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PostPosted: Sat Feb 06, 2010 8:22 am
by Shannon
Thanks Pete. Looks like it's working just fine so far. Did you make the crush plate yourself ?

PostPosted: Sat Feb 06, 2010 10:09 am
by peter
Hi Shannon....I got a couple of big steel washers at a farm machinery store...2'' I think, and had to get the centers of them reamed out to fit over the 1'' collar on the one side of the hub....this works well because it allows you to slip the crush plate onto the hub and drill the plate dead on using the hub for a template....they are lots strong but heavier than I'd like.....The center hole in the props is 1''.
I should be able to get the both motors mounted on the plane this weekend to see how they run....I want to run them quite a few hrs. to see how well the mounts are going to hold up......cheers .....Pete

PostPosted: Sun Feb 07, 2010 10:57 pm
by peter
Hey Guy's, here are some newer pictures of this project.






Here is the link to the Part 2 Youtube video.

Here is the link to the Thrust calculator.


PostPosted: Mon Feb 08, 2010 9:32 am
by Shannon
Hi Pete things looking and sounding great ! In order to assist you with weight and balance I'm posting this information. This W&B information came with the JPX engine upgrade kits. What you are doing is very similar to the swap from 185s to JPX's on a Series III. In order to correct CG when swapping to JPX some weight calculations are made and pilot weight is figured into the equation. For a given tail weight the seat is moved a prescribed amount for a given pilot weight.

Based on things I've done-seen in the past I have an idea that some seat-tank adjustment may be necessary on your plane.

PostPosted: Mon Feb 08, 2010 9:33 am
by Shannon
W&B 2

PostPosted: Tue Feb 09, 2010 12:28 am
by peter
Thanks so much for the CofG info Shannon....I had never seen those charts before.....I'm hoping I don't have to move the seat back, but if I have to I have to. I was wondering if anyone has simply added a few ounces of lead to the tail to correct a minor nose heavy situation?...I'm aware that we want to keep it light, but other than that, and more stress on the tail wheels etc., why not?....I'm thinking less than a pound of course....I'm really getting ahead of myself here until I find out just how much the c of g has changed.....How do you go about moving the seat and tank anyway?..drill out the rivets and slide the seat tubes back?....I'd far sooner use the seat out of my old Snoopy and get rid of that uncomfortable banana seat, but that is maybe more radical than I want to get.....anyway, I'll work on that later...Right nowI've found that the engine floods out after a min. or so idling under 2000 rpm...It appears the fuel pump is overpowering the float and needle perfect with the gravity feed tank....I'm going to try a strait 1/4 in line from the 5 gal tank tomorrow to see if the little extra weight of fuel to be lifted will make any difference....I was concerned the pumps wouldn't be able to pull the fuel up, so when I replaced the original lines I retained the 1/8 in. line configuration and now I've got a bit too much....the motors run great over 2000 rpm, and will idle ok for a min. or so before they start to flood.....I've ordered a fuel pressure regulator from ebay, and apparently they will work ok to turn the pressure down....I'd rather find a simpler solution...any Ideas anyone?....what about putting a T in the line with a return to the tank?....might work.
Anyway, fun and games...........cheers Pete

PostPosted: Tue Feb 09, 2010 10:56 am
by Shannon
Hi Pete, Hopefully you will not need to move the seat but if you do you have something to go by. Pretty easy really. Just find your weights and use the chart to find the correction if needed. With the Nosepod on and engines mounted a bit farther forward than the 185s you may need some adjustment. The seat-tank is moved by drilling out the 5 rivets in the A302, boom tube seat attach bracket (G-27), and tank support. Everything is simply shifted back a bit and remounted to make the correction. Adding weight while it does work is the least desirable method vs. adding trim tabs.

PostPosted: Tue Feb 09, 2010 10:30 pm
by Chappy
Hi Peter,

Glad to see all the progress you've made on the your 4 stroke project (just now watched your second video). I'm going to blame you for dragging me into playing with these engines too. I was digging in my barn and came up with a pair of 35X10 props made by Aymar-DeMuth that I got for the 210cc Solo engines - 22 years ago. At least I think the pitch is 10, trying to check on it right now if Mike DeMuth still has the records after all these years. So now I have an engine (HF Blue GX 200 clone) and prop to play with; all I really need now is a prop hub to get going. I plan on making a custom one as soon as I can get the aluminum rod stock and broaching tools (to cut the keyway) delivered (have been ordered). I found my old antique 4.5" rotary table so I should be able to drill the hubs for the prop bolts very accurately on my lathe. That was my immediate concern in making the hubs. BTW, the Aymar-DeMuth props are almost exactly the same as the Prince props, they just don't have the "P" tips. (Update: Mike says he thought he made them for the 185 Rotax. I don't think I had any 185's when I ordered these props. I guess I'll have to measure the pitch.)

I fear that you may be putting a bit too much reliance on the thrust calculators. I've run them and they all seem optimistic to me. Have you used a good old fashioned spring scale to get some hard numbers yet, or are you just going to fly them and see how they do? It will be very interesting to see how the unmodified (CHEAP!) engines perform. Can't wait, can't wait...

I used a single dual-outlet pulse pump to lift fuel on my Avenger even more height than the Lazair, and it feed a 503 well enough. (I guess you've already figured that out for yourself on seeing you're second video).

Have you seen the dyno charts for stock and modified engines here? ... -results=7 I found them extremely interesting.

I'd like to see what these engines are capable of so I do plan to modify mine. I'll be shooting for about 12 -13 hp at 5000 max. The thing that concerns me the most about these engines is the very low rpm's where the peak torque occurs - something like 2500 rpm, and then it rolls off pretty quickly. The dyno chart for the Superbox spec. motor appears to have a somewhat higher rpm torque peak, but even better than that the torque doesn't drop off much for a couple thousand rpm. That is good, as then the engine will continue to build horsepower and should be capable of making somewhat more thrust. To that end I plan of installing a flat top piston, billet rod with replaceable bearings, aluminum flywheel that I will machine off all the cooling fins from, offset flywheel key to get the ignition advanced quite a bit, probably some upgrade on the carb but haven't decided which way I want to go there yet, and a camshaft. I think the cam may be the most limiting part of the stock engine, along with the very low compression ratio and very conservative ignition timing. I want to move the torque peak upward while trying to widen it too. From looking at the dyno charts I think that's doable. I also have a GX 160 clone motor on a water pump I used when I built a house a few years ago that I can steal the head off of to see what even higher compression can do, but not sure I want to stress the crank and block much past the 13 hp point.

Peter, I have real, serious concerns about the prop "hubs" you are using. A proper hub should be much longer so that it reaches back over most if not all of the keyed portion of the crankshaft. I know that a 5/8" shaft is a nice, big, fat crank for the power we're talking about these engines putting out, but what worries me is the treaded bolt hole going 1.25" deep into the crank. Coupled with the keyway, that's a lot of "meat" missing out there right on the end of the crank where your "hub" is installed! Better to have a deep hub that doesn't put all the stress right there on the very end. I plan on making my prop hubs as deep as possible. At least these are single cylinder 4 stroke engines that are not nearly as hard on the crankshaft as the opposed 2 stroke twins that try to twist the crank ends off with their huge power pulses. That's exactly what the Westlake engines Ultraflight originally tried to use did. Even KFM's, with their heavier crankshafts, have cracked theirs out at the prop hubs.

Are your props drilled for a typical UL engine hub too?

It's too bad the exhaust port angles out toward the power takeoff side of the engine causing the pipe to crowd the prop.

BTW, I looked up the similarly sized EX21 Robin-Subaru engine, and the primary difference to the Honda is that it has a chain driven overhead cam and 15 cc more displacement and make a bit more horsepower than the stock Honda. It appears to be a very well built motor that's a bit less expensive than Honda brand motors, but since it's just starting to be used for sanctioned go-kart racing they are just beginning to generate demand for hop-up parts like with the Honda/clones. Maybe down the road...

FYI, Harbor Freight has a sale coming up on March 12-14 with their blue Clone "Grayhound) engines priced at 89.95 each! I plan on getting a couple more then.


PostPosted: Wed Feb 10, 2010 1:23 am
by peter
Hi Shannon and Chappy......It looks like moving the seat isn't going to be quite as big a job as I first thought, and I'll likely have to do it as I only weigh about 155 lbs in my flyin clothes.....Most of the time the bigest part of the job is getting at it.
From what I've read, these engines seem to hold together remarkably well when they get the modifications for more speed and power. the ppc guys are getting 8000 rpm and 14 plus hp with redrives....I'm sure with those props you have and if you do the modifications you plan, you will have some fantastic performance ....I think that thrust calculator is a bit optimistic too Bob, but I know I can drive a 31x10 at 5050 rpm with the yellow clone with N R racing's kit no 1. and 5300 with the rotax. so with the 34x12, and the rpm down where the engine is developing way more power and torque, I recon I'll be getting a bit more thrust than the rotax....I have the dyno testing from arc racing...I stumbled upon that a while back before I ordered my motors....that really helped me decide to go ahead with this project I think....If I could get 9hp at 4700 from a very slightly modified engine, then why shouldn't it work?....But you're right about the hubs...Glen Dewsbury dropped in yesterday to help me do some troubleshooting with the engine flooding, and we discussed this...he designed a hub that I really like.....It is attached to the prop shaft by a torque bushing that locks it to the shaft without a keyway....slips over the 3/4 shaft, and inside the 1.25 in. hub, tighten the expansion nut and there you are...they can still be safetied by the shaft bolt and washer.....they shouldn't be too costly to make either....I have room to move the hubs back on the shaft about an in. and still clear the stack by a nice bit...and I'll probably try that first but I need to get .75 x 1'' sleeves made to shove them back.....the eggmotor guys are using these hubs with no problems so far that I've read about.
Got the other engine started today with the same flooding situation at idle, and to top it off I think I got a bit of dirt in the carb as it leans out a bit over half throttle....swapped jets and etubes to no avail.....ran perfect on the test stand.
When I built that stand by the way, I made it so I could slip a set of bathroom scales behind the motor....didn't work...Enough vibration to unwind the adjusting mecanism and wreck the scales....I would have been better off to rig up a pulley and weight system. When I get to do the w and b, I'll tie the tail to the new scales and let her rip......I did that before with the biprops screaming close to 6000 and all it could do was around 95lbs pull.....I don't think those type of scales can work on the vertical because it think I read somewhere that a well tuned rotax with biprops should give 62 lbs thrust....Does anyone know for sure? I'd be interested in knowing and also what the total weight of the rotax and nacelle is.
GSC will drill the props for standard hub configurations, and a normal 1'' center hole....I didn't know what hubs I would be using so I had to drill my own.
Glad you're experimenting too Chappy. My idea is to keep the engines as close to stock as possible,....just do what is needed to get enough power to give reasonable performance .............Cheers Pete

PostPosted: Wed Feb 10, 2010 7:02 pm
by Chappy

I think your goal of using the barely modified, inexpensive clone engine as a viable replacement for the Rotax 185 is terrific. What, you're whole set-up won't cost much more than a CD ignition upgrade kit from Wildfire for a 185, will it?

I will be going down a different trail as my goal will be more thrust w/o too much more weight for my enclosed cockpit series 3. If I can get more thrust, much better fuel mileage, better "drivability" and less fussiness, and better reliability than the current 2 cycle engines, then I will be very pleased. If the modified clones pan out for my use, I'll probably then build up actual Honda engines for my personal use in an attempt to get the very best long term reliability. The Honda GX 200's turn up now and then on the Internet as new equipment take-offs and manufacturer's surplus at pretty good discounts making a Honda based modified engine package possible at only a couple hundred dollars more each than one based on a clone. That will give me a viable cross country UL motorglider with decent range that I can use later in the season here in Virginia when the weather is the best (unlike right now where we have just pasted 80 inches of snow this winter). Anyway, you are way, way ahead of me and I hope to pick you clean of good ideas as you go along!

I'm glad you are taking my prop hub/crankshaft concerns seriously. Do the Egg's really have many actual flying hours on their engines? Also consider that in our installation we would expect to be putting much more stress on the crankshafts from generous gyroscopic prop loads that they will see just because we are so much more maneuverable (at least the way I fly).

In looking over the engine's shape and size and CG, right now I'm thinking I'll mount the engines left from crankshaft centerline about an inch on the mounts in relation to the nacelle's. I think that will split the static and dynamic loads fairly well on the nacelle mount. By that I mean that if I mount the engine so it is balanced on the mount, the crank centerline will be about 2 inches to the left, or if I mount the engine with the crank thrust centerline to the nacelle centerline, the engine's offset weight will be trying to twist off the mount to the right side. I'm hoping that will yield a viable compromise and not require a fancy, complicated design. I plan on a bed mount with rubber dampers to absorb engine vibration before it can get to the rest of the engine mount/nacelle (somewhat like the engine mount on the engine mounted on the right side of your plane - can't make out the other one). I've seen first hand the effects of under-estimating engine vibration on rigidly mounted engine mounts. I ended up having to increase the thickness of the mounts on my Pioneer re-drives 50% over what I thought were generous mounts to begin with. I'm still playing with ideas on secondary mounting off the top back of the engine to the nacelle. That way the bed mount won't have to be as strong (and heavy) to support the engine's weight. I've ordered square 6061 aluminum tubing to use on my first build.

Are you still using the stock cast iron flywheels? I seem to remember reading somewhere that Honda offers an aluminum flywheel that has the keyway moved a bit so that it advances the timing. I think that is an advantage over the aftermarket billet flywheels with the stock timing. I am leery of using a radically offset key alone for advancing the timing as they would be much more prone to shear from an engine backfire. My modified engines will probably be using somewhat more timing advance than your engines. On the other hand, with a lightened flywheel and a prop mounted to the crank acting like a second flywheel, that may not be much of an issue.

I hope you get your carb issues sorted out easily. In your second video on youtube it sounds to me that your engine is misfiring quite a bit, although it's hard for me to be sure due to the quality of the rebroadcast videos there. If so, have you determined what was causing it? Mixture or some other cause?

This is similar to one of the old scales I use with my test stand on wheels to measure static thrust. It would be better if it was rated for about half as much weight, but it works well enough and it was given to me so the price was right. It has an adjustment screw so it can be calibrated for vertical use too: ... s-300.aspx

IIRC, 62 pounds static thrust sounds about right-on for a 185 with bi-props.