Gas Engine Break In?

[Chris]

I have a converted Ryobi 31cc engine here. It's on C&H ignition. It was a brand new engine when I installed it in the plane. It is NOT cowled. Just hanging out there in the breeze.

I know that many many people have said that it's a bad idea to run a gasser on a test stand for break in, because it may not cool as well as in the air. And, I have even suggested that people just mount the engine up and fly it for break in.

But, this one is not turning the RPM I need for good thrust and speed. It's only turning about 6200RPM with a 17-8 prop now. Thats after about 3/4 gallon of fuel. The engine picks up a few RPM after every flight, but it would really help flight performance if this thing would crank 7000RPM +/-

The plane is flying very sluggishly. It's NOT fun to fly. I've calculated my fual tank size and figured it's going to take me about 120 flights to get 5 gallons through the engine. Thats an awful lot of sluggish flying.

So, on to the question:
Can I put a few gallons through this engine with it mounted in the plane? Just strap the plane down in the driveway and hook it up to a 2 gallon can? I'm not running a super lean oil mix in this thing. Just standard chainsaw oil at 40:1. Maybe run it a little rich to make sure it's not geting hot?

I know some of the GS racing guys hook their engines up to a 5 gallon jug and walk away. They aren't cooking engines like that, or they would quit doing it real quick.

This is a relatively cheap engine compared to my other gassers. I have Fox, ZDZ, Zenoah and other brands of engines. But, still, I don't want to cork it in the driveway.

Thanks

[wizard]

with it being a converted engine, it is made to cool without being in the air. I would think that as long as you weren't running wide open for long stretches it should be ok.

[Chris]

But, they are cooled while in the weedie. The magneto spins and throws air into the shroud. That shroud is wrapped around the engine and directs the airflow over the cylinder.

I really don't see it heating up too bad with a prop throwing air on it all the time. But, I'd like some other opinions.

[feral63]

how many poeple do you know that run-in their ryobi weed whackers before getting into that long grass?

[Chris]

I don't know ANYONE who puts fuel through these weedies before cutting grass. The engines break in over the course of a season or two while cutting weeds.

But, this is different. I NEED the power right now to fly this plane. I don't want to fly it for 2yrs before the engine ever gets broke in.

Cutting weeds isn't something where it's critical to have max power from the machine. Its okay if it takes a few seasons to break in. Airplanes are different. I know it will break in over time--but I'd really like some more power out of this thing right now. I don't want to fly it around like a trainer for 120 flights.

So, thats why I came on here and asked you guys what you think of a "bench" break-in, in this situation.

[feral63]

i'm on my third desert aircraft engine. from the start i have never bench run any of them.
they do get stronger after a few gallons.

[tl3]

Hi, I'm far from a 2 stroke engine guru, but here are a couple of thoughts . . .

"It's only turning about 6200RPM with a 17-8 prop now. . . but it would really help flight performance if this thing would crank 7000RPM +/-"

It's unlikely that you'll see the 800 + rpm gain your're seeking after the engine is "broken in." The most direct way to increase the rpm by that much is to reduce the load . . . smaller prop.

Check to make sure that your exhaust system is not too restrictive. Some of the weedie mufflers (assuming that's what your using) can choke the engines down quite substanially.

Bench running is generally not needed with gas engines, but can be done. Commonly, people set the rpm at about 2500 with a light load prop and let it go. I would also suggest checking your head temps on a regular basis to make certain it's not getting too hot. Hope this helps.

t

[LookNatU2]

Contact this seller on RCU, Sells or can make you an after market muffler for your engineif you think you might need or want one.

http://www.rcuniverse.com/market/item.cfm?itemid=197434

[Chris]

Well, there I go leaving out critical details.

It's got a Wacker Engines aluminum muffler--errrr, I mean exhaust divertor. Wide open and loud as hell. It's nothing more than an aluminum box with a couple 5/8" tubes coming out the bottom. The guys in the pits certainly know it when I fire this baby up. fg57

I'm checking the exhaust duration, and putting a thinner base gasket on it to bump the compression a bit. I'll have to grind a bit off the top of the exhaust port to compensate for the thinner base gasket and get my exhaust duration back to at least stock. I can go up to around 145* or 155* and still get real good performance without a pipe. I'm tired of with this thing. Time to slap a degree wheel on it and find out all the timing numbers and then start grinding.

I'll post back here if you fellas are interested in the modifications and the final outcome. Otherwise, lets let this one die and archive it to save bandwidth.

Thanks for the help.

[flipflop]

Well, since I'm not paying for the bandwith, I'll tell you about mine. The last Ryobi that I did (out of a Bolens weedeater from Lowes) with a B&B muffler and a stock two needle carb (a couple of years old before they started going to the single needle carbs) would turn a Bambula 18x8 a little over 7200rpm. Last weekend I took the exhaust timing up to 145* from the stock 130*. Now it's turning a MA 18x10 at 7240rpm on a stock muffler that I installed a single tube exhaust on(the B&B is now on my Homelite 45). Just for kicks, I tried the Bambula 16x8 on it. Yeow, 8260rpm and the stock muffler was not a bit happy running that fast (some kind of sympathetic, harmonic vibration. I don't know, I'm not going to run it that fast anymore) I left the base gasket out and sealed it with Ultra Copper. Keep tinkering with it, there's some horsepower in there, you've just got to find a way of getting it out.