SGC

Nice work on the G-Mark glow buttons Andy.

Jaspur_x

My Feedback: (1)

I placed an order for some nelson flat coil plugs and headclamp kits. These will fit my cox teedee 049 and norvel 061`s. and this will allow total clarity of the flatcoil set-up.
Meanwhile , [email protected] does this conversion for the cox teedee 020 for $35 and is willing to give the G-mark 03 a try. There is the good news of that.
The less than good news is that he requires the engins shipped to him to ensure quality in the head modification.
He says he has seen as much as 0.008 variance @ tdc in the cox teedee .020`s and performs work accordingly. And  it is 3-4 weeks turnaround time.
I will call him monday afternoon to make all the necessary arrangements and to get total clarity.
I still have to work on switching to my cox teedee020 with a throttle sleeve to keep on flying at that point ( My norvel is for my LMH110 heli , I do not even have planes for the other norvels yet and I`m not sure I like the idea of flying my littlest stick or farcebug with an 061.......................................

Chris , I did read thoroughly,I`m not the only person that read it as you were raising the cylinder and raising the head which would lower compression , I think you mistyped that portion a few posts back.

Andy , if you want to give it a shot with the nelson flatcoil plugs I will send you a glowhead or more depending on which heads you desire  ( I have spare coxes) and  some plugs including the head that is coming with the plugs just for reference  to start with when they arrive 

gkamysz

My Feedback: (19)

I understood what Chris was saying about raising the cylinder. I just made the comment that if you try to improve breathing by raising the liner you must compensate for changes in the combustion chamber to make any real determination of what the change did.

AndyW

My Feedback: (1)

When I made the glow button, at first it was flush or flat at the bottom face. When installed, I found that the piston would bump into it at TDC. If you look at the first picture, at the stock plug at left, you can see a small ridge at the bottom face. Amazingly, the tolerances of this little gem are so good that the piston comes up JUST shy of inner part of the plug face. So there's a bit of squish band there by design. Looking at the insert I made, with the clearance required to eliminate the bump, you can see considerably more squish band. This might be a good thing, or not. [X(]

Jared, I appreciate the offer. If you're willing, I'd compensate for that by adding an adjustable airbleed to your throttle.

Stewart, thanks, and thanks Jared for the inspiration to try all of this. I was getting short of engine projects, (not) The good news is that we're getting above freezing weather during a month when we should be getting 40 below. That makes bench running far more pleasant. [:@]

Chris, I went back to read your posts several times and I can see how some elements of it may be misread. With the utmost respect, may I suggest to break up things a bit more with paragraphs. I find myself doing this all the time when proof reading for better clarity.

Raising the cylinder to eliminate SPI will reduce the compression ratio. IF you're making plug inserts with reduced combustion chamber volume, just do that a little more to compensate. OR, you could turn down the top deck of the cylinder a bit. But again, in my opinion, SPI is there for a reason, I think it should be left alone. You're dead right though, that the timing changes that will result may have effects that might need to be compensated for. Messing with crank timing is something I rarely do.

I only have one G-Mark .03 left, and haven't run any for nearly a decade so I don't know how it might compare to, say, my Fora. I guess I'll have to break it in and see what happens.

Jaspur_x

My Feedback: (1)

AndyW,
I am willing to send my engine out to "guineau pig" for this endeavor. I will gladly send you ( or anyone else)some glowplugs if you wish once they get here. I may take you up on the airbleed offer as well , its quite tempting.

I`m working out mounting up my teedee020 to fly it so I can send out my G-mark 03
It will be much more cost effective to do it this way versus my buying a lathe to work these parts up.
Once I get to speak to Bob I will know for definite , but I was planning on sacrificing my remaining good glowhead as well , to have a second head wilt the flatcoil glow plug. the reason for the second is I will pass it around to anyone who wishes to give it a test or try to copy it.
It would be wrong in my thinking for me to ask Bob to make me parts to turn around and sell ( even at no profit), but if you try mine and like it I`m certain he will make you a copy.

Chris ,
I meant no offense at all or in any way , I just want us to all be on the same page. I have found that no matter how much knowledge I have in any one area , I still have that much more to learn as I never seem to run out of questions to be answered.

As for SPI ,
I can see both ways of thinking on its use and efficiency. it absolutely is an issue worthy of attention.Possibly leading to more efficiency if eliminated.
My cox peewee .020 ( 2 of them actually) has this as well , but my teedee .020 does not.
There are too many variables involved for me to prove or disprove the spi issue at this point. It wouls be quite time consuming to truly go through it.
I will simply leave that thought on the back burner , and perhaps adress it if I am still unsatisfied with the results of the 03 after resolving the glowhead and compression situation.

Should anyone decide to seek resolution to this matter ; may I be so bold as to ask that you would do it as scientifically as you posibly can ,recording all changes , variables ,results and please share with "us"

gkamysz

My Feedback: (19)

As soon as SPI opens, air rushes in past the piston to fill the crankcase due to the difference in pressure. From plots I've seen crankcase pressure is lowest before TDC. If we think about it, pressure should be lowest when the piston is traveling quickly. As the cranks nears TDC piston motion slows.

My .03 measured out to a CR of 9.78 not including the plug coil recess. I also have the odd situation where the piston protrudes above the cylinder deck by .005". SO tolerance stack up might have a big influence here. If the piston was flush with the top of the cylinder compression ratio drops to a more normal 8.6:1.

Jaspur_x

My Feedback: (1)

ok , here we go lo
One reason that spi could be inherently counterproductive is that as the piston travels up the cylinder it reduces crankcase pressure and in most casesthis results ina slight vaccuum orsuction effect which helps the fuelto reach the combustion chamber and would also help the piston on its return downward..
But,as the botom of the pistonpasses the exhaust port edgeair is permitted into the crankcase , reducing this "vaccuum or suction"and actually posibly retarding the pistons downward return to an extent as the piston is now creating compression in the crankcase.

There are two "schools of thought " on this matter which will truly require scientiffic proof to one conclusion or the other.

Jared.

ffkiwi

Again people please READ what I have written in previous posts. My comments about SPI were specifically about power, not about throttling. OK-in summary-and on separate lines so we are all on the same music sheet can I reiterate:

(1) SPI is quite common in small engines-generally older type designs of cross flow or reverse flow porting-not common to find it in schneurle engines
(2) SPI normally results in a slighty power increase through better aspiration-IN AN OPEN EXHAUST SETUP
(3) in a muffled setup, an SPI equipped engine the engine will suffer a significant power loss compared with the open exhaust setup
(4) SPI is not a 'defect' in the engine design or manufacture, but can appear as an accidental outcome as opposed to deliberate design.
(5) Manufacturing tolerances can result in quite a lot of variation in SPI, since it is determined by a) exhaust port height b) piston skirt length
and c) conrod length-all of which have the potential to affect SPI-and all of which are subject to manufacturing tolerances

To remove SPI-with the intent of eliminating the power loss when muffled-you have only three options-make a new piston with a longer skirt, make a longer rod, or raise the lower edge of the exhaust port by shimming the liner or cylinder. The first option does not affect timing, the others do-and the first two require considerable machining skill. The EASIEST method of removing SPI is shimming the liner-but this will require a concomitant adjustment to the head to restore (or even increase) compression from the original standard setup. With a larger engine, it is usual to machine the cylinder head (or head button) to allow the spigot portion to project further down into the cylinder, as the piston is now lower at TDC, because the cylinder has been raised. Then you test-and fine tune the adjustment with additional shims/gaskets.

We are discussing options for the G-Mark with its integral glowhead-a fairly low compression design-and unobtainable in any case. To produce more power, we can simply face a bit off the existing head to produce a higher compression head. As I indicated yesterday, this would be around 0.020-0.022" max before the underside of the head bottoms out on the top cylinder fin-and you start losing seal in the head gasket area.

In any case-none of us seem to have sufficient supplies of spare heads to embark on this experimentation [without checking I think I have one spare glowhead for 5 G-Mark 03s in my collection] So we are left with the one option of doing some kind of conversion-and a variety of solutions have been mooted here-of which the GloBee Nelson insert seems to be the one with most success potential.

For those of you who haven't yet-can I recommend getting hold of Andy's missive 'Kit Bashing 1/2A engines' -published in Flying Models some years back-it is a truly excellent report-and shows the depth of Andy's testing and machining skills.

Andy-there is only one area I disagree with you on-and that is the muffler effect on SPI engines. I can produce enough published engine test data to drown you in-and it all says the same thing-once you fit an SPI equipped engine with a muffler, you get a major power loss-in some cases astronomic in % terms

I also fail to see the significance of the ridge you refer to on the G-Mark head-this ridge seals on the head gasket on the shelf area inside the top of the cylinder-it is too narrow to project into the bore, so cannot have any squish effect. To create a squish effect, you would have to face down the combustion side of the glowhead sufficiently to produce a flat area adjacent to the hemispherical surface that projects sufficiently far into the bore to have some effect on the charge movement.

Finally-as promised some pics-

ChrisM
'ffkiwi'

The first picture shows one of my G-Marks with 0.018" of SPI. The second the GloBee Nelson insert in relation to the G-Mark head, the third the insert removed from the nelson plug thread carrier, the fourth the insert fitted to a Galbreath 049 head [and this is the head style we should be aiming for in the G-Mark] and a row of heads and inserts-Russian button, GloBee 1/2A button, Nelson Globee, the G-Mark and a Cox 020 for size reference

Jaspur_x

My Feedback: (1)

ChrisM ,

That Galbreathe style head/plug system is the desired method that Bob is going to try to producing using a modified glowhead.

I see the point of the spi issue in our instance ( and have understood it all along once you ponted its existance out ) I just do not have the time to work on this issue at this point.
Cutting the shims for under the cylinder would be the most challenging aspect of this for me.
I was going to ask Bob to look into this for me.

AndyW,
OOOOOOOOOh so you are that andy ( of FM fame) Now it comes into perspective lol
Is there a way to get a compiled form of your "works" I can`t go gthrough my old back issues without getting side tracked by all the distractions in the mag.

gkamysz

My Feedback: (19)

Here's my turbo head minus threads and tightening slot. I ran out of time today. The combustion chamber dome chattered because all I had on hand was an XL ball nose end mill.

[link=http://www.edfinfo.com/x/temp/03turbohead.jpg][/link]

Jaspur_x

My Feedback: (1)

You guys that can do this sort of work should do a u-tube video on it.

AndyW

My Feedback: (1)

Jared,

Chris gives me too much credit but I appreciate the kind words. I have all my articles on file, I can send them to you via PM.

OK, now about SPI, [>:][>:]

I went and checked some of my collection.

VA .049 MK1 = .010"
Norv. .074 = .016"
Picco .06 = .005"
VA .049 MK2 = .004"
Fox .049 = .016"
Cx Spc Bug = .016"
CS BB .049 = .008"
TD .020 = .012
Brdk/CS hybrd= .0025
Fora .020 = .0005

The VA MK1 to the CS, BB .049 are all nib, not altered in any way. All have SPI, most are modern, "schneurle" ported engines. Now, the question is, does this SPI hurt top end performance when adding a muffler? Does a muffler NOT hurt top end performance when that feature isn't there?

As most larger engines, say .40s, don't have SPI, is it true that taking off the muffler doesn't give you more power. In my experience, no,,, when you take off the muffler, you get more power. Mufflers rob power in ANY engine. Back pressure is the culprit. In fact, throttle sleeves affect throttling by applying increasing levels of back pressure. So a muffler of any stripe, has the effect of throttling an engine.

Now, it just might be that SPI makes this far, far worse. Most of the engines cited were designed with simple venturis and WFO in mind. Mufflers and throttles seem to have been added just to try and capture our small market. The exception is the Picco. It doesn't have much SPI, but it's definetely there. This was measured with various bits of shim stock. The Picco is a car engine and that takes a tuned pipe. Or a tuned something. Yet Picco, who definetley know what they're doing, gave this engine SPI and knowing them, it wasn't from a ganging of tolerances. I'm speculating that if you wanted to avoid SPI, you wouldn't cut the cylinder and piston so that average ranges in tolerances would foil your plans.

None of this proves nor disproves the point. What's needed is an experiment using an engine that came with SPI and one that didn't. The feature could be added or subtracted, with and without muffler. Or, if the feature is missing, as in later, VA MK2s you could shave the bottom of the piston on one side to an average SPI of say, .010". Run it with and without muffler, with and without SPI. Power, handling, throttling and anything else should be docmumented for further discussion.

I just have to dig up one of my VAs that doesn't have SPI.

Now, back to making plugs/inserts for the G-Mark to improve performance. Consensus says that this engine is undercompressed and could get more power by correcting this feature. A couple of solutions have been offered as a starting point. I had mentioned that I had made up a button for the Fora .020 that Japanman made up for me. He made it to take a Nelson plug but like a dork, I screwed in a turbo and ruined the threads. No room to make a turbo button so I found the perfect solution by adapting a TD .010. I had done that for the VA .020 with mixed results. But I erred when I said that it was the Fora that had the piston come up shy of the top deck of the cylinder. That was the VA .020. In any case, Japanman was curious as to how I did it and below is a crude drawing.

The top stem is turned down to the top of the bottom fin to the diameter that fits your head clamp. Flipped over in the lathe, you now turn off the plugs threads. Then you make up a collar to JB Weld to that stem and finally, you turn down the outside diameter of the business end to suit whatever engine you have on hand. The Fora takes the largest diameter over a TD .020, the G-Mark .030 and the VA .020 so a TD .010 plug can be adapted to a variety of 1/4A engines if you need to reduce compression. Note that the original, TD .010 combustion chamber volume isn't altered in any way. And the shape has already been optimized by Cox. How thoughtful of them. By luck, I have a good supply of TD .010 plugs, got them from clear out inventory at an old hobby shop in Toronto for 3 bucks each.

So now, thanks to this thread by Jared, I now have the potential to improve on all my .020 and .03 engines. This might even help in my efforts to throttle the TD .020. Jared, a PM is forhtcoming.

ffkiwi

Jared, Andy W is one of the most talented (and modest!) machinists out there-we are fortunate to have him on this forum. Interestingly-or ironically-I was reading his missive last evening (its coming up 5pm here in NZ as I write this) but mine is a photocopy, and other than identifying it as coming from 'Flying Models' I cannot tell you exactly when it was published-early part of this decade I think. IIRC it may have extended over several issues of FM. The sheer depth and investiveness of Andy's experimentation blows you away.

Anyway-the whole SPI thing is interesting-but perhaps a red herring in this whole business-which ultimately is about getting some kind of workable replacement head for the G-Mark. I think we would all admit that we would be happy to get a bit more power out of the engine-which with 50% more displacement than an 020, is only putting out somewhere between the power of a Cox Pee Wee and a TD 020 on the same props-ie (based on published figures for those engines-somewhere between 0.035 BHP and 0.05 BHP. Certainly the design is conservative when it comes to porting and compression.

Getting back to SPI-and the shimming business-it would be an interesting exercise to see the effect of adding 1 x ,2 x or 3 x 0.005" shims under the cylinder-and see what the effect is. Although I measured mine at 0.018" SPI-there is appreciable slop in the ball end of the rod, so 0.015" would probably zero it out. The fun thing is-you can always take them out again-leaving the engine unharmed. What I would expect to find-and Andy's article indicated the same-is that the top end power band would be moved further up the rpm scale-torque would be reduced. In practice this might mean going from the 4-1/2" prop to a 4" one. The automatic reduction in compression-if not rectified-would allow you to run more nitro-but I'm not advocating much more than 30-35%-because you're likely to burn out heads-and this whole thread is about heads after all. That being said-I suspect the Nelson Globee insert will take anything we can throw at it. And try out the whole with/without muffler and throttling business.

And if you look at the photo of my std one-you will see what appears to be a burr at the top front of the tank. It isn't-its heat damage!! Running the engine without the muffler, the exhaust started to melt the top of the tank-obviously the material is softer and not as heat resistant as the plastic used by Cox on the 010 and 020-but I'd have to say-seems less susceptible to aging effects. This engine would have last been run ca 1987 or 1988.

What I was proposing with the shimming was essentially an extension of what KK used to do for TD 049s. He manufactured a shim holder and a range of shim thicknesses. The holder-with as many shims as was required was placed under the TD 049/051 cylinder base and the cylinder screwed back in. This was used to set the cylinder timing to optimum-as even with Coxes, there was +/- tolerance ganging from time to time-and once set you could then apply your choice of heads and gaskets.

Those of you (Andy in particular) familiar with the VA 049 Mk1 will know that one version of this came with adjustable timing as well-the piston could be unscrewed, and shims placed between the underside of the piston and the top of the gudgeon carrier, then the entire assembly reassembled. Basically the same outcome as shimming the cylinder, but working by altering the piston height rather than the cylinder.

One issue I see that will need to be addressed-and I'm not sure how we will do it-is the provision of new head gaskets. There will need to be a means of adjusting head clearance-mainly for fuel-but sometimes for atmospheric, or altitude effects. I haven't measured the G-Mark head gasket, but I imagine it is 0.003" or 0.005" copper shim [well I know its copper-its the thickness I have yet to determine] or the nearest metric equivalent. Someone is going to have to tool up a punch and die to manufacture gaskets-it may be Bob Beecroft or someone else in that sort of line (Doug G. perhaps). There's nothing else out there we can use as a substitute either, given the dimensions of the G-Mark-11mm OD and ~8.5mm ID

....Greg-is your turbo head machined from bar or have you converted and existing head?

ChrisM
'ffkiwi'

AndyW

My Feedback: (1)

Jared,

Here are all my articles in FM.

lildiesel

I believe you are right in thinking a flat coil would be your best bet. It would improve performance, too. Anybody who does a flat coil reworking of a burned out Cox .020 head on a commercial basis would probably take on a G-Mark .030 conversion.

Jaspur_x

My Feedback: (1)

AndyW,
Thank you for the compilation ofyour good works , now I will not be so distracted by the rest of the mag. lol
Chris is right , you are far too modest from my view as well. ( you would rate 3 thumbs up , but I only have 2!


Another thought on SPI........ altering the cylinder height in this way could result in a lower power production. The flutes in the cylinder in which the fuel is drawn up may no longer be totally sealed off by the piston , or would no longer be in the original timing at the least.
I have not handled my engine much , It is my pride and joy in spite of it` flaws , I basically just love the rareity and carbeuration of it.


I`m going to all this " trouble" just to keep i in running order , and above all gt a little more performance out of it of course. And of course the burning curiosity that I have had for years.

I do not use the stock tankmount , I have a aluminumbackplate that Imounted in a ( teedee style ) cox tankmount , and have not ran it without themuffler.

The fact that my engine will be away for about a monthhas eaten up a bit of time scurryingaround to suitably replace it for flying in theinterim.
I will definately have Bob giveus a full report , and do up a second head just to pass around to whoever wants to try it.

Jaspur_x

My Feedback: (1)

There is aG-mark 03 c/l version on "neverfreebay"  2days20hrs. left in case anybody is interested in expanding their collection.

AndyW

My Feedback: (1)

Chris,

Thanks and to that end, I may be able to come up with a way to cut multiple gaskets for the G-Mark. I found a way to do that on the lathe for my Tanaka project. Let me have a look and I'll get back to y'all.

That may take a week or so as I may be busy with getting my brother to more radiation therapy in the next city. We'll see.

Kit Bashing 1/2A Carbs was published in 97, Bashing Engines in summer of 2001 and a ski article was published in the SPRING, yes, a ski article published in the spring of 1999. I'm having trouble posting the rest of the articles, it's getting late and I have a big day tomorrow. [] So I'll get that done tomorrow night.

ffkiwi

Andy do you recall the article Doug G published in NFFS Digest, on reworking the MP 061. He did extensive mods (I have two such modded engines) and got them up to AD 06 performance levels-no mean feat. In this article was a drawing of the punch and die he made to cut gaskets, and the mandrel he made (a telescoping one) to true up the OD, cleaning up a stack at a time.

Meanwhile, if you think glow engines use a bit of SPI, take a look at the diesels below-all from my 'user' [as opposed to display] range. The Frog 150R has a full 1/16" of SPI, the Argo slightly over 1mm, the Amco and Barbini more like our glows

Jared-yes it is possible that shimming would reduce performance-but unlikely-in this case we would be offsetting the slight loss of performance caused by removing the SPI against the likely significant increase derived from increasing the exhaust timing. Again-once we have the new heads-it will be a relatively simple-and reversible-experiment.

ChrisM
'ffkiwi'

gkamysz

My Feedback: (19)

I made that head out of bar. I drew up the design over a year ago, but never got around to making one to try. My gasket measured .156mm.

AndyW

My Feedback: (1)

Here are the rest of the FM articles.

ffkiwi

Hmm-0.156mm-thats near enough to 0.006" on old money. Cox ones IIRC are 0.005". Now all we need is Andy or someone to make us a heap-and the testing can begin.........

ChrisM
'ffkiwi'

Jaspur_x

My Feedback: (1)

I do not have a clue where to start trying to find a die to match the 03 head , just 1 more tooling hurdle for me to overcome , need a lathe and endmill ,or at least a better drillpress than my dremel jobby ( it only slows down to 5k rpm ).
Also , Isent both my glowheads with the engine, so I`m busted on that for now , perhaps. I have 1 last hare-brained scheme to try next.
so I will have to put my tinkering with that on hold for now. ( long road to hoe as they say)

I figure I will have to give time for transit , and let him tool up , probably 2 weeks til I give him a call and see what he is up to for us.

I did order a tap( that I am still waitingon)that was listed on here , I`m pretty certain it was for the turbo plugs , and I got my turbo plug in today.

I figure I will throw that turbo plug in my teedee 020 , I have planty of those heads to sacrifice one of them for an experiment , and another for a flat coil when they get here.

gkamysz

My Feedback: (19)

I haven't finished the .03 head yet. I have to thread it in the mill because my lathe is imperial and the thread is metric. I think this head will work OK. The trick is getting the compression ratio correct when the glow plug makes up a substantial portion of the combustion chamber. I might try to take a video of the machining when I make the next one.

Jaspur_x

My Feedback: (1)

Awesome news! my luck has finally turned.
I won the 03 uc on "neverfreebay" , hurray!

So I have an engine to tinker with as soon as the spare glowhead I bought for $10.50 gets here I can timker with that too ( whichever gets here first).
And of course , tinker with a carb or throttle project on this uc model , perhaps just a quicky norvel / lite machines style throttle.

This adds a totally new dimension to my engine that is out for head prototyping/testing ( pm forthcoming AndyW )

Now I`m set , my engine collection is completed!