A tiny diesel design of .020 c.i. capacity the Wee Dee

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Sydney Australia
Project of the Month Winner
Jun 14, 2013
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Sylvania, Sydney Australia
Elsewhere on Work in Progress is the design and build of the Holly Buddy. This was a 2.5cc diesel that was relatively easy to build and the thread took readers from the design to the final article running. That was started about a year ago and in recent times I have had a hankering to make a really small diesel using a process of inserting a tube vertically into another tube to create a nice round crankcase getting away from the slab sides and hard cornered ones that are invariably part of home machining.

I have roughed out some placements and specs to achieve the 020 with a bore of .2813" (9/16") and a stroke of 0.32" - this gives 0.0199 c.i. You will see in the attached diagram that the piston will be 0.33" long and that it will have a piston port induction and very modest timing. I think modest timing gives the piston a bit more stroke above the exhaust to better aid with any compression seal loss, which with a very small engine like this is hard to minimize without creating too much friction.

As for the cylinder vertically inside a cylinder - I have done a mock-up with Loctite and I think this may work, I have spent a lot of time trying to come up with something that stabilizes the join but am yet to hit on an idea that is satisfactory. One thought was to insert very thin rods to assist and I have done this on the mock-up but I don't think it is a good solution. It may be that eventually a crankcase has to be carved out of solid, but in the meantime if I don't try this we'll never know if it can work.

So here is probably a few hours of planning and thinking about the design so far - not much to look at on paper but it is where I think all designers start the process. The other photo is of a .5cc engine I designed and built that the internals of the Holly Buddy used - the mock-up of the cylinder inside a cylinder and of the Holly Buddy. The .5cc engine is a little beauty has at least the power of a 50's/60's sport engine of the same capacity and starts very easily. I have spoken to Steve Jenkinson about doing some CAD plans for it but we haven't done it yet - my fault not Steve's.

I will do the same as the Holly Buddy and try to write up each phase of the design and build. ............ Ed

PS if someone has a programme that can map the timings of the engine - that would be great ..


Fantastic news - Steve Jenkinson said he would do the CAD plans for the engine, Steve's work on the Holly Buddy was terrific, in my opinion a lot easier to follow than some other plans I have worked from.

Here are the next 2 phases of design. These drawings are 1mm per .01" or 100mm per inch. When working in this large scale you have to keep reminding yourself just how small this engine will be and I am trying not to over-engineer it by using much smaller sections than I have in the past. Also I haven't done a sideport engine like this before and there are still some things I am not sure about how to make them work, so as in the past get some of it made and see what can be done then. One of the design problems a sideport gives is you can't use a screw in cylinder, not only does it make aligning the hole for the inlet difficult but it also becomes critical that the thread causes a change in timing depending on where it has to go to line up. So in the end I have chosen a method not unlike the Mills .75

The cylinder outer and the crankcase outer are only 40 thou different - so it will be very interesting to see how one fits inside the other. One aspect of this that is beneficial is that the Loctite will have a greater surface area to get a grip.

You will see that there is a larger ring machined on the rear of the crankcase - that will be the radial mount for the engine, a lot of it will be removed and just 2 slots will remain for bolting down - have used this process in the little .5cc engine and it works very well.

Hopefully in the next few days will start some machining then i'll get a good idea of just how small it will be.

Happy New Year everyone.

Sheet 3.jpg

Sheet 2.jpg
Have finished making the 2 halves to the crankcase. Now starting to doubt this is going to work, but buoyed by a mate who has used Loctite in automotive situations with great success, like I said before nothing ventured nothing gained. About 8 hours work to get to here.

One thing I would do different, I'd make the nose crankshaft tunnel 50% longer so will incorporate that into plans. Waiting now the 24 hours for the Loctite to set then to recreate inner crankcase back to a void as it is hlaf filled with the upper cylinder. I've used 609 but 638 would be better, so we'll see how 609 goes - already had it that's why I used it - but not as strong as 638.



When I worked for a Loctite industrial distributor in the distant past, we sold 680 as 'weld in a bottle' for permanent assembly only.
Thanks Cosgsy, will use that if the 609 fails.

Machined the inside of the case this morning, not without some trepidation, you have 8+ hours work hanging by not much in the chuck and doing an interrupted cut - sure was glad when it all came out ok.

Next job was to make the crankshaft, never made one this tiny before. I used a (grade 5) 1/2 bolt was surprised how soft it was so hope it will be ok. Used a 4 jaw to do the crank-pin and took it down to 80 thou, it seems so tiny, have to keep reminding myself that it is only a very small engine so stresses won't be that bad, but have to be very careful not to compression lock it with too much fuel.

Here are some photos - note I took the crank down to its 3mm outer end and 4 mm inner end in steps of about 8 mm to reduce the stresses of machining. I roughed it down with a carbide tip then used a HSS tool for the finish cuts and then wet and dry to polish it. The HSS tool worked beautifully. he fit inside the tunnel is as good as I hoped, no rock and very little drag.

1. is creating the internal thread for the backplate. I use a Bokum internal threading bar.

I can't stress enough just how remarkable and fantastic these Bokum tools are ... http://www.bokumtoolco.com/

2. Doing the interrupted cut using another Bokum cutter.

3. The HSS tool used to get a very nice finish on the crankshaft.

4 & 5 Crankcase and crankshaft. Shaft yet to have the taper done for the prop-drive.





Don't want to make anyone jealous - but this is my tin of Bokum tools and you can just see the end of the tool holder I made for them. I came by them purely by a fluke, a mate was given them, and realized he would never use them and knowing my passion for machining small things asked me if they were any good. I looked at them and realized they were the answer to a huge problem I had for internal boring and threading small holes. They really are remarkable little things.

Crankshaft finished - prop driver and washer made, thread on crank end is 3 mm. Spins nice and free with the 5.5 x 4 Tornado prop attached.

Next to make will be the cylinder, all 9/32" of it .... not 9/16ths as I said above ... !!

Note the tiny Bokum boring tool to make the 4 mm to 3 mm 10 degree taper for the prop drive.


A bit more progress - yesterday our western suburb in Sydney, Penrith was the hottest place on the planet 47.3 - thankfully my workshop is under the house and it rarely gets about about 27 degrees. Sylvania where I live is more towards the coast and yesterday only got to 42 outside.

The progress - made the cylinder but yet to lap it, have a nice finish from the reamer I used so hopefully shouldn't take too long after I make a lap. Thankfully my bore gauge has a probe small enough to explore the bore interior with great accuracy.

Some pics attached ..




Been fixing a number of ED Bees and a very nice Taifun Tornado then a couple of Taipans and a Fuji glow so haven't had much time to work on this project till this afternoon.

Here is the next installment .. done the drawings for the piston, the conrod and the contra now and as I usually do I started with making the contra. It is so tiny that it really is a one shot as to size because once its parted off I can't see any way of holding it to make it smaller. Doing the contra first and getting a good fit gives a great indication of piston size, normally 2/10ths smaller diameter does the trick but this is so small it might not be the same.

Maybe need to go back one or two steps - I have a wonderful bore gauge and I lapped the bore of the cylinder to have a 1/10th of a thou taper above the exhaust opening - so if I got the contra to there tightish, I figured I was within the ball-park for a pinch fit at the top. I left a bit of meat behind the contra when machining to get to this area of the cylinder and it worked pretty good - well maybe not as it turns out, the contra is definitely too tight to "come off" with the tiny firing it will have so will have to find a way to hold it after all.

So here are some photos of the progress so far.

1. machining contra.
2. just entering bottom of bore
3. measuring with micrometer (Starrett my wife's fathers's)
4. linishing process, note how you can see if holding without cocking it by the snail trail on the emery cloth.
5. tiny isn't it !
6. the wondeful dial gauge, 1 to 2 is 1 thou in 1/10th divisions .. how good is that !
7. in cylinder at top of bore but too tight so will have to linish down slightly - bit of a challenge ..







Wow that is tiny! Maybe superglue it onto a small rod to linish it more, then heat to release it. Or maybe it's just easier to make another now you know the exact size you need. Good luck, you're doing a great job so far.
Managed to hold the contra between a bit of stock and an arbor attached to the live centre and got 2/10ths off the contra, Made the piston with all of a 1/16th gudgeon then made the rod. Made that out of steel as there was no way alloy would stand up to the thinness of the extremities. To make the rod I used some 4mm silver steel linished it down to 2 mm thick by linishing 1 mm each side ( see photos) and drilled/reamed the bigend and gudgeon holes then cut it off the 2 foot of rod. Made the piston 1/10th smaller than the contra. Put the rod on the bigend and was a tad tight so used some diamond paste and hand lapped it, came up a treat. Cleaned it all with Nulon carby cleaner and assembled it all with a few drops of oil.

Well blow me down, it turned over so nicely and with no leakage, but, with an engine so tiny a drop of oil is going to seal it better than a big engine I figure. However if you rotate it ever so slowly, the prop fires around as soon as it gets over tdc - so I guess that's pretty good.

Have now drawn the muff and the backplate so hopefully tomorrow will get a chance to do those then have to decide on the inlet tract and needle valve arrangement.

A few pics from today's effort.
1 holding the contra
2.piston in process of machining
3.rod 4mm silver steel linished 1 mm each side
4.holes made in rod now to shape it (done on the linisher - mind the fingers gets hot !) Note it is 2 mm thick top to bottom on the flats and linished down on the width.
5.bits to assemble
7.1st assembly







Got it trial assembled yesterday,after muff and backplate made - just the venturi needle valve and compression screw to go. Couldn't resist a bit of fuel in the exhaust port, had a few pops, but realised the Loctite was failing. So will get some 680 as Gogsy advised and try again. The piston to cylinder seal seems very good. A few pics of it so close but yet so far ...

Have to say at this point in time, I think it would be easier and quicker to just make the case out of solid as per usual .. but will persevere with this and see how the 680 goes when I get some ...






Good luck with it Ed. I won't guarantee the 680 will work on such a small contact area and what is probably a fair amount of force, but as far as I know it's your best shot at it.
I built three off Gordon Nano engines, which are 0.1 cc, which is .006 cubic inches. They were a real challenge, but all three eventually ran. The only way I could start them was with a homemade weak starter motor! I know one is not supposed to use electric starters on Diesels, but this motor was purposefully weak enough to stall before anything broke.

Good luck with you tiny engine!!
Love those Nano 010's ... thanks for sharing rklopp.

Was hoping that the postman would bring the 680 Loctite today, but it didn't arrive which means it won't be here now till Monday at least as it is our Australia Day tomorrow the day Australia was settled in Sydney between where our famous Sydney Harbour Bridge is located and our equally famous Sydney Opera House.

I have now finished all the ancillaries with making the compression tommy bar and the inlet tract and needle valve. The latter made from brass rod. The photos best describe them as follow. Can't wait to try the engine to see if it does in fact run. If the Loctite 680 fails, then I will speak with the tech department there and see if they have another solution, if that fails then my welder can run a small bead of weld around the bottom of the cylinder housing and permanently attach it to the lower crankcase.





31/1/18 Yesterday the 680 finally arrived and after scrupulously cleaning the mating surfaces the two crankcase halves were joined. 24 hours later, about 1/2 hour ago the engine was mounted and fueled and starting operations commenced.

It popped many times, ran for a few seconds, bounced back and forth a few times, settings gradually being found. Then on what was its last run the cylinder gently popped off the crankcase lower, held from going too far adrift by the fuel tubing.

So the experiment of using Loctite hasn't worked. I think it may have but I get the impression looking at the debris of the Loctite that it has been weakened by the diesel fuel mixture.

Oh well, I haven't seen my good mate Darren the welder for a few weeks so I'll wander up his way tomorrow and see if he can coax a bit of weld between the two halves for me.

I got the impression it will run nicely when the settings are found, I think I had it a bit rich and on the short bursts it did it sucked in too much mixture and then went to bounce mode instead of full turning.

Can't wait to try it again. First photo 24 hours of holding together - 2nd photo - self explanatory !


Yesterday rode my push bike the 3 km and 400 foot rise to my mate Warren the welder. The first photos are the great job he did of joining the two halves. Using JB Weld put the venturi back on and waited the 24 hours for it to set 100%

This afternoon back into the test rig and it was firing nicely and giving brief runs of a few seconds. A bit more comp and the runs got a bit longer, a bit more and a bit longer - then it ran quite nicely, total time from first flick probably 5 minutes. Compression is very nice hot or cold and restarts were no problem either way, although it doesn't get very hot !

It has now had about 10 minutes running and as I thought might happen, the alloy crankshaft tunnel is probably a little short and it has developed a little rocking of the crankshaft which is not good for the internals. I will now put a bronze sleeve in there and it should then run even better.

Guess the design is sound then, it seems to like the little prop - about 7200 on a 5 1/4 x 4 Tornado can't be too bad I guess especially seeing it is a side-port engine not a front rotary valve one. Took a short video of it and posted on Youtube and a link here.




Bushed the nose this morning with some bronze that used to live inside a tap in the bathroom under the handle. Put it in with a bit of Loctite and the Loctite went off within a few minutes. Assembled the engine and now all the rock had gone from the shaft. I mixed some fresh fuel about 40% ether 30% kero and castor oil and a dash of DII. Well it took a while to find the new settings - this fuel batch meant it is only happy running a lot leaner setting than it was on the old fuel. Once the settings were found it ran very happily and restarts "hot" were just as easy as cold. I have to say it seems a bit more temperamental than say a .5cc engine, but it usually is running within 30 seconds or so of 1st flick. The piston and liner have now had about 30 minutes running and the bronze bushed main bearing about 10 minutes.

I used a Tornado 6 x 3 prop this time and seen a consistent 7600 rpm, which I have to say is better than I thought it would deliver considering it is a sideport design and only .33 cc. From experience I would say this would get better by around another 400 to 500 revs with more running.

Now a question --- Steve Jenkinson said he would do the CAD plans for the engine, but I don't want to put him to that trouble if no one is going to build it.

The engine is not a beginners engine, more like a 3rd rather than a 2nd engine as the fits that have to be achieved are very fine. Also it was designed as a separate 2 piece Loctite together crankcase which hasn't worked, the 2 pieces had to be joined by welding. This means the engine case would have to be hogged out of solid, not that difficult really, most other home machined engines have this, but this one is pretty small and that complicates the process. If you haven't got them you will need to buy some very small boring bars, I use Bokum ones.

So before we do any plans I would like an indication if there is anyone out there that wants to build it please.
ED, I'd like to say I am interested, but it is too small for me! My sausages/fingers are having a hard time manipulating small things these days.
Pat(Holly Buddy builder)