Removing the air deflection shield on 4 stroke engine

[michael whiteman]

Seeing as these engines are not any longer used in a stationary application and are moving down the road with air flowing over the fins, is it still necessary to retain this shield? How many of you have removed this?

 

[Chainlube]

Seeing as these engines are not any longer used in a stationary application and are moving down the road with air flowing over the fins, is it still necessary to retain this shield? How many of you have removed this?

Even though you're moving the covers, especially the pull start side, are an important part of the cooling system. The fan moves more air than riding.

 

[Old Busted Hotness]

I removed it with no ill effects. Pretty rare for a power washer to hit 25 mph, and at idle there's still air moving from the fan.

 

[JerryAssburger]

I had pondered that point in another thread- my thinking is, keep the shrouding on, since the engine and finning were designed for it. If you look at a typical non fan-cooled motor, they have pretty healthy sized fins compared to a fan-cooled motor. Also, from the Olde Days, when people were yanking their belt-driven fans off of their cars for those precious-few extra horses, the recommendation was "anything over 35mph doesn't use the radiator fan". My bike doesn't see much over 25mph, typically.

Now time for some REAL NERDISM... I found, a few years ago, an engineering paper written by the developers of the Kool-Bore engines for Briggs & Stratton. It was absolutely an amazing read. In it, they spoke of stress-testing the prototypes by blocking fins, removing fins, removing fins from the flywheel, etc, to see how the design would fare... the astounding part that they found, was that the one piece aluminum block did a great job of conducting heat from the hot-spots, down to the crankcase and whatever the motor was mounted to. And it makes sense, in the case of a typical B/S Flathead... they generate roughly 1hp for every 3 cubic inches, so they're not a stressed design, stock. NOW- can I find that paper or webpage ANYWHERE on the "net" now? Nope. If I ever DO find it again....

In the case of the HS 142F and 144F motors, I'd think that they NEED the cooling in place, because they are spinning much faster and putting out almost double the HP per cubic inch of a B/S flathead (stock).

 

[michael whiteman]

Thanks for a scientific answer there Jerry. What you have stated makes sense.

 

[JerryAssburger]

Thanks for a scientific answer there Jerry. What you have stated makes sense.

Thank you- this might be the One Time this year, that I did something right.

 

[Nirve]

I am using a permanent temp gauge on my spark plug and I have not noticed a higher temperature at all without the metal air flow covers.
Have not tested removing the shroud.

 

[JerryAssburger]

My ride to work is 5 miles each way, and it's funny how the little bugger doesn't heat up that much. My exhaust pipe is turning colors, but the block- you can pretty much hold your hand to it. Amazing little motors.

 

[Cannonball3]

This is a 45 yr old Briggs cool bore 3hp that I trimmed the cylinder fins on and removed the airguide. It had a flat aluminum casting over the fins in the front and sheet metal one on the side. I rounded the cylinder to look more motorcyclish.
Most of the cooling is done on the head any way. As Jerry said these are low out put engines, but I do run it pretty hard. Never any issues. The Rotax light aircraft 2 strokes could be run fan cooled or free air. They of course had to have proper airflow, and the twins had baffels to catch and duct the air thru the cylinders. If you ride a lot of traffic definately leave all guides in place.

 

[darwin]

More heat will reduce the lifecycle of the motor if you use common sense thinking. Science may say otherwise but no data to back that up yet in here. Think about a car engine, more heat is not good for it. Designed to run at 195/220deg, any more and things deteriorate faster.