Hi!

As my cut fingers will prove, I am a newbie to RC in general and I have a couple of questions about starting these diesels. I have already learned the hard way to use a chicken stick, but my question is how far do you screw the compression screw in to start the engine. Does it have to push down on the head to increase compression or does simply screwing it in make the head more compressed? I have two engines, on one you can turn the screw all the way in and it still wont touch the head, the other one does touch and allows for a little play, hence my confusion.

Also, you choke your engine by covering the venturi and flipping the prop a couple of times, right?

Thanks,

Canabian

Hi..
If you lose the original setting of the compression screw, prime the engines then flick to start, meanwhile with the free hand screwing IN compression 1/8 turn between flicks until the engine fires. You are then within 1/4 turn either way of the cold start setting.

Hot re-starts are the same procedure, BUT from the last best hot running setting (max. speed under load) it will be found necessary to UNSCREW the compression lever 1/4 to 1/2 turn first. This will become unnecessary when the engine is fully run in, and a really good flick is learnt.

COLD START = HOT RUNNING SETTING PLUS 1/4 TO 3/4 TURN IN OF COMP. SCREW.

HOT RE-START = HOT RUNNING SETTING LESS 1/4 TO 1/2 TURN OUT OF COMP. SCREW.

No, do not prime to much, can cause more compression and difficult to start and get damaged wristpin/con.rod. Read above as i wrote.

Jens Eirik

Canabian,

If I understand your question correctly, in most diesels there is a contra piston that is moved down by the screw. When you turn the screw out, compression moves the contra piston up to the screw while you flip the engine.
Instructions that came with one of my diesels said to turn the screw in until the contra piston touched the piston at the top of it's stroke, then back off 1.5 turns. That established a starting point.
Most diesels come from the factory with compression set to a running position. If you hand a diesel to a friend, invariably he will mess with the compression screw...unless he runs diesels also.
What diesels are you referring to, someone may be able to offer specific hints for that engine.

George

Thanks for the help.

One is Russian can't remember the name right now, the other is Chinese and the manual that came with it only says 2.47cc. I got them from Carlson Imports and their site has been down since I got them so I can't get any specifics.

The manual that came with the Chinese one said the first thing I should do is take it apart, clean everything, and lube it before starting. During this process I took out the screw since I didn't know any better.

The weird thing is that the screw now won't even touch the contra piston, just spins until it is fully screwed in. Can the contra piston be pushed down too far and not come back?

Thanks again,

Canabian

Yes, it sounds like the contrapiston is too far down. Fit of the contrapiston is a tricky thing. Too tight and it will not move back up after being pushed down. Too loose and it leaks. I'd suggest you push the contrapiston up until it touches the screw screwed partway in. Before you start flipping, turn the prop over by hand to be sure the contrapiston isn't too far in. Choke the engine a couple of times, finger over the intake, and start flipping. If it does not fire after a half dozen flips, turn the screw in maybe 1/8 turn. Again turn the prop over to see that it is not hydraulic locked. Flip another half dozen times. Keep this up until it fires. If it bites you it is overcompressed and flooded. If the prop just ocellates back and forth, it is overcompressed. Diesels flood easier than glows and do not like to start flooded.

Once the engine starts you will probably need to back the compression off a little at a time. If the engine is overcompressed, it will heat up and slow down, with black exhaust. If it is undercompressed it will misfire and the exhaust will be clear. Run your engine undercompressed a little the first few runs. If the needle is too lean, the engine will misfire and die. If too rich, it will have very oily exhaust and act overcompressed. Run it a little rich the first few runs.

Jim

This method are calculated of treads at the screw.

To example the screw are 6mm with treads 1 mm, and the cylinder volume are at 2.49ccm.

You want to set 16:1 compression ratio as start point.

How to find:

To calculate all volume i am using centimetre instead millimetre and it is easier...

Bore: 1.475 cm ,stroke: 1.457cm = 2.49 ccm

The contrapiston has diameter 1.475 cm and stroke are variable with compression screw.

To example we set 1 turns with compression screw and the screw are moving up 0.1 cm cause treads are 0.1 cm (M6x1 metric screw).

Now we calculating headvolume: 1.475 cm:2=0.7375 ,

then calculate volume 0.7375mm x 0.7375mm x 3.14 x 0.1cm = 0.17 ccm

2.49ccm + 0.17 ccm : 0.17 ccm = 15.64:1 Compression ratio

It is near to 16:1 in compression ratio, now you are ready to starting the engine..

Jens Eirik

Jens,

Those are some very impressive calculations.

The engine I mentioned was a MARZ 2.5 (MAP3) and I just set it at a turn and a half, then started flipping and adjusting until it fired. The original compression seal on the engine was terrible but increased as it broke-in. Apparently these are assembled but never run.

George

The one on the left is the one I was writing about.

This is definetly helping, I'm getting a lot closer. I am just not sure the prop is going all the way around when I flick it and not just bouncing back.

My ultimate goal is to run biodiesel in these to take to schools and workshops to demonstrate how biodiesel works. It may or may not work, but I first need to get these things to fire on regular diesel fuel. I read the ether content helps to get it fired, I think I will pick up some GUNK from the auto parts store and try using some of that. Anyone else try something like this?

Canabian, what are you using for fuel now?

Model diesels run on a mixture of kerosene, castor oil, ether, and an ignition improver such as amyl nitrate. Kerosene is for power, castor oil is for lube and cooling, ether lowers the compression ratio needed for combustion, and the 2%-3% amyl nitrate makes it all work better together.

Some have used substitutions. Most go back to the standard mix.

Gunk? What will that do except keep it clean?

I would suggest you purchase a can of ready-made diesel fuel and leave the experiments until the engines are broken-in and you are familiar with diesel starting and operation.

You may find the longer stroke engines such as the Mills replicas more tolerant of other fuels.

Good luck,
George

I bought a can of diesel fuel from Carlson Imports. The Gunk has a high content of ether in it and supposedly helps with starting tight engines. Of course I only heard this once, that's why I was asking about this here.

Can you give me a source for the Mills? Carlsons site is still down and that is the only one that has a good selection in the states I have found so far.

That must be GUNK starting fluid. I thought you meant the degreaser.

My Mills replicas are from Carlson. If you call him he can fix you up over the phone.

George