Advice pls: cam end cap blowing out

I'm looking after a friends 1999 996 c2 3.4. On a high speed run it blew the left hand upper cam cover cap blew out resulting in a severe oil leak as you can imagine. I bought a new plug - 99610421554 - and fitted it along with new oil and filter but on startup it immediately blew out again. I cut open the old filter and there's very little trace of metal so I think I've saved it from the worst. The cap supplied is green but I see the lower cap on the car is black. 1. Are these meant to fitted with a sealant to hold them..? 2. I think someone has had the cam cover off at some point, judging by the amount of sealant on the cover. I have seen on youtube there could be an issue with over sealing bunging up an old drain. My question is if anyone knows a way of clearing the drain with the head in situ? i've managed to get the smallest pipe cleaner I could find into the drain but I think i'm coming up against a bend as I can only get it so far/ Welcome any advice!

I'm going to guess based on what I've read. One or both scavenge pumps might not be installed the right way. This can cause positive pressure in the crank I believe. The four bolt holes don't stop you from installing it the wrong way There's scavenge pump on bank 1 (left side as you stand behind the car) in the front of the engine. There's another on bank 2 at the back of the engine. For the 996.2 at least they're the same part number but need to be installed in different orientations based on bank1/bank2 install. I believe the same for the 996.1 The face of the scavenge pump as 1-3 and an arrow and the opposite side of the face 4-6 and an arrow. The arrow needs to be pointing towards the crank. I'd start by checking that.

My understanding is if there is enough oil pressure to blow the caps off, then something is over pressuring the system.. blowby?

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Oil pressure would be controlled by the pressure relief valve?

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I'm not sure, blowby would be more likely? Someone like Porschetech3 will come along soon

Have the cam covers been removed and replaced? If so, it is possible to have excess sealant block the oil drain passage below the end cam bearing surface. This will cause excess oil pressure at the cam plug causing it to blow out. If the drain hole is blocked by sealant the oil that flows into the cam bearing has nowhere to go and blows out the plug. Mark

How long has your friend owned this car without this problem showing up? What was the last service done to the car? It's weird that it would be OK for sometime and then blow out at both high and low loads.

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There�s a really good PCA/Jake Raby YouTube video on this particular thing. Definitely worth investigating if they�ve been off recently. https://youtu.be/ocntYwozZBY?si=YY75DaMvQY2hqOUD minute 26

Your positive crank case pressure is not vented and it blows out the cam end caps. Look for plugged up vent hose, or AOS.

Thanks all. As mentioned in original post I do think someone has had the cam cover off at some point judging by the amount of sealant. I am thinking to try some plastic strimmer wire to check the drain is unblocked in situ and then replace the plug with some loctite seal. then park it and stick to my 928!!

You may be able to push a small piece of wire thru the passage to open it and allow the oil to drain. The drain passage is a small area the runs down under the camshaft bearing boss between it and the bottom of the head. It is easy to block. If too much sealant is applied to the valve cover, the excess gets squeezed into the passage as the valve cover is tightened. If you are not able to open the drain passage, you will have to remove the valve cover to clean out the passage. When replacing the valve cover, put a small piece of o-ring in the passage and leave the end sticking out of the hole the plug goes in. After you get the valve cover tightened down you can pull the piece of o-ring out. If the passage is not open, the oil pressure will build up between the end of the cam and the plug and force the plug out. I do not think Loctite will work against 70 psi oil pressure. Good luck with it Mark

^^^^^^ Mark is 100% correct.....This is a very common Rookie mistake on the M96 so don't beat yourself up over it... This oil channell makes a sharp turn so i doubt you can get a wire down through there,and if you do you will be pushing silicone into the engine.... Best to just bit the bullet and R&R the cover to do it right....Use a piece of the scavenge pump o-ring lubed with vaseline to keep the channell clear then pull it out after the cover is torqued down....