Oil in my vacuum advance unit

[The73vetteman]

I just took out the distributor from my L48 to replace the shaft and get the tacho running again. Once I had it on the bench I noticed oil dripping from the advance unit, maybe as much as a thimble full.

Anyone got any ideas where this has come from?

For background, there doesn't seem to be any oil in the vac hose. I recently had the heads rebuilt with new valve seals. (It had been suffering with oil running down the stems.) The engine has only run for 30 - 40 minutes since reassembly so could the oil be due in some way to the valve seal problem?

Last point: how much force should it take to operate the vac advance?

 

[Jack]

That's a good one. Dunno about the oil in vac can? Which side of diaphragm is oil at?...distributor or manifold? Is the diaphragm leaking air (won't hold a vaccum)?

Great tech & specs links by going through the tech center button at top of page.

There you'll find this great link by Lars w/ specs of vac cans that should get you in the ballpark as to how many inches of mercury (vacuum=force) is required. http://www.corvetteactioncenter.com/kb/question.php?qstId=447

JACK:gap

 

[The73vetteman]

The oil came out on the manifold side of the diaphragm. I'm going to borrow a gauge to check if it will hold a vacuum.

Thanks for the link - lots of good info there.

'73

 

[wishuwerehere82]

It may be old evaporated gas residue rather than oil, and it is not unusual since it is hooked to the intake manifold, and has fuel/air mixture running in and out of it all the time as the intake vacuum increases and decreases. If it holds vacuum without leaking, I don't think you should worry about it.

If it is indeed oil, you may have a leak in your intake manifold gasket between the valley and one of the intake ports on the heads. Dump it out, and run it for awhile. If it reappears after a month or so, and it is oil you may need a new gasket set.
Not a big job. Good luck.