Rebuilding GSM026's BME-115

[dbcaster]

Kris,
I am not really trying to make things complicated. The only reason I tried that with mine and would suggest it is because it eliminated the possibility of airflow causing the problem. Mine did the same thing on the ground that it did in the air.

[KrisW]

	Quote: Originally Posted by dbcaster
	Kris, I am not really trying to make things complicated. The only reason I tried that with mine and would suggest it is because it eliminated the possibility of airflow causing the problem. Mine did the same thing on the ground that it did in the air.

I was kidding DB. I had intended on flying the engine soon anyway, so I'll ge ti ttuned on the bench for the standard diverters, then swap it into my 35% Yak and see how things go. With the stacks I have for it, the needles are almost unreachable, making tuning a total PITA inside a cowl, so I'll have to pull the cowl for any adjustments. That's why I'll be doing a lengthy bench tuning session before I go flying with the engine.

TonyC. . I can'/t believe you did not take me seriously. I don't know whether to be insulted or laugh. . .

Gremlin, the engines APPEAR to be lean, because the different scavengiing efficiency and flow of the cylinders makes one slightly more diluted with exhaust gasses, causing a more of a passive EGR condition compared to the other cylinder. When you get exhaust gas contamination, it makes the engine APPEAR to be running richer than it is, because the diluted mixture burns slower and cooler. When one cylinder is noticeably more efficient and scavenges better than it's counterpart, it has a lot more heat making potential, less Exhaust dilution of the intake charge, higher cylinder pressures, and is more prone to heating and detonation.

You can modifiy the engine to change the tuning to each cylinder, as Dick has given several examples of companies doing so. You can also reduce compression, change your exhaust flow characteristics to either help or reduce intake flow, or even set up an ignition system that retards the timing slightly on the more efficient cylinder, all of which are steps at reducing the combustion chamber pressures, and reducing heat.

I once tried to convince Keith to modify the intake side of the engine, to help even the flow between the cylinders, but he never did it. My idea involved canting the cylinders at 30-45 degrees, exhaust pointing aft, then machining dedicated passages inside the crankcase to even out the flow between the cylinders, at the same time angling the carb and reed block forward, with the carburetor moved aft slightly, to help shoot the mixture toward the front transfer ports of the cylinders and even out the flow and mixture distribution. A bit of an effort to get it done, but I think it would have improved the smoothness a bit and probably helped in overall top end power. Welp, he stuck with conventional thinking, and that is where we all sit today.

I'll get some pics up in a little while of the work I did to the reed spacer block.

[KrisW]

Allrighty. . . getting the silly bolts on the carb mounting plate to not stick up is easy. Simply replace them 10-32 flat head steel screws.

first remove the carburetor
remove the front two bolts. The rear bolts are countersunk or in reliefs, so they wind up flush with the plate.
tape off the carburetor hole
countersink the holes
Fit two screws for length, and install
remove debris
remove tape
bolt the carburetor back on.

VOILA!!!!!!!!!!!!!!!

No more fugly screw heads sticking up 1/4 inch and getting in the way.

Okay, I'll be the first to admit, phillips head screws are not most the "El Coolio" looking fasteners,. which is why I have somed flat head allen screws on order of the proper length, to take their p[lace. When they get here, I'll also countersink the rear two holes, and finish out the process.

I'm simply aghast that the bolts were allowed to stick up that way in the first place. . .GEESH.

[KrisW]

Well, the only way to PROPERLY test the engine is in the air, right?

Enter my 35% Harris and Anderson Yak-54. Take off the 110, install a 5/8" spacer, modify the throttle linkage, make an adapter plug to match up the different ignition pickup and the CH ignition, install a choke rod, refit the cowl, bolt on the Mejzlik 28-10 and flip and go.

I spent an hour getting the engine onto the plane, including the time required to remove the old engine. Luckily the carburetor adjustment scews clear the bottom of the 110 sized exhaust stack on the left side, so I'll be able to adjust the mixture from outside the cowl. I was really dreading having to remove the cowl every time I had to make a mixture adjustment, but this worked out very well for me.

Tonight I'll have the installation finished. The weather report for Thursday is good, so after the engine gets about an hours run time on the ground at my house on Thursday morning, I'll be off to the field in the afternoon to see how it performs in the air.

[tonyc9075]

KrisW, my post about you being serious was just for the fun of it.

I do have a question about the one hour of run time on the ground. This goes against everything I have read.
I am a new BME 115 owner. So far I have bench run it 4 times for 1 minute each time just to see how it runs. It starts easy and runs strong.
Could you please tell us who are new to BME how you tune in your motor on the ground? I think a lot of people will benefit from this information because lets face it there are several owners out there that have had a problem. I have read from other owners that the BME tunes counter intuitive to other motors.

Tony

[KrisW]

	Quote: Originally Posted by tonyc9075
	KrisW, my post about you being serious was just for the fun of it. I do have a question about the one hour of run time on the ground. This goes against everything I have read. I am a new BME 115 owner. So far I have bench run it 4 times for 1 minute each time just to see how it runs. It starts easy and runs strong. Could you please tell us who are new to BME how you tune in your motor on the ground? I think a lot of people will benefit from this information because lets face it there are several owners out there that have had a problem. I have read from other owners that the BME tunes counter intuitive to other motors. Tony

Tony the one hour of ground run time is to get some wear on the new rings and help seat them a bit. sort of a catch-up to th eother side of the engine.

For ground tuning, I go for three things. . transition. . good idle. . and no sagging on the top end. Since idle and transition are the most important part, I work on them first, using only the low end needle.

Get the engine started, and let it idle at a fast idle for about a minute, then try to transition to half throttle. If it burbles and clears it's throatit's rich, so shut down and close the low end 1/8 turn at a time adn repeat the start-transition attempt until it's relatively clean. Only after this is pretty clean do I try the top end shot. If the engine will go to full throttle, and hold it, I listen for roughness or mid-range burbling as I back the throttle down. Usually, if the top end is too rich, you will get a burble about 3/4 throttle (if it's really rich) and lower if it is leaner. I don;t try to set the top end by accelerating the engine, but by backing down and leaning the top end until I can go to full throttle, then back it down to 1/2 throttle or lower withut it sounding rough or rich. THEN go for the idle-top end transition. usually, if you have set the idle to be clean, and transition well to 1/2 throttle, going from idle to full throttle, after getting top needle set, will be pretty smooth.

After all that is said and done, now it's time to see how lean the bottom end really is. After warmup, let it idle for 30 seconds then try to transition to full throttle quickly. If it stumbles, spits, and acts rich, youneed to tweak the idle a bit leaner, but not much. go about 1/16 turn at a time until it will idle for 30 seconds then transition cleanly to full throttle. THEN . hold the engine at about 1/4 throttle, which is the transition point for the carburetor between the low and high needles, and repeat the 30 second run to full throttle. If it stumbles and acts rich NOW, it's probably too rich on the top end. Again, 1/16 turn leaner until it cleans up. If you are going leaner, and it goes to full rpm then sags, go richer on the top end, because you are getting the initial blast of gas, and then it is going too lean and losing power.

After you have set those three conditions .. idle, transition from idle to mid throttle, and transition from 1/4 throttle to top end with no sagging, then open each needle 1/16 turn, and fly it. Watch for sagging, especially on long verticals and after 30-45 seconds of hovering. If it sags, open the top and try it again. If, during 1/2 throttle fight, you roll over and it burbles and sags, the top end is probably too rich, and needs to be addressed by slightly leaning it out. Be careful to check the top end for sagging under prolonged vertical climbs if you are trying to get rid of a rollover burble by leanign the top needle.

Remember, under flight loads the engine unloads a bit, so the mixture changes. You'll have to play with it a bit, but I've found that getting it set to my liking on the ground, especially the 1/4-top end transition and making sure the engine will not sag on top, is a goo dway to ensure that the engine flys well from the first flight.

[tonyc9075]

Thanks KrisW; You have given me something to work with.

Tony

[KrisW]

Ya know, I hope you guys aPPRECIATE all this ! !

It's freaking 37 degrees outside!!!!

And there I am running a BME-115 with 28-10 Mejzlik, and standing in front of the stabilizer when doing full power blasts over and over again!!!

I'd say the wind chill is close to -50C. . . .

Okay, getting the motor to initially fire was a pain. It's cold, and I had no idea what is going on with mixture or anything. Base needle settings were 2 on the low end and 1.25 on the top end. I had the cowl on, thinking everythign would work peachy keen. . but NO, the carb was dry and refused to pull gas properly, so I had to take the cowl off, pull the plugs, and use a drill to spin the motor over for a while to pump gas through the carburetor and get things wet inside. Still it would not fire off, though, so I wound up doing a "glo engine prime" by shooting gas right into the carburetor throat with the throttle wide open and choke off. Then I choked it, set it to idle and it fired on the 2nd flip. Turned the choke off, and it started 4 flips later, and never missed a beat from then on.

Okay, engine is running. After about a minute I started seeing where the needles were set. The bottom was very rich, so I had to take it in to 1 5/8 turns before it even hinted to cleaning up, but eventually it smoothed out a bit. Then I started the top end adjustments, 1/8 turn at a time. From 1/4 throttle to full it would bog and catch up and then run well, so it was too rich for sure. At 1 turn out it started to clear up, so I gave the engine about 5 minutes at 3000 rpm, just to let it settle in, then started playing with the throttle again. The top was still too rich, and the bottom was acting rich. I shut down to turn the top end in another 1/8 turn (7/8) then restarted. On the top end pull it picked up an easy 200 rpm, and sounded much cleaner on the transition. OOOOH LA LA!!! now we got some stones!!!

The Bottom still seemed rich, so I took it in another 1/8 turn (1 1/2 out) and it cleared up a little. Now the transition from idle to 1/2 was very good, as was from idle to full throttle, without even a hint of stumble or hesitation. From 1/4-full, after 10-15 seconds at 1/4 throttle, it does not sag a bit, goes immediately to a peak, then a second later goes about 200-300 rpm higher, indicating that the top end is still a tad rich, but very flyable at this juncture.

So. . needles are set at:

HIGH: 7/8
LOW: 1 1/2

I expect to take in another 1/8 on the top, and possibly a little bit on the bottom, depending on how flight testing goes, but for now things are working very well.

My ear tells me the BME-115 is turning in the 65-6600 range, and the Mejzlik 28-10 is "singing" pretty loudly. I'm not going to bother with a tachometer, but the power is obvious, and the prop really let's you know that you are turning it well. Right now I'm more interested in finding out how well the engine will run with Stack style exhausts (which I absolutely HATE) , and if the problem with roll-over sag can be eliminated. Judging from the way the engine is running, and how I can tell it's rich at certain points in the throttle position, so can adjust things leaner by a good margin at this time, I'm sure there will be little problem getting the carburetor tuned to run cleanly no matter what attitude the plane is in.

I'm also not worried about top end power, the engine is really turning up well, and is very smooth, with no evidence of heating up (in 37 degree weather. . DUH!!!), or any problems with throttle response. In about 4-5 gallons the new rings should be totally seated, and things will be at 100% (barring unforeseen problems) so for now it's flip and fly and tune the carburetor and see what happens. After break-in I'll get some hard tach numbers, but for now, just the way the prop is singing, I'm very hapy with the power level.

It's going to reach a sweltering 48 degrees this afternoon, with clear skies and light breezes, so I'll be at the field from 3-dark, running the motor and having some fun.

[Hinckley Bill]

Hey KrisW,

I've got a first generation BME 115 just begging to go into the new H-9 Sukhoi so all of your work is definitely most appreciated, as is all the information past on by FG members.

Keep up the great work,

Bill

[Cracky]

	Quote: Originally Posted by Hinckley Bill
	BME 115 just begging to go into the new H-9 Sukhoi

holy smokes!!!! Can you say vertical drag racer?

[guitar dave]

Hello Kris W. I am just wanting to thank you for all the valuable information you have given. It is so nice to see someone with a great passion for understanding how things work and being willing to take the time to share this information with everyone else. Thanks. BME 110 owner. Dave Sylvest.

[tonyc9075]

KrisW, wow 37% thats kind of hard on the flying fingers. We do appreciate you. By the way here in Louisiana we see that kind of cold at leas twice every year. Keep reporting, we need your dedication.

Tony