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Author Topic: Four strokes  (Read 17490 times)

glennb2006

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Re: Four strokes
« Reply #25 on: February 08, 2007, 02:49:51 PM »

Doesn't appear to. Normally they are part of the centrifugal clutch on the cars.

G
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BobF

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Re: Four strokes
« Reply #26 on: February 08, 2007, 04:24:14 PM »

Hi All,

Just thinking about the no fly wheel won't run theory.

How do plane engines run then?    ;D

Bob

(Cat Pigeons etc).
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Made it to 80 (25p Richer now)

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Re: Four strokes
« Reply #27 on: February 08, 2007, 04:55:27 PM »

Put your finger in the way whilst one is running you will soon find out  :o :o
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Seaspray

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Re: Four strokes
« Reply #28 on: February 09, 2007, 03:20:47 PM »

The propeller does the flywheel business
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BobF

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Re: Four strokes
« Reply #29 on: February 09, 2007, 03:55:10 PM »

Hi  Seaspray,

Sorry, but I can't except that the prop does the fly wheels job. I'm not saying that you're wrong, but I can only see the prop giving resistance, and not inertia.

I would like one of those technical explanations, similar to the one given on electric motors '16 TURN 10 TURN WHAT'S ALL THIS ABOUT' thread.
Even then, I will still have my doubts.  ???

I'm a very inquisitive person, and I have already forgoten more than I ever learned.

Bob
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glennb2006

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Re: Four strokes
« Reply #30 on: February 09, 2007, 11:58:06 PM »

Hi Bob,

You won't believe me, and right now I can not be bothered to do loads of typing reference momentum and inertial mass etc., but, when a prop falls off an aero engine - guess what - it stops.  :(

Really - it does. The prop on an aero engine if you think about it has a fair bit of momentum in it when it gets going, as does the flywheel on a marine or car motor.  :)

Technical explanation to follow...... :-\

Glenn

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BobF

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Re: Four strokes
« Reply #31 on: February 10, 2007, 01:09:38 AM »

O K Chaps,

My next project will be to start one of my engines which are fitted with a recoil starter, but with the fly wheel removed!
As it's 1.06am, I will leave it for a few hours. After I have walked the dog and had breakfast, I'll strip down my Cachalot and give it a go.

I'll post the results latter this morning.

Bob
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BobF

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Re: Four strokes
« Reply #32 on: February 10, 2007, 01:57:02 PM »

Hi all,

Just down from the modeling room, where I have been running my OS 32 with no fly wheel.

Unfortunately it's raining cats and dogs, and blowing a gale, so I had to do this in doors, as I have no shed.

It started as easily as usual, but with the exhaust and fly wheel removed was out of tune. Because of the noise smell and smoke, I did not have time to re tune it, but from fast tickover and upwards, it ran OK.

I also have a Thunder Tiger Out board motor, and the fly wheel on that is tiny and made of alloy, so virtually no fly wheel action. That also runs and ticks over with no trouble.

I wonder with regard to an aero engine stopping when the prop falls of, wether this could be because with the prop on, the throttle will be open wider to keep the motor running. So when it falls off the loading changes, as will the throttle setting to keep the revs the same. With no resistance, it would require a lower throttle setting.  If you see what I mean.

I wait with interest.

Bob

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BobF

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Re: Four strokes
« Reply #33 on: February 10, 2007, 02:11:00 PM »

Hi all,

 I just had another thought. Unlike with a plane and perhaps a car, (talking models) the loading on a boats prop varies, especially if it's a speed boat. The fly wheel does controll the time it takes the motor to rev up or down. With a cruising motor, the heavier fly wheel keeps the motor and varying changes of revs smooth.

With a racing motor, the fly wheel is much lighter, to enable the motor to increase or decrease revs quicker. Smooth running especially at lower revs is not required.

As I have said in the past. I reserve the right to be wrong at any time.

Bob
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BobF

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Re: Four strokes
« Reply #34 on: February 10, 2007, 02:14:07 PM »

Only me,

I have just realised that this thread is about four strokes, so all of the above ramblings, are referring to two strokes. Can't test the four stroke theory, as I don't have one.

Bob > :(  :-X  :'(  :-*
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tobyker

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Re: Four strokes
« Reply #35 on: February 10, 2007, 03:23:15 PM »

Interesting. I'm surprised it ran at all, but there is probably some mass in the bit of the recoil starter that is attached to the crankshaft, and assuming the engine is forward induction through the crankshaft, there will also be some in the diameter of the shaft. But as you say, would that amount of inertia be enough to get a 4T round two revs and over compression, and would there be any slow tickover?. The acid test would be an aero engine started with an electric starter on a very light spinner but no prop. One then wonders if you could build a super-light racing boat sans flywheel, but could you ever get it into the water with the engine running?  Thank you for sharing your experiment with us.
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HS93 (RIP)

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Re: Four strokes
« Reply #36 on: February 10, 2007, 03:35:28 PM »

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BobF

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Re: Four strokes
« Reply #37 on: February 10, 2007, 04:09:49 PM »

Hi tobyker,

There is no mass in the recoil starter. It uses a one way bearing. The crank just locks to it when the starter is pulled.

It did occur to me that the motor itself is a fly wheel. The mass of the crank and attached parts etc. as you suggested.

I only did the test out of interest, and not to prove any one wrong or right.

Bob
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Seaspray

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Re: Four strokes
« Reply #38 on: February 10, 2007, 04:44:01 PM »

Hi BobF

http://www.infoplease.com/ce6/sci/A0811114.html

Rotation tends to cause these forces.
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BobF

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Re: Four strokes
« Reply #39 on: February 10, 2007, 04:57:44 PM »

Hi Seaspray,

Thanks for that.

Loads of words for me to try and understand.  ???  :(

As I once said to someone.
I know you think you understood what I just said. But do you realise that what I said, wasn't what I meant.

Bob
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Seaspray

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Re: Four strokes
« Reply #40 on: February 10, 2007, 06:13:30 PM »

Try and find an engine the doesn't have a flywheel,centrifugal clutch or propeller fitted and you'll find it to run erratic. Just click on the highlighted underscored words and they'll give there meaning.


Then there is the Wankel  engine
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edible_engine

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Re: Four strokes
« Reply #41 on: February 10, 2007, 10:26:40 PM »

i Sean this in a photo once on the end of the engine thee is the bit that covers the crank witch is held on with 4 bolts in the picture someone had put a piece of 1/8 aluminum over this and put and taped it to take 2 nipples so the inward bit would have water ruining throo it this would help cool down the engine
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Martin [Admin]

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Re: Four strokes
« Reply #42 on: February 10, 2007, 11:21:51 PM »


Something like this.....

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edible_engine

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Re: Four strokes
« Reply #43 on: February 11, 2007, 12:58:43 AM »

Yup thanks it sorta explanes it better.
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glennb2006

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Re: Four strokes
« Reply #44 on: February 11, 2007, 01:01:39 AM »

There you go Bob, Seaspray said in his link exactly what I could not be bothered to type out last night!!  :D

I must say, you are keen to test a theory, I was really suprised that you got a motor to run with no prop / flywheel fitted. Must be the crank moment forcing it round and keeping it going.

Thanks for sharing the experiment result. Thinking further down the line, guess that an assembled boat motor with shaft, coupling etc etc will have even more inertial mass resulting in increased momentum. Maybe this will be the kick off of the flywheel less race engine.

Cheers,

Glenn

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tobyker

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Re: Four strokes
« Reply #45 on: February 11, 2007, 12:51:10 PM »

I remember watercooled crankcase backplates. I seem to remember they were used in conjunction with w/c heads. I reckon these modern engines don't need anything like as much cooling as the old ones, so maybe any part of them you can suck heat out of will help. I suppose to some extent they are oil cooled since they operate on a total loss ("dead loss", Sandy Skinner used to say) oiling system. Good point, EE, I'll bear it in mind.
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Seaspray

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Re: Four strokes
« Reply #46 on: February 11, 2007, 06:01:28 PM »

HI edible

My ole O.S. 20 has a factory fitted cooling crank/back plate fitted.

The cooling tube runs from the pick up scoop to the bottom nipple on backplate out the top backplate nipple up to a head nipple out the other nipple returning the the water via the output on the side of boat.You can adjust the temp of the output water by squeezing the cooling tube a little till the temp you require is obtained.

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Seaspray

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Re: Four strokes
« Reply #47 on: February 11, 2007, 06:05:17 PM »

Hi Bobf
Did your test engine run smoothly on tick over speed ?
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BobF

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Re: Four strokes
« Reply #48 on: February 11, 2007, 06:19:59 PM »

Hi Seaspray.

I was running it in doors, so could only run it for a few seconds. Noise smell smoke etc.
I had removed the complete exhaust system to get the motor out of the hull to remove the coupling and fly wheel.

When it started, it would rev OK but would not tick over. I assumed this in part to be caused by the mixture settings being out.
Bob
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Seaspray

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Re: Four strokes
« Reply #49 on: February 11, 2007, 07:49:00 PM »

Hi BobF
Lets know how it goes.
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