[djustice]

I got the chance to borrow a garage with a pit for a day. so i did some testing. started car fully warmed up til fans kick on .

At idle there is no leak at all . i got a person to stay in the car and press the throttle, after about 30 seconds at about 2-3000 rpm i could see a tiny amount comming from the lip on the hump running back towards the centre rubber nub and collecting around that nub, but very slowly.

I removed the pan all pan bolts. and found that i had used silicone against the rear main camp, but no silicone between gasket and oilpan hump, so i brake kleened the hump on the pan about 4-5 times and i also got a q-tip with brake kleen barley op to scrub the gasket for oil.
Used a liberal amout of RTV ultra black let it set up for a little while then loosley tigthend the oilpan bolts, let is sit for just under 1 hour.

Repeted the same test again with no leak. for good mesure i backed the car out and took it for very short but spirited drive up to about 5000 rpm (1.st gear since i was drivng to densly populated area. Back on the inspection pit i found it had started leaking.

From this i can only assume i am not pulling a vacuum in the crank case with my current pcv system. I am heading up the later today with a vacuum gauge (messures both vaccum and pressure) so wil do some testing with a fixed orifice valve i made myself with a 0.100" opening and a standard motor PCV Valve V112 . After doing some reading on this forum it seems the old stock valve for a pontiac 455 i guess flowed about 4.5 cfm.

To find out what orifice size is needed at any given vacuum i found an intresting chart at an aircompressor site:

Vacuum Flow Through Orifices
Figures in body of chart are in air flows in SCFM (Standard cubic feet / minute)

Orifice Diameter (In)” Vacuum in inches of mercury
2″ 4″ 6″ 8″ 10″ 12″ 14″ 18" 24″
1/64″ .018 .026.032 .037.041 .045 .048 .055 .063
1/32″ .074.100 .128 .148 .165 .180 .195 .220. 250
1/16″ .300. 420. 517 .595 .660 .725 .780.8801.00
1/8″ 1.20 1.68 2.06 2.37 2.64 2.89 3.12 3.53 4.04
1/4″ 4.78 6.74 8.25 9.52 10.6 11.6 12.4 14.0 16.2

Source: https://trident.on.ca/engineering-in...orifice-table/

[djustice]

I am back from the testing, and i had currently no vacuum in the crank case. i removed 1 of my 2 breathers, and locked it off, fitted the home made fixed orifice pcv but was still not pulling vacuum.

So i put a restrictor in the fresh air hose breather going from passenger side valvecover to the aircleaner now i had 3 inhg constant vacuum. at idle and at elevated 3000 rpm free rev.

Ging to see if i can boroow the inspection pit again and confirm that this reduses or eliminated the oil leak.
I am feeling hopefull.

[jamaca85]

have you checked the rear of the pushrod cover (valley pan)?

[djustice]

Yes , everything is dry, every gasket and seal is new, less than a year. it is only the rear lip of the the oilpan that drips under elevetad rpm, that i am almost certain is beacuse of pressure and not vacuum in the crank case.

[djustice]

Update: I passed the second inspection. wheel cylinders replaced, and the 6 contact points where the brakeshoes rest was coated with copper grease, it took 2-3 tests on the rolling road brake tester for the brakes to grab evenly and with the same force. I drove it about 200 yards from where i fixed it to the inspection station so no brake testing was done before the test.
Now for The oil leak; i resticted the fresh air hose going from the aircleaner to the valvcover so it had less flow than the pvc valve hose pulling 5.5" inhg of vaccum on the crank case. i got a comment on a hanging oildrop, but it did not hit the floor so i passed, but apparantley just barley.

I can't help but think about modern cars and their undertrays. i dont think i have ever seen a clean undertray on "newer" car when you snap it of to change oil, there is always fair amount of oil on that tray. We are at a serious disadvantge on older cars where eveything is exposed.

Edit: this was the last ever inspection as the car is now 50 years old and is registerd as a historic vehicle, it is now exempt from inspections.