Stock Oil Coolers. AIR-TECH

In this article we will talk about the stock oil coolers main on the upright engines. For those of you with pancake style motor, please read as a lot of it still applies. I will take you through what I think happened at the factory and what they did to improve upon the first design.
        The first style oil cooler came in motors up to 1970. There were slight differences in the cooler but the concept and function were still the same. It was a metal cooler that stood up in the fan shroud. Right  in the air path of number 3 and 4 cylinder. Now this did work ok on the early motors (as in 36hp and 40hp). Why? Well for one those motors had 7 to 7.5 to one compression. As you know, the higher the compression the more power and more heat. As the motors got bigger (1300,1500,1600) the compression went up to 8 and 8.5.  Yes more power but that came with more heat. Does the early cooler work in the bigger motors? Kind of. One thing to note here, is next time you have the fan shroud off look down on the cylinder tin. You will notice it’s not centered over the two cylinders – it favors number 4. In other words number 3 cylinder is kind of tucked back in the tin. And what cylinder usually has problems? Yep, you got it, number 3.
        So let’s look at the path of the air that goes over 3 and 4 cylinder with the early style cooler. Air comes in the back of the shroud; then blows through the cooler, heating the air as it leaves the back of the cooler, then over 3 and 4 cylinder, favoring number 4. So the air is now hotter than the air blowing over 1 and 2 and we are not blowing as much air over 3 as we are 4. Is this a problem? Well it can be. Hanz and Franz at the factory must of thought so as they changed it along with other things in 1971. They came up with what we call the dog house cooler system. Why is it better? Read on.
        My guess is Hanz and Franz at the factory saw what I just explained and solved the problem by moving the cooler out of the path of 3 and 4 cylinders. This is what they did - They made an adapter that would kick the cooler out of the path of the air that goes over 3 & 4 and give it its own air path that would not heat up those two cylinders. The cooler bolted to the adapter and basically now was on the back side of the fan shroud. They made the cooler out of aluminum which would shed more heat faster. They then designed the fan shroud with ducting to blow air through the cooler out the back side of it and down under the engine. To do this they also had to make a wider fan. This wider fan gave the shroud more air as they were using some of it now to blow through a cooler and out on the ground. A much better design. Now number 3 and 4 cylinders don’t get the preheated air that the earlier design had.
        Can you put this newer style set up on an older engine? Yes, but please get all the pieces. Here is a list of what you should have: Adapter, cooler, fan shroud, rear ducting tin (the two pieces the bolt to the back of the fan shroud), rear bell housing tin that has the hole in it for the ducting tin, wider fan and the correct oil cooler seals for what you’re doing.
        Now the important part - installing all of this. This holds true if your motor is a later motor and already has all the pieces. Bolt the cooler to the adapter. Then the adapter to the case with the correct seals. If you’re not sure which seals to use phone a friend and make sure you get the correct ones. Now the part most people miss. I use camper tape the widest stuff I can find. I place it on the cooler from front to rear over the cooler. In other words; start your foam tape at the adapter and go over the cooler and down to the two nuts the hold the cooler to the adapter. If you do this you will make a tight fit in the fan shroud. That way the air has to go through the cooler and not around the sides. Make sense? Ok now onto the fan. Take your old narrow fan off the gen/alt and throw in the neighbor’s yard. Install the new wider fan and test fit the whole set up in the fan shroud and give it a spin. If you don’t hear any rubbing then you’re good to go and bolt the gen/alt to the shroud. If you do hear rubbing you will need to shim the fan so that it doesn’t rub the shroud. Now place the shroud onto the motor. It should be a snug fit on the cooler. We are half way there. Place the bell housing tin on, leaving the two screws that hold it on loose. Then the two rear ducting tin. The bottom piece had two rubber gaskets to insure an air tight fit. Well as air tight as it can get. If you don’t have the rubber gaskets use something to fill the gaps. On the top tin you will notice a step where it meets the fan shroud. That had a piece of foam in it from the factory. I cut down my camper tape and place it in the step. Now go ahead and install that. Look at it all and see if you have an air tight fit. If you do then tighten all the screws. You’re now good to go.
        I have to say the stock tins fit way better than any aftermarket tins I have seen. You can get the aftermarket tins to work, which I do all the time, but you will have to work at them to get them to fit and work right. One other thing here, if you have a street car or any car that the engine compartment is enclosed then yes all that tin is very important. We want the hot air to exit under the car, not get sucked back down the fan. On open air cars: ie. baja or sand rails, trikes etc, then I leave off the bell housing tin and the two ducting tins.
        So there you have it. I have to give props to Hanz and Franz at the factory, they did a great job improving upon the earlier cooler