DICKEYBIRD

A friend of mine a while back made up a fixture to hold the piston and an external lap sorta like AJ's. We lapped down an old worn out of round .051 piston down to .049 size. It took forever and by the time I finally got it close, I was out of patience and didn't watch carefully enough and got it too far undersize. I didn't try the process again but the diamond lapping stuff that's available now might help.

The other thing is that I don't know what the "magic" taper fit is that REALLY makes 'em run. If I knew that, I would try it again. All those well known speed tricks don't really work as well as they should unless the fit is "RIGHT."

ajcoholic

My Feedback: (10)

Msaint, I dont. Read my post above regarding heating and shrinking cox cylinders...

Andrew

AndyW

My Feedback: (1)

Msaint,

Get an .051 piston and lap an .049 cylinder to suit.

Jeff,

After posting, I realized that I might have overreacted. So, I did a search of your past posts and came to the realization that you're just as sick as the rest of us. You were just kidding. You must have been. Taking a VA to 35K puts you in some kind of category outside of mere mortals.

All my VAs get sloppy at the piston pin end if I push them. An all castor fuel helps. How are your rods standing up?

Andrew,

Me too, no expert. Experts have a tendency to spoil the fun. It's the learning process that I enjoy, by trying things and experimenting. You've contributed a great deal to that and I appreciate it, as do many others.

Most of what I do is to try and make an engine as usable as possible for my purposes. That includes max power, low and reliable idle, excellent transition and durability. All achievable with modifications. Interesting the first few times but a chore thereafter. Too bad we can't just buy it and fly it,,,, yet.

ZAGNUT

My Feedback: (1)

lately i've been playing with big gas engines and electronic ignition. i'm so hooked on the ignition systems that i've been trying them on smaller glo engines with good results. power, idle, and transition can be totally reliable without any nitro but size and wieght of the ignition are a problem. now i'm planning a micro system that could use a disposeable lithium battery that gives about 4 hours run time and have an all-up wieght less than 2oz. this might be a perfect solution to the cox plug and throttle problems if the extra load isn't a problem.

is this worth the effort?

dave

Msaint

My Feedback: (5)

That would depend on the results!

But how will you know what the results will be without putting forth the effort.

Also I think cost should also be kept in mind.

AndyW

My Feedback: (1)

Dave/Zagnut,

Yes, it could very well be worth the effort. Just for the unique, neat factor. I suspect that on gas, it might swing a bigger prop slower, with more torque. That might be useful in some applications.

Andrew Coholic has done up at least one Cox .049 on ignition and I hear it runs real well.

BTW, I'll get your psiton and cylinder out to you tomorrow.

Jeff Leavitt

Andy,

You caught me! And, I'm a sicko too.

About the VA rods. Mine are holding up good now. It wasn't always that way I'm sorry to say. Keep the head space above .008 minimum. My best results are around .010-.011. Oil content needs to be 20% with 75% of that being castor. Don't over prop, and you'll get good wrist pin wear. I had over 80 runs on one last season before it got to sloppy to produce good rpm's

Rgds, Jeff

ZAGNUT

My Feedback: (1)

gas in a cox? never thought about that, doubt it would cause overheating like in some "normal" glo engines. getting it to needle reliably might be a pain. i was thinking about good idle and transition with a throttle coupled spark advance. got the CDI worked out in my head but nothing concrete yet. should be about $20 in electronics and hardware and will use a tiny trigger-transformer like those found in strobes and flashes for the coil. yet another project to find time for.

dave

AndyW

My Feedback: (1)

Jeff,

Thanks for the tips on the rods. What all of us sickos need to do though, is avoid any vaccine they might come up with.

Dave,

I'd bet that like me, two lifetimes of spare time might not be enough. Maybe we all need to join Projectoholics Anonymous :spinnyeye

big max 1935

My Feedback: (9)

Think you Canadian guys spend WAY too much time snowed in !! Must be nice to have so much fun . MAX H.

Japanman

Well finally i finished my turbo plug conversion head.
I had it running yesterday on my modifiyed norvy .074 ...
And it seemed a success. I cannot either give tach numbers or even a straight sound comparison with a norvy plug, but i can tell you it was up on par with the norvell plug.
The difference between the Turbo plug and the no.8 was, to say the least, huge. With the no.8 the engine couldn`t get to full resonance on the pipe. With the Turbo it was instantly obvious... Boy that engine pulls a few revs!
I suspect that the plug i chose - the O.S medium was also the correct heat range for the stuff i am doing. It was starting to get a bit sensitive on the idle- not rough, but needing a good mixture.
All good so far.

A few things that might help if you make a head for yourself,
The thread is a M8 fine (M8 by 0.75mm)
Also a plus type screwdriver attachment for a cordless drill is almost a readymade Vseat cutter for the head-
J.M

Walt-RCU

Gentlemen
This is a very interesting subject.
I would like to ask a question.
If I put two or more head gaskets under the head (Glow plug), I am lowering the compression but am I also changing the timing.

Walt

Msaint

My Feedback: (5)

Not if you are only shimming the glow head.

Now if you were to shim up the cylinder you would be changing the timing because it would raise the ports.

ajcoholic

My Feedback: (10)

a drastic change in comprssion MAY change the timing due to the ignition point also being retarded.

If an engine is over compressed it will predetonate (fire too soon BTDC)

So, yes, to some degree you can change the timing by shimming the head, if you are talking about the ignition timing!

The "timing" however usually refers to the opening and closing (duration and relation to TDC and BDC in degrees) of the exhaust, intake and transfer ports.
These are not changed unless you rasie or lower the sleeve or entire cylinder in an engine (well, the intake is the same if we are talking FRV)

AJC

AndyW

My Feedback: (1)

Walt,

AJC and Msaint are correct. You have to be careful as to which timing you're referring to.

Altering the compression ratio (within limits) can have benefits. As pointed out, the ignition timing will be changed by altering the compression. Increasing the compression will advance the ignition timing and reducing the compression will retard the ignition timing.

If you have a fixed airbleed, or no airbleed at all, and your idle goes rich and runs rough on you, you can compensate by reducing the compression. Reducing the compression will cause the need to lean out the high speed needle some and this in turn will automatically lean out the low speed. Even if you have a means to adjust the low speed sometimes that need falls outside of the range provided by the airbleed or low speed needle. Reducing the compression can often bring you within the range that allows the low speed adjustment to have an effect.

Very often this isn't the fault of the engine manufacturer. A ganging of tolerances can give you a particular engine that is just enough over compressed to cause problems. Ganging of tolerances become a bigger factor the smaller the engine.