I'm fairly certain of the answer but just wanted to run it my you.
As you know I'm getting my T ready to crank and am just tying up loose ends. I took apart and thoroughly cleaned the oil sight gauge that goes into the bottom threaded hole with an original type petcock in the upper hole.
Although my sight gauge has small round rubber gaskets at the top and bottom of the glass tube (protected by a brass housing), I'm dabbing some "Right Stuff" RTV sealant on each end of the glass tube to make it really oil tight.
There is a long slot headed machine screw that goes all the way through the glass tube and threads through the bottom and once tightened is locked in place by a square nut which I have also sealed with RTV at the bottom.
I was thinking about applying RTV around the screw head to keep oil from escaping out the top, but then thought that, if I did that, I might be making it too air tight in not allowing a way for the air in the tube to escape so the oil could rise to the level in the crank case. If I do not apply RTV around the screw head at the top, will that be sufficient to allow air out of the tube so that oil can rise to the correct level in the tube?
Shouldn't the crank case be filled until the oil level is about halfway between the two petcocks? Jim Patrick
I must have a taller sight gauge than you have. Years back I drilled a tiny hole in the cap so it would read the oil level correctly. I also replaced the glass with plastic tubing from the hardware store...
You don't need to seal that screw head or the rubber gaskets either. If the rubber gaskets are old and hard, cut some new ones out of rubber or vinyl hose. The trick to it not leaking at the top is to not add too much oil. At four quarts, mine came slightly under the top of the tube and it didn't leak. I think the next oil change I will stop at a little less that four quarts just to be sure.
Also, you must be certain that it has a way to vent the tube. Mine, which is the common one sold by the vendors(30790 at Langs), had no provision (that i could see), to vent the tube. I thought that maybe the screw originally had some sort of washer that allowed venting under the head of the screw and was lost. I tried to make one to no success and finally, simply filed some slots on the top of the tube under the screw head and it works like a top. I think that the oil level is accurate now since it goes down with the engine running and comes back up when i shut it off. I didn't drill a hole in the top because i was afraid it might leak but now i think that would have been the best solution.
I was about to pull it off and put something different back on but now i am very happy with it.
I agree with Roger. I have one and wouldn't wish otherwise. But it IS a GOOD idea to check it before you start AND when the motor is running - to check that it's empty and not blocked or stained.
Jim, I'd take Micheal's advice above a switch the glass tube out with acrylic.
My glass oil sight gauge works best on the shelf in my workshop. I replaced it with the std. dipstick that all T vendors offer---I can get an accurate oil level reading consistantly by just looking under the hood and reading the level on it. YMMV!-----Paul
I'm with Paul but then, I'm not too worried about "originally". I had an eyeball to eyeballs? confrontation with a Black Widow spider a while back under my car, when it was parked for a long period of time.
I drilled a small hole in the top of mine. Work fine that way. Acrylic might be good, but wouldn't it be more incline to fog and stain?
For those readers who use the petcock as the oil stopper:
8mm clear vinyl tube is a push fit onto the petcock (eg VT081 from Bunnings in AU);
8mm elbow and tee fittings available also.