Friday, June 1, 2007
HELP? (More on Plugs)
Help? About a dozen people asked that as they tackled the 1/2"-NPT thread for the bushing that accepts the oil temperature sensor. Relax; it’s no big deal. Clean things up then just follow me through.
National Pipe Thread or NPT has a taper of 3/4" to the foot. To cut a smooth NPT thread you begin with a hole that is big enough and has the right taper.
Root-diameter of the hole has to be at least .77". Since 1/2-NPT only has about half an inch of thread, the bottom of the hole has to about .015" smaller than the top or .77-.015 = .755... which is pretty close to 3/4" so start with that. Then open it up with a 47/64" for a depth of about a quarter of an inch and try your tap.
No guarantees for the above. I usually start with an 11/16" hole then use a 1/2-NPT reamer. The point here is that tapping the hole is no big deal if you start with a hole of the right size. (CAUTION: Too big a hole and you’ve screwed the pooch.)
HEADS & OIL
Several people expressed surprise that oil for both heads gets there via a single 5mm drilling... which can be partially blocked if the wrong aluminum plug is installed. Here’s a picture of that particular plug, now replaced with a 1/16-NPT pipe plug. But don’t take my word for it; go see for yourself. A fiber optic light-wand or even a length of safety wire as probe will allow the engine to explain things to you.
Yes John, you can plug the cooler ports, as shown in the pix. The oil cooler is then installed downstream from the oil filter. No, I’m not saying you have to do it that way, I’m simply saying that’s the way I do it; you may build your engine anyway you damn well please. Thank you for sharing your opinion. You may be sure I’ll give it all the attention it deserves.
On ‘71 & later engines you’ll need a 1/4-NPT for the outlet port (ie, the one nearest the flywheel). 1/8-NPT works okay on the inlet, for both old & new crankcases.
Some years ago I had the line to the oil pressure gauge break on me. It was only an eighth-inch line but it didn’t have a metering orifice installed at the engine nor was it fitted with a shut-off valve. Lotsa fun :-)
Since then I’ve used an electronic oil pressure gauge whenever I can. Unfortunately, the transducer is fairly massive, plus it completes its circuit through the crankcase, meaning you gotta twist it tight. Mounted in the original location, jutting out to the side, it tends to work itself loose, resulting in an oil leak and erratic OP readings. So I’ve taken to mounting it vertically, with a diagonal stay between the body of the transducer and the existing oil cooler pad. But I still use the stock OP port. That’s where I connect the garden sprayer I use as a pre-luber, before firing up the engine.
On the front of the engine (Front means FRONT on Volkswagens) you can see where I’ve installed 1/16-NPT pipe plugs in the oil galleries serving the cam followers.
On the main oil gallery be careful not to install the plug too deeply as it butts up against the drilling that carries oil to the #1 cam bearing. And to the oil pressure control valve. That’s the two plugs underneath the main oil gallery. The upper one is the drilling for the pop-off port, which dumps excess oil into the crankcase at the outboard end of the cam-follower for the exhaust valve on #3 cylinder. The lower plug seals the drilling that allows leakage past the control valve’s piston to escape into the sump.
FULL-FLOW OIL FILTRATION
On the pulley-end of the crankcase you can see where I’ve threaded a 3/8-NPT to AN8 hose fitting into inlet to the oil cooler gallery. This is immediately adjacent to the port to the oil volume control valve, which on racing engines is usually opened up and replaced with steel seat for a ball-valve, doing away with the usual piston. The oil volume control valve port is 6mm in diameter. When you plug the oil cooler ports it’s customary to open up this port to 1/4" or even 5/16" to ensure adequate cold-oil flow. Also note the 1/16-NPT for the #4 main bearing. This drilling intersects with the drilling for the #3 main bearing and when plugged, forms a blind corner that likes to trap swarf. The upper-most plug is 1/4-NPT and marks another blind corner.