Go Back  RCU Forums > RC Airplanes > "1/2 A" & "1/8 A" airplanes
Reload this Page >

G-mark .03 glowheads?

Notices
"1/2 A" & "1/8 A" airplanes These are the small ones...more popular now than ever.

G-mark .03 glowheads?

Old 01-20-2010, 12:45 AM
  #1  
Jaspur_x
Senior Member
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2009
Location: Friedens, PA
Posts: 360
Likes: 0
Received 0 Likes on 0 Posts
Default G-mark .03 glowheads?

Does anybody know where I could get some of these? I recently installed my last.
Old 01-20-2010, 01:13 AM
  #2  
skaliwag
My Feedback: (1)
 
skaliwag's Avatar
 
Join Date: Jan 2003
Location: Corralitos CA
Posts: 2,469
Received 2 Likes on 2 Posts
Default RE: G-mark .03 glowheads?

1/2 way down the page.... May still do them.

http://www.tnet.com.au/~lion/Taipan_Glow_Plugs.htm
Old 01-20-2010, 06:04 AM
  #3  
Jaspur_x
Senior Member
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2009
Location: Friedens, PA
Posts: 360
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

Thanks skaliwag , I just tried them , the email addy on the page comes back undeliverable.
My local shop just said good luck finding those, and to fly bigger models or switch to electric. I said maybe someday when all other resources are expended.
Old 01-20-2010, 10:50 AM
  #4  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

Here, http://www.rcuniverse.com/forum/m_45...tm.htm#4533758 you might try converting blown heads to take turbos. Or, you might try here, http://www.hobbycentre.com.au/TAIPAN07.html
Old 01-20-2010, 05:22 PM
  #5  
DeviousDave
Senior Member
 
Join Date: Feb 2007
Location: , MI
Posts: 1,781
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

I don't have many to spare, but if your search in Australia comes up dry I might could part with one of mine.
Old 01-20-2010, 08:35 PM
  #6  
Jaspur_x
Senior Member
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2009
Location: Friedens, PA
Posts: 360
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

DD I may have to work you a deal in the future , but for now I would feel bad for shorting you of your suply ( I did this to myself a couple of years ago)
I think I may have found the solution without going out and buying a drillpress. I got an email from a guy that does a conversion to glowplugsusing the nelson flatcoil plugs. [email protected]
He also does other custom work and glowhead conversions for teedee 020`s etc I`m waiting to see if he will try my g-mark 03 glowhead. I`m considering sending my little beauty to him just to see what he can really do with it , stock G-mark claims were 6-18,000 rpm respectable I supose , but what if he can work som power in there? Theoretically it is posible.


I am in no way affiliated with this man , or compelled in any to help his business. I merely posted inof. to help my fellow modelers out.

Jared
Old 01-21-2010, 01:06 AM
  #7  
ffkiwi
 
Join Date: Jul 2005
Location: Upper HuttWellington, NEW ZEALAND
Posts: 1,601
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

Best of luck Jaspur-if successful you will have paved the way for several followers-me for a start (have 5 of the wee things!) I wouldn't be at all surprised if fitting a flat coil globee style Nelson plug DId improve power-the standard head as you know is a low compression hemispherical type.

'ffkiwi'
Old 01-21-2010, 02:50 PM
  #8  
Jaspur_x
Senior Member
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2009
Location: Friedens, PA
Posts: 360
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?



ffkiwi , have you found any of the taipan glowheads ? They were last known to be in your area so-to-speak?





I will let you all know if I come up with anything



Jared

Old 01-21-2010, 03:03 PM
  #9  
gkamysz
Senior Member
My Feedback: (19)
 
gkamysz's Avatar
 
Join Date: Jun 2003
Location: Crystal Lake, IL
Posts: 3,397
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

I have a G-mark .03 RC. I've never run it, however. I've been thinking about making a Glow head to take a turbo plug. So many projects and so little time.
Old 01-21-2010, 11:31 PM
  #10  
ffkiwi
 
Join Date: Jul 2005
Location: Upper HuttWellington, NEW ZEALAND
Posts: 1,601
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

Jared-I did make some tentative inquiries a few years ago, with a view to buying a card's worth or box of them [I forget which] and was referred back to their NZ distributor who wanted 3 arms and the soul of your firstborn for them. As I already had a couple of spares I balked at the price-and it wasn't as if they had them ex-stock, they were going to order them in.

Lion also did Cox 049 heads in two heat ranges and some other useful plugs such as bolt on lead types.

I don't know if they're still in business-a pity if not, as they did some useful bits no one elsewhere seemed to do.

I think the suggestion of an approach to Merlin is probably the best-it shouldn't take much work to either machine up a new insert body, or alter an existing aftermarket Norvel one-to fit the G-Mark-and then bore out the burnt out head to use as a retainer ring. Certainly far better than tapping for a 1/4-32 conventional plug. I do have a number of GloBee 1/4-32 flat coil plugs however-and these might reduce the rpm loss normally associated with the use of a conventional plug in a tapped out head, as there is no dead volume-but there is still the issue of the face of the plug relative to the head combustion surface-ie, proud of, level with, or recessed-and that will depend largely on the threaded length, and to a lesser extend on the thickness of the sealing washer.
One day-when I have the time...............

ChrisM
'ffkiwi'
Old 01-22-2010, 12:30 AM
  #11  
Jaspur_x
Senior Member
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2009
Location: Friedens, PA
Posts: 360
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

ffkiwk, Thank you for your insight in this matter.
I believe that I will start by getting a merlin plug , and a nelson flat coil plug and see what my brain can work out. ( the plugs themselves are quite reasonably priced.
As I observed with the naked eye , and then with a micrometer just for curiosity sake , the norvel .061 plugs will not work without modifying the base of the plug itself. The norvel plugs base is a larger diameter than the 030 glowhead base is ( not that a norvel plug would be any good in this application at all anyway , but for curiosity sake of comparrison I checked). Therefore any plug that it similar to the norvel plug is a project for tedious work and very fine work equipment by tested or trained hands at best.
Basically , it is beyond my current state to be able to do this work.

I have 2 leads on the "custom" head work to check into.

However , if anyone has any old burnt outglowheads , I would purchase them at a reasonable price and pay shipping of course.

I will of course post anything I find out or come up with right here.

Thanks guys for all the info. and help,
Jared
Old 01-22-2010, 09:16 PM
  #12  
ffkiwi
 
Join Date: Jul 2005
Location: Upper HuttWellington, NEW ZEALAND
Posts: 1,601
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

Jared-I didn't mean to imply that the Norvel plug insert would work unmodified-what I meant that as Merlin (and MECOA for that matter) are already producing the bodies and fitting elements, it should be a relatively simple job to machine the insert bodies-possibly even the complete assembled unit-to fit the G-Mark 03. I imagine this would consist largely of machining down the contact face OD till it fits the G-Mark head ID-then the burnout head is drilled and bored to match the modified norvel insert OD, and screws down over it to hold it in position, just as in a std Norvel.If the market is there, Merlin might be persuaded to either do a run of modified plugs (perhaps 100? 200? 500?) for the G-Mark, or even introduce it as a std catalogue item.

This sort of adaptation is nothing new-in the mid to late 60's, the Germans in particular, ravaged the world supply of Cox TD or Spl 15 glowheads-which were machined down to a button and used in modified ST G15 engines for CL Speed and FF FAI Power. There was nothing better available-until the rossi 15 came along-with a button head as standard..........

At the same time the possibility exists for the G-Mark 03 that the modified one-or A modified one-the flat coil globee option perhaps-has the potential to improve the performance of the G-Mark-and while the originals are nice-I doubt anyone would turn down the chance of a bit more power.........
So here's hoping for some positive outcomes-no matter what. The G-Mark is a great little engine-and the R/C one is the best throttling small engine out there bar none-it is a tragedy that they went out of production-for they set a std in that area that Cox should have been able to surpass-but never did.

ChrisM
'ffkiwi'
Old 01-22-2010, 10:25 PM
  #13  
skaliwag
My Feedback: (1)
 
skaliwag's Avatar
 
Join Date: Jan 2003
Location: Corralitos CA
Posts: 2,469
Received 2 Likes on 2 Posts
Default RE: G-mark .03 glowheads?

I tried to mate a Norvel insert into a Gmark .30 head a long time ago.. I seem to remember that there is not enough meat in the Gmark head to do it...

Reading along with this thread another way I have been thinking of is to take the standard Cox head and turn it down and thread it at that end.. Can't find my mothballed Gmark at the moment to take a look. Not simple I know unless you have and or "R" a machinist.
Old 01-22-2010, 11:18 PM
  #14  
Jaspur_x
Senior Member
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2009
Location: Friedens, PA
Posts: 360
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

I will get a merlin and a nelson plug and see what I can come up with. I`m going to get one of each st up for my norvel .061 and see how it is intended to be used.
I made a couple of contacts today , but I am certain that it will be easier to show a machinist the finished example and explain what is required to get the desired end product.
An .020 head is too close in thread diameter to use unless chopping it down to use like a glowplug for the original head, which I had considered , however the 020 head is dished much deeper than the 030 is which should yield lower compression than stock.

I will have to go out to the shed tomorrow and get a glowhead from an 010 and see if that might be better suited.
But I still think my best bet will be the merlin or nelson plug style..
Old 01-22-2010, 11:45 PM
  #15  
ffkiwi
 
Join Date: Jul 2005
Location: Upper HuttWellington, NEW ZEALAND
Posts: 1,601
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

Skaliwag, Jared et al-what I was thinking-is that it might be possible to take a Norvel insert and machine down both the wider part which forms the combustion chamber and also the 'stem' area to produce something resembling the old GloBee Cox 049 insert setup.It might require a stack of gaskets to generate the right head clearance though-and obtaining these might be harder than the machining! [I know of no way of producing these that does not involve the use of a custom made punch and die]. I'm thinking that provided you end up with at least 1/16" wall thickness in the retaining ring portion of the original head, you should retain sufficient strength-and ultimately, theres's no particular reason why the shank or stem of the Norvel insert should be any particular thickness, beyond that necessary to support the element, the swaging process for the top contact, and resist bending. The head retaining ring portion would need some taper on its underside to match the top profile of the insert where it flares out to form the top side of the combustion chamber.
Come to think of it-has anyone tried the old GloBee insert for size against the G-Mark? Might also be worth a look-as you can still pick these up on the Bay-and they are virtually indestructable-from an element perspective.

ChrisM
'ffkiwi'
Old 01-23-2010, 01:14 PM
  #16  
Jaspur_x
Senior Member
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2009
Location: Friedens, PA
Posts: 360
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

I`m not familiar with the old globee at all , I`m going to check ebay and see if I can locate that , might be a ticket there.

As for the norvel glowplug , it has the same BIG problem as standard plugs; too much open area or "void" space between the inside wall dimension and the coil inside it. The hole for the coil inside the maller glowheads 010 , 020,030
As the 030 was a low compression engine in the first place ( its biggest flaw) it would really just kill the performance of the engine alltogether.

This is why my best shot to get this running well may very well be the nelson flacoil plug. I`m going to order one or two from somewhere and go from there.

A cox 020 glowhead seems to have a much higher dome than the 030 , so I would think that it would not be the prime candidate either.
I still have to scrounge up one of my 010 glowheads and see what that may pan out like.

The more I work on the idea of making our own glowplug for this engine , the more likely we are to get a better running engine by increasing the compression of it.
Old 01-23-2010, 01:33 PM
  #17  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

I have a flat coil, turbo plug. This along with facing off the stock head should give substantially more compression than stock. Another thing to try may be to turn down a TD .049 high compression head and make a plug insert. The trumpet shape should give us the higher compression required.
Old 01-23-2010, 03:03 PM
  #18  
ffkiwi
 
Join Date: Jul 2005
Location: Upper HuttWellington, NEW ZEALAND
Posts: 1,601
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

Jared-I had a bit of a fiddle last night after getting off the computer-and found some various inserts and did some rough sizing. I think we are wasting our time with both Cox 010 and 020 options-they simply aren't big enough to seal. Every engine that I can think of that uses a button or an insert, seals with the button face or flange abuting on to the cylinder flange-regardless of whether there is an 'insert' portion projecting into the cylinder. Ie there is a gasket between the button/insert surface and the cylinder top flange. In this case, the flange is a la Cox-a ledge at the bottom of the female thread portion of the cylinder. If we machine down a Cox 020 head to the thread base diameter-there will be insufficient diameter to create a seal when fitted to the G-Mark head-and its not even worth trying the 010.
The only workable options would be:
a) machining down the OD of an existing other engine insert-Norvel, AP, Cipolla, GloBee etc till it is a snug fit in the G-Mark, using the original head as a screw down retainer ring, and setting compression with a stack of gaskets as required.

b) fitting a Nelson (or a Turbo-as Andy suggests) plug to an original G-Mark head-and I have some reservations about whether there is sufficient metal in the G-Mark head to cut the angled sealing face AND still have sufficient depth remaining for the plug thread

c) machining a new screw-in head for Nelson/globee plug from scratch-complete with double bubble or trumpet head shape as determined by trial and error.
[I don't have the skills to do this-but if anyone can-I'm prepared to buy up to five-and convert my entire G-Mark 03 'fleet']

Here is another thought to begin with-I had a look at my only accessible G-Mark last night-a std F/F-U/C (has anyone ever flown U/C with one?) version whilst doing the head fiddling stuff-and noticed-seeing the muffler is off it-that there is quite a significant amount of SPI-I didn't have a feeler gauge handy-but eyeballing it says something of the order of 15 or 20 thou. This will undoubtedly reduce the engines power when a muffler is fitted. If we are going to go whole hog and come up with a new head for the G-Mark, particularly one that is much higher compression-then we could also look at removing the SPI by placing a shim UNDER the cylinder base. This also increases the exhaust timing-and under normal conditions-because the piston is now lower at TDC-reduces compression-BUT if we are then fitting a high compression head which has to be shimmed, then there is no problem-and the muffler can be refitted with much less-if any power loss. What the effect would be on throttle response I can't say-but top end power should be markedly improved over standard.

Worth playing around with?

ChrisM
'ffkiwi'
Old 01-23-2010, 07:57 PM
  #19  
Jaspur_x
Senior Member
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2009
Location: Friedens, PA
Posts: 360
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

AndyW and ffkiwi , I do not have an extra teedee glowhead , I was going to get  an aftermarket head/plug set for my teedee due to that.
It would also give me a design to copy for the 03 , hopefully using the stock 03 head as the clamping unit for the flatcoil plug, thats my best plan so far.  Im certain gettind a die for the threads of the glowhead for building a plug clamp will be more than just a challenge , can any of you guys reading this help me out on this? 
I`m looking into buying taps and dies to do the work on getting us off the ground here ( I looked at harbor freight , their smallest lathe still looks huge for the scale of work required for this , and it`s $300 , plus the drill press I will need to buy ) I`m still debating on this move.


ffkiwi ,  I`m not getting your meaning with the muffler and the  SPI and the 15-20 thou. discrepancy.   Please explain farther to me.......I`m not understanding how  the cylinder is too low in the crankcase?........Is the muffler porting  off in relation to the cylinders exhaust porting?

Old 01-23-2010, 08:57 PM
  #20  
ffkiwi
 
Join Date: Jul 2005
Location: Upper HuttWellington, NEW ZEALAND
Posts: 1,601
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

Jared-I take it you know what SPI (sub piston induction) is? [also-and somewhat erroneously referred to by some as 'free porting'] Many small engines use it-sometimes deliberately, sometimes by accident, depending on tolerances. Specifically-any engine where the LOWER edge of the piston clears the BOTTOM edge of the exhaust port for a period around TDC has SPI. The resulting crankcase depression as the crankcase is opened to atmospheric pressure sucks MORE air into the crankcase to supplement the existing fuel charge. This usually (but not always) results in the engine producing more power than if the piston did not clear the lower edge of the exhaust port. Conversely-in any engine that does have this feature-putting a muffler on it immediately GUARANTEES a significant power loss-for several reasons-firstly the engine is now sucking in burnt exhaust gas not fresh air-so the fuel charge is diluted, and secondly this gas is hot-so it results in fuel charge expansion and a lower density fuel charge-a double whammy. So there are recorded test instances of a 30-40% power loss resulting from the fitting of a muffler to SPI engines. Cox discovered this the hard way in the 1960s with the QZ 049 engine-essentially a Babe Bee with a muffler. In order to maintain the same power, muffled, as the unmuffled Babe Bee, they had to remove the SPI by raising the exhaust port lower edge, use a twin transfer ported cylinder (like the TD) and a high compression head.

Now mufflers are desirable for social reasons these days and the maintenance of good relations with the neighbours. It is usual to expect some power loss compared with the unmuffled engine-typically 5-10%-15% at tops. More than this and you are at a disadvantage. The ST G20/23 engine was one example where the fitting of a muffler dropped the power by nearly 40%-and this was a classic case of the SPI effect.

Yes-in a sense you are right-the cylinder porting is incompatible with the muffler [mufflers themselves don't have porting-merely volume, and outlet sizes-which also have an effect.] The G-Mark muffler is a simple unbaffled expansion chamber-so muffling-and to a degree the power loss-is determined by the overall volume, and the size of the outlet-which sets the degree of back pressure. Most model engine mufflers are a bit on the small side-and you will no doubt have noticed that many of the bigger manufacturers have simply added an extra section-sometimes with a muting baffle-to their standard designs to produce the so called 'quiet' mufflers. Makes good production sense too if you have a two part muffler design. The G-Mark muffler is (i) fairly small and (ii) has a rather restrictive outlet hole.

All 2 stroke model engines are compromises-it is impossible to design a single cylinder one where all the porting is optimal-the designer has to compromise for all sorts of reasons-mechanical strength, fuel suction, throttling, balance-which is where the engine tuners and reworkers make their living/reputation-pushing designs that little bit further-or a lot further in some cases- from the original specs. I'll do some timing figures on the G-Mark to illustrate the point later [I'll have to lay my hands on a 360 protractor which I don't have handy] SPI can vary from none at all-to a merest smidgen barely detectable by eye-to a colossal amount where the bottom of the piston clears the TOP of the exhaust port [the British Elfin diesels were about the most extreme case I can think of] I would hope that the designer of the G-Mark settled for a reasonable intake period, and an average exhaust and transfer. This would give an engine that handles pleasantly, is not too peaky, has adequate fuel suction, and throttles well. The SPI may have been a deliberate design feature-or merely a consequential one-since they were clearly influenced by the Cox TD range when they designed it. Shimming the cylinder up increases the exhaust and transfer timing-but obviously leaves the intake unaffected-to influence that you have to alter the crankshaft port dimensions-and I'm not advocating that. I already explained the other consequence of shimming the cylinder in my last post-reduced compression-but if you are going to shim the cylinder-you are generally looking at making a new head for the engine in any case! [and this is the situation we are facing here anyway] By shimming, I am talking about adding a thin washer-0.005", 0.010", 0.015"-those sort of dimensions under the base of the cylinder where it screws into the crankcase, so it doesn't seat quite as far down. This will reduce the degree of subpiston induction (which should see an improvement) if not eliminating it completely-but you can't go shimming indefinitely. All other things being equal, we could expect to get quite a lot more power from the standard engine simply by going to a higher compression head-and as you have noted-and Andy has suggested-the standard head is quite low compression and could be shaved-by facing in a lathe-to give a higher compression. This would at the same time also produce a squish band effect-that might also be useful. KK (Joe Klause) used to do this for TD 049's in the 80's-and these were quite effective-but then the Nelson plug and the Galbreath head appeared. Stand by for some pictures later today.

ChrisM
'ffkiwi'
Old 01-23-2010, 10:12 PM
  #21  
gkamysz
Senior Member
My Feedback: (19)
 
gkamysz's Avatar
 
Join Date: Jun 2003
Location: Crystal Lake, IL
Posts: 3,397
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

I do think that these little engines have relatively low compression ratio. I measured the volume of the .03 head but haven't measured the volume of the engine to see what the real compression ratio is.

Chris, If you raise the cylinder you have to lower the head be an equal amount or CR drops. More actually if we are talking effective CR not geometric. I think I have an AME .049 that has paper work quoting RPM figures for FAI fuel, that's right no nitro. With proper CR it should be fine. but things get tight quick in small engines when you want to increase CR.
Old 01-24-2010, 01:34 AM
  #22  
ffkiwi
 
Join Date: Jul 2005
Location: Upper HuttWellington, NEW ZEALAND
Posts: 1,601
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

Greg-if you look back a couple of posts you will see I did advocate increasing the compression-there is no point in raising the cylinder otherwise, unless you happen to have a particularly overcompressed engine to start with-and I doubt that has ever been a problem with the G-Mark. I think we could create a much better head for the G-Mark 03 -be it a double bubble type, bowl and squishband, or trumpet as part of the process of integrating an insert option

Anyway I promised some figures-and here several hours later-they are. Damn but the kiwi eyeball is accurate! I guessed at 15-20 thou SPI, and checking with a feeler gauge I got 0.018" SPI. I also measured the external head clearance-ie the gap between the lower side of the head spanner flange, and the top of the cylinder-which on my example came out at 0.025" So we could face off 0.020-0.022" from the bottom of the head, and still have it seat properly. The thread size is 11mm metric (10.90 measured by micrometer) on both the glowhead and cylinder base threads. In comparison, the Cox 020 head is only just over 9mm diameter across the thread root.

Shortly I'll post some photos of inserts etc.

ChrisM
'ffkiwi'
Old 01-24-2010, 02:09 AM
  #23  
Jaspur_x
Senior Member
Thread Starter
My Feedback: (1)
 
Join Date: Dec 2009
Location: Friedens, PA
Posts: 360
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

ffkiwi , I looked at my 03 after youu made this point apparent to me. Yes , mine has the same problem with spi , so there is another weak pointto this engine ,and gkamysz is correct and you had it backwards. Raising the head by adding the timing washers would further lower compression so if you shim "up" or raisethe cylinder , the head needs to go down closer to the piston at least as much equal in distance as the cylinder went up or compression is actually lowered.

Old 01-24-2010, 02:34 AM
  #24  
ffkiwi
 
Join Date: Jul 2005
Location: Upper HuttWellington, NEW ZEALAND
Posts: 1,601
Likes: 0
Received 1 Like on 1 Post
Default RE: G-mark .03 glowheads?

Jared you've still missed the point-and I thought I explained it in some detail. Raising the cylinder has NOTHING to do with increasing the compression-in fact it does exactly the opposite-reduces it. You need to read my posts thoroughly! I proposed that we could raise the cylinder to remove the SPI whilst developing a new high compression head option. Raising the cylinder REQUIRES adjusting the compression to restore the correct compression ratio-the reverse does not apply-we can increase the compression by a number of methods, and leave the cylinder unchanged. This means that the loss of power due to the SPI when muffled will still occur-the actual % may be more-or less-I would expect more if the top end power is increased. Raising the cylinder by 0.015-0.020 will eliminate the SPI, and reduce the power loss when running a muffler that SPI must cause. By itself-in open exhaust form-you would expect some reduction in power-we have reduced by a small margin-the amount of air aspirated per cycle. You cannot simply just raise the cylinder without making other compensatory changes-chief of which is increasing the compression by approximately the same amount as the cylinder was shimmed [note APPROXIMATELY-not necessarily the same amount-you have altered the engine timing, so the compression ratio required will be different to the standard-it may be higher or lower by a margin for the best operation-and the fuel used will also have some effect. And this is BEFORE we start playing around with the head and combustion chamber shape.

We are dealing with a dynamic system, and changes made in one area have effects elsewhere.

ChrisM
'ffkiwi'
Old 01-24-2010, 04:00 AM
  #25  
AndyW
My Feedback: (1)
 
Join Date: Jan 2003
Location: Timmins, ON, CANADA
Posts: 2,912
Likes: 0
Received 0 Likes on 0 Posts
Default RE: G-mark .03 glowheads?

Sub piston induction works by allowing the incoming charge to "flow through" and not suffer a sudden interruption when the piston stops at TDC. Pneumatics is very "rubbery", unlike hydraulics. When the intake port opens as the piston moves up, suction lags a bit. By the time the piston reaches TDC, suction is at it's max, having caught up. But then the *&%$ piston stops, just when suction is at its greatest. Picture that incoming charge developing a wave pulse back out the intake port in response to the sudden stopping of the piston. SPI allows the incoming charge to continue to flow and some charge may even spill out the exhaust port. SPI in small engines is NOT a defect, in my opinion.

And I don't believe that adding a muffler contaminates the fresh charge of fuel at all. I believe that the incoming charge, flowing through, is strong enough to overcome any blow back by the muffler. SPI was once blamed for poor throttling in 1/2A engines and yet, some VAs and most Norvel 1/2As, with SPI, will throttle just as fine as you please. As long as you have a means to adjust the mixture at idle.

SPI also doesn't hurt throttling at the intake. Neither does it hurt when throttling at the exhaust and in fact, the best example is the LiteMachines engines. It's only Cox engines that have throttling affected by SPI. LiteMachines, exhaust throttles, have a bullet shaped plug intercepting the exhaust outlet. Cox engines have a throttle sleeve mounted directly to the cylinder and in that case, the restriction is very close to the piston and clearly is detrimental. The muffler of the LiteMachines exhaust throttle has a buffering effect to this action and this proves my point in the preceding paragraph.

No need to eliminate the SPI, it's there for a reason,,,, more power,,, and it doesn't have to hurt throttling. What hurts throttling most is not having a means to adjust the mixture at idle. Be aware that if you increase the compression ratio, you'll need to richen the needle valve. This will also richen your idle automatically and going rich at idle is the problem with a throttle that doesn't have an adjustable airbleed.

But seeing as all my throttles get this feature added, I went ahead and made up some glow buttons for the G-Mark .03

The first three pics show a button made from a plug insert donated to me by Dan Rutherford some 15 years ago. This was for some much larger Russian engine. But it's a really cold plug so it may cause problems.

The other pics show a button made from a standard compression, Cox .049 plug (which appears to be the same heat range as the stock, G-Mark plug). Lots of meat there, unlike, as mentioned, the .010 and .020. I DID adapt an .010 plug for the Fora .020 made up for me by Japanman but the piston in that one, doesn't ride up all the way to the top deck of the cylinder. And it took an extra ring and some JB Weld to make it all work.

All of this is just my opinion, of course. What works for any individual, at any given time, is what's important.
Attached Thumbnails Click image for larger version

Name:	Jh16180.jpg
Views:	46
Size:	65.6 KB
ID:	1362988   Click image for larger version

Name:	Id97841.jpg
Views:	35
Size:	46.2 KB
ID:	1362989   Click image for larger version

Name:	Bg91908.jpg
Views:	44
Size:	130.6 KB
ID:	1362990   Click image for larger version

Name:	Pn37340.jpg
Views:	31
Size:	114.6 KB
ID:	1362991   Click image for larger version

Name:	Cx74809.jpg
Views:	39
Size:	121.8 KB
ID:	1362992   Click image for larger version

Name:	Di98698.jpg
Views:	36
Size:	118.3 KB
ID:	1362993  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.