Oil in intake manifold

[gaPhil]

So a while ago I during a carb swap I noticed oil pooling in the bottom of the intake manifold. I took the manifold off and noticed some of the intake studs were only finger tight and when I took them out some oil pooled in the threads.
My thinking was that oil was drawing out the intake studs and getting sucked into the manifold.
I sealed up the threads and reinstalled, thinking I had solved the issue.

This week I noticed that the problem is still there, oil pooling in the intake.
Other than the intake studs not being sealed up well enough, I'm stumped as to where it is leaking from!

NOTE - the crankcase breather is connected to a catch can and not hooked into the intake.

Anyone have thoughts on why/how this is happening.

[yno26galant]

is it acutally getting any blow by? do a leakage test ? maybe one of ur valve guide seals is letting the slightest oil thru.

[gaPhil]

I thought about that, but how would it collect in the bottom of the intake?

I had a good look at the head today and couldn't see anything unusual. There didn't seem to be any oil residue on the tops of the intake runners in the head. Stems seemed ok.

[gaPhil]

Couldn't see any cracks anywhere either.

[tandanus]

Porous head?
They are common at this age and its really difficult to detect.
Worth a check....
T.

[Superscan811]

The only reason for oil on the intake runners is either the vacuum port or the valve guides.

If there is a lot of blow-by (bad rings), the catch-can may not be catching all the oil.

Most likely, it's the valve stem seals, as the standard ones tend to fail quickly.


From memory, 8mm Gemini valve stem seals are a direct replacement for the standard ones and they tend to last longer as well..


Cheers.

[gaPhil]

The head is reconditioned though.

Catch can has a breather connected, not hooked up to the intake at all.

There was some oil leaking from the oil filler cap onto the rocker cover and running off. The air filter was clean, but is it all possible the oil soaked through the intake gasket, like around the back of the thermostat.

I can't see how valve stems would leak oil back to collect in the intake.

[LukeAussie]

Hmmm, no I wouldn't have thought there'd be an issue of leaking through the stems, not into the inlet anyway.

Is it definitely oil in there, and not some other fluid (gasket goo/water/some mix of the above?) The only thing I would have thought is the suction line pulling from the top of the rocker cover, but you say you've removed/put in a catch can. A possible suggestion is to use some clear hose to link that up and see if any gunk is actually flowing through.

Interestingly, does anyone know what the exact purpose of that suction line is, and how important it is? I have a feeling since my last carbie recon that I'm getting too much suction and it's affecting performance. I'm considering plugging the vacuum line and blocking the hole on the rocker cover. Had that set up on a previous Gal (and she flew! Never been able to get the same thumping performance out of my Orange baby), but also don't want to adversely affect anything. As far as I can tell, it's just for emissions purposes...

[davetrees]

It's just a breather for the rocker cover ..... there is no significant suction on it.

The amount of "oily air" going through a tube that small into the intake would make no significant difference to the fuel/air ratio, I expect.

[gaPhil]

I think it's a hairline crack in the head somewhere near the intake.


Time for a head swap me thinks.

[LukeAussie]

Hairline crack sounds nasty... Hope you sort it out soon!

Just on that suction line on top of the rocker cover, once we overtightened the bolt and I think the brass tube was a bit close to the oil in the head, and boy did it suck up plenty of oil. After installing some new rings, the car was blowing smoke as if it was sending smoke signals home to Japan! It was funny to see, but sad after having done all the work. Since everything was new, we figured it must have been from that suction line, and replaced it with a clear hose. In about 30 secs of running, the tube was black! So we changed the under-side of the brass tube, and put some spacers in there, and then the only thing coming out the exhaust was good ol' CO2 :-)

It may be a small hole, but has some nasty potential :-)

[gaPhil]

I put the intake back on the car the other day because I think I'll need to swap the head anyway to fix the problem.

I took it for a drive and left the breather open with no filter. There was no signs of oil coming out.
So I think the motor is ok, which makes sense seeing it has good compression.

[BAD-SIG]

I had a similar problem with my reconditioned Astron II. But to add to my sorrow, there was mainly coolant in the intake and a little bit of oil. So I thought it was a cracked intake manifold, so I swapped it with a better ported one I had spare and problem still there. So I decided to remove the head and check the head gasket and head. So far, the head gasket was 99.9% ok with only very minimal oil and coolant starting to push itself past the holes, but not leaking yet. The problem then must be a small casting crack in the intake side of the head somewhere. The worst cylinder was numbers 3 and 4, near the rear coolant passage that goes to the intake manifold. The engine oil was clean and without metal or coolant. The coolant was also clean. Quite strange.

[Superscan811]

Hmmm, no I wouldn't have thought there'd be an issue of leaking through the stems, not into the inlet anyway.

The inlet ports are in vacuum most of the time so if the guides/guide seals are worn, the oil will get sucked in by the manifold vacuum.

The exhaust ports always have pressure so unless there is a lot of wear, you won't get an oil leak from the exhaust guides.


Cheers.

[gaPhil]

Bad-sig you're problem sounds very similar.

I'm not really any closer to solving the problem yet as time has been limited as always.

I opened up the throats today straight after it was running. There seemed to be no oil at first and then it slowly collected.

It doesn't blow much smoke though, just a little on hard acceleration.

I'm not really sure where to go from here.

If I pull the head then the car is not mobile and that's my only car at the moment.

Maybe sourcing another head is the way to go. I just need to get this motor running reasonably reliably.

[LukeAussie]

Hmm, fun times! If it is something like the valve stem seals, it's not too hard to get sorted out, and doesn't take too long... though without another car, any time is too long, really!