trike question: how necessary is the fan box on an exposed m

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I have a trike that I have been building over the last year. I have a 1971 type 1 engine that had the oil cooler inside the fan box. It was rusted out, and leaked, so I am replacing it with an external oil cooler with the oil filter kit that EMPI sells. I have this same conversion on my 72 Beetle, and I love it. My question is, unlike my Beetle where I need the heat from the motor to heat the inside of the car, the trike motor is totally exposed. So I am wondering if the fan box and fan is needed at all. It seems to me the motor would get enough air to stay cool on its own and would probably stay cooler without all of the tin on it. What would your opinion be?

[keifernet]

A motorcycle engine it is not... It would be toast pretty quick if street driven. You do encounter stoplights and traffic right? and what would your plans for a charging system be? Get a 36 horse fan housing if your going to mount the cooler elsewhere so it gets airflow when driving or is it riding in your case????

[[email protected]]

The charging system is an alternator connected to the oil block just like always. I guess my point to why would a fan be necessary in this application is the fan never blows directly on two of the pistons anyway. And with the fins exposed instead of wrapped in tin, wouldn't air be in greater supply? I still plan on an electric fan being added, but I am hoping to get away from that big ugly fan box.

[58Type2]

Actually if you have the 2 pieces of tin that mount on the bottom of the cylinders, the air that comes from the doghouse blows on all 4 cylinders, if not directly.

[Aussiebug]

The short answer is YES - you do need the complete fan shroud and fan.

The VW uses about 4-5 horsepower for it's cooling, and you WON'T get this from tooling down the road with exposed cylinder/head fins.

In fact cooling would be all over the place, as well as insuffucient.

The normal VW cooling has the air coming in from the top of the cylinder/head fins, pushed down/around the cylinders, and through the "gaps" in the heads, and then underneath it's pushed fore and aft through the underside fins by the flat plate deflectors mounted under the heads and cylinders.

This makes sure that all fins "see" the cooling air, for even cooling all round.

The doghouse VW cooling fan provides 25cf/sec at about 5psi above atmospheric, and the engine NEEDS this pressure as the air travelling through the fins expands as it heats and forms a mobile "plug", resisting the inflow of more air. The 5psi pressure is needed to force new air in and old air out in sufficient quantities.

Having exposed cylinders/heads in a trike would result in uncontrolled airflow around the engine, and not enough of it. The front cylinders would get a little more cooling and the rear ones very little at all. The rear sides of all four cylinders would get very little airflow and the rearmost exhaust valves would run VERY hot since that area would be "shaded" from the airflow almost completely.

So why do aircooled motorbikes just have exposed cylinders? Well, they adjust the size of the fins to suit, they place the hotter exhaust port at the front in most cases, and they don't expect anything like the life out of the engine as a VW gets - the uneven cooling always results in reduced engine life. The larger bikes use water cooling because of this - even cooling via the water jacket and then shedding the heat through the radiator.

Even when used in a light aircraft, the VW engine usually has a pressure cowling, which makes it work like the cooling fan and shroud in a VW - in this case you have a near constant 70-80 knot airspeed to give you the pressure, and the pressure cowling brings the air in over the top of the cylinders and turns it downwards so the flow is the same pattern as in a car). On those few aircraft which just have the cylinders hanging out in the breeze (Evans Volksplane and similar) the engine life is maybe 200 hours (in a car it's about 2000 hours).

Use the fan/shroud and ALL the tinware and your VW powered trike will give you reliable fun for a long time.

The 71 engine should have a doghouse fan and oil cooler (the oil cooler is in a "box" on the front side of the fan shroud). This is the best cooling arrangement for the VW engine - the amount of airflow to both the oil cooler and cylinders/heads is controlled by the engine speed, which closely relates to the heat being produced (horsepower being used).

External oil coolers are OK, but unless you put a thermostat and electric fan on them, they overcool in cold weather and undercool when sitting in traffic.

Regards,
Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.geocities.com/aussiebug1970/

[[email protected]]

That was the answer I was needing. I do have one more question regarding this subject. In VW Trends magazine, I see many bugs that the owner has done away with the lower tin and just has the upper tin on the motor. With what Rob just said, wouldn't these motors still heat and cool unevenly? It seems to me that the back two cylinders would be hotter that the ones just below the fan housing.

For some reason my motor did not have a doghouse fan and oil cooler. It is just like the pre-doghouse motors. I apreciate all of your answers.

[Aussiebug]

The lower cylinder tinware (underside plenum) is very important in getting the airflow right.

There is a high pressure area under all cars and the plenum tinware is designed so that the used cooing air is turned backwards to the rear of the car and is sheilded from the high pressure turbulence under the car.

>It seems to me that the back two cylinders would be hotter that the ones just below the fan housing.

Well - in fact the fan sit squarly over hte centre of the engine, but since the cylinders are offset one side to the other (to allow the crank throws to work), the shroud side slightly forward on one side and slightly aft on the other. That's no biggy in itself - the tinware guides the air whaere it needs to go, but yes - cooling will be reduced if there is no under-side plenum tinware in place. Even if you have J tubes instead of heat exchangers, and the area where the heat exchangers were is now exposed (they formed "sides" to the underside plenum); new sides should be made up to cover the plenum in so the used cooling air can only escape out the back.

Re the non-doghouse cooler - I've seen later engines rebuilt with "whatever is lying around" and it's amazing what a mixture you can get. As an example, I recently saw a 69 bus with 71dp 1600 engine, retrofitted with a non-doghouse shroud and single port heads (probably from the original engine), with a 30PICT/1 carby from about 66. It was a real bitsa (bitsa this - bitsa that) but he'd just driven it from Queensland to Victoria and then over to South Australia (where I live), and it ran fine.

In the lightly loaded trike, it's not a big problem if it's got a non-doghouse cooler. If all the tinware is in place and well fitted, it will cool the engine just fine.

The D, E, F, H and B series engines used the older cooling shroud and the double-letter engines (AB, AC, AD, AS etc) used the dobhouse cooler.

The only word of caution if it's been retro-fitted with a non-doghouse shroud - it should then also have been retrofitted with a No3 retard distributor. It's easy to check if you have one or not - time the engine normally on No1 cylinder and then check the timing on No3. If the timing mark has now moved a few mm to the left - it's a "retard" distributor for a non-doghouse set-up. If the timing stays in the same place when you check No3, then it's an even firing distributor for the doghouse cooler engines.

009 distributors can be either - they started making them before 71 (non-doghouse) but the later ones are even firing, so you SHOULD check them too.

Regards,
Rob
Rob and Dave's aircooled VW pages
Repairs and maintenance for the home mechanic
http://www.geocities.com/aussiebug1970/

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my uncle told me about a bug that some one cut up made a convertable out of it, and had the engine complely exposed. the only tin on it was the tin that mounts under the cylnders between the pushrod tubes. it only had the alternator stand! my uncle is tim, and you most likely see him on the site all the time, except lately, he has been slacking. his e-mail is [email protected] if you want to ask him about it. the guys response to my uncle asking him if it overheated was: does a motorcycle over heat? i guess you will have to figure it out for yourself
bjorn