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Can you test run a 2-stroke engine on bench without load?

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Built2Fly

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There are so much unknown with the 2-stroke engine I have, I am not even sure if it will run. So I am planning on bolting it onto a temporary bench and working on it piece by piece. That's very much like how I worked on the engine on my bike, getting it to stable idle, rev up a bit to make sure that it is at least running.

Until I read this article, Engine Test Run, Unloaded

Long story short, it says that running a 2-stroke engine without load is a bad idea. So here is my question, how does it work for you guys? Is it a bad idea to test run a 2-stroke engine on a bench without load? Or do you always build the airframe first and then work on your engine with it bolted on the airframe with propeller on?

I am trying to figure out the order of my tasks that makes the best sense. Your input is very much appreciated. Thanks.
 

Hot Wings

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Until I read this article,
Would love to see the video. :popcorn:

I've test run all kinds of 2 strokes on the bench with no load - the first being a Clinton kart engine when I was about 10 by putting a couple layers of cloth where the carb should have been and dripping gas on the cloth from a Dixie cup. :eek: Just make sure you can control the experiment and don't stack up so many failure points like the example given.
 

TFF

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It’s not good to run it without a prop. Because the oil is mixed or metered, there is usually not enough oil for the RPM. 10 second burp, probably is not going to matter. 5 minutes is probably bad. You also don’t know where the RPM will stop. It might over rev at idle.

What is the entertainment worth to you? I have had plenty of models pitch a prop. I have seen some race engines get destroyed. If you want to run it on the bench, put some sort of prop on it. If it’s meh, film it.
 

cblink.007

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I've revved plenty of two stroke bike engines. For quick blips, no problem. But, that won't tell you much about the engine.
From my old Yamaha KT-100 open pipe kart experience, I learned that idle only without a load is okay, but any serious run-up should never be done without a load. But, in 105 races over the years and countless rebuilds, I learned that 2-cycles are witch-doctor science, but, for some reason, a blast to tune and maintain!!
Brian10.jpg
 

Built2Fly

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Outdoor test stand? I can only dream.

I am working from a one-car garage. So my thinking is getting the engine to run, then mothball it. Then working on the fuselage and bolt things together after I trailer it to the airfield (when I am lucky enough to rent a corner of a hanger from some generous club members). It will be shuffle dance for spaces.
 

TFF

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Just pickel it now. Save potential damage and get the project going instead of playing with something that can’t be used for years. That or build a stand, and break it down or repurpose it after you run the engine.
 

pictsidhe

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Running it indoors is very dangerous. Drag it out of the garage to run it. Test stand can be made from 4x2 lumber. If you can't manage that, you probably should give up on building a plane.
 

Built2Fly

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Thanks for the good data points, folks. My priority is (1) space, and (2) minimizing steps that can be avoided.

Taken all the input, my current path will probably be working on the frame first and some smaller pieces (such as the carburetor, the fuel pump). Then hopefully I can put the engine on the frame and test idle in one weekend (and disassemble afterward). At a later time when I get to the airfield, I will continue the engine test with higher power setting (with the propeller and everything on) at that time.

Thanks for the inputs.
 

wsimpso1

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Until I read this article, Engine Test Run, Unloaded

Long story short, it says that running a 2-stroke engine without load is a bad idea. So here is my question, how does it work for you guys? Is it a bad idea to test run a 2-stroke engine on a bench without load? Or do you always build the airframe first and then work on your engine with it bolted on the airframe with propeller on?

I am trying to figure out the order of my tasks that makes the best sense. Your input is very much appreciated. Thanks.
Why not? Lots of boat and motorcycle and chainsaw type engines will run in neutral at low power, be run up to modest power and significant rpm without loads. The forum thread cited had load OR flywheel. Flywheel is the important thing and this is coming from a guy who spent a little over 23 years on powertrain engineering. On an airplane, the propellor is a massive flywheel. Having "enough" flywheel effect is important, and engines are designed for "enough" inertia.

Check the flywheel or other rotating Inertia used with your engine. Get one of those on the engine and it should be fine.

Billski
 
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Armilite

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There are so much unknown with the 2-stroke engine I have, I am not even sure if it will run. So I am planning on bolting it onto a temporary bench and working on it piece by piece. That's very much like how I worked on the engine on my bike, getting it to stable idle, rev up a bit to make sure that it is at least running.

Until I read this article, Engine Test Run, Unloaded

Long story short, it says that running a 2-stroke engine without load is a bad idea. So here is my question, how does it work for you guys? Is it a bad idea to test run a 2-stroke engine on a bench without load? Or do you always build the airframe first and then work on your engine with it bolted on the airframe with propeller on?

I am trying to figure out the order of my tasks that makes the best sense. Your input is very much appreciated. Thanks.
================================

First, you're not going to hurt it to turn it higher rpm for a Short time. Skidoo/Rotax Blizzard Engines were rated Stock at 10,000rpm. For Tuning purposes, you have No reason to turn them higher than rated. All Rotax UL Engines are rated at 6500rpm except the 185UL (5000rpm) and the 618UL (6750rpm). Get a Cheap Tach for your Test Stand, as low as $22 on eBay. For a little more you can even get one with a Tach & CHT. If you have a Car, Truck, Suburban with a Trailer Hitch, you can make up a Test Stand something like this Bike Rack with a Plate, a Mini Gas Tank and your Gauges.
 

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akwrencher

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It won't hurt most 2 strokes to run unloaded, but there is limited info you can gather. It takes almost no throttle to rev an unloaded engine, you won't be able to tune it or even know if is making any power. I used to have a 30hp Suzuki outboard with 3 carbs. Every spring I would fire it up, it would run fine on the stand, but invariably it would have at least one stuck float. If I didn't go through the carbs it would dog out on the boat and be useless. So, it's not going to hurt to check to see if it runs, but that's about all you can do, practically speaking, until you can properly load it and tune it.
 
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