1938 Aveling DX Road Roller

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1938 Aveling DX Road Roller

This topic has 8 replies, 5 voices, and was last updated 18 May 2019 at 22:11 by Neil Wyatt.

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4 May 2019 at 11:37 #407691

Chris Miller

Participant

@chrismiller66692

I am restoring a model of the Aveling DX Road Roller that was build following Edgar Westbury's 1938 article in Model Engineering. The 'Roller had not be used in over 15 years and was missing several parts, not least the ignition system.

Having stripped the model down and cleaned off the rust and removed and checked out the 4 stroke i.c. engine I now have a functioning model. I have added a MinMag ignition system with a hall effect contact system which, along with a new spark plug is working ok. ( With some advice from Julian and Bernadette who run MiniMag on the IOW on the best way to set the system up).

The problem I have is that although the engine kicks over it does not continue (the most life I have had is that the engine kicked over 5/6 times and stopped).

I have checked that the fuel (Aspen4) is being 'sucked' up to the carburettor from the fuel tank, by the simple method of removing the jet screw and with a plastic pipe finding out if the 'petrol' is at the carb.

Does anyone have any experience with this model, and any hints/tips on starting a i.c. engines in general?

Thanks

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4 May 2019 at 11:37 #40529

Chris Miller

Participant

@chrismiller66692

Edgar Westbury’s Model Engineering Article

4 May 2019 at 14:06 #407705

Bazyle

Participant

@bazyle

…..but is the fuel getting through the hole in the jet? This is the most common problem in the hundreds of strimmers, chainsaws and mowers that will be failing to start this bank holiday weekend.

4 May 2019 at 14:16 #407706

Jeff Dayman

Participant

@jeffdayman43397

Hi Chris,

If you have good compression and the spark is present and timed right, you just need to get it some air and fuel and it should run. I'd also check the cam / valve timing even if the compression is good, ie 90 psi or more.

For fuel – I find a squirt bottle with some fuel is handy to give a blast of fuel/air mix right into the inlet while spinning the engine. if it runs doing that, but not otherwise, you look at fuel delivery to carb or at carb function.

All of the above assumes that the bearings are free and mechanical clearances are not excessive, and the exhaust is not blocked. If the engine has run before, the flywheel weight should be OK. On an untried engine, some engines have had issues with excessively heavy flywheels, or ones that were not heavy enough. As a general guide the flywheels on engines like the roller's should be heavy enough to just carry the engine 1 1/2 to 2 turns by inertia after spinning them.

Good luck!

5 May 2019 at 10:32 #407802

Chris Miller

Participant

@chrismiller66692

Thank you both for the advice. I will certainly follow it through.

I removed union inlet to the carb' and found that the 'venturi' inlet had been a little damaged by the end of the jet screw which I cleaned out and with a little work remade. ( The jet screw is a long screw with a point turned at one end that, fully turned off, will/should engage with the venturi and stifle the incoming fuel). The carburettor itself is an 'automatic suction carburettor' that sucks up the fuel from the tank which is lower than the carb' something I found difficult to believe but it seems to be working as there is certainly appears to be fuel up at the inlet valve.

So the question is what else is preventing the stuff getting to the combustion chamber?

I made sure when I stripped the engine that any cams and timing parts where marked to that I could put them back together in their original position. Slowly turning the engine over and checking with the timing diagram from the book seems that I put them back correctly so I am reasonably confident I don't have a problem in that area. Early on though I did think the exhaust valve might have been stuck, but stripping the head off the engine block disproved that, but did enable me to ensure that both valves were seating properly.

Thanks again still lots to try

Chris

5 May 2019 at 12:23 #407818

Bazyle

Participant

@bazyle

The 'automatic suction…" is the venturi effect. Where it starts wide, then gets narrow, then wide again. The fuel hole has to be in the middle of that narrow bit where there is a lower pressure when the engine is running. When you prime the engine initially by closing the choke (that has to be on the outside of the venturi point) turning over the engine sucks fuel up from the fuel tank and it must get up the tube and be free of bubbles but then there is also the danger of flooding the engine.
The initial few ignition cycles of an engine are running on the fumes and fuel that you sucked up initially but then it has to have established enough air flow in the venturi to suck up more fuel. Having the choke part closed helps provide more vacuum at slow revs to help this. The engine sputtering and failing to run is often because the initial fuel is used up before the new flow gets going. Too many air bubbles in the fuel line can be a problem as only a few revolutions without anything to burn brings it to a halt.

Off topic: The trouble is petrol is fussy about the air/fuel ratio at which it will explode, So too much or too little stops the engine. Air saturated with petrol will burn but is so reluctant to go bang that it was used in Victorian times as a substitute for coal gas lighting in peoples homes. (petrol-gas lighting has been explained in ME

1960	122	3059	244	G.Lambert	Petrol-Gas Plant
1960	122	3059	244	J.E.H.Jones	Petrol-Gas Plant
1960	122	3059	244	Chas. J.Francis	Petrol-Gas Plant
1960	122	3063	341	Vulcan	Petrol-gas plant

5 May 2019 at 12:31 #407825

JasonB

Moderator

@jasonb

I find that most of these model engines need a very small needle valve opening if you are going the get them to run, often just a crack sometimes 1/8th of a turn. One way to see if your air/fuel mixture is about right is to hold a flame a couple of inches from the exhaust and turn the engine over. A big orange slow burning flame will show it is to rich, what you want is a quick blue flame and you should be in the right ball park.

One other problem with engines that have a low mounted tank is that the fuel can soon drain back if there is not sufficient suction to keep it at the carb, a non return valve helps prevent this. For testing you can just rig up a temporary tank which can be raised and lowered to see if that helps.

18 May 2019 at 11:10 #409747

Chris Miller

Participant

@chrismiller66692

Thank you all for your help and guidance. Though not engine specific ( why would it be after all this time ) the suggestions and general discussion around model internal combustion engines was very useful. Especially lighting a match next to the exhaust which was quite illuminating. But, it did show me that following the advice in the manual gave me a fuel mix that was too rich.

The articles also gave me the confidence to strip down the engine block to access the valves which I have cleaned and re-bedded. Which led me to discover that there is a compression leak between the inlet valve casing and the engine head. The piston rings seemed thankfully ok along with the cylinder and piston. The gap between the cylinder liner and the piston is 0.003" and is correctly made to the manual for an aluminium piston to allow for expansion.

So once again thank you all from a complete modeling novice. I'll let you know if I achieve my goal of getting the beast to move.

Chris

18 May 2019 at 22:11 #409823