Big block old Guzzi - strange head oil leak

[blues_mack]

My 1989 Guzzi Mille GT starts leaking oil on the left cylinder head.
First I thought the oil is leaking on valve cover gasket, so I've replaced it, but it still leaks.

Now I think that the leak is coming from these plugs (or whatever) that I marked with arrows on the photo.

Am I right? Does anyone had a problem like that and how to fix it properly?

[Antietam Classic Cycle]

It is a plug, factory installed after drilling an oil passage. If it were me, I'd remove the plug, tap the hole and use a threaded plug with thread sealer.

[pehayes]

Now I think that the leak is coming from these plugs (or whatever) that I marked with arrows on the photo.
Am I right? Does anyone had a problem like that and how to fix it properly?

blues-mack:  You are correct that your arrows indicate plugs.  When the head is produced, there are internal oil passages which make a right-angle turn.  Never saw a drill bit work a 90 degree hole.  So, the machinist drills a second hole at 90 degrees through the first hole and then plugs the outer end.  It is my understanding that these plugs are tapered zinc and they are hammered into place to create the outer seal.  Can they loosen and leak and fail?  Perhaps.

I had just such a leak on my 98EV while it was still under warranty.  I didn't want to disturb the cylinder or sealing so we tried everything we could to stop the leak.  Even got permission from the dealer to hammer on it with a pin punch in hopes of expanding it to recreate the seal.  No joy.  Guzzi eventually gave me a replacement head without question.

Now ignore that.  One of the primary leak sources on big block heads is the sealing o-ring under the top/center head bolt cover plug.  If  you do any head work or torque the heads, then you have to remove that top/center cover inside the rocker chamber to access the unique top/center head bolt.  On early round heads, that sealing was with an aluminum crush washer.  Square head motors had a top/center cover with a recess to hold an o-ring.  It is definitely NOT a lifetime sealing item.  Should probably be replaced every time you remove that top/center cover.  (at least every other time).  The constant heat/cold cycles and potential of high heat on an air cooled head make the rubber o-ring flat and brittle and no longer resilient.  I would quickly replace that o-ring on both sides of the engine.  Cheap and it eliminates one common source of oil.

Next I would wash and de-grease that head area fastidiously.  Spray all around with cheap foot care spray talcum powder.  Go for a ride and you should quickly see brown staining emanating at the leak source into the otherwise white powder spray.  Wash and repair.

It might be possible to seal the plug leak by adding something external.  There are oil-tolerant sealing compounds (such as SEAL-ALL which I have used a lot.  Maybe JB-Weld?  Maybe JB-Weld specific for high temp exhaust repairs?  Holding up just fine on my camper's cat converter.)  However, this location is going to get very hot and the oil behind that plug is under pump pressure so might be 60 psi or more.  Hard to seal that from the outside unless you are the Dutch boy at the dike. 

Please return with a post to explain how you resealed your leak.  Last resort, get another head.

Patrick Hayes
Fremont CA

[bmc5733946]

I would get that area fastidiously clean with brake clean or acetone and then use Loc-Tite wick-n-loc. I've seen it work in similar situations.
YMMV as always.

Brian

[blues_mack]

Thank you all.

@pehayes -  I know about top center head bolt, both of my heads were taken off recently and both o-rings there are new. So, for now I'll assume this isn't an issue.

I will definitely try with that powder-diagnostics now, for start.

[blues_mack]

I didn't find the time to solve the described problem, but yesterday I had a problem with the lights, so I had to solve that one urgently.

And, since I already had the tank removed to approach the connectors, I took a riveting iron and a hammer and tapped that plugs a little.

It seems that I solved the problem, at least temporarily. The leak is gone. 

[JoeW]

Looking at the photo, I suspect the valve cover gasket is the leak. There is oil present at the mating surface. Oil rarely moves up, usually down and back. Always locate the highest most forward spot with oil on it and start there. Get good quality gaskets, I like the green ones, clean both surfaces and stagger torque the cover down to 7ftlbs. or 84inlbs.

[smsw]

It might be possible to seal the plug leak by adding something external.

Generally speaking, one patches a leak on a boat from the outside (where the water is trying to get inside). You stop the leak on the high pressure side.  I think trying to seal this particular leak from the outside with a sealant is doomed to failure.  One would have to get the aluminum scrupulously clean and get a perfect bond.  Too many things can go wrong.  I'm in the suggested drill, tap, and screw in a threaded plug (with thread sealant) camp.

[blues_mack]

I didn't find the time to solve the described problem, but yesterday I had a problem with the lights, so I had to solve that one urgently.

And, since I already had the tank removed to approach the connectors, I took a riveting iron and a hammer and tapped that plugs a little.

It seems that I solved the problem, at least temporarily. The leak is gone. 

Added few hundred kilometers to my Guzzi, there is still no leak. I'm good for now. :)