Author Topic: Cooling Fan for model I.C. Engines  (Read 6796 times)

Offline Brian Rupnow

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Cooling Fan for model I.C. Engines
« on: July 06, 2014, 12:34:36 PM »
As you are probably all aware, I have just finished a two month build of my version of Malcolm Stride's engine, the Jaguar, which is essentially half of a Bobcat. My engine ended up with many changes, and got rechristened the Canadian Cub. It is a sweet little engine, with a totally enclosed crank-case and an oil sump and splash lubrication. The only trouble is, the engine runs terribly hot. Malcolm ran his with a propeller, which no doubt kept it cool thru the air movement the propeller created. I am afraid of propellers, because at hi speed they become somewhat invisible, and have a tendency to cut off fingers from old fools who inadvertently stick their fingers in the invisible propellers at speed!!! THUS--I have determined to create a small. belt driven cooling fan to keep the temperature down into a reasonable range on my engine. I haven't seen any posts before on similar subjects, so you may find this of interest.
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Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #1 on: July 06, 2014, 12:41:31 PM »
As you can see, my engine is not very big, being only about 5 1/2" (140 mm) tall, with a 3" (76 mm) diameter flywheel. This only leaves me 2 1/2" (63 mm) for a fan and fan shroud, as I only want to cool the cylinder and cylinder head. The crank-case is not overheating, and a larger fan would completely overwhelm the engine.

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #2 on: July 06, 2014, 12:46:08 PM »
My original thoughts were to use a computer fan, which is close to the right size. Unfortunately, computer fans are all driven by a D.C. motor, and the fan hub is part of the motor housing. This leaves you with an enormous center hub and very little blade. I need airflow in that center area, so decided to search for a small (2") diameter fan with a small hub.

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #3 on: July 06, 2014, 12:53:52 PM »
Fortunately for me, I was able to find a 2" diameter 10 blade fan with a small hub and a 3/16" (5 mm) center bore with set screws. The pitch is correct to blow air over the cylinder when driven clockwise, which is the rotation of my engine.


Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #4 on: July 06, 2014, 01:02:11 PM »
At speed, I am sure that this little aluminum fan would wreak bloody mayhem with unsuspecting fingers as well, so it will have a shroud fitting around it, which I will make from 2 1/16" i.d. steel auto exhaust tubing. The center hub will be a piece of 1/2" (13 mm) o.d. mild steel, with a bronze bushing of 3/16" pressed into it, and the hub will be supported concentric to the outer rim with 3 pieces of 1/16" (1.5 mm) mild steel plate welded or silver soldered into place. The shaft and pulley will be turned from one piece and the groove in the pulley will line up with the groove in the starter hub on the face of the flywheel. I will use a 3/32" diameter rubber o-ring for my drive belt, and the fan will turn at roughly twice the engine speed.

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #5 on: July 06, 2014, 01:09:42 PM »
The fan shroud will be supported by a couple of brackets which pick up one of the cylinder head bolts and one of the cylinder to crank-case bolts. These brackets will again be made from 1/16" mild steel and silver soldered or brazed into place. The fan shaft is cantilevered out the side away from the engine cylinder, so the fan should be easy to install in the shroud from the non bearing side. When installed on the engine, the cylinder itself will serve to keep pokey fingers out of the fan. I believe that since the engine itself is all built from brass and aluminum, I may resort to painting the fan and supporting shroud---possibly red for the fan and flat black for the shroud itself.
« Last Edit: July 06, 2014, 01:55:29 PM by Brian Rupnow »

Offline Graham Meek

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Re: Cooling Fan for model I.C. Engines
« Reply #6 on: July 06, 2014, 01:16:55 PM »
When I decided to build an air cooled version of Edgar T Westbury's Seagull engine, cooling the engine was always going to be a challenge. An engine driven fan was considered, the fan wanted to be efficient and not draw on too much engine power. I thought of using an old power supply cooling fan but driven by a belt drive off the crankshaft. Talking it over with one of the electronics engineers at work he suggested using the 12v DC power supply from the ignition and running it through a bi-metal thermostatic chip so the fan would only cut in as required.

I chose a chip that closed at about 90 degrees C as it is around this temperature that most auto-mobile thermostats open. In use the fan works a treat and the engine will run for hours on end, it is a great source of amusement with my Grandson who regularly reminds me to top the tank up. The chip was sited at the rear of the engine so as not to be in the direct air stream from the cooling fan.

My best regards
Gray,

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #7 on: July 06, 2014, 01:17:00 PM »
This is the engine which the fan will be installed on. I am just waiting now for the fan itself, which is supposed to take a week to get here when ordered from Acklands of Canada.

Offline philjoe5

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Re: Cooling Fan for model I.C. Engines
« Reply #8 on: July 06, 2014, 02:00:43 PM »
Quote
The only trouble is, the engine runs terribly hot

Brian,
I'm curious, did you take a temperature measurement?

I'm sort of in the same boat.  My recently completed air cooled Bonzer runs a head temperature of about 285 F after a half hour run.  I was wondering whether this was a bit too hot.  Last time I mowed the lawn with my air cooled Briggs/Stratton the head temperature was 440 F at the end.  So I'm thinking the Bonzer is way inside the safe limit.  I do get some pre-detonation near the end running with Coleman fuel but I think I can eliminate that by switching to gasoline.

Not to say a fan wouldn't be a neat addition.  So I'll be following along here.

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #9 on: July 06, 2014, 02:04:24 PM »
Philjoe--I see that Princess Auto has a hand held scanning thermometer for $15 Canadian.  May buy one before I make this change just to try and get comparative figures.---Brian

Offline Ian S C

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Re: Cooling Fan for model I.C. Engines
« Reply #10 on: July 06, 2014, 02:32:59 PM »
Here is one of my early hot air motors with the fan from a computer driven from the motors own generator.  The motor is my version of James G. Rizzo's Dyna.     Ian S C

Offline philjoe5

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Re: Cooling Fan for model I.C. Engines
« Reply #11 on: July 06, 2014, 03:05:30 PM »
Brian,
That's what I used to take the temperature measurements.  Works great.

Ian,
I like that setup.  Would you have a video of it in action?

Cheers,
Phil
If you pick up a starving dog and make him prosperous, he will not bite you. This is the principal difference between a dog and a man.  - Mark Twain

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #12 on: July 07, 2014, 08:52:42 PM »
Well Damn!!!---And I do mean that with all my heart. I got a call today from Acklands that my fan had come in, so I rushed right over. The diameter was right. The hub bore was right.---But the direction of pitch was exactly opposite of the picture showed on their web page!!! I pointed that out to the lady on the counter, who immediately told me that was no problem---just turn the fan around. I think I was able to get it through her head that it wouldn't make any difference. Only changing the direction of rotation would make the fan blow instead of suck!!! She seemed a bit dazed, but said she would return it and there would be no charge. So---I guess I will build my own fan after all. Already ideas are percolating through my head. I would rather use brass than steel, because the hub and blades have to be silver soldered together, and I find the brass a tiny bit easier to silver solder, plus the color of the silver solder matches the blade color.---Brian

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #13 on: July 07, 2014, 09:27:42 PM »
Well---That doesn't look so bad!! The hexagon hub measures 0.541" across the flats x 3/8" long, the blades are .430" x 1/16" x 0.729 long. Overall diameter is still 2". I have shown the fabricated fan in a second model beside the overall assembled model to show better what it looks like. Of course, this will require some kind of jig to hold the blades in exact position while I solder them to the hub.

Offline Brian Rupnow

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Re: Cooling Fan for model I.C. Engines
« Reply #14 on: July 07, 2014, 10:07:11 PM »
Okay--this will work for a soldering jig. My only concern is that after I get one blade soldered on, will the heat from soldering the next one on make the first blade fall off. I can avoid this to some extent by cooling the assembly off between blades and "skipping around", but as more blades get added, this becomes harder to do.