Cam and rocker oil tubes

[porscheboy1]

I need to clean out the oil tubes in the cam towers for my 1978 911SC engine rebuild project. I can't get good fluid flow through some of the holes in the tubes and will have to remove the plugs at one end of the pipes. I read somewhere, but can't find it again, that the plug can be removed and the hole can be tapped with a one fourth inch NC pipe tap and a one fourth inch pipe plug inserted after cleaning to seal the hole. Is this correct? Any other advice on how to clean these tubes.

John

1964 356SC coupe
1987 911SC sunroof coupe
1982 911SC sunroof coupe

[KTL]

The plugs are removed by drilling them and tapping the drilled hole. Be careful drilling into the plug. You want to just stop short of going thru the plug entirely. Stopping short is important because the fragile end of the spray bar is nearby on the back side of the plug and you can damage it with the drill.

I like to use M6 threads to pull the plugs out. I have tried M5 x 0.80 threads and they do not have enough bite to pull the plug out. The threads pull out instead.

A simple puller can be made by running an M6 screw into the M6-tapped plug, then slip a suitable depth socket (1/4 in. drive 11mm size works good) followed by a nut & wide washer on top of the socket. Turn the nut down onto the washer to draw the plug out of the housing & into the socket.

Once you have both plugs out, you can GENTLY tap the spray bar out of the housing with a suitable sized punch on the outer edge of the spray bar. GENTLY. If it doesn't want to come out, stop, heat up the housing a bit and try again. The thing should theoretically slide right out, right? Heck, it's been soaked in oil for decades. Nope, sometimes they don't want to come out.

If you do get it starting to come out, once the end is poking out of the housing you can slip a suitable sized punch into the larger cross-holes and use that punch as a T-handle to gently wiggle & tug the spraybar out of the housing. Make sure to note the orientation of the spraybar pin holes before you take them out. They can be put back in place backwards and that will starve the cams of oil!

The original press-fit alloy plugs are cheap and easy. Just use a bit of epoxy (JB Weld) on the surface to ensure they stay put- just like the engine oil gallery plugs. It's not like you have to take these spraybars out all the time. Up to this point they've never been removed! But if you really want to install removable plugs, use 1/8 NPT steel plugs.

The existing hole in the housing is the perfect size for an 1/8 NPT tap. I prefer zinc plated steel plugs because brass or aluminum plugs are very easy to strip-out when you go to loosen them later on, especially when the threads bind, as NPT threads are prone to doing. Ironically, a stripped NPT plug defeats the purpose of having removable threaded plugs! So use a steel plug that is less likely to strip.

The trick to using the NPT plugs is to cut the threads to a depth that will set your plugs deep enough, but not too deep. Remember that NPT plugs work based on tapered threads interfering with the straight plug. You don't want to tap the threads too deep or else the plug will hit the end of the spraybar before it is tight/sealed. Don't cut the threads too shallow or else your plug will stick up above the surface of the housing. This stick-up is only a problem on the side of the housing where the chain boxes must seal with the cam cover plate.

Cleaning the tubes is best done with them removed. There always seems to be some dried crud inside them that looks like brown glue. I don't know if that is some adhesive the factory used to lock them in place? Nonetheless, you can run a small rifle bore brush in there or a very long semi-blunted thin flatblade screwdriver to knock any bits out of the tube. For the small spray holes, just run piece of stiff wire (safety wire?) thru them to ensure they're clear.

Do a search on this forum and you'll find a few topics about it. I've done this on a number of cam housings and it works very good. Just have to be patient getting the spraybar out and be cognizant of how deep to cut the new 1/8 NPT threads.

[cgarr]

If I was to do it again I might just use a brush and go thru the tubes and flush them out real good. I removed mine in the past but you really need to seal the tubes where the cams get oiled or you loose a lot of oil where the tube slides thru the carrier. When I tested mine with the cams installed oil was pouring out that area which reduced the amount of oil for the rockers. If you can install the cams and pump fluid to the inlet and watch where it goes.

[porscheboy1]

KTL and cgarr thank you for your detailed and very informative replys.

John

[KTL]

Craig makes a good point about leaving the tubes in place. They do need to slip tightly into the cam housing to ensure the oil is sent to the cams vs. leaking out between the spray bar and the cam housing. I'll be sure to seal my tubes when I reinstall them!

You could pull the plugs, tap the holes, flush the tubes and install new plugs w/out removing them. Just have to be careful with your tapping depth to avoid hitting the end of the tube.