Hi all,

At my wits end so seeing if anyone on here can point out my obvious mistake.

Replacing my track car head with a better flowing one, valve springs etc. Immediate head gasket failure on assembly and start up.

Gasket squish doesn't appear good enough/non existent.

Have taken Original head on and off before without issue for cam replacement

What I know:

  • New head lightly skimmed and crack tested without issue
  • Block appears flat with straight edge.
  • Compression test 175-180 prior to this
  • Head bolt holes clear of fluid/debris
  • Big 44mm valve oval head gasket used as my car is a 74.
  • Lower size water pump o-rings used and pump loosened to help lower it.
  • Torque specs and procedure followed

Keen for any advice. Must be something fundamental I'm completely missing? I'll concede my knowledge isn't huge but it's not the first time I've put someone like this together either.

Thanks!

    jjperko Where did it fail? ie in the centre between pistons, if so which pistons. send a photo of the head front section around water pump holes.

      Always cylinder 1. As if water pump o rings are somehow holding it up. Necessary to remove water pump completely for head installation maybe?

        jjperko it might be worth trying with the pump removed, maybe even with the bolts slack it was binding up or something and keeping the head from seating correctly.

        Worth checking the head surface for flatness too, especially given it has just been skimmed. Did you happen to see where the most material was removed during skimming?

          jjperko Always cylinder 1. As if water pump o rings are somehow holding it up.

          rUh rOh.....

          What's the thickness of the (machined) head?
          What thickness head gasket are you using?
          And what's the height of your two water pump O-rings?

          Pages 24 and 25 in Group 2b of the 140 73-74 parts books (Drawing 11716) shows there's a number of different sizes of O-rings and head gaskets.

          IIRC the thickness of the cylinder heads is in the 73 and 74 Green Books - the B20E has the least meat on it with its higher compression, and the B20B head is a little thicker from stock. But I guess it depends how much has been skimmed off your head, it may be closer to B20E spec now.

            Will have to put calipers on the head once I get a chance. Wasn't an aggressive skim for big compression was just to rule out any issues. Report from machine shop was it was pretty much fine anyway.

            Specs are

            0.8 oval b20e or f gasket due to the larger valves (same as what was originally in the running car)

            8.5mm o rings (lower profile of the 2 specs that im aware of)

            Old Head- late model b20b with blank boss where injectors would be and 44mm inlet valves. Did a track day before disassembly without incident.

            new head - no injection bosses. 45mm inlet valves.

            I had the water pump a little loose but not fully off and hanging down. Not game to try again as head gaskets are adding up.

            Hoping it's not a crack somewhere else lower. It's alarmingly wrong not just a slight leak. Water pouring into cylinder 1.

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