profgigawatt

My Feedback: (6)

I have run the 1/4-32 plugs on All my conversions, ST to Ryobi, with no problems what so ever. CH advised that it was OK to use the small plugs except on the larger, higher compression gassers. I have observed little or no difference between plug size. I have used the oil supplied with the Weedeaters to Redline in ALL my conversions, ringed and ABC, at one time or another. Gas and Klotz synthetic was recommended by an engine expert for an R/C mag that I emailed. I use redline because I have it. Some of what I have done is on the (6oz Flywheel post) so I won't bore you with a repeat. Alot of us are doing the same thing kind of on our own or so I thought. All good info! Prof G.

mrbigg

My Feedback: (21)

Do you guys have any pics of your set up? Will I have to fabricate a bracket for the hall sensor or does CH make it? I didn't see it listed for the smaller engine.

profgigawatt

My Feedback: (6)

CH in their FAQ, suggests that 40 size engines are too small to do. They SUGGEST. Because I did so much electric with NICADS up to 30 cells I believe that the weight of ignition is nothing compaired to large numbers of nicads. The first question is usually weight. As to mounting the hall IC. You will most likely need to design something to hold the sensor yourself. On most engines there is enough room for mounting the senser on the case. The prop drive can be drilled for the magnet, basic stuff. Some prop drives are not "Keyed" but rather use a split taper to keep the prop in place on the shaft. After I established my magnet location on my ST I used an old worn down Dremel disc about 1/4" dia to mark (Just enough to see) a point on the crankshaft and the drive washer that can be alligned with the visable split line on the taper to mark the timing. There are any number of ways to do this, this works for me and allows changes, if required. I have been able to change timing at the field and return it. The taper holds well. I have used a small 1/4" wide "hose clamp with a short piece of 1/4" brass channel soldered across the strap of the clamp to mount a sensor, it is also adjustable. You will very likely get other and better suggestions. Prof G

mrbigg

My Feedback: (21)

you have any pics? I'm not worried about weight. Plenty of wing area on the trainer with the .90 and if it works good, then I will use it on the .51 which is on a profile funfly.

Jezmo

I am in the process of building a new Super Sportster for my gas 51. The old one is kinda ugly as it's been planted a few times and rebuilt. (It's about 7 or 8 yrs old) I will happily take pics of it but you can't see much so maybe it would be better if I take them when I switch the engine to the new plane. What the heck, I will take a couple and see how much you can see and if it is OK I will post them.

profgigawatt

My Feedback: (6)

mrbigg, Check the "6oz flywheel" thread in the conversion forum, page1, post 9. There are two engines with the clamp and brass channel mount. The engines are two different models of weedeaters but the mounts are simlar. One is CH and the other is my copy. CH has them on their site. I believe that this type would almost be universal for nitro engines. The brass can be cut to a length that works for your instillation. Prof G

Jezmo

Here are some Pics. The ring slips around the front bearing housing on the crankcase and has two set screws on the opposite side from the hall effect sensor. The screw can be loosened to change timing without pulling the prop drive hub. When I remove the engine I will try to remember to take some better pics.

Please excuse the plane, I was going to throw it away but it found new life as a test bed for this project. It's been broken in half more than once and it's quite heavy from all the splices and epoxy it is carrying around. Does the job though and never complains.

Jezmo

I finally got the engine out of the old Sportster and when I tore it down I couldn't believe how good everything looked. The piston looks brand new on the sides, no carbon at all, and just a little carbon on top. There is no carbon on the head side of the chamber at all. The ring is just now starting to break in. (Although it is touching all the way around it's circumference it still has some areas width wise that aren't shiney yet. Real close though.) The crank and rod look great with no visible wear. It is between 9 and 10 hrs run time now.

I am running it at 16:1 oil ratio and I am using Pennzoil only as this is what it seems to run the cleanest with. (I can try another oil brand and when the plug get's a little carbon on it from that I can put the Pennz back in and it will literally clean the plug back to like new) It's almost a dead heat between Pennz and Zenoah full synthetic but the Pennz wins because it's less expensive and I see no real difference between the two otherwise. The insulator is a very nice tanish brown color and the rest looks just like it came new when running the Pennz. (My Redline order hasn't come in yet and I will report back when I try that but it runs very clean in a friends R/C race boat with a Zenoah G26.)

I have also started running Sunoco unleaded 98 octane race gas in it mainly because I have it and it doesn't have any alcohol in it which seems to reduce to storage life. IMHO. It will also allow me to start raising the compression to get some of the power back that was lost going from Nitro/Methanol to Gasoline. I am going to slowly raise it until I get into the 11:1 range and see how it progress's. (Don't want any detonation)

So it's in the new Sportster and all ready to go for it's first weekend and we're supposed have a nice one in the Houston area. Keeping my fingers crossed and I hope you all have a good one as well. I'll keep ya posted on the compression results.

P.S. I also ordered needle bearings for it and I am going to try to put them in the rod so I can cut the oil back some more. I'm shooting for 32:1 on the oil ratio. I'll also keep up with that info.

Jezmo

Some new notes for the ST51 project. I have bought needle bearings to put on the ends of the rod and since there is not enough metal in the rod to just machine it for the bearing I am making a new one. It will be made out of titanium to give me extra strength as I will have less material surounding the lower bearing and I want it to be as strong as possible. This mod is not for the inexperienced as it requires considerable machining skills and some specialized tooling. (I have access to a CNC mill that most of the work will be performed on) The engine is running great and on the teardown looked as good as brand new so the ONLY reason I am doing this is to be able to reduce the amount of oil in the fuel. I could go all the way to 100:1 like the bigger engines but I don't even run my Zenoah that lean on oil. What I am aiming for is to be able to use the same fuel in all of my Gas engines which I normally mix at 32:1. Makes it easier to keep up with which fuel goes in what and two cans will cover all of my flyers. Blue for Glow and Red for Gas.

I will post pics of the Rod and Bearings before I put them in.

P.S. I will also be adding a hardened crank pin at the same time.

Jezmo

Even though it was very windy and drizzly in Houston today I went out and flew the Sportster. I had my first problem with the conversion as the timing ring lock screws came loose and allowed the timing to go way advanced. I could tell it was starting to lose power and after just a short time I could hear it detonating from the ground. I cut the throttle and landed and after quite a bit of head scratching finally figured out the timing ring holding the Hall Sensor was loose.

I returned home, removed the engine and reset the timing and tightened everything back up. While I had the engine out I checked the bearings again and found no noticeable wear. The piston and ring and cylinder are looking very good as well.

I decided to increase the compression by 2 1/2 points to 10.5:1 and I also changed the ramp angle on the throttle barrel in order to slightly lean the mid-range. It picked up a bunch of power. The ramp change has my little G51's throttle response as linear as any engine I have ever owned. From idle to wide open is as smooth as silk. I was somewhat worried that the increased compression would cause heating problems but quite the opposite happened. It runs about 20 to 25 degs cooler now. I had to open the main needle just a tad after raising the compression so maybe the extra fuel is helping keep it cool. I'm not complaining because now it's back down in the high 200's. I am looking to have the needle bearing conversion ready soon so I can run it at 32:1 and hopefully there won't be any more problems.

Jezmo

The G51 fouled it's first sparkplug this weekend and I can't say with 100% certainty, but I think it was due to the fact I have been running 100LL avgas in it for the last couple of hours. It is at 25 hrs. approx. and other than the fouled plug is still running strong. The plug looked fine and would run OK up to just over half throttle then would start misfiring. Changing the plug fixed the misfire and all is well again. (No more avgas for me)

mrbigg

My Feedback: (21)

It still lasted longer than any glowplug I've ever had.

av8tor1977

My Feedback: (6)

Yeah, avgas will do nothing for these small motors, other than carbon them up and cause plug fouling. I´m rather surprised that it ran for two hours with avgas without fouling the plug sooner. Most people think avgas is more powerful, but the truth is an engine will make slightly less power with avgas. A big bore aircraft engine, or a large high compression racing type engine is a different story...

AV8TOR

Jezmo

I was doing it mostly because avgas will stay fresh longer than our wonderful ethanol spiked pump fuels. Plus, I love the smell of avgas when it burns. I know sometimes there is a power loss with higher octane fuels but in my case both my Zenoah G26 and the little ST G51 turned the same rpm's with avgas as pump unleaded. Not sure why. Oh well, I guess it's back to Sunoco unleaded.

Ralphbf

My Feedback: (27)

I wish I could get Sunoco.

Some people will complain about anything.

Does Sunoco still have the best gas around?
There use to be no comparision.

Jezmo

The Sunoco I am buying is the same unleaded Nascar is running. I haven't tried any of the other Sunoco blends in about 5 years (since I quit racing cars and Sunoco was my preferrence back then) but I sure like the Nascar blend. This is the first Racing Unleaded I have run and can't tell that it's unleaded from the way it looks, smells, and runs. (Looks and smells exactly like 100LL avgas) The other fuel that worked real good for me back then was VP. I tried others but always went back to VP or Sunoco. They sold Sunoco at our local track so that worked out great but now most of the oval tracks around here are running methanol in everything and don't carry any gasoline. I have found a small speed supplier near my house that carries VP, Shell, and Sunoco racing fuels. He also has most brands of high end oils in stock which works out good. (He carries Redline oils and although he didn't have the two stroke racing oil in stock, he ordered it for me) My only complaint about Sunoco is the price. I was getting the avgas for just a tick over 4 bucks a gallon and the Sunoco is quite a bit more. If regular unleaded keeps going up the Sunoco is going to be a bargain. I hear you guys are already over 4 bucks a gal. for regular and the summer driving season isn't even here. Oh well, happy flying Ralph.

Jezmo

I am a little behind writing on the ST51 project but a lot has happened since I last wrote. The needle bearing project failed causing case damage so I put a new short block in and broke it in. I used the old ST40 head that was already modified and the old ST51 carb which was also modified. Everything else is now brand new. (Well 3 hours on it now including break-in) The cage failed and I can't blame it on the bearings because I had modified it slightly. The piston, ring and sleeve are fine but the case got damaged in a way I was not comfortable reusing it. Also, I thought it had fouled a plug a while back, possibly because of avgas, and that was not the case. The intermittent miss was caused by the Hall Effect sensor wiring being chaffed. Some heat shrink on that and all is well in the ignition department. The new one runs identical to the old and I took the head off today for an inspection so I posted this pic. Not much to see though. It has been on Redline Racing oil since new. (Broken in on it as well.) The break-in was very unscientific and some are going to call me nuts but since the old carb was reused and all settings were duplicated I just fired it up went full throttle and let er rip for about thirty minutes.

We're having our Founders Day Fly-in this weekend and this is going to be one of the planes I'll bring so I wanted to check it over good and get it ready, hence the teardown and inspection. I remain impressed by the power and economy of this engine. It's been a very good project.

Edited: Sorry forgot the pic.

JIMARRINGTON

Are you still running with the bushed bearings and 16:1 oil ratio? I have a G90 laying around and a carb adapter and walbro carb that I might give this a try on. I am supposed to have one of those cheap Chinese igntion systems on the way also. Getting out of glow and switching to gas. Made the mistake of buying a Zenoah G20. Now have no desire to fire up a glow motor any more. If the glow engines will survive doing this it would sure help me out. Still have a Top Flite FW190 kit on the shelf and several 60 size plans I would like to build. Gas motors are too big for them. Would be great if I could convert the glow motors I already have. More economical too.

Jim

Jezmo

Yes Jim, I am using Redline Two Stroke synthetic at 16:1 and yes it is still bushed. The needle bearing rod didn't work out as planned. I am converting a G90 to needle bearings like the BME and the ones Ken Lambert does. There is enough room in the case of a 90 to do them right but there just isn't enough room in the 51 for bearings. I am also putting a walbro on my 90 and have ordered a couple more CH ignitions for it and my Saito 91. They been sharing with the 51 until this week. Good luck with yours.

JIMARRINGTON

Thanks Jezmo,

I dont have the machining tools or skills to change to needle bearings. Do you think the bushed bearings will survive on the 16:1 mixture in the G90?

BTW, Ken Lambert is the guy that gave me the carb adapter. Met him just as he was selling his house last year. Super nice guy. He showed me one of his G90 conversions.


Jim

Jezmo

Hi Jim,

Yes, it should last OK at that oil ratio. On my 51 I have been enlarging the oil holes on the lower end of the rod by two drill sizes. (Can't remember how many thousanths that is) I also chamfered them nicely and it seems to be doing good. I ran it with the datalogger attached this morning and I will put a pic in this post of a screen shot of the top rpm. Most folks aren't going to push it near as hard as I do so the rod won't see as much abuse. I am hammering this thing pretty hard for a 51. It's running darn near 15,000 in this shot and on some days it's just over 15,000. I am going to find out what it unloads to in the air this weekend. I haven't been able to fly it with the datalogger in it because I have too much junk inside already. I spent a couple of hours last night rearranging things inside so the datalogger can fit in. (also ran the pitot for the speed sensor) I'll post how fast she runs and how many rpm's it unloads to next week.

tkg

My Feedback: (1)

Checks in the mail

mrbigg

My Feedback: (21)

What number Walbro are you guys using on the .90? I have one here that I would love to convert.

Jezmo

Thanks Terry, I keep telling these folks how awesome you guys are. Customer service is the best. Sure hope you're feeling better, those darn stones are bad medicine.

Jezmo

I'm using a slightly modified WT173 and I am not sure of the number but the BME's have a ZAMA on them. Maybe Ken Lambert will pop in, he's using ZAMA's I think. Anyone else with Zama numbers?