Here's an idea

Does it iron on also?

Can I pick it up at Staples?

Hi Ralph, the last time we tryed to talk about vinyl for conversion planes it was moved on us

Check post #1052 on page 43 of this thread. Thats about where the covering talk starts. Sign vinyl is available over the net or maybe free from sign shops. (scraps) It's self adhesive and some say stretchable with heat.

Getting back to gas to glow. I've looked, (only briefly I will admit) to find any reference to compression ratio when going from gas to glow. My understanding is that increasing compression ratio without altering port timing can yield good results.

From, http://www.oneillbrothersracing.com/...ption/dome.htm

We have their product, a "dome", a bolt on insert head that's available with the following ratios.

This is a removable dome for the CY 27cc and 29cc head kit motors.

11:1 Dome- 87 octane or higher
12:1 Dome- 89 octane or higher
13:1 Dome - 92 octane or higher
14:1 Dome - 95 octane or higher
15:1 Dome - 105 octane or higher
16:1 Dome - 112 octane or higher
17:1 Dome - 116 octane or higher
18:1 Dome - 120 octane / alcohol
19:1 Dome - Alcohol



It appears that any gas to glow conversion would benefit from increased compression ratio. And octane rating affects optimum compression ratio. Wonder if this might shed light on some of the experiences related on this thread.

Comments?

So far I've done Echo 23.6cc engines, Homelite 25 & 30cc engines, a Ryobi 31cc, and a Poulan 42cc on Gas/Glow. At some point in all our beginning experiments, Aeronut reported some detonation in a Ryobi 31cc. We switched to using Premium in the gas part of the mix, and the problem went away. I just now use premium in all my engines. My Poulan 42cc is the only one that has a rpm drop when the glow plug power is removed, suggesting that it could use a touch more compression to be optimal. (Or a touch more nitro in the glow part of the mix.)

But as always, experimenting is great and often leads to useful new information.

Good luck,
AV8TOR

I know this is a very general question.

When you raise a port, say on your Echo how much do/did you raise it.
Not in degrees but in .001s?

To raise the compression to the "Proper Level" how much would you have to remove
from the bottom of the cylinder?

Are these amounts even close?

Just wondering.

AV8tor,

That's encouraging. Looks like the CR for glow is about the same for gas. I note though, with a little research that an ethanol gas (E85 for your car) raises the octane rating. That doesn't mean more power, just the reduced chance of detonation. E85 with premium gas is said to have an octane rating of 105.

So when we go to a gas glow mix, especially in the proportions recommend, we are REALLY boosting the octane rating. But how much? This, to me implies that we should be going to a higher compression ratio when converting to a heavy gas/glow mix. However, this is compensated for by the presence of the glow plug and methanol, I presume.

The catalytic effect of the glow on the methanol does it;s job and ignites the methanol, then the gas at the same timing as pure glow fuel. Somehow it works as we've seen here many times.

The reason for this line of enquiry is that I'm at the stage of making the heads for the Tanaka. Tanaka advised that the stock engine had a 7.5/1 compression ratio and that's about in line with most. And, research shows that that matches about what glow engines use.

THEN I stumbled on the O'Neill Brothers website and was surprised at the CRs they list. Much higher. They also seem to have some real kick butt engines in their line which seem to operate at those CRs just fine. And look, Zenoah upgrades.

Has anyone ventured to do a gasser conversion using one of their engines? I'm especially intrigued with their bolt on heads and "stuffed" cranks. And look, a bolt on reed kit with carbon reeds. And they offer ported, polished and timed engines done by hand. Too much. Gonna call them tomorrow.

Ralph,

Those are good questions. I'm inclined to think that if one could play with compression ratio and port timing independently, one might be surprised at the gains with a gas/glow mix. With my modified Tanaka, I can do that easily by shaving the base of the CASE by two or three gaskets and then add or delete them to tweak port timing and then compensate for and or tweak the compression ratio with shims under the bolt on head.

I had to butcher the Tanaka to do this, not something most can do but the O'Neill engines are done, right out of the box.

So far, at 7K on an 18 X 6 Zinger, the Tanaka, in its stock form is under the Zenoah. I hope to get it to at least 8K but it sure does sound sweet as it is. What a roar. These old ears have been enduring 19 to 22K for too long, I think. [:@]

I have to admit I have never actually measured the compression ratio on any of my engines. All I do is cut out the squish band, if any, and then lower the cylinder to get a nominal piston to head clearance of .015 to .020".

Two things though... A small bore engine can tolerate a bit more compression before getting into detonation. Also, there are two ways to measure compression ratio with two strokes. One is full stroke, as is done with four stroke engines. The other is "effective compression ratio" which is measure from exhaust port closing; not full stroke. The two methods will give you very different numbers obviously. I am rather sure the numbers you quoted from O'Neils are full stroke compression ratios.

Also, E-85 will not work for our use, as it is made with ethanol, not methanol. Methanol is necessary for the catalytic reaction with the glow plug.

AV8TOR

Thanks AV8tor,

That's an excellent observation about CR numbers. Will try to get that clarified with the O'Neill guys.

Good point about E85. I was assuming that adding any sort of alcohol would raise the octane rating some but that may be wrong.

With E-85 you do have a high octane fuel, and it works great with ignition systems, but it doesn't work that good to keep the catalytic efect on the glow plug and make our engines work without the use of a battery at al times.

Ralphbf ...

I think I answered your question about lowering the cylinder in my last post. As far as port timing, every engine is different and you can't spec port mods by dimension. You just have to go ahead and use a degree wheel to figure out what you need to remove.

AV8TOR

About how much can you remove from from the base of the cylinder when increaseing the compression?

I know this has to do with the length of the stroke.

I'm only looking for a ball park answer.

If you have done this, which engine was it, how much did you remove and what was the results?

Aero Nut,

I'm still in RC glow mode, I guess. [:@] Yes, the Oneill heads take a sparkplug for spark ignition. This thread is not about that at all. Sorry guys. New here.
What threw me was the referrence to alcohol in the last two heads. But that would still be on ignition, of course.

In any case, it looks like gas or alcohol, both respond to about the same CR.

I think Ralph is just looking for a trial and error starting point to get his feet wet in raising the compression ratio.

And I guess I was kind of wondering too what benefit we might see with a gas to glow conversion if the CR and the port timing could be fiddled with in combination.

That sort of thing sounds like a whole new thread.

But for the moment, if you shave some off the bottom of the cylinder, or the top of the case, you'll bring down the cylinder some and increase the comrpession ratio. That would mean your timing would be affected, maybe to the better, maybe not. If not, does that mean you have to grind into the ports, bypass AND exhaust to bring the timing back to specs? What of disturbing the integrity of the plating. Will it peel?

Here's a thought. Say you drop the cylinder down too much, not enough to bump the piston, but clearly overcompressed. In that case, could you not just shave some material off the top of the piston to decrease the CR? Yes, you'd be very careful not to let any shavings go astray but it could be done, I think.

Lowering the cylinder does not affect the stroke. It raises the compression, and decreases the exhaust and transfer port timing and increases the intake timing. You can regain the lost exhaust and transfer timing, and/or increase it by grinding on the top of the ports. You must always chamfer the port edges afterward!

We haven't had any plating peeling problems. You can't just randomly lower the cylinder without checking the piston to head clearance. It should be .015" to .020", and ideally you should take out any squish band in the head area as well so you can lower the cylinder more. These engines definitely benefit from increased compression whether they are run on gasoline or Gas/Glow.

I have lowered cylinders anywhere from .020 to .080" depending on the application, but once again, you can't just whack some off, or leave a gasket out without checking clearances.

If you are not experienced in engine modification, be prepared to lose an engine or two in the learning process unless you're lucky, but it's all good fun!!

AV8TOR

I have a couple of Gas/Glow engines that I want to play with.
One is a 32cc Mac.

I want to raise the compression, how much is enough?
Can I simply put a piece of clay in the head, turn the engine over and measure the flattened clay
subtract .020 and take the rest off the bottom of the cylinder and then raise the ports the same amount?

Will this simply tell me how much raising the compression helped or hurt?
Then I could raise the ports to a predetermined degree and call it good?

If I took .020 off the cylinder couldn't I bevel the piston to regain the port timing?
Could I bevel the piston and not raise the compression and gain much?

Would I be better off playing with the port timing instead of the compression?

Inquiring minds want to know.

If you remove squish band, isnt that going to effect the squench area as well as flame front?

Check this out.

http://www.bolly.com.au/1998%20Bolly%20Book%20v3.pdf

Lots of GOOOOD stuff.

I don't see anyone bringing the issue of the engine durability. To my understanding the original engine is designed for particular CR that creates given load on piston, connecting rod and crankshaft. Increasing CR I believe will increase the engine performance for sure, but at the same time it will increaso the load on these parts that may cause premature engine failure.

I wouldn't try to squeeze every bit if HP from "garden" engines - they are not designed for that. Something's gotta give. I would rather focus on the engine reliability running gas-glow plug combination. To increase the spped of flame you can use nitro, for detonation prevention - higher grade of fuel. For engine timing - the grade of glow plug. This is my understanding.

I have one thing to worry about tho. Did you guys experienced low lifetime of the glow plug running gasoline/oil only? Some time ago I run my engine on regular gas/oil mixture keeping the glow plug on the battery all the time, but the glow plug failed after about 20 minutes. Did I have bad luck or there is an issue there?

Agreed, many thanks.


Ralph,

Good info indeed, thanks.

About garden variety, you're probably right. A hedge trimmer for an average summer will see maybe a half dozen light runs. But in the case of the Tanaka that I'm working with, it's from an industrial, portable drill meant to run all day, every day. The used one had a lot of wear and tear. Insdie there was a distinct ridge in the chrome at top and bottom where the ring stopped at each end of the stroke. The chrome on this engine is not a light deposit but is a measurably thick layer. I made up a hone to take out the ridges and now have a smooth, light, crosshatch.

I've read a number of referrrences that said not to leave your plug lit for too long once the engine starts. This is why, I guess, we add the stock glow fuel so that the plug can run without any amps applied.

These small industrial engines are over-engineered and detuned. This is done to make them "idiot proof". They are designed so that the average person can just grab one, throw some gas and about any kind of oil in it, and run it full throttle all day. They often get the cooling fins all filled with grass, dirt, wood chips, whatever, and are run until they quit with no service or kindness, then get a spark plug change and do it all over again. They are designed to do this, and survive!

As such, they respond readily to mods to increase the performance, since they are supplied in a detuned state to begin with. They have a much nicer life in our model airplanes, with adequate cooling, relatively short runs, usually better care, etc. I have had virtually no reliability problems with my converted and modified engines. I have a Homelite 30cc that I run at 9500 rpms, and the boat guys regularly run the same engine over 10,000 rpms! It has been said that "You won't live long enough" to wear out one of these engines in a model airplane given decent care.

All hop up endeavors are best done in "combinations". One modification compliments another. Yes, you could gain performance by just raising the exhaust timing, and yes, the same by just raising the compression. However, a well planned program of mods that addresses all aspects, including carburetion, muffler, port timing, compression, etc. is what really produces good results.

I have noticed no negative aspects of removing the squish band, though doing so in larger engines does impact detonation resistance. An easy way to measure deck height is to insert a piece of 1/8" thick solder into the spark plug hole, bent so that it touches the edge of the cylinder. Then turn the engine over a few times. The piston will flatten the solder and you can then measure it to get your deck height.

Finally, I have heard that leaving the "glow heat" (battery) connected to a glow plug will decrease it's life, but I have no direct experience with this.

Good luck,
AV8TOR

Thanks, I see your point and cannot disagree.

Do you run your engnes on gas/glow fuel or gas only?

RC engine's glow plug is very fragile, and maybe the heating element is running to hot, that why it breaks. Maybe something like "on-board glow driver" will be more usefull as it would regulate the current and keep the temperature of the glow element within the reasonable range.

I run most of my engines on Gas/Glow now, though I do have some on regular ignition. With the Gas/Glow, (done properly), glow power is necessary only for starting, and I have had no problems with glow plug life. If one wants to use onboard glow heat, I would recommend a driver that turns the glow heat on at low throttle as you suggest.

AV8TOR