Broken bolt or plug? 72 Head

[mikec]

I've attached two pictures for reference on what I have seen on the head of my 72 GT. I cant tell if it is a broken bolt or a plug that resides in a hole just beneath the front right manifold bolt hole. The big red arrow points to the item in question. I would like to know if I have to remove it or leave it in place. Thanks in advance.

72 Opel Head 1.jpg

72 Opel Head 2.jpg

[BQS4]

It's a casting thing, leave and pay it no mind

[kwilford]

It's a plug, filing up a hole drilled during the manufacturing process, probably to bore a coolant or oil passage. Leave it be unless it was leaking.

[jeff denton]

Exactly. It corresponds to the little hole near it on the head gasket surface, which is the oil feed from the block to the front cam bearing.

[hrcollinsjr]

Plug to an oil passage. It can leak. I put one engine together that leaked from this hole. Since I'd never seen one leak from the plugged area we looked to the head gasket for the problem. After the second gasket for me and B'ham Bear installed the third one he spotted the problem. 2.0L head gaskets aren't cheap either. The leak was just enough to be annoying.

Harold

[jeff denton]

I believe that. I've not had a problem with one, thus haven't had to fix one. I do drill and tap the internal ones and use pipe plugs there, as well as the one in the back of the block. Surely the same could be done with the location in question.
Annoying oil leak? Heck, one drip of oil under our race cars can get you parked for the night.

[hrcollinsjr]

Originally Posted by jeff denton I believe that. I've not had a problem with one, thus haven't had to fix one. I do drill and tap the internal ones and use pipe plugs there, as well as the one in the back of the block. Surely the same could be done with the location in question. Annoying oil leak? Heck, one drip of oil under our race cars can get you parked for the night.

I've seen two of the AL plugs fail in the rocker oil gallery but never thought much about the plug on the side of the head. There is just enough stuff around to make it difficult to diagnose especially in a GT.

Harold

[GTJIM]

That hole has been plugged at the factory by driving an ali (or steel!!) plug into it - no threads!
It is always a good idea to remove oil gallery plugs, clean out the drilling behind them and replace the drive-in plug with a threaded one.
Often short in-hex (Allen head) grub screws can be used - just measure the hole size and select a thread size with the tapping drill closest to the existing hole measurement.
OR 1/8" BSPT (or NPT!!) hex pipe plugs as used in air valves can often be used.

[kwilford]

Originally Posted by GTJIM ...That hole has been plugged at the factory by driving an ali plug into it...

Are you certain that this particular plug is aluminum? I know that the cam bearing oiler holes are plugged with aluminum plugs, but I think that this plug looks like steel.

Has anyone ever removed this particular plug. On my CIH's, I had all the aluminum plugs drilled out and the holes tapped for threaded plugs, but this one is still "as is"

[RallyBob]

Originally Posted by kwilford Are you certain that this particular plug is aluminum? I know that the cam bearing oiler holes are plugged with aluminum plugs, but I think that this plug looks like steel. Has anyone ever removed this particular plug. On my CIH's, I had all the aluminum plugs drilled out and the holes tapped for threaded plugs, but this one is still "as is"

I remove them on every head I build. Access to clean the oil feed passage to the head.

I then tap them oversize to 1/8" NPT, and put in a pipe plug. The plug must be below the surface of the intake face, as some exhaust manifolds will overlap the plug and having a plug 'proud' of the surface means the exhaust will then leak...

In this pic, you can see the plug has been removed.

HTH,
Bob

[kwilford]

Originally Posted by RallyBob I remove them on every head I build. Access to clean the oil feed passage to the head. I then tap them oversize to 1/8" NPT, and put in a pipe plug.

Thanks Bob. Is it a steel or aluminum plug? Do you drill it out, or extract it some other way such as drilling and tapping in a pulling bolt? And finally, how long a plug is it, and does the replacement plug have to reach in a certain depth, or simply plug the hole?

[RallyBob]

Originally Posted by kwilford Thanks Bob. Is it a steel or aluminum plug? Do you drill it out, or extract it some other way such as drilling and tapping in a pulling bolt? And finally, how long a plug is it, and does the replacement plug have to reach in a certain depth, or simply plug the hole?

I have actually seem them in both steel and aluminum. Probably changed to steel due to the proximity to the exhaust system? Just a guess....

I drill them out completely, as the 1/8" NPT plug needs a larger hole to get the tap started anyway. You just have to plug the hole, that's all, so any shallow plug works fine.