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How to bench test Nitro inboard engines

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How to bench test Nitro inboard engines

Old 11-12-2011, 12:02 PM
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hobbyflyer09
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Default How to bench test Nitro inboard engines

Ihave two nitro outriggers and need to set the neddle valve settings. Ive never done rc boats but have airplanes and helicopters, but due to engine setups i cant put on my normal test stand and put on a airplane prop. i need to know the best way to bench test a boat without burning up the engine
Old 11-12-2011, 01:44 PM
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Default RE: How to bench test Nitro inboard engines

The only way to really TEST a marine engine is to run it under load. This means, preferably, running on the water or, if absolutely necessary, mounted in a test stand with an appropriately sized aircraft pusher prop. What you can do is run a flex cable through a tube with a 90* curve in it to clear the tuned pipe as I'm assuming that is where your problem is. As for cooling, you can use a two liter soda bottle with the top set up to work like a fuel tank suspended above the engine with a needle valve to control flow so you can maintain a constant temperature.
With all the above said, TRYING TO SET THE NEEDLE ON A TEST STAND WILL NOT GIVE YOU A GOOD NEEDLE SETTING!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!
Due to the density of the water and the much higher pitch of a marine prop, the only way to really set the needle is by breaking in the engine and tuning ON THE WATER. Compared to an A/C or car engine, a marine engine requires a much richer setting to run properly. The only way to get the needle set correctly is run, adjust then repeat as needed till the engine runs properly
Old 11-12-2011, 01:50 PM
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Default RE: How to bench test Nitro inboard engines

would putting it in a big tub of water of water and gravity feed it work. that would put the prop under load and keep the engine cool. i just dont want to have to fish my boat out of the pond all the time when it dies while trying to set it
Old 11-12-2011, 01:55 PM
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Default RE: How to bench test Nitro inboard engines

In short, no it won't. What will happen is the prop will push a majority of the water out of the prop blades, unloading the prop and, very likely, cause an over-rev that could destroy the engine
Old 11-12-2011, 02:08 PM
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Default RE: How to bench test Nitro inboard engines

ok well me and my dad tried bench testing earlier today with just gravity feeding water in it and nothing on the prop and it would take off and rev high and i would kill it quick i thought that was happening.

thanks for the help ill just have to stick it in the pond and go fishing when it dies
Old 11-12-2011, 02:20 PM
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Default RE: How to bench test Nitro inboard engines

Welcome to the world of R/C Nitro boats. There are three simple rules you need to follow:
1) DO NOT SWIM AFTER YOUR BOAT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! People drown every year doing this as a little rigger won't hold you up
2) Regardless of how good of swimmer you think you are, if you must go out on the water to retrieve your boat, wear a life jacket as chase boats do capsize if the occupant isn't very careful
3) If possible, do not run your boat alone. One wrong move and you could be missing a finger, or worse. Props need to be sharpened and balanced and, due to being sharpened, they will cut you severely. If your props haven't been sharpened or balanced, check out http://www.props4u.com or,better still, talk to the owner, Mark Sholund. He can give you advice on props, set ups and much more
Old 11-12-2011, 03:06 PM
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Default RE: How to bench test Nitro inboard engines


ORIGINAL: hobbyflyer09

ok well me and my dad tried bench testing earlier today with just gravity feeding water in it and nothing on the prop and it would take off and rev high and i would kill it quick i thought that was happening.

thanks for the help ill just have to stick it in the pond and go fishing when it dies
If it's screaming on shore then it is too lean most likely. You will want to richen the needle before throwing it in the water. You are better of running rich than lean. A lean boat will most likely stall when launched. A rich boat will usually run, just slower. Also make sure you are not over proped. With a prop too large the boat will always stall or never run fast.

I would try bench starting it again and see if you can get it blubbering rich. If you can't the engine may have an air leak some where.

Old 11-12-2011, 04:47 PM
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Default RE: How to bench test Nitro inboard engines

it didnt seem to lean i have run many airplane and heli engines it had some white to the smoke and the engine wasnt getting that hot but it would idle good and then randomly speed up and go crazy
Old 11-12-2011, 06:28 PM
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Default RE: How to bench test Nitro inboard engines

As I said in my earlier posts, YOU HAVE TO SET THE NEEDLE RICHER WITH A BOAT ENGINE As Blackout said, you need the needle set so that the engine is very rich on the bench and not like you would run your aircraft. As far as aircraft and boats are concerned, knowing how to set the needle on one means you don't have a clue on the other unless you already have experience with the other type. Since you say you're new to boats, LISTEN TO WHAT WE ARE TELLING YOU, SET THE NEEDLE VERY RICH OR THE BOAT WILL NOT RUN ON THE WATER, PERIOD!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!
Old 11-12-2011, 06:38 PM
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Default RE: How to bench test Nitro inboard engines

ok sorry no need for that. i didnt figure it would be that different i will try and be a better listener
Old 11-12-2011, 07:41 PM
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Default RE: How to bench test Nitro inboard engines

I don't like to be harsh, but when you're asking for help, you need to listen. Let me give you an example of what Blackout and I are trying to tell you:
You're driving down a road and you have come to a hill. Unless you push harder on the gas pedal, the car will slow down until the engine gets to the point where the fuel going in is sufficient to keep the engine running at a constant speed with the car moving. Your boat is the same way, you set the needle like you would one of your aircraft, when you throw the boat on the water, the fuel going into the engine won't be enough and the engine will slow down until it totally stalls UNLESS YOU ADD MORE FUEL. Unlike your car on the hill, hitting the gas won't increase fuel flow, just air. You need to give the carb more fuel by opening the needle so the engine will be able to run with the load of a spinning prop in the water
Old 11-12-2011, 07:55 PM
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Default RE: How to bench test Nitro inboard engines

ok sorry i was think it would be just like a airplane engine but now that you put it like that i understand more. a airplane engine and when i used the heli engine i used a air prop its not gonna change when i put it in a plane or heli but a boat prop pushing air is different when pushing water.

could you go into more details of why the engine will just take of and go crazy like it did it was idling just fine then went to  like full throttle with out me moving the controls
Old 11-14-2011, 06:15 AM
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Default RE: How to bench test Nitro inboard engines

Did the carb Open on it's own? Or did it rev up with throttel servo sitting still and No Needle adjustment?
IF it reved with No servo movment or needle movement then you have a Air Leak causing it to Lean Out.
Is the engine Broke In?
What size and Brand engine is it?
Old 11-14-2011, 01:38 PM
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Default RE: How to bench test Nitro inboard engines

Its too lean.
Old 11-14-2011, 01:57 PM
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Default RE: How to bench test Nitro inboard engines

well that boat has a ops 60 size engine ive never hear of them and the other is a K&B 3.5

it rev up on its own i never moved the controls we

as far as i know the motor is broken in i bought it off ebay used it has great compression still
Old 11-15-2011, 07:06 AM
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Default RE: How to bench test Nitro inboard engines

Just my two cents, since I have the most experience and research on the K&B engines.

They warn against running their engines too rich, especially when breaking them in because the type of piston and liner; ABC.
Evidently the engine has to get hot enough for the liner to expand for the proper clearance otherwise it will gall or seize up.

So, not too rich or too lean. I have 2 of these engines over 25 years old that still run fine.

I have seen picture of engines that people tried to breakin using an electric drill and ruined them compltely.
Old 11-15-2011, 11:09 AM
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Default RE: How to bench test Nitro inboard engines

Yep I agree, running one To Rich will cause as many problems as To Lean( I'm not a fan of the Blubbering Rich Practice).
When it's the First time I run an engine On the Water I generally try to set the HSN Just Rich enough that I get A Little Hesitation when Blipping the throttle, not an Instant response, and toss it in the water. Then I run a few laps and bring it Straight in and Check Temp at the glow plug and adjust accordingly. Works Well for ME[8D]
Old 11-15-2011, 04:24 PM
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Default RE: How to bench test Nitro inboard engines

ok thanks for all the help now the only problem is i live in iowa and its a little cold on the water now days i might have to wait till next year
Old 11-15-2011, 04:28 PM
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Default RE: How to bench test Nitro inboard engines

If the water isn't hard, it's still running season
Old 11-15-2011, 05:40 PM
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Default RE: How to bench test Nitro inboard engines


ORIGINAL: amrharrymac

Just my two cents, since I have the most experience and research on the K&B engines.

They warn against running their engines too rich, especially when breaking them in because the type of piston and liner; ABC.
Evidently the engine has to get hot enough for the liner to expand for the proper clearance otherwise it will gall or seize up.

So, not too rich or too lean. I have 2 of these engines over 25 years old that still run fine.

I have seen picture of engines that people tried to breakin using an electric drill and ruined them compltely.
That's why you run the engine rich with no cooling water. You can do this on the bench and moniter head temps. You should be around 200 degrees. I had to do this with a new O.S. sleeve/piston that were super tight. I had to run two tanks through before the engine would start without a heat gun. No 110v at the pond. The sleeve expands properly and you get plenty of oil from the rich fuel.

BTW, The reason to run blubbering rich on the bench was to prove that there was no air leaks somewhere.....

Old 11-16-2011, 11:18 AM
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Default RE: How to bench test Nitro inboard engines

It's not just Heat that is affected by running blubbering rich.
When you add more Liquid to the fuel mixture it increases Density so the mixture doesn't compress as well adding More stress on Rod bushings and Crank Bearings, add that to the already Tight Piston\Sleeve Fit and you can Over Stress Both Real Easy. In extreme cases it Can cause Hydro Lock which can Bend Rods, and Destroy Bearings\Bushing[:@] Been There, Done That[:'(][X(] But Everybody has there own Preferences, Mine works well For Me but may not for others.[8D]

As HJ said,,, If the Water ain't frozen You can Run It. I lve in FL. so my ponds never freeze, I can run Year Round,, and Have,, I get some of my Best Speeds when it's cold I have run in Air Temps as low as 28*F But Didn't like it much At All,,, The Boat Loved it,, But I Didn't[&:] The ONLY Time I spend time Outside in anything colder Than That is Hunting Season[8D]

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