Lower cooling tins? (under push rods)

[petew]

Just got a 56 oval today. Upon checking, the (judson equipped) 40hp motor is missing the two cooling tins that come down from the back of the motor and run under the the pushrod tubes. The motor is also only running J-pipes as opposed to heater boxes and original exhaust pipes. Hence why I think the engine builder left them off.

I live in Sydney Australia and it gets kinda warm down here. Is this lack of lower tins a serious issue? Do I need to find a set or will it be ok?

[theKbStockpiler]

The best explanation I have read is that this piece of tin keeps the air flow that the top tin creates the way it should. Otherwise ambient wind and breezes will effect the intended air path. It's not worth not having them on for what they cost. Also without the sled tins , the air does not wrap around the cylinders/heads and does not proceed towards the cooling plate. The cooling plates makes the air wrap around the inside circumference of the cylinders. The stock vw cooling design was well planned and is not overbuilt so you should have all of it's parts installed.

[Marc]

Until early in the `63 model year, 40HP engines didn't have "sled tins" - they used NFA heater boxes similar to those found on 25/30/36HP engines (but not interchangeable with them). Early cases therefore lacked the two m6x1.0 threaded holes in the bottom of each case half where "sled tins" would normally attach. I hope that your hotrodded engine is built on a later case with insert cam bearings (9xxxxxxxxx or "D" case), but if it isn't there'll be nowhere to attach the sled tins on their inboard edge. That's not a big deal if you can support them adequately from the outboard edge at the exhaust pipes, just don't let them chafe against the case if they aren't secured to it.
Since 40HP sled tins were only used from early `63 through `65 (in the US market, anyway) they could be a little hard to find. They're about ¼" narrower than the 13/15/1600 bits. Early ones had a 1-piece RH component with a round access hole to reach the thermostat bolt; later versions had a 2-piece RH part similar to 13/15/1600 - just narrower.

For your unique application, I'd try to emulate what was stock on gas-heater-equipped 181/Thing/Trekker vehicles.
You probably don't have any sort of functional thermostat system (too bad, engines tend to last longer with one) so it's not of paramount importance to keep the spent/warmed air coming off of the heads & cylinders captive in order to optimize the thermostat action, but it's still worthwhile IMO to have the sled tins in place if only to protect the pushrod tubes from road hazards.

[petew]

ok, I think I could bend something up from some sheet metal that would work.

[Marc]

http://www.thesamba.com/vw/forum/viewtopic.php?t=401943

[aussiebug]

If you read that Samba topic, and the stuff above, you'll note that several times the sled tins are described as "protecting the pushrod tubes".

Yes they do that, but MUCH more importantly, they direct the hot used cooling air out the back of the car. If the underside plenum (sled) pieces are missing, the used cooling air just spills down under the car. Unfortunately, the underside of every car has a lot of turbulent high pressure air there, so the used cooling air cannot escape smoothly, and cooling suffers. Without the tinware in place, the hot used cooling air also spills around the rocket covers, which are part of the cooling system (there's a lot of hot-oil splash on the inside of the rocker covers). And if you find THAT hard to understand, then think of this - in the 60s, VW supplied "arctic kits" for VWs operating in super cold climates, and these contained bright shiny alloy rockers covers which KEPT SOME HEAT IN THE ENGINE. The stock black rocker covers remove a measurable amount of heat and don't need used cooling air interupting that job.

VW never spent a cent they did not have to, but did a lot of work with the cooling system, keeping the upper side of the engine sealed from the undersides, and directing the cooling air very carefully, both into and out of the engine finning.