rctimm99

My Feedback: (34)

Anyone converted one of these? I hear they sound really cool. Anyway, I am looking for a motor for my Cub (82 inches clipped) and was wondering if anyone had any exposure to this engine.

Thx
Tim

DougT

My Feedback: (1)

Tim,

When they first came out with this engine, an engine guy named Carlos (grigerra?) did a conversion. I'm not sure of his last name or phone # but he is a member of the Walla Walla Prop Twisters in Walla Walla, Washington. I believe they have a website and you could find his contact info there. I talked to him at the Puyallup expo that year and he said they were not overly powerful and were heavy and suited for a sport plane with a light wing loading. Hope this helps.

Doug

mglavin

My Feedback: (31)

I've got a converted Honda with some spares. Never ran it myself. It's FOR SALE! I'll take some pics and post them it's an interesting engine.

C&H Ignitions and Carr Machine have info and parts for these conversions.

Dave_Gherardini

Ive just completed first testing of a GX31 and 22. The 31 came out at 5 lbs9 oz {no/pipe) and will turn a APC 16x6 8k rpm . Both blocks can still lose a couple oz's of weight. The oiling system has got to go to get weight where i want it. Im currently working on the 22's new oiling system. Il let you all no how it goes. The 22 made its best run with pipe and 16x6 apc at 7250 rpm. Both engines are bone stock except the 31. It has the small crank and flywheel. I found a 200 rpm increase with pipe over the muffler. The pipe still has not been tuned so possibley a little more in there. I wont pursue it any further untill a new oiling system is devised to reduce weight.

jerry dotson

I have one (GX31) on my 1/4 scale Fleet biplane. I have been flying it since 1999. It came out exactly 5 pounds with oil in it and ignition and battery. I have flown it with everything from a 18-6,18-8,18-10 qnd a 20-4. I have settled on the 18-8. It turns 6800 on it and has about 10 pounds of thrust. I use the CH Syncro Spark. The engine is 6" wide and that really limits the planes you can put it on. The Fleet weighs 20 pounds. It flies really scale(very slow climb rate). Sound.....I have never heard an engine on a model sound better. I run a straight exhaust pipe and it is nowhere near as loud as a G23 with a muffler! I would rate its power about like a G23 also. It will idle all day without loading up. I use a 12 ounce tank and fly up to 30 minutes and have plenty of gas left. Some gent from North Alabama had a Honda on a Bridi Big Bee??...about 8ft span. It performed better than my Fleet because it only weighed 14 pounds. I am using past tense because it intersected Mother Earth at a right angle. Same guy had two of them on a Giant Telemaster. So summing up... would I convert another one...probably not...too much work and $$(240 for engine and $140 for ignition) to get it so I was proud of it.

Dave_Gherardini

I have to agree. This engine is built to the hilt. But its just to heavy for a cheapo(or not so) conversion. Jerry, Im suprised yours is 5lbs with the ele ign system. I assumed it would be a bit lighter. Sure would like to see a pic of that Fleet. Is it in your avatar? The fuel cunsumption is cool. I was suprised but ive been using the stock carbs for both engines. They work just fine to. Ive made a modifyed mag to kreep up the timing a bit, So i can try some methanol. Il try an post a timing curve if a get it wrote down. Im still eluded on a different method of lubrication but il keep thinkin about it. Heres a pic

tcat

I am installing a Honda GX31 in a model tug boat and am in need of the clutch housing and clutch bell with shaft for the weed wacker version. Mine came off a rototiller. Anyone have these parts for sale?

Captain Ramius

Small Engineware
(www.smallenginewarehouse.com)

Has a clutch for the GX31 its $75.00 its more compact than a trimmer clutch housing but its a shaft style output. An adapter could be attached to the shaft , and adapter can be made from the clutch and shaft from any trimmer stick you can get.
Sticks for the Honda are few and far between. Most of the trimmer clucthes I've seen are splined not square drive, so this presents its own set of problems if you want to run 1/4" sq. drive cable and manage to find one.

* Edit*
I got a line on a clutch. PM me for details.

av8tor1977

My Feedback: (6)

Has anyone had any luck finding or using different carbs for this Honda GX31 engine? I just bought one, and the carb has no mixture adjustments at all. I don't like that one bit. But of course the "smog lords" know what's best for us right??? I once had a kid that worked for me do a test with his class in a college auto shop. They took all the emissions readings on a freshly and perfectly by the book tuned car. They then removed all the smog equipment, retuned the car to run properly, and took new emissions readings. Guess what.... yep, less emissions.

Anyway, I would really like to swap this one out for one that has mixture adjustments if anyone has any info on that.

Thanks!
AV8TOR

gtisme

AV8TOR,

I'm in the process of converting a Ryobi 4 strk. The factory carb on it is "non-adjustable". It doesn't just have caps on the needles, there never were any needles, and this carb lists for $98. It appears that all new engines are and will be produced in this way because of the emissions laws. We had better be learning how to make these carbs adjustable, or at least learn how to re-jet them because the old 2-needle carbs are going to more and more scarce!

Gary

motorhd

My Feedback: (15)

I am in the process of converting 2 Honda GX 31's. Two different Walbro WYK carbs have been ordered. They both have adjustable high and low needles. After talking to Walbro, it seems there isn't much difference of one WYK to the next if they are the same venturi size. There may be slightly different fuel lever and spring settings. These are easy to change and I don't think the would make to much difference anyway. I ordered a WYK 1-1 10.5 mm and a WYK 38-1 12.2 mm . Also ordered were the fuel pump springs P/N 98-3310 to add to the fuel pump chamber so the fuel pump will work on the negative pulse of a four stroke engine. One of these engines has a badly horizontally scored cylinder from corrosion but it seems to run fine. All hop up experiments will be done on this engine with the 10.5 mm and 12.2 mm carbs. W'll see if it requires a 13.5 WYK. That seems a little big.
Jimer

rcbilly

My Feedback: (9)

Great to hear Jimer, Keep posting, I'm doing one also. Are you using the stock ignition system? Where did you order your carbs from?

motorhd

My Feedback: (15)

I am useing C&H with synchrospark on the Honda GX31. I have an account with the local small engine parts wholesaler so the price of the WYK carburators was pretty fair. Try the Walbro site and you should find a list and phone numbers of wholesale distributors in most larger cities. Rightfully so, they will probably direct you to a retail small engine shop. Try to be real nice and they might sell to you direct , can't hurt to try. Most of the tricks listed in this and other threads were tried to make WT Walbro's work on the four stroke including adding fuel pump springs and useing other sources for impulse to run the pump. The results were less than remarkable and it felt like I was spending a lot of time with little gain. There will be several hop ups tried and I didn't want the results clouded by carb problems. When the carbs arrive in a couple of weeks and some real numbers are obtained I will try to list what hop ups worked or not.
Jimer

Captain Ramius

To install the pump springs in a non spring equipped carb , you need to machine a seat in the diaphragm housing area. It a simple matter of selecting an end mill with a flat bottom of the springs approximate diameter and making a simple plunge cut
You may not need the spring at all.Honda equipped the M4 engine line with carbs that had the pump spring and some did not.Our investigation showed in may have been related to the orientation of the crankshaft IE: vertical or horizontal not the fact the engine is a four stroke.
Myth, rumor, fallacy or other misinformation has many people thinking the pump spring makes the carb a four stroke carb, it does not.

rcbilly

My Feedback: (9)

Jimer, I ordered the CH ignition earily in the week but have not gotten it yet. How much does it weigh? and how long is the prop adaptor? So I can can an overall length. I finished my motor ount today looks OK forhome made and is pretty light.

motorhd

My Feedback: (15)

rcbilly, right now it is mounted on the test bench but it was weighed earlier and if my memory is correct it was 4# 10 oz all up with engine, prop hub, mounting bolts,header,carb,ign,battery,wood prop and spinner. I made the spinner 2' long from the face of the cam cover to the face of the prop hub, it could be shorter. The engine is bolted directly to 1/4' plywood useing washers that sandwich a short piece of fuel line. A hole was made to allow the rear shaft and housings to have clearance. Face of firewall to face of hub is 7'. Jimer

motorhd

My Feedback: (15)

Thanks Capn, I just assumed that, since I could not make the Gx31 run decent without the springs in 3 different WYL carbs that came off of Gx31's , the WYK would also need the springs. The GX31's were from a pump-horizontal, a rototiller-veretical, and a trimmer-? When testing Wt carbs the springs were installed just the way you mentioned. I wonder if the volume or area of the WYL is larger and has more capacity with less impulse?? On another subject, I wonder if a mold could be taken of the combustion chamber to see if tnere would be enough room to weld a 1/8" aluminum plate the top of the piston to increase the combustion ratio?? Any pitfalls? any advice would be apprieciated. Jimer

Captain Ramius

1/8 plate on top of the piston would close the chamber up to almost nothing
Molds of the chamber have been made.... years ago... yawn.......

motorhd

My Feedback: (15)

Capn, I would need my own mold to machine the 1/8' plate, on the top piston, to the proper squish at the top of the cylinder. If you made your own molds previously you must have been down this path before. Could you fill us in on all the details of Gx31 performance enhancements. I looked at all of your previous posts and saw that you wrote very little about this engine. I really would like to have an exchange of ideas. These are the first posts I have ever made and I'm not sure but it feels like you are trying to ridicule me. Please stop ! Jimer

Captain Ramius

Stop? no problem
Ridicule? Just sharing the facts.

My previous posts reveal little or nothing of the amount of knowledge I may or may not have on this particular engine. The fact of the matter is that I have direct communication with the guys over on ASMBA who have the GX31 expert over there.They have been working on the GX31 for over 3 years and done more with it than anyone else.
When I see something posted here that should have a qualified response , I contact one of them and post the answer here,its a time consuming process so most of the time I don't bother.
Most ideas have been considered or tried over there.

motorhd

My Feedback: (15)

Thx Capn for the tip on ASMBA, they have gone a long way with the Honda GX31 for boating. Perhaps we can continue disscusions on improvments for aircraft use also. I would still like to know how the compression is increased on this engines. Jimer

Captain Ramius

Pretty simple really, the welded plate idea and building up a welded area was looked at, there are some issues with that approach.Weld material sitcking is a problem, due to coefffiecient of expansion of the materials. Plus Honda has coated the piston with a hard material that would need to be removed to weld to the piston itself.
Then you have the problem of the top of the piston is basicly a popup which presents potential issues with preignition and such, flat top pistons are preferred.Popup or bumper pistons are known to block flame propogation in drag engines. it gets complicated

But there is a simple and efffective way:

To make a long story short, to bump the CR from stock, which varies a little from engine to engine. Simply offest bore the wrist pin hole in the piston by .025" (move hole location to increase the distance from top of piston to wrist pin hole) until you have a round hole and then rebush back down to wrist pin size. This will put CR to 9.6:1 minimum and depending on engine it may go to 10.25:1
This should only be done to low hour or new engines , old high hour engines have a ridge at the top of the bore and may break rings if this is attempted.
This increases the CR and reduces squish making the chamber more efficient in one operation.
You need to be aware that raising CR in an engine with the stock cam may increase cylinder pressure to a level that promotes detonation, most of the time raising CR is done to restore cylinder pressure because of radical (late) intake timing.
Keep in mind the compression release in the stock cam can mislead you on the actual CR, either by feel or compression tester. Take out the compression release and you will see a difference in cranking pressure.

Hope this helps.

motorhd

My Feedback: (15)

Capn, Yo da man, thanks for the info. I'm still a little confused as to the shape of the bushing after redrilling. Would it look eccentric?
Thanks, Jimer

motorhd

My Feedback: (15)

Capn, The light just came on. If we drill the new wrist pin bushing hole with it's center .025" towards the crank and give the od of the bushing a .025" wall thicknes that should do it, right? And the radius of the bushing would be the radius of the wrist pin plus .025", right? Thx, Jimer

Captain Ramius

I believe that is correct,they use a small boring head in a bridgeport, this keeps the hole round and straight. It takes a boring tool to ensure the hole is straight and round. Grab the piston in between vee blocks. Not excessivly tight.
Find the centeline of the hole then move it off.025" bore till it round again ( the few cuts the boring tool only cuts on one side of the hole)
The OD of the bushing would be approx. .05 bigger in diameter than the wrist pins.
You can go a little larger to get thicker wall, so the press fit stays tight. The limit to the hole size is the location of the oil control ring,you don't want to make the land between the bushing and the ring groove too thin.

Ream the wrist pin hole after pressing bushings in to make sure the size is right, and don't forget to run a drill through the oil holes on the bottom of the pin boss.
The piston I saw, had flanged bushings pressed in from the inside so if they ever loosened up , they wouldn't back out to the cylinder wall and ruin it.
BTW press the pin out with a press or the wrist pin tool Honda makes, they warn against hammering on piston in the service manual.
The CR does stay within safe cylinder pressure limits.But higher octane fuel would probably be a good idea.