My O Pinion,, It was necessary to put tooling in from there to make the oil passages, so, they had no choice but plug it. Just so happens, its handy for folks who want to slap an oil cooler on.

& while Lancer is correct in How the port is used,l still think the ports came into existence not by an engineer simply wanting a plug there, but because they had no choice. If the wanted an oil galley, they had to drill it, so theres a hole that must be plugged. If it was just so theyd have a way to hook up an oil gauge, then there would only be one.

I have a different opinion, see if you can catch me:
The engine was at the beginning in a different frame, the Tempter a 400 cc engine. The plug could be removed to drain the oilfilter housing.
If it was only there to make an oilpassage the engineers would save the machining and installation of a threaded plug. Instead the would have plugged the hole with an alluminum plug, permanently.
BTW the plug facing forward is indeed for the oilpressure gauge.

I'm trying to figure something out from the diagram above showing the direction of oil flow, specifically the part highlighted in pink.

With a pressure gauge connected to the front-facing "out" port, oil still flows through the crossover to the passage in the clutch cover. Here's where my tiny brain starts to go, "Huh?" How do they get an accurate pressure reading when oil doesn't particularly "need" to go down that little dead passage to the gauge? I don't doubt that it works, I just don't understand exactly how. So there's pressure pumping through the system and oil will go wherever it can. Is it that even when the oil can't go anywhere, pressure is the same everywhere? Is it that the pressure isn't just in the direction of flow, but in every direction?

Now for part two of my brain fart. If there's an oil cooler connected between the two highlighted ports, it seems to my tiny brain that only part of the oil would flow through the cooler while the rest flowed through the crossover. If that's the case, then at what point does the resistance in the oil cooler and lines have the oil thinking, "Screw this, I'm taking the shortcut," leaving very little willing to make the schlep through the cooler, leaving it full but rather stagnant? Or does the thermal change encourage flow through the cooler?

There's a right angled turn to go thru the cover port, so like most things oil will tend to go straight.  This creates a stagnant pool for the oil pressure to accumulate, giving a more accurate reading of the oil pressure.  And I think the cover port is slightly smaller than the passageway.

BTW, pretty sure all the plugs are the same size.

HEY!    I got's one of those port adapters for the pressure port.  We've been discussing pulling out one of the plugs in the head cover to mount a pressure gage.  No need, there's one of these plugs holding in the rocker shaft.  

verslagen1 wrote on 01/05/11 at 17:22:09:


I measured them a little while ago. The one in the crankcase is an M14 while the one in the clutch cover is an M12. Both are 1.25 thread pitch, though.

MotoBuddha wrote on 01/05/11 at 17:31:29:


Well dag gummit, you're right.  
front plug and rocker plug are M14.
bottom plug, oil drain and sparky are M12.