the road.

Thank you Charles, I appreciate that being threaded it's a bit hit and miss but they do look quite close. I'll see how it goes as is, I could always replace them with some basic strips of metal drilled/reamed as a pair to check that everything else is in order.

[Jasonb]

You could keep the same basic rod design, even one end could be screwed on and held with Loctite so it did not turn. Make the other end a push fit so it can be slid into place and again retained with Loctite as there is no thread you will not be spacing the ends to the nearest half a thread pitch.

Or you could just unscrew one end and turn down the male threaded end of the rod . make that the push fit end but use an epoxy like Araldite rather than Loctite so it fills the thread in the existing rod end.

Ideally when you assemble make a simple jig - just two pins sticking out of a piece of flat bar which will hold the two ends to a set distance while teh Loctite sets on the unthreaded end.

[PaulR]

You could keep the same basic rod design, even one end could be screwed on and held with Loctite so it did not turn. Make the other end a push fit so it can be slid into place and again retained with Loctite as there is no thread you will not be spacing the ends to the nearest half a thread pitch.

Or you could just unscrew one end and turn down the male threaded end of the rod . make that the push fit end but use an epoxy like Araldite rather than Loctite so it fills the thread in the existing rod end.

Ideally when you assemble make a simple jig - just two pins sticking out of a piece of flat bar which will hold the two ends to a set distance while teh Loctite sets on the unthreaded end.

Thanks Jason, all good ideas in case it doesn't come together 'as is'. 

[PaulR]

Still getting no joy with this one. The holes in the rods are spaced as equally as I can get them but the valve is still oscillating rather than rotating. I could try making a new pair of temporary rods from some flat bar using a jig but I can't see it being any more accurate as I'd be doing it in the drill press. Also, if the distance between the holes was identical but didn't exactly match distance between the two crank pins I might have the same problem. 

<a href="https://www.youtube.com/watch?v=7cGWTnAAJgM" target="_blank">http://www.youtube.com/watch?v=7cGWTnAAJgM</a>

I'll give it another day or two before consigning it to my 'non runner' collection (that'll make two so not too bad!).

[Jasonb]

Clamp the two pices of flat bar together and drill through both then the hole ctrs can't be different.

[crueby]

Looks like you have the two rods/pins 180 degrees apart? If you make them 90 degrees apart, then they will not oscillate. Just like a two cylinder crankshaft - one is going past top/bottom center while the other is in the middle of the stroke. I'm assuming the two valve cranks are connected to a common shaft through the valve?

[PaulR]

Clamp the two pices of flat bar together and drill through both then the hole ctrs can't be different.

Yes that's the plan but I was thinking about the distance between the holes as well.

[PaulR]

Looks like you have the two rods/pins 180 degrees apart? If you make them 90 degrees apart, then they will not oscillate. Just like a two cylinder crankshaft - one is going past top/bottom center while the other is in the middle of the stroke. I'm assuming the two valve cranks are connected to a common shaft through the valve?

Yes there's a single shaft between the valve cranks and the pins are *about* 90 degrees apart. I'm not convinced the distance between the holes in the rods is correct - I need to get the crank pins on the jaw of a vice to check and at the same time measure the distance between them. The other variable is the throw of each pair of pins but they should be identical as I made the discs in pairs. Need to find a bit more 'shop time this week to try to sort it out.

[crueby]

Boy, looking at the video the pins sure look 180 out from each other, end to end on the same shaft. Hard to tell without a side/end view though! Another thing that HAS to be the same is the distance from the center of each disc out to the center of each pin, on all four pins.

[PaulR]

Boy, looking at the video the pins sure look 180 out from each other, end to end on the same shaft. Hard to tell without a side/end view though! Another thing that HAS to be the same is the distance from the center of each disc out to the center of each pin, on all four pins.

The throw looks good on all four. I was just disassembling while making the temporary side rods and the Loctite on the crankshaft decided to come apart    I'm not having much luck with this engine and my patience is wearing very thin - one more attempt before it ends up in the scrap!

[john mills]

what is the distance between the side rod hole they need to be the same as the two shafts   the crank pins at each end should be in the same position
 at each end
john

[PaulR]

Thanks John, I've made two temporary side rods from some scrap aluminium (drilled at the same time) and now that I've got the shaft back together I can turn the engine over and the valve rod is rotating properly instead of oscillating. The only problem I have now is that there's some horrible binding that I need to track down, once that's done we'll see if it will actually run.

[PaulR]

I'm afraid to say this one is getting shelved. In principle I think it should work ok but having four cranks disks held by screws was a bad design choice, trying to set them exactly in pairs with the big end in the right place and taking account of the valve timing is horrible. Not only that but I think there's too much lateral force being exerted on the piston and a slight difference in height of the centre line of the cylinder and the centre line of the crank. So that's bad workmanship as well as a bad design  Never mind, it's all grist to the mill of experience.

[Sanjay F]

Never mind, still good going - I think your record of successes vs failures stands up for itself! 

Onwards and upwards .........what's next? 

[dudeface]

If the cranks for the side rods are set 180 degrees from each other, that won't work. They have to be 90 (the way locomotive side rods are set).
(Bentley once made OHC engines using the same system to drive the camshaft, so it certainly works.)

[PaulR]

Never mind, still good going - I think your record of successes vs failures stands up for itself! 

Onwards and upwards .........what's next? 

To quote Mr Lennon, a new one just begun!

[PaulR]

If the cranks for the side rods are set 180 degrees from each other, that won't work. They have to be 90 (the way locomotive side rods are set).
(Bentley once made OHC engines using the same system to drive the camshaft, so it certainly works.)

Cheers. They are at 90 deg, I think I've made too many small errors and my implementation just isn't great.