A Lightweight Husky

All interesting stuff, I may have a play with the moving bits at some time to see if I can tame it's down a bit but as I have just got some measurements of the next one in the series will probably concentrate on that instead.

I was in two minds as to what to make the cylinder from. Cast iron would have been nice but not so easy to solder the exhaust to it, Bronze and brass would have been easy to solder but it's a bit of a lump and I did not have much suitable in stock (at least that I wanted to cut into) so I ended up going for 230M07 (EN1A) as it's not really any more likely to rust than iron particularly as I'm mostly going to run on air.

So a piece was sliced off a 2" bar with the trusty Femi band saw, faced each end and then mounted on the CNC. The two ctr drilled holes are to make it easier to locate the bores for machining on the manual machines.

While the mill was switched on I also did the entablature. The fit of the cylinder's spigots was very good into the holes and would have been a good press fit but that was a bit tighter than I wanted so a quick adjustment of the tool diameter in F360 and an extra 0.01mm was taken off the bores which gave a firm push fit.

I then held the cylinder in the 4-jaw, clocked the ctr drilled hole true and then drilled and finally bored it out to 18mm



The valve hole was a bit too far off central to make holding in the 4-jaw easy so I used the mill to drill and ream the hole out to 6mm with a machine reamer



To make sure the cylinder cover holes were lined up correctly I screwed the cylinder to it's entablature and with a couple of 10-20-40 blocks between that and the fixed vice jaw was able to hold it true, locate bore and then drill and tap the four M2.5 holes and later the two M1.6 holes to retain the valve cover plate.



An existing mandrel was quickly altered so the cylinder could be held horizontally in the 5C indexer firstly to drill the inlet passage and then the three exhaust holes each side which are at 20deg spacings.



A suitable former was turned from delrin, the 8mm copper tube filled with lead and then bent around the former. I then clamped the "U" shape to a bit of MDF and used the boring head to cut the circular profile so it would slide over the cylinder.



Next the vice was swung round to a pleasing angle and using a long series milling cutter for non-ferrous material both ends were milled to the angle. After this the lead was melted out and the exhaust soldered to the cylinder, I had intended to have the slash cut facing upwards but changed the way I held things for soldering but forgot to turn the pipe up the other way. Still it saved having to paint the inside of the exhaust as it is now just in dark shadow.



After cleaning up the outside the last thing to do was lap the cylinder on a make shift lap turned from a scrap length of thick wall aluminium tube.

The piston was fairly straightforward turning and then over to the mill to drill and ream for the 3mm wrist pin before sawing off from the bar and facing the top.



The last item I have a photo of is the conrod which was cut from some 1/2" square brass bar on the CNC but I finished the other sid eon the manual machines.



The only other part of any note is the cam which I also did on the CNC but could quite easily be done with a rotary table. The flywheel, valve and valve follower were all basic turning so I did not take any pictures of them being made.

After putting it all together I did need to make a little adjustment of the profile of the cam follower to get the valve to stay open for a longer period and up the pressure from my usual less than 10psi the engine was off and running with a good flick of the flywheel. It was then stripped for painting. As you can see there are not that many parts to this one which makes these little engines a nice change from the longer more complex builds.





And this is what they go together like













Running on about 30psi (note the balloning silicon tube) which it seemed to need to be able to get the piston back up to TDC. It is quite lively if not clamped down so could probably do with the plain disc crank web being shaped to add some counterbalance and the piston and conrod could also be lightened a bit if needed. 1600rpm Tacho reading if you can wait until the end.

The next one in the series of these small marine engines is about to start being drawn up. I know some on here poo poo facebook and I don't frequent it that much but within an hour of asking on the right group for some key dimensions I had been provided with them along with several good photos of an original from 1926-28. so should end up with a fairly close reproduction Simplex.

Nice to see & hear it running, looks like it might be a fun project to make and experiment with..

The bane of uniflow engines exhausting to atmosphere is compression. The following relies on my reading the drawing in the original mag correctly (it's not that clear), but the distance from the top of the exhaust holes to the cover is 0.534" and the distance from the piston to the cover at TDC is 0.058", so there is a volume compression of 9.2, and as the compression index for air is 1.4, an even higher pressure ratio. As the exhaust holes close, the pressure is 15 psia, it will rise to a high figure at TDC, and when the valve opens the pressure will drop as a slug of air is be pushed out of the cylinder back into the feed pipe. It then takes in air at feed pipe pressure for quite a bit of stroke, but you can see why it needs quite a high line pressure to run. uniflow engines exhausting to atmosphere is compression. Uniflow engines either need a very high inlet pressure (as in flash steam hydroplanes), or a very low exhaust pressure (as in mill engines). The Atkinson Uniflow waggon had auxiliary exhaust valves to overcome this. Husky would probably run on lower pressure if the clearance volume were markedly increased

A Question primarily for JasonB.

I've been looking at the Husky cam design. The valve movement of 1/8" is the same as the port diameter. If the valve is set to fully uncover the port it seems likely to allow air/steam leakage into cylnder when closed. Is there any benefit in slightly increasing the valve travel to provide a better margin for port closure?

Another doubt that occurs is that the cam boss is 5/16" id x 7/16" od. Not much meat for the grub-screw to thread into.

I'd be very interested in any comments.

TIA

I felt the same so left the valve long then on final assembly put the end of the digi callipers down the valve hole and trimmed the valve so that it came 0.25mm above the top of the inlet hole when in the fully up position

As part of the slimming down of the engine I reduced the crankshaft to 6mm dia and the boss is 10.5mm so I gain a little bit more depth of thread but a 12mm boss would be better though the cam would need enlarging to suit.

Thanks Jason. I fancy making a Husky as an interesting exercise.Your reply will encourage me to experiment a little bit with the valve arrangement.

Wonderful engine, (or is it a very elaborate device for blowing raspberries... )

Neil

Happy Christmas Jason

Your re - design certainly improved the look of the engine not so bulky and more open. It runs nicely, certainly can get a lick on, sounds good to.

Very nice.

Ron

I've not built a uniflow engine up until now so here's my take on Husky, inspired by this thread. Not as elegant as JasonB's but it runs.

Basic dimensions are pretty much to the magazine plans. I've slightly increased the cylinder clearance volume at TDC to reduce compression. The valve travel is slightly longer in an attempt to lessen leakage into the cylinder when the inlet port is closed, also the flywheel is heavier.

(This post is also a first try at embedding video)

https://youtu.be/gZmFcMgk7eY

Edit:- was hoping the video would open automatically, however, the link seems selectable and clickable but not ideal.

Edited By Clive Brown 1 on 23/01/2022 10:07:22

Edited By JasonB on 23/01/2022 10:22:23

Looks to be a good runner and a lot less jumpy than mine unless you have a secret fixing holding it to the bench top

Thanks for moving the video Jason. It's not fixed but it does start to wander around the bench if I tun the pressure up.

Before jumping in I thought I'd redraw the Popular Science drawings in CAD. Either I'm missing something or the inboard bearing should be moved 3/32 to the left, not as shown in line with the right hand pillars. Anyone else found this? Jason's models/photos seem to be as PopSci, but the cam looks different, lobe not central

If this is going to appear as a series in ME I'll has hold off

Just had a quick look at the PS drawings and I make it 1/32" difference , did you allow for the flats on the cyl and valve?

After resizing mine came out to 21mm for both, I also increased the boss on one side of the cam as 3mm would have been a bit small to get a half decent sizes grub screw into.

I don't think I will be writing this one up for ME.

Duncan,

I made mine to the imperial dimensions in the magazine and it fitted together OK. Can't think where the 3/32" could come from. I did at first wonder if you had turned the con-rod so that the big-end boss took up that dimension, but it's 1/8". The cam and valve rod centre lines would be displaced if you moved the inboard bearing.

Other changes I made wouldn't affect the bearing position.

Hmmm. If I put the conrod boss in as per left hand view the cam is offset from the valve, if I put the boss out as per Jason model I have to move the bearing, still can't see where I've gone awry. Yes I've allowed for the 1/32 flats

Sorry about the picture, it's a png from a screenshot converted to jpg using Paint, anyone know how I can make it bigger?

try this

That's better and I can see the problem now.

If you look at the light blue line representing the ctr line of the middle column that is not on the same ctr line as the cylinder by what looks like about 1/16" marked in red which is why you are getting 3/32" yet the drawing "error" is only 1/32"

Move the cylinder and columns to the same ctr line and also make the crank pin a bit longer so you have some float and it wil run with bearing lined up with end pair of columns

Gotcha, Thanks