Well, I put some more running time on the Honda on my Eindekker, fine tuned the engine, and changed to an 18 x 6 APC prop. That seemed to make it come alive. It turns the 18 x 6 at 7700 rpms, and pulls the big Eindekker around very nicely. Loops from level flight are no problem, it climbs well, and it takes off at less than 1/3 throttle with it's super light wing loading. Straight stack exhaust sounds great and not too loud. Neat project and I'm happy. I'll get some more pics posted when I get back home after Turkey day.

AV8TOR

I have found this and other threads on Honda engines facinating.
I have converted a new GX-35 recently and it's going very well with a few changes.
It's turning a Master Airscrews 18 x 10 at 7100 Rpm and a 20 x 10 at 6600 Rpm. Great touque.
The changes are,
GX-31 piston fitted with .025" machined of the top this gives 10:1 compression (measured). This give about .020" squish. The original piston runs .050" down the bore and has a dish.
WKY 194, 10.5mm Walbro carby (adjustable mixtures) on drilled out manifold, no fuel problems.
Inlet port filled around valve guide area and ground to smoother profile.
Combustion chamber cleaned up, mainly unshrouded the valves, it's very bad on the standard engine.
GX-25 cam fitted with decompressor removed, the cam profile and gear is the same as the 35 but the lobe centre line is in a different position, same top end performance with much smoother idle, about 1300 Rpm.
RCXL ignition set at 32Deg BTDC.
GX-25 muffler with 12.5 outlet and baffle removed. From my testing it's about 300 Rpm better than an open pipe.
Most of these mods have been mentioned in this forum.
I hope someone finds this useful.

Nice work. Now you've got me wanting a GX-35.....

AV8TOR

Hi Gents,

now I'm a bit confused about Mono's conversions.

In my understanding the valvetrain of GX 25 and GX31 is driven by pushrods and rockerarms.
The GX35 cam is toothbelt driven.
The GX35 is the successor of the GX 31
If so, such parts will not be interchangable.
Maybe in Australia Honda is using same names for different engines??

Who can update me?

Thomas46
Check with Bob at RC Boat World.He developed all the mods for the Honda GX31 and GX35 and helps me all the time.His GX31 spins a woodpusher 20X8 to 7400 rpm.
I called him about the cams because hes modifiying a GX35 for my giant Telemaster.

The GX22 and GX31 are push rod engines.

The GX25 and GX35 are OHC.

The model designation doesn't change by country.

The bore size in the GX31 and GX35 are the same so the pistons will interchange, modifying the compression height of the GX31 and putting it in the GX35 can yeild compression ratios from 10:1 to 12.5:1 with no valve interferance on stock cams.

The GX25 and GX35 cams do not directly interchange as the hub length of the GX25 is longer than the space in the GX35 but can be modified to fit.

They are also timed differently as noted above, a GX25 cam in a GX35 can advance or retard the lobe centerline 15 crankshaft degrees.

15 degrees is normally considered too far retarded but on the stock engine the timing is so short it won't hurt especially if combined with a CR increase.
Retarding the cam moves the torque peak UP the rpm range.

Mono

try the advance at different settings, on Bobs high rpm boat engines its running @ 22 btdc for max power.

heres a picture of my giant Eindekker. Its a foammy 104" wing span and alot of fun I just installed a 3000 super tigre to replace the 2000 that was on it and didn't fly the plane very well.Haven't weighed it yet so don't no how much it weighs.

Nosedragger Can you provide contact info for Bob and/or RC Boat World?? I did a web search and couldn't find info.

Thanks,
AV8TOR

check your pm

Things like this should be posted for everyone to see.

not really, forum rules don't allow links to other boards

Nosedragger, thanks for the info on the ignition timing, I need to do a bit more fine tuning, I've just been running this engine in, after this last weekend it has had about a dozen flights and seem to be freeing up nicely. With larger props I did notice a top end miss sometimes and suspected over advance.
I would be interested to talk to the cam guy as I think that the biggest improvement will come from this area. Can you please pass on his details.
I dont ever expect to get the performance of a good 2 stroke but the way it idles, starts and the fact that there is never any oily residue on the aircraft make it a winner for me.

I bet this would work out good on that giant Endecker! http://rcuvideos.com/video/Kavan-K50...un-on-no-nitro

Hi just joined the forum, looks really awesome!!

I currently have a GX31 and am looking to increase the compression ratio from the standard figure of 8:1 to around 10:1

I have heard that with a GX35 engine, a piston from a GX31 can be used to increase the CR, but can the connecting rod of a GX35 be used in a GX31 to have the same effect of increasing CR?

No.

Welcome to RC Universe. May you enjoy for many more years . . . .

now thats it lunch time and I have time to explain.
The connecting rod in the GX35 is longer than the connecting rod in the GX31 by .197" The piston will collide with the head. There is not enough material to machine the top of piston, long before you lower it enough the ring grooves will be gone and there will be a large hole in the piston. No room to machine combustion chamber either.
Not to mention splitting the crankshaft to remove the rod and for reassembly requires special tools.
Plus you cannot buy connecting rods, they only come on crankshaft assemblies.
The only way to increase compression in the GX31 is to offset bore the wrist pin hole to a larger size and bush back down to wrist pin size.

(tig welding the top is not recommmend)

Pardon the intrusion. Would someone please tell me how to disable the compression release on the Honda GX 35??? Thanks.

Grind the rolled over end of the pivot pin off.Pull the plate off and everything will drop free.You should grind until you are able to pull the plate off with you fingers, don't hammer on it.

Giant Eindekker/Honda GX31 update.... I was just out flying my Eindekker/Honda today. Since the engine is pretty well broken in now, I was trying to get the carb settings nailed down, but I was having problems getting the carb dialed in perfectly. Some of you may recall I am using a WT type carb. It acted just like one does when the cowl is pressurizing the regulator vent hole, but I had that vented to static air via a tube and hose. Finally, when I was just about to give up and decide that it really needed a WYK type carb, I noticed that when I had my hand near the carb, the mixture changed. I didn't expect much in the way of "stand off" or "reversion" with a four stroke, especially one with no overlap in the cam timing, but I had put a 1" velocity stack on it to straighten out airflow into the carb none the less. But even with the stack, there was a difference if my hand was near the carb. So I allowed for that, and set the carb accordingly and flew it again. Perfect!! When my hand was near the carb, it would lean out and I was consequently setting the carb too rich. It sounded ok on the ground, but would go blubbery rich in the air. Once I set the carb without my hand nearby, (I modify my high speed needles with a "t bar" so that I can adjust them by hand), it was fine in the air.

So, if you are having problems with tuning the Honda, try a longer velocity stack, perhaps a 90 degree velocity stack turned rearward, or just tune yours like I did mine.

Also, I went from an APC 18 x 6 to a Top Flite wood 18 x 6. It just looked so much better with a wood prop. But there is no doubt, the APC is a more efficient prop. The plane definitely lost performance with the Top Flite, though it still has adequate power for a good climb, loops from full power level flight, etc. Yeah I know, get a Zoar or other quality prop.... but the nearest one is 250 miles away!!

Lastly, running the engine inverted, and having it sit inverted between flights is no problem at all. However, while in storage quite a bit of oil does drain down into the spark plug area. I take my spark plug out, and a good bit of oil was lost after sitting for a week or two. So I made a stand to store mine with the airplane inverted and the engine "right side up".

AV8TOR

Nosedragger,

Thanks.

actually there is over lap 52 degrees if I recall correctly

Guys, I am selling my Honda/Eindekker. Ad number 608282 here in RC Universe.

Thanks,
AV8TOR

I can't find the GX31 shop manual on this Honda site as quoted above: http://www.honda-engines-eu.com/en/w...engine-line-up

Am I looking in the wrong place?

This is my very first post on these forums. Thanks to all contributors for a very helpful and informative thread.

Jim.