Actual Metalworking -- Cox engine head

(yes, I'm reposting -- I realized that the title was a bit uninformative)

Just finished running it -- ran through a whole tank of 10% nitro fuel. I couldn't do that with the stock head; I think it just didn't have enough compression. This head has stupid-high compression* -- it runs better with a stack of three head gaskets than it does with none (I need to try it with one or two).

_And_ it starts with a ni-starter -- Cox glow heads _demand_ a good dry cell battery, and just sneer at you if you try to give them 1.2V from a nicad.

• Note that it was built with more compression than the drawing indicates, and wider fin spacing.

Whoever took the pictures - nice hustle, but perhaps you could use the macro setting to focus close-in, or set the aperture to a higher F stop (like F 5.6 or greater)

On some pics, you can see things came into focus past the object.

PS. Of course, higher F stop means less light. F 8 brings everything into focus, but reduces the amount of light.

That .3v per cell matters at times.

I took the liberty of putting links in for you.

Did you rework it or did you make it from scratch?

Wes

I was going to apologize for the crappy pictures. That _is_ with a macro, although it's the camera's built-in macro setting which, while it does put a pretty picture of a flower in one corner of the view screen, doesn't let you get much closer than a foot. I should have gone back and taken more pictures when I found just how bad it is, but I'm lazy.

Maybe today.

From scratch -- I only have one high compression head, and it's still good. There's no way I'm cutting that up!

I find that a textured background helps the camera autofocus a lot. Most cameras cannot autofocus on mirror surfaces.

What also helps is a big flash to fill the room with light.

And, to respect the lens' minimum distance, but it's easy to get fooled.

Joe Gwinn

Nicely done. I tried to do this back in '68 when I was 16. I had a Wen-Mac engine and couldn't get glow plugs for it any more. I don't think I was able to tap a good enough hole and I never got mine to work.

Nice. What were the closest tolerances that you had to hold? Bob

Didn't think of it -- I just took an aluminum bar and hacked away everything that didn't look like what I wanted.

I don't know that doing so would have been a public service, other than an example of how one hack-job amateur took care of the work.

I'm planning on doing a few, to experiment with compression ratios and combustion chamber shape, so I'll think about doing it then.

I'm on a bit of a mission. You can get these adapters, but the word on the street is that they don't work as well as the Cox heads, because not much attention is paid to combustion chamber shape. So I'm interested not only in "can I make this work", but "can I make this work well", and "can I make this work for low nitro fuel".

Did you take pictures of your setups as you made it?

Wes

That's pretty nice! I have a Norvell engine that I'm not sure if glow plugs are still available for, if not I may be making an adapter similar to that some day.

I used to want one of the Davis Diesel conversion heads for the COX .049s but never got one. I still think it would be fun to play with, just not sure how practical they are.

I have a "Tarno" carburetor from years ago, fits on a Cox TD.049/.051 engine and gives you throttle control, I never used it, they may be worth something these days.

RogerN

No, the kids have been keeping us running flat out for the last sixteen years. Now that #1 son has turned from "kid" to "young man" and has taken up driving the number of errands that need to be run has dropped dramatically, so I may start getting chances like that.

A fresh carbon zinc is closer to 1.55 volts. 1.2 volts would be a little over a 40% reduction in power dissipate in the glow plug.

I know how that works. I've been working away on a Gatlingun and the camera has never been in the shop. I really should take pictures.

Believe it or not, showing a way is a service.

That would be fantastic.

I hope you have success. Have you ever been to NAMES or one of the other model engineering expos?

Wes

It goes lower than that when you load it up with a glow plug. The power reduction wouldn't be quite 40%, as the resistance goes down with temperature -- but it's still enough of a drop that the engine gets to be quite a bit harder to start.

It doesn't take much, plus I've seen people try to use a lot more wire than they need which adds to the droop.

There seems to be a lot of difference in the internal resistance of the batteries too. For example, it would be interesting to measure the voltage at the glow head using a Sub C Nicad versus a C cell carbon zinc, I doubt there would be a 40% difference, the Nicad might even deliver more voltage to the glow head. However using a 1.5V lantern battery sized carbon zinc cell would get the voltage up there. For glow plugs I use either 1.2V rechargeable or my power panel glow driver, I guess the power panel would be better for Cox engines but I haven't used them enough in R/C to notice a difference.

RogerN

For the Cox engines I was told to use two D size alkaline cells in parallel. I do that, with good thick wires, and it works like a charm. I use 3/16" (I think that's the size) copper tube on the batteries, which is just the right size for banana plugs, good thick not-too-long wires, and a Sulivan clip. It works like a charm.

For the conversion heads with glow plugs, I use a little bitty Ni-starter -- whee!

The resistance of both types go up with age. Some people use an ESR meter to measure the internal reistance of each cell.