Back of Cylinder Head LEAK
 

Hi
So I just finished up head gaskets. I just purchased new steam pipe bolts and seals. But I’m still leaking from the lower inside bolt holes. Not sure if it’s supposed to be plugged? I had the heads surfaced and cleaned. Did I or somebody else miss something? It’s the one circled

1995 z28 just to be clear

You sure you have good seals on both sides of the crossover fitting? Banjo bolts are snug and not cross threaded?

Should be a seal between head and crossover, then a seal between the crossover and banjo bolt.

Correct I have 4 seals. I had issues tightening the old bolts so I purchached new ones that came with the seals for $18 all together compared to the $32 for the 4 seals from gm. I was nervous of screwing up the threads that I didn’t want to wrench on it to hard. As far as I can tell the fluid is leaking from that lower hole. I believe it is threaded. I can’t find any good images online of all the passages in the head

So its the hole below the steam pipe bolt? I don't think that is supposed to be opened to the water jacket. Its a blind hole.

From what I can tell yes. Does my image appear. It is the hole circled. It should be below and towards the center of the block from the steam pipe bolt location.

The holes that are not the steam vent, are not into coolant. So they cannot leak.

Try snugging the steam line banjo bolts up a tad. I would try and find a torque value but if the motor is in, good luck getting a torque wrench back there.

Did you clean the threads out on the heads prior to install?

Just checked a set of heads I've got on the shelf. That hole is a blind hole. Are you SURE it is leaking from that hole, and not leaking from the steam pipe bolt or seal and running down?

I did not run a tap through but I assumed the machine shop did. I guess it doesn’t pay to assume. In total I have 8 seals because I bought them twice. I assume this is a no no but could you consider doubling up on seals if it’s close? I suppose it could be from the banjo bolts. But I feel I’ve put quit a bit of force behind it?

pic of seals used?

I don’t have images of the seals with me. But the gm part number is 12552974. I purchased the new banjo bolts with additional seals from Davies Corvette parts that had the same interchange number

Reason I asked is I tested the tensil strength of that reverse cooling tube when I took the engine out of the car. When I bought a new one it came with banjo bolts and seals, but the seals were a small diameter with a thin seal. Got some A/C ones that were the same size as the GM part number. If you haven't already, examine the seal and see if it's ripped. Or just replace them with the extras and see what happens. Don't double up the seals.

These are the steam pipe seals I bought (1010-8689)...did the part # change to 12552974??

and isn't the threaded bolt and head "tapered".....and if so if the threads were chased on the head....would that have killed the taper??

Been awhile since I put my motor in and can't remember if the steam pipe bolts are tapered or not

From what I can tell those appear to be the same seals. The banjo bolts are not tapered. I have like an 1/8 of an inch gap between head and spacer

I don't recall my banjo bolts being tapered, either.

What you can also do is get a coolant pressure tester, put the 18lbs or whatever it is the cooling system is rated for on a cold engine and see what happens.

I suppose I haven’t been clear. The driver head is leaking when I add coolant. I’ve yet to start it since head gaskets. Can only imagine what other issues I may have. I can not get the bolt snug but it won’t turn anymore. From what I can tell it is aligned properly and not in sideways

I would unbolt it and put the new set of seals you have back on it and see what happens. I also agree I don't believe the bolts are tapered.

Hoping for the best,, the blind hole on the end of the head doesn't that back up to the water jacket? I have had a mounting bolt hole bottomed out by a shop replacing a bolt and it broke through, wasn't fatal, I just had to start using RTV on the bolt so it couldn't leak..

maybe the threads in the head are furber at that depth...you could get a thread chase the size of the banjo bolt threads and run it in to see if that cleans them up to allow the bolt to thread all the way in

have these heads been on your motor and in use before?

I’ve unbolted and started over several times with both sets of seals. They were the original heads to the motor. I do question if the threads have been altered. I’m not sure how to check and see if the steam pipe itself is bad