An absolute beginners journey to restore a Viking 2.5cc Diesel

[Admiral_dk]

Hi Ramon

Thank you very much for checking in and giving advice to a novice  and your kind words from an expert are appreciated too 

I new you where right - I couldn't find the prop I really wanted to try it with, so I took the next best (or not). One reason for using a big prop came from an advice from Ron Chernich - I have a nice old FOK 15 sport diesel and I had no luck running it with the 7/5" (if memory ...).
Every time I tried to start it, I got a heavy hit on my finger when it fired - it's so fast that the normal smart flick isn't fast enough to get your finger out of harms way. Next step was to try starting it with a stick - that just smashed the prop, since it is more solid than my finger  (there really ought to be a scared emoticon too) - with parts of the prop flying fast all over the shop  - This is why Ron advised me to learn to handle the FOK with a much bigger prop and a 9/6" work wonder on that engine. This was actually the prop I was looking for to test the Viking.

Your comment made me go down to the workshop and look for all my props (not that many) and in the box with engines I found a 1HP 7.5 cc glow with the same size prop that I had on the Viking - OK, that is really in the very heavy over prop territory 
Soon after I found the FOK and the 9/6" was still on it - took it and drilled it up to 9.5 mm so I could mount it on the Viking and tried to start it again. A little harder to start than with the bigger prop - smaller flywheel effect being 2" smaller in diameter - it ran quicker, but not enough. Found a 8/4" and tried that too - much better, but still no joy in regards to get it up to flying speed.

I'm sure the 8/4" is the right prop (or very close), but it still can't "clear it's throat". It runs fast enough to easily see that there is a big spray back out the carb - bigger than what can be seen leaving the exhaust. This kind of confirms that size not always scales down well and that I really need to get my hand on some cast iron for a new piston, so I can make a new much closer to the original inlet timing. I do also think that I might need to make a new carb or find a way to cure the original of any leaks - though that will only happen if a new piston can't cure the problem.

[dieselpilot]

To me it sounds like that engine is not running but oscillating. The exhaust note is very weak.

[Ramon]

Hi 'DP' -  yes that was my first thought too on the initial viewing but having watched it several times concluded that it was actually running but as said obviously well overloaded. That said it does actually have that look about it but I have a feeling something is awry with the timing as well I would say .

Per - just a consideration - are you certain the liner is in the correct way round? IE the exhaust is on the correct side. Many have been caught out on this (yes, guilty as charged  )  particularly on the Mills .75 - the piston has a step which if re assembled the wrong way leads to some very poor and erratic running and difficult starting.

The fact that you removed some material from the piston skirt has probably contributed to the leakage of fuel out of the venturi - if the port is just not closing - if only fractionally - then not only will that happen but you will be losing crankcase pressure too which will also contribute to the running characteristic you have.

The engine, being a side port will have conservative and even porting - not the kind of engine that is really suited to high revs and fast running but you should be able to get a nice steady beat out of it with an 8 x 4. If not, assuming your fuel is okay (I would say it is given it does start and run after a fashion) it's definitely something 'internal'

Good luck with the next stage 

Regards - Ramon

[Admiral_dk]

Hi Greg and Ramon - thank you for your thoughts, much appreciated.

I feel rather confident that it wasn't oscillating and it is running faster with the smaller props, but I can't guaranty that this is the case. I still does not sound right at all - it runs rough, speed increases with higher compression, but it sounds worse if I increase it over a certain amount. Leaning it makes it run very smooth but also quite a bit slower - though it is still faster that way with the 8/4" than it was with the 11/6" (rather logical).

As to the piston vs. cylinder - The Viking and most old Danish two-stroke model engines are inspired by a fellow Danish Engineer - Jørgen Skafte Rasmussen, the man who constructed the German DKW car and motorcycle engines - so they are Schnürle ported with flat piston crowns (or in this case, chamfered). I might have the cylinder a few degrees wrong - but I can see the right ports aligning with the holes in the block.

They where when I assembled it. When writing this I when down to the shop to check again and the cylinder has turned itself some 5-10 degrees, so I corrected this and tried again. It didn't really run any quicker, but the cylinder has turned a few degrees again - they where known for some of them to have this problem 

If the cylinder liner is 180 degrees out, both the exhaust and inlet is completely blocked.

As to the fuel - this is the stuff I bought a year or two ago and solved my problems with the FOK together with the bigger prop on that. It's in a steel container with seals - so I'm hoping that the ether hasn't evaporated - but if it is less good than as new, I would expect starting problems and I have none.

[Neil-Lickfold]

I suspect in both videos the engine is over compressed and is oscillating rather than running. I have never heard a running engine sound like that in your video. That to me is clearly an oscillating engine.  Try backing off the compression and restarting, slowing increasing the compression until it starts and runs.
A basic fuel is 1 part ether, 1 part castor oil and 1 part Kerosene or low odour kerosene. Then if you have any, add 1% to 1.5% of diesel ignition improver. It can be bought as diesel fuel cetane improver.  In the old days it was IPN or Amyl  Nitrate.
An 8X4 prop sounds right for a 2.5cc engine. 

An update if you got it solved would be nice to hear.

[Admiral_dk]

Thank you very much for your input Niel    but do not forget that my mistake modifying the piston gives the engine a way too long inlet duration, so a big part of the fuel is pushed back out the carb 

I write this from my lunch break at work, so I can't go look at the tin, but the fuel comes from a respected supplier of modern CI engine fuels and includes 1.5% ignition improver

Oh, I forgot to mention that I did try to lower the compression, but the engine just stops when I do.

Best wishes

Per