Engine Tinware

I am assuming that you are speaking of either the roughly 3" square pieces of tin tucked up right below the cylinders or the tin that is connected between the engine case and the heaterboxes (heater channel tin). The 3" square pieces of tin is really important because it serves to route the air along the fins on the underside of the cylinders. Higher pressure air has the tendency of looking for the path of least resistance to an area of lower pressure. Thus, without that tin, it would just go right between the cylinders to the outside without ever touching the bottomside of the cylinders.

I guess folks think that the heater channel tin is there only to protect the pushrod tubes from road debris. But it also serves to complete an air enclosure (plenum as those HVAC people would call it) to maintain and control a flow of cooling air around the pushrod tubes (which are carrying heated oil from the heads back into the case). So, these are also important; make sure to replace if they are missing. I personally believe that these would be hard to copy (there are 3 pieces). Plus, there are folks who sell new ones. Or you can look for a junk engine, and clean and repaint its original German tin (my method).

Don't forget the Rear Deflector Tins that you can see against the rear side of the cylinders when you remove the rear breast plate as well as those little 1" square pieces of tin that snap up below in the middle of the heads. I remember a good article about the cooling system on

Geoffe Elias '74 Super Beetle

Thanks

I was referring to the tin between the engine case and heater boxes. I strongly suspected it affected the cooling due to air pressure changes, just wanted to confirm! Fortunately only the centre piece, the one below the pushrods was missing, so it was quite easy to make, just a bit of flat metal cut to size and a lip bent into it. The problem with this engine was that it was missing a few important pieces, luckily I've got most of it that was the last of it.

Thanks for the help Regards Kevin

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Dear Kevin (and the Group),

The pieces comprise the lower plenum chamber.

On aircooled engines there is an optimum ratio of inlet to outlet pressure. For a given air-density the pressure dictates the rate of flow. This is usually referenced by the differential between inlet & outlet, expressed in inches of water. On engines fitted with cooling air blowers (as opposed to aircraft engines which use only ram-air pressure) the differential is generally rather high, typically around 9" of water.

The lower plenum chamber and the area of the outlet of that chamber, ensure even distribution of the air flow down through the fins. If these pieces of tin-ware are removed the forward motion of the vehicle can raise the pressure under the vehicle to such an extent that the flow of cooling air down through the fins will be upset.

In addition, the thermostat is installed in the lower plenum chamber on the right-hand side of the engine. IF the lower tin-ware is not present and properly installed, the thermostat will not respond in the proper manner.

The engineers at Volkswagen knew what they were doing. Everything on the engine is there for a purpose. Removing some (or even all) of the cooling system compoents will not prevent the engine from running but it WILL shorten its life.

-Bob Hoover

Thanks Bob,

I rather suspected it had something to do with cooling. Thanks for the explanation, it was very informative. I'm definitely not thinking of removing them, in fact I had to make up one using flat metal, it seems to be working, but time will tell.

Regards Kevin

If you have the metalworking tools still out, you should definately make one or a bunch of these too:

They are frequently missing or rusting away. There's no replacement part that you can get anywhere new. But, they are just as vital as any other piece of the cooling system because it makes sure that the oil cooler is perfectly sealed to get 100% of the cooling air to go through it and not around it.

Geoffe Elias '74 Super Beetle

While we are on the tin topic........I have a quick question for Bob. I have all the correct 1600 dog house tin in place including the "Hoover Bit." The new Mexi type thermostat opens properly when warmed up. Should there be a noticeable rush of air through the doghouse outlet or is it slower and more subtle? I know there is no blockage in the tin. I sort of expected more of an an air rush through that assembly. Help? Eric 68 Bug 62 Ghia both topless

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Yes, there is an appreciable flow of air through the cooler's core even at an idle. (The thermostat controls the flow of air down through the fins of the heads & cylinders.)

Make sure you are using the proper FAN. It is about 10mm WIDER than the non-doghouse fan. The wider fan is what pumps the air into that collector scroll you see on the front of the blower housing, which feeds directly to the oil cooler. In effect, the dog-house oil cooler arrangement is an EXTERNAL oil cooler since it is entirely separate from air used for cooling the engine.

The dog-house conversion article in Hot VW magazine makes no mention of the gasket bracket needed to keep the oil cooler housing in position at high rpm then goes on to say that the wider fan is OPTIONAL... that the system will work with the original fan. Which is dead wrong.

Lots of posts on this topic here and on the bus mailing lists.

-Bob Hoover

-PS -- Lots of folks call the sealing frame 'The Hoover Bit.' It's not mine, I simply pointed out that it is a necessary part of the installation. (Next thing I guess is to call the wider fan a Hoover fan... or the required barrel nut a Hoover nut :-)

.....please no pictures of Hoover nuts...

...Gareth

I think we know who the Hoover nut is... ;-)

Max

I hardly ever work on Beetle engines, but when I do, I'm always worried about this. Can you tell me a simple way to tell whether I have the right fan and shroud combination?

Exactly how thick are the two latest type 1 fans at their outer edge?

How many different type 1 fans did VW use?

Is there some rather fixed amount of axial clearance between the outer edge of the fan and housing that I can compare to make sure I have the right parts?

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----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Could someone explain what a barrel (Hoover) nut is? I did a doghouse conversion on my 70 bus last year and thought I had everything correct including, Hoover bit, wide fan, weatherstrip, correct offset flap connecting rod, etc. Phil

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