Dean Wise

there's been airplane,boat and car guys who have tried to make that honda go. but it seems that it has been purpose made so it can't be hopped up. compression can't be raised ,valves are to small and because it uses plastic cam setup instead of overhead cam that can't be improved eitheir. Carr precision would like to try working on the GXH 50 mini honda engine and I'm thinking about it. but have'nt made up my mind yet.

rmh

Iskenderian once made a "5 cycle" camshaft.
Maybe this would help on power?
Probably only the old drag racers will remember that one -----
I ran Isky cams -in a full blown flathead.

Willdo

How about bigger valves, higher compression piston, and some of those new fangled steel cams eg. like you get on B&S engines ( made to ISKY 5cycle specifications, ?? - Dick explain yourself ), bigger carb etc.etc. Can't buy HC pistons? try making one!
Pushrods work ok. so long as you are not looking for F1 type power.

No harm in trying anyway, but please just get away from the notion of using a gas/oil mixture in a four stroke, otherwise the two stroke is the better solution by far (except for the sound).

Are they legislating against pollution? or are they just using blanket legislation against the poor defenceless two stroke?

BajaBob-delete

BULL!
It can be hopped up.
CR can be raised.
Valves may be small for 12,000 rpm operation but are good for anything less.
Plastic cam can be improved.
It may be far from perfect 4 stroke hobby engine but its a good start.

"They'll take my GX-31 from me, when they pry my cold dead fingers from around it"

Willdo

ORIGINAL FROM DIABLO
The YS supercharging system would work just fine with a twin.
You would want to make it alternate firing in order to smooth out the power pulses, and then it would be about as smooth as a two stroke of the same displacement.
It would need a plenum chamber to store the compressed fuel mixture that was pumped out of the crankcase.




Diablo,
What you were saying was mostly correct, except that I don't believe that it is necessary to have any plenum chamber with a boxer twin and alternate firing.
If you think carefully, the 2 pistons coming together, there will be supercharging, and this supercharged mixture will go straight to the cylinder with the inlet valve open.
The next time the pistons come together, the supercharged mixture will go to the other cylinder, which will have it's inlet valve open, therefore no need for a plenum chamber.
If it is a simultaneous firing boxer twin ( as before with 180 Deg. crank) two plenum chambers will be required, one for each cylinder, so it will behave in the same way as a single.


Baja Bob,
Remember I am the guy who supports the little Honda to the hilt! and I'm glad to see that your attitude to it is the same as mine.

Dean,
There would not be a modestly powered engine on the planet which couldn't have it's power increased by at least 50% ( give or take a couple of percent ).

BajaBob-delete

Willdo,I see Dave Jones is a satisfied user too.We need to keep in mind as in the case of the Zenoah hobby engines their origin,yard tools.I don't think that any manufacturer is going to offer a hobby product off shoot without knowing theres sufficient interest. They have to justify the cost of making changes that would make these engines more suitable for our use.

lbianchi

Baja Bob, I'm agree: to have engines "specific" for aeromodelling it's necessary the direct participation from the producers, but they make them if there is the certainty to sell a sufficiently high exemplary number. In alternative, we will have always motor only in part suitable for our use.

Willdo

First my apologies Dave Jones for not mentioning you, I had checked out your videos etc, and it is a little more heartening to actually see the motors in action!

You last two guys are absolutely correct, no big manufacturer is going to make a dedicated model aircraft engine but I would have thought that some small buisnesses would be able to cash in on converting the more suitable and available ones.

A few of the big companies it seems are using four stroke machines with oil/gas mix, which is really not addressing the supposed problem of pollution, and it seems to me that the legislation is aimed at the "two stroke" engine rather than "pollution". ( maybe someone could enlighten me on this ).
If this is so, it is a tragedy for what was (and is) an excellent powerplant, (the 2 stroke that is ).

Honda however, with their vast experience of four strokes have come up with an innovative and cheap solution for lubrication, almost tailor made for model aircraft, and virtually non polluting, yet almost everyone ignores this.

What amazes me is the number of people who state that " it can't be done because ......".
Where is the pioneering spirit? are we going to sit and wait till all the parts required pop up on the shelves and we take them home, follow the clear and precise instructions and bolt them up, or till an assembled "ready to roll model" arrives on the doorstep all gift wrapped?

I must admit that I tend to look at things from an engineers point of view, rather than from a fliers point of view so please don't take my criticism too much to heart.
.

DougT

My Feedback: (1)

Willdo, BajaBob, Dave Jones,

Great thread! Do you ever check out the "engine conversion" forum? If not you might want to. I'm an advocate of the Ryobi 4-stroke as are a few others. You will find a lot of threads/posts on this engine. Even though it's a different engine, the principles are the same.

Doug

Daryl Martel

My Feedback: (3)

Willdo - there is certainly lots of "pioneering" spirit in the hobby. I am constantly amazed at what skilled craftsmen there are in the hobby - some of the things that have been done are truly remarkable - miniature turbines, turboprops, high tech carbon fibre layups, CAD designed laser cutting and milling... heck, it is simply amazing how light and strong some of the pattern planes available are... but very few people are fabricating home brew engines. That must say something about the difficulty level. Not everyone has access to the materials, the facility - machine shop equipment is very expensive, or possess the skill and knowledge to put it all together. I remember a while back a fellow from Edmonton (Dave Pape I think), designed and built a scale 5 cylinder 4 stroke radial engine he actually campaigned in scale meets on a plane he built. There are people out there doing it - it's just no small task.

Antique

My Feedback: (4)

The 4 stroke weedeaters that use oil in the fuel meet the California regulations, toughest in the U S ..............

tkg

My Feedback: (1)

Giving enough money you can do anything, but the Honda does not easily allow hopups.
The head is non removable so the only way to increase the compression is to raise the crank, lots of re-machining. OR a new pistion with a higher crown.
Valves are OK but the intake/exhaust ports are terrible, each is just two holes drilled at right angles to each other.
The cam is a single lobe so you can't tune the power by changing overlap and having asymetrical valve timing. The valve lift is laffable
A good start not so. A good start would just be a Saito 180, then all you need to do is add a needle rod and a walboro carb.
This is not just hot air. CH flew the first Honda GX31 over years ago. We spent lost of time geting regorund cams and finding a proper adjustable carb. In the end a nice scale J-3 engine

BajaBob-delete

Saito has the same type of uniblock contruction and is nitro to start with,a gas conversion is impossible on this with out concessions made to lubrication problems,igntion would add weight.Ports are made the same way as Honda.just drilled,which there is nothing wrong with,ports are supposed to be round anyway.Saito has all the same problems as Honda from the hop up perspective.
Its always a compromise,but you have to look at the other reasons our choices,granted the Saito in stock form is lighter and offers more power, the Honda is 220 dollars cheaper than Saito to start with.You can tag sale a GX-31 that has a lot of life left for less than 100 bucks.Runs on pump gas thats 20 bux a gallon cheaper too.
My experience with the Honda is that it wakes right up with a few modifications,you don't need a ton of modifications either.A simple cam and carb change does a lot.

Willdo

Daryl,
Yes, I think I'm a little spoilt , always having access to machine tools at work and having some at home as well, also quite a lot of machining experience, but at least my comments seem to have got the thread humming along.
Maybe I'll have to start putting my money where my mouth is, buy one of these little Hondas and try to make it do what I have been talking about.
These guys that you talk about are much higher up the scale in technical ability than I am, and are really very exceptional people, seeing the machinery they produce.
However, I would just like to see ordinary people try to understand engines and experiment a little more, rather than wait for ready made results, or give up.
My flying ability and understanding of aircraft setup is not so hot though, and I'm sure that many of you won't be able to comprehend that!

RCIGN1
Are these new regulations likely to eliminate all two strokes? Do you prefer the Honda lube system over the oil/gas system in some other four strokes?

TKG
Probably you are right about the expense, I tend to take these machining jobs for granted, I guess you've been there and done that, I may still try it though, given the initial cost of the Honda.
If the Saito is plain bearing, then too much oil required in the oil/ gas mixture, doesn't agree with spark plugs. Needle big end would be in order.

BAJA BOB
With you on all of your observations, what else can I say? the Saito runs nitro in stock form, and if you ran the Honda on nitro/alcohol, it would probably be just as powerful ( and very expensive to run).
This is an often overlooked point to remember when comparing gas engines with glow types.

locoworks

yes i do see now that an alternate firing boxer 4 stroke using the YS SUPERCHARGING, would work because 2 pistons are pressurising into 1 cylinder. ( who wants to make up the necessary bits and report back? ) i did not realise that a 4 stroke was wanted for emmission reasons though which would obviuosly cause problems with an oil/fuel mixture. i assumed it was for a torquey motor with a nice, more realistic sound

mklarich

I read through many of the messages and replies on here and thought I would throw in my 2 cents worth or maybe just a couple pictures because they are worth much more then my 2 cents.

These are 2 shots of my Saito .72 that I converted to run on Regular Unleaded 89 Octane Gasoline. I am mixing oil with the fuel, this is not a wet sump system. I am using Klotz full synthetic oil that mixes with the gasoline at approximately 10-15% lubrication. I could easily go higher on the lube but I have found this to be enough. The ignition system is sold by CH Ignition and I am using a small regulator on the fuel. I will say the mixture is very touchie and I need to machine a new needle or change carbs.

Below the motor is an onboard starter I purchased from Hobby-Lobby, I installed all of this for a "Last Man Down" contest I fly in at Terre Haute, Indiana. When flying in that contest I used a custom made brass fuel tank that I soldered using .004 and .006 shim stock brass.

The motor is mounted on the front of my Senior Telemaster, it flies it quite nicely and I haven't noticed any loss in power in the conversion. I have another .72 Saito that is older then this one that I fly so I do have some comparison. One of these days I will do a more scientific reading on the motor and actually measure the difference in performance.

Matt Klarich

Antique

My Feedback: (4)

Spark plug fouling is not a problem...Early outboards ran 1/2 pint oil to a gallon of gas...All small airplane 4 strokes have plain bearing rods...10% oil works fine...
Oil in the fuel is easier than a sump and a pump....

BajaBob-delete

locoworks, I like gas four strokes,sound, torque are the biggest reasons,the emissions are considereed but not the only parameter.

mklarich, Thats pretty slick.


Willdo,I have access to machine tools also.To make my position clear I like to state for the record,that I'm not arguing for or against fuel type or engine maker,I'm simply stating facts regarding the GX-31 and sharing my observations.As long as the GX-31 is compared apples to apples it stacks up fairly well,a fair comparison would to another mini gas 4 stroke trimmer engine.Comaring to purpose built hobby engines is not an equal or fair comparison.

If the GX-31 doesn't meet your criteria by all means go ahead and run what you wish.I have a fair amount of experience hot rodding the GX-31 and have had satisfying results,with out spending a fortune on it. My goals are to see what can be done with this engine in particular,not meet some speed or weight requirement.

tkg

My Feedback: (1)

The Saito has the uniblock as you state, but it has enough compression to begin with (9.5 vs 7.5 for Honda) . With the Hemi head design the intake/exhaust joins at a smaller angle and flows better. A battery powered ignition weighs less than a magneto. It also has a two lobe cam.
What it lacks is a needle bearing rod, a good "gas" carb and an oiling system. The rod would go a long way solving the oil problem.
What is needed is serious demand for an engine like this, then Honda, Saito or somebody will design from scratch and there won't be any compromises
The Honda GX 31 can be flown, we have done it. But after all the mods we did to one, cam, port work, new carb a 30cc Homie was lighter, cheaper and made a bunch more power.

ketil

hope to see some big gas 4 stroke soon

Ketil

BajaBob-delete

With the same load, my modified Honda is with in 300 rpm of a 30cc Homie with big bore carb..I'm at 6 pounds with Honda ,the homie is 5 1/2

DougT

My Feedback: (1)

BajaBob,

What prop and rpm are you talking about?

tkg

My Feedback: (1)

We got the Honda down to 5lbs and the Homie is at 3.5lb. The Homie is turning a 19x8 MA Simitar @7700rpm. the Honda a 18x8 MA Classic at 6400 RPM

Willdo

BAJA BOB,
I totally agree with you on all the things you say about the Honda, was your earlier message meant for one of the other guys?

LOCOWORKS,
You are right, it now seems to me that people are not thinking about pollution when they change to four strokes, it's more fashion, and sound ( great sound ), and maybe torque, but two strokes can be made to produce good torque too.
Would love to make the parts and see if it would work, but this damn computer is taking up most of my spare time now, - think I'm getting old and at least I can go to sleep in front of the computer, but not in the workshop![sm=redface.gif]

RCIGN,
Sure, some of the old two strokes operated on 10:1 gas/oil ratios but look what they did to the public perception of the two stroke!
The early Johnson outboards, the British Seagull outboards, the old Villiers powered motorcycles, the East German Trabant car ( which probably had an oil pump) to mention a few, polluted a large portion of the earth.
I seem to remember when plug fouling, whiskered plug gaps etc. was quite a problem, and we put up with lots of things like high speed seizures ( happened to me on my Ariel twin - not funny ), but we still had to put up with it all and now we don't have to.
Today, most engines don't do that, yet I have been told that some model aircraft engines use up to 18% oil (5.5:1), this has got to be ridiculous, especially when highly stressed motocross engines can manage on 80 - 100:1 !!!
Now some people are talking about using oil/gas mix on plain bearing four strokes! - However, if it works ok. and nobody complains, we'll still do it - it's just that we don't have to anymore, needle bearings can't be such a great hurdle!
Honda appear to have the perfect simple solution, but nobody wants to know.
Why anyone (with a conscience ) would want to inflict this filthy habit on the already clean burning four stroke defies all logic.

Glad to see that there are more experimenters around than I thought, don't be too modest about your achievments, many people on this forum will be interested in the results of your efforts. Any more out there?

I don't have a great experience in model aircraft flying or building, but my interest in engines and reasonable machining ability goes way back, I have converted an old 56cc Stilh, and am looking to convert a four stroke next.

By the way, I'm not a Greenie

BajaBob-delete

Willdo,my comments aren't really directed at anyone in particular,unless I'm addressing them by name like I am here.

Rather my comments are in response to other comments made so that someone reading this thread can see whats going on and what I have done.I happen to like this engine,I'm not knocking other power plants or the choices of other modelers, so don't get me wrong,however I know what I have done.
Some of the experiences I have heard about using this engine run the full range,some are happy,some have mixed feelings, I'll get some test results and post them when I have a chance.