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Laping or scraping may be a bit extreme, but some fine abrasive paper/cloth fixed to a flat surface may be sufficient. This also has the advantage that if you are not so good with the figure of eight action the surface will tend towards convex which will help the sealing. I guess you would have...

Ok, I was wondering if the compression might be too high. Next question how flat are the sealing faces of the head and the block? If they are concave you won't get it to seal.

Did you aneal the copper head gasket? How thick is it? Can you measure the compression pressure?

I have this picture series from a pre war copy of the 'Modern Diesel'. A quick internet search suggests that the first picture is under vacuum, the middle picture is at atmospheric pressure and the final picture is around 200psi (~13 bar).

All these developments are derivatives, the TJI can be seen in the HVID ‘diesel’ design as well as the early German Diesel pre combustion chambers that were an attempt to replace the air blast injection. The HCCI is a valid development if it can do away with the complicated high pressure...

There are a couple of other points to consider with modern electronic fuel injection systems. Spark ignition engines often use various stratified charge systems to allow leaner mixtures and higher compression without pre ignition/knocking. Spark ignition engine fuels are still designed to have...

This is one of the good questions, how far does the fuel spray travel in air at 30+ Bar as against in open air, will it reach the piston? I haven’t had the head off for a while but last time there was no obvious washing of the piston bowl, just signs of contact between the piston and the valves...

Here is the plan of the piston and combustion chamber. Can you read .DWG files?

I think it would be better to harden the plunger while it is round and then grind the helix otherwise the unequal sections will distort when hardening. I moved from hardened and lapped silver steel to commercial pin gauges for my plungers.

There was nothing available commercially in the sizes I needed so I decided to do it the hard way, learning how to deep drill, ream and lap with a series of experiments. Avoiding bell mouthing is quite an art although the problem can be reduced by making the cylinder a bit longer than required...

Crankshafts are fun :) I fix a bridge over the crankpin gap using the counterweight fixings to keep everything straight when finishing off the shafts. All single cylinder engines are intrinsically unbalanced (probably like me 😜) This is a 25mm throw crankshaft.

I think the difference may be related to strokes and volumes. My injection pumps have a 2mm bore and a typical working stroke of a fraction of a mm. In this case any trapped gas volume will cause problems so the seal must be at the top of the piston. If the working stroke is several times the...

I think that the seal is at the end of the piston. As soon as the inlet port is closed by the piston the pressure starts to rise. In the case of my helix pumps the seal is just the active land of the helix, not the full length of the plunger.

Some semantics here. To me a plunger pump is one with the seal is where the piston enters the cylinder. This is probably not suitable for fuel injection due to the likely hood of air being trapped around the piston. A piston pump is where the seal is at or close to the end of the piston which is...

I believe that if it is too far advanced the air temperture has not risen sufficiently to ignite the fuel. I was told by a diesel fitter that the main purpose of the excess fuel device fitted to older diesel engines as a starting aid prolonged the injection period to give a chance of something...

It is quite sensitive to injection timing, too much advance or retard and it won't start.

I use a split clamp for my starting dog. I doesn't damage the crankshaft so much and will act as a mechanical fuse if something jams whilst you are cranking with a drill. Congratulations on the first puffs of smoke 👍 :)

There is a generally accepted delay between the commencement of injection and the commencement of combustion. Various attempts have been made to reduce/control this delay such as a small pilot injection to start combustion followed by the main injection. This obviously produces additional...

Both. I think my 20cc four stroke is injecting into full compression and igniting as the injection start is 10-15° BTDC. In it's two stoke version it was not.

I have looked at various possibilities for making very small injection pumps. Some key points are: 1) It must be possible to bleed all the air out of the system. A small bubble trapped somewhere in the pump will cause inconsistent or no injection. 2) The start of injection and the injection...