20 cc Horizontal 2 Stroke Diesel

[Roger B]

Thank you Zephyrin 

I have a copy of that magazine. It was one of the the things that started me off on this project. From it I knew that it was possible to make such an engine and I also knew that there would need to be a lot of experimentation 

Some of the details were confirmation of my calculations. He states 1mm3 of fuel at maximum output for  a 7cc engine, I calculated 2mm3 for a 20cc engine (with the poor volumetric efficiency of a 2 stroke I probably have more like 15cc of air). His engine has a 2mm fuel pump plunger and a needle type injector which was my first choice. Most of the other sucessful small diesels seem to use bigger pumps and poppet type nozzles.

I believe that I am injecting at around 100 bar but it is difficult to detemine, I am calculating from the force on the pump plunger at low speed. The pressure at 1000rpm or more may well be higher.

[Zephyrin]

I suspected that you were aware of this mini diesel, one does not venture into such a pioneering project without full information.
A really first-class thread for me!

[Roger B]

Some success and a potentially big problem 

I took the engine into the welding area at work again for some more trials. It fired immediately and after a small adjustment to the timing (advance) it ran consistently. I found it ran better if I reduced the fuel, it was apparently drowning  Then it suddenly seized absolutely solid  no movement at all 

I took it home and removed the cylinder head. All was free again    Something was jammed between the piston and the head and had made some significant marks. It could be a very squashed M3x3 grub screw that was used to seal the end of the big end oil passage or it could just be something then fell in/got left in at some point  I will have to strip the crankcase down to confirm if it was the oilway plug.

<a href="https://www.youtube.com/watch?v=ATVJN0N9YLo" target="_blank">http://www.youtube.com/watch?v=ATVJN0N9YLo</a>

[fumopuc]

Hi Roger, I can feel your pain.

[Admiral_dk]

Great that you found the timing improvement 

The attempt to "do forging" inside the combustion chamber .... did at least only have minor consequences - whatever your feelings might have been at the time         .... I don't know.

[Roger B]

It was certainly a worrying moment  There was absolutely no movement of the flywheel or crankshaft, there is normally a little end float. I guess it must have acted like a toggle lock at TDC.

I took the crankcase side plate off and found the plug still firmly in place. After some more thought I realised that the gudgeon pin was retained with the same grub screws. Off with the cover plate and out with the piston and rod. The big end looked ok as did the piston but there were bite marks on the con rod and sure enough one of the grub screws was missing  Luckily the gudgeon pin had not drifted sideways and scores the bore.

That must have been an interesting journey through the crankcase without jamming solid, down the 3mm high transfer passage and into the cylinder  Comparing with a new grub screw my forging press looks to be quite good.

Well nothing is seriously damaged, the marks will polish out but this time I will use longer grub screws and Loctite for the gudgeon pin retainers.

[fumopuc]

Roger, but I do like the smoke signals of Smoking Joe.

[Zephyrin]

it's a pity, just when you've found the right intake setting, and that the engine was running regularly.

the hammering marks are impressive, there is really a great deal of pressure in the cylinder !

[Roger B]

Thank you both    In the previous nearly runs video it also blows a smoke ring at the end 

It looks like I have made my engine strong enough, the connecting rod in Find Hansen's first experimental diesel bent 

I am not quite sure what was going on in the combustion chamber  All the marks are at the top of the cylinder, three have sooted up and one jammed solid. The screw must have been in the cylinder for some time, apparently held up by the turbulence, but only jammed up in one position. If it had dropped to the bottom of the cylinder it could have easily escaped via the exhaust ports, which are bigger than the transfer ports. I designed it with the exhaust at the bottom rather than the side to minimise the chance of hydraulic lock.

[Roger B]

I reassembled the engine and carried out a compression test to check for any other damage. It was much as before , a rapid rise to 20-25 bar then slowly to over 30 bar with a leak off at the end.

<a href="https://www.youtube.com/watch?v=glmQ5oORU_Y" target="_blank">http://www.youtube.com/watch?v=glmQ5oORU_Y</a>

I knew that the nuts had fallen off the injection pump cam follower pivot but on closer investigation I found that the thread was also damaged. The anti rotation pin for the cam follower had also disappeared  I made replacements and put it all back together (with Loctite in the appropriate places)  to see what will break/fall off in the next trials 

[Roger B]

Another trial series. I made some adjustments to the timing, but I am not sure if I am in the right area. Injection start is around 15° BTDC and injection has finished before TDC. Maybe I need to make a new cam to extend the period 

<a href="https://www.youtube.com/watch?v=VBvq00gCIkk" target="_blank">http://www.youtube.com/watch?v=VBvq00gCIkk</a>

This trial came to an end when the starter dog started slipping  This has happened before so maybe I need to find a new solution, but I don't really want to use a key as I want some form of mechanical fuse if the engine seizes 

[MJM460]

Hi Roger, that is looking very encouraging.  Must be in the right area surely.

MJM460

[Kim]

It really took off there for a while, Roger!  You've got to be getting close!
Kim

[Roger B]

Thank you 

The crankshaft under the flywheel was not too badly scored. I had a commercial alternative taper lock but it was too long so I decided to remake the existing taper bush but from cast iron and a larger diameter with M4 instead of M3 grub screws. The top slide was set to 3° for the bush and kept at the same setting to bore out the flywheel. Unfortunately the interrupted cut due to the old fixing holes caused the cross slide to move (I should have locked it  ) and I bored the flywheel more than required so I had to make a second bush  This fitted ok and all seemed to run true when spun on a piece of 12mm ground rod.

[Laurentic]

Roger - I have designed and built a slightly different style of taper lock bush for securing a drive gear.  I am not suggesting you use it in your current application but you may wish to consider its merits for the future.

Basically the item to be secured, in my case the drive gear (a 30t 1.25" dia 24DP), has a tapered recess and includes an end flange that is a close-ish fit on the shaft, in this case the shaft is 0.5" diameter.  The taper is five degrees (or 10 degrees included) angle.  The bush is also a very close fit on the shaft, has the same taper obviously and fits inside the recess in the gear.  Four M2.5 equally spaced clearance holes on a suitable pcd are drilled through the bush, and the M2.5 socket cap screws screw into tapped holes in the gear end flange.  A gap between the end of the bush and the flange allows the bush to be pulled in, but the movement in reality is not a lot.  The bush is slit partway through at BDC and totally through at TDC.  There are two M2.5 tapped holes in the bush at 180 degree spacing at 3 and 9 o'clock to enable the bush to be withdrawn by inserting suitable withdrawing bolts.

The idea is that being a very close fit on the shaft it doesn't require a lot of pulling in to lock securely.  The four M.25 socket cap screws have plenty of thread engagement, are not "half-in, half-out" of a thread but totally in a thread which I think is more secure and together with the taper allow a very even pull-on around the bush.  It all appears very solid when locked up. 

I have used it in an application where it provides an easier and more secure method of securing a part in a particular position than say using a grub screw and it won't damage the shaft where it locks up either.

Chris