Well that's different.....

Hi all,
I parked up my P6 a while back due to a lot of oil coming from the rocker breather on the drivers side and valley breather. Had a mechanic do a compression test (I had asked for a leakdown test but that's a different story), and he came back with #4 and #6 a lot lower than the rest, and all quite low.
So the car has been parked up and for sale.
I've since decided not to sell it as the market just wont give what I think it's worth, so I finally got into looking at the problem. The first thing I did was my own compression test, and lo-and--behold they're all pretty even albeit a little lower than I'd like! I did do the test on a cold engine though so maybe I could get a few more PSI when she's hot - anyway...I'm starting to think oldmate who had the engine before rebuilt it as a low compression or used the wrong pistons - maybe wrong head gaskets? Anyway I digress. I removed the rocker covers to check for blockages and they're squeaky clean. My son then pointed out that a bolt retaining the rocker gear between #6 and #8 was standing proud. I mean this bold was not even threaded in. I pulled it up and there's a lot of oil through it.

So, my question is, do you think this bolt being undone has anything at all to do with oil coming from the breather (I noticed there's a lot more oil still in the head on this side than the other)? Or is it just a lucky find while I work my way down further into the engine to find the real cause?

That would be piston 6. With a loose bolt, the shaft would bend ever so slightly with the valves on cam thereby causing them to open slightly less. However it shouldn't stop them from closing completely so not a compression dropping issue. (the oil pressure in the hydraulic cam follower shouldn't be high enough to bend a rocker shaft I would think but happy to be corrected and often am):rolleyes:
On the other hand, the breather hole in the rocker cover is rather close to this post and not being bolted down will cause oil to squirt from underneath it in all directions so could quite possibly end up the breather pipe. (No flame traps?:eek: They're there for a reason:hmm: and cheap as chips.:LOL:)
Cheers, Pete


Well-Known Member
Just as Peterv has said, if the rocker gear isn't bolted down firmly than oil will certainly squirt up from beneath the loose rocker pedestal, and is very likely the cause of your oil leaks from the breather and rocker covers. It all looks nice and clean in there, at any rate.


Well-Known Member
Do up the bolt and run the car, see what happens, no point striping the engine now you are finding even compressions and clean insides.
Check the pedestal bolts on the other bank too and torque ALL of them.
Cheers guys - no flame traps as I've converted it to a Holley. In diagnosing the problem I removed all the PCV gear and just put breathers on to see what happened. If the bolt walking is the problem I'll re-configure the PCV back into the manifold with a PCV valve and catch can, I think. :)


Well-Known Member
If those loose bolts are above cylinders 6 & 8 and you have P6B rocker covers fitted then you should have baffle plates bolted above the rocker gear. There should be another baffle plate on the front of the other bank under the breather outlet as well.


Well-Known Member
Whilst I concede that the P6 baffle plates are large and efficient looking devices, they are not as effective as they seem. I transferred P6 baffles into my 4.6 after suffering high oil consumption issues and finding oil in the intake from the PCV system. The baffles although reducing the oil consumption a little did not stop it.
I have my PCV valve directly over a baffle, and correctly spaced up from it. If I pull the valve out of its grommet I can see oil on top of the baffle.

I had to fit an oil separator in the line to the manifold to cure the problem.

The baffles bolt under the pedestal bolts and run in close proximity to the rockers.


Well-Known Member
If you do fit baffle plates make sure you fit them the correct way around. The will fit both ways, but the wrong way stops the valves from closing fully.
I replaced my air filter & housing, hoses and flame traps as soon as I got my car. Hoses were as hard as rocks.The old flame traps were full of sludge and a p.o. had sorted that out by shoving a screwdriver or something through it. The air filter was an old beaten up chrome one with no air flow control characteristics. Engine doesn't have baffle plates, probably because this engine's out of a Range Rover that have different rocker covers. On the outlook for some baffles if anyone in NZ has a pair lying around. Although I don't seem to have a big oil problem up the hose, when I check, there's mostly only a few drops of moisture up there. Also with this 3.9, there isn't a breather pipe off the back of the motor:hmm:. Why is that I ask... Rob, just in case you hadn't noticed, that's a Holley too:thumb: 20201024_130449.jpg
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Active Member
Oil comes up into the rocker shaft at the front pedestal - the bolt is waisted to provide room for the oil to come up around it and into the shaft. ALL the bolts are waisted, even though oil only comes up past one of them. Therefore with any bolt not done up there will be room for oil in the shaft to leak out....and possibly produce your problem.
So while I wait for my baffles to arrive I've been contemplating other contributing factors. For those of us heathens, with Holley carbs - how have you set up your PCV system?
Looking at the photo above, Follow the breather hoses through the £2 flame traps to a tee that goes into the carburettor side of the air cleaner. As mentioned above, there is no breather from the crank case on this 3.9 but if there was, it can also go onto the tee if its a LOWER case Tee as this one is. (see photo of old crappy air cleaner housing)
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