Announcement

Collapse
No announcement yet.

good info on blown head gaskets and AL heads

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • good info on blown head gaskets and AL heads

    I can't verify the source, but am giving credit as it was forwarded to me.

    Found this in A. Graham Bell's "Four-stroke performance Tuning"
    -------------------------------------

    Many head gasket failures, however, are not due to inappropriate head gaskets being fitted, incorrect tensioning, or a block deck that is not perfectly flat. The problem, if it is an aluminium alloy head, could be that the head has been annealed when it was previously overheated and blew a head gasket. What happens is that the hot gases destroy the heat treatment and the head goes soft.
    Consequently it will no longer hold a head gasket and it has probably lost its crush on the valve seats as well.
    In this state the head also changes shape; it will be shorter and narrower.
    Hence a head that does not easily drop down on the block dowels or is
    jamming on the head studs is probably annealed. If you use head bolts rather than studs and you find trouble getting the bolts started into the block, it means the same thing;
    the head has gone soft.
    This can be checked with a Brinell or Rockwell hardness tester. On the Brinell scale a good head will read in the 95-plus range, and anything under 75 is too soft. When testing on the Rockwell B scale this translates to a hardness in the 48 to 60 range being ideal, while anything under 38 is soft. Obviously the place to test is in an area where the gasket has blown. Do not be content with a hardness test in just a couple of places. A casting flaw could throw the reading way off, so over an area of about a square inch test in at least 10-12 spots.
    If the head is soft and you have a lot of money invested in it, it may be worthwhile to have it heat-treated afresh. This is not cheap and it may not be possible in heads where the cam runs directly on the aluminium. Ask around to find what specialists can do, or if it is a head from an after-market supplier, get them to give you a price. Basically the seats and guides are knocked out and it is then heated in an oven at 520°C for around 5 hours (some manufacturers specify up to 20 hours).
    Then it is quenched in 80°C water and tempered (reheated) at 200°C for another 4 hours (up to 20 hours), then allowed to cool slowly in the air.
    Following this the head will be machined for oversize guides and seats and the deck will have to be resurfaced. This all costs a lot, but if the head is a good one with lots of fancy port and chamber work, you will not want to throw it away. Note also that any time a head is welded close to a head
    gasket fire ring line or valve seat it will also require a fresh heat treatment
    87 Turbo: Stock VG33, stock cams, maxima intake, T5, DXD stage 3 clutch, tubular stainless headers, GT3582r, full 3" stainless exhaust, E85 680cc inj. and Nistune
    current time: 13.39@106, 2.05 60' 12psi with old stock 85T motor and street tires!

  • #2
    Head Gasket Failure...Engine Management
    I don't see the similiarities.
    Our vg30's have issues or potential issues with HG failures?...No.
    Only un-maintenanced VG30s do(clogged/sludged coolant passages)
    *13head bolts per head explains a little...Nissan built a bullet.
    ~Good info I suppose?..
    I am here to help...

    Comment


    • #3
      sounds more like social lounge type stuff, but it could go into an unrelated faqs thread

      Comment


      • #4
        i was in here and i didnt think about it, it was a posting spree.
        Gary
        87 Turbo: Stock VG33, stock cams, maxima intake, T5, DXD stage 3 clutch, tubular stainless headers, GT3582r, full 3" stainless exhaust, E85 680cc inj. and Nistune
        current time: 13.39@106, 2.05 60' 12psi with old stock 85T motor and street tires!

        Comment


        • #5
          A. Graham Bell's


          Like, the telly?
          BLOZ UP.com
          It is not recommended to confirm proper installation by driving into walls or other barriers as this could cause personal injury or damage to the vehicle.

          Comment


          • #6
            He has written a lot of good books.

            For the hardness of the aluminum to drop, it will have had to experienced some extreme temperatures. What he describes is nothing short of warped heads to the nth degree, which I have never seen of VG heads. I think steve88t told me about a guy who drive for almost an hour on an overheating VG and short of the head gaskets, nothing else seemed "wrong" about it on tear-down.

            Comment


            • #7
              afair annealing cast aluminum would take >400 (something like 600) degrees

              you'd probably notice the low coolant by the exploding hoses and steams all over the windshield, but what do I know

              Comment


              • #8
                Haha, I just put a head on a Daihatsui for the same reason. I had it resurfaced cause it blew HG's. When I put it on yesterday, had the dowel and bolt issue. I'll keep you updated.
                sigpic

                Comment


                • #9
                  AKA "warped head".

                  Comment


                  • #10
                    Grrrr...

                    The L series head is a lot longer than yours and warps easily.

                    Oh well, at least we only have one of them to worry about!
                    1976 280Z 2+2 Turbo
                    '81 L28ET, '84 Turbo ECCS, '84-'85 rotors + Toyota 4x4 front calipers + 240SX rears, Z31 DXD Stage I clutch kit, Evo intercooler, Tokico lowering springs and HP blues
                    "I drive an S30...your stock equipment is my future upgrade!"

                    Comment


                    • #11
                      hahaha someone actually brought in a Daihatsu.... that's a cool unto itself, similar to driving a trabant and rolling it in a hard corner haha

                      Comment


                      • #12
                        G-E wrote: hahaha someone actually brought in a Daihatsu.... that's a cool unto itself, similar to driving a trabant and rolling it in a hard corner haha
                        Don't they make a lot of equipment that he might maintain?

                        Comment


                        • #13
                          I don't know their full line up, or their popularity in every field.... most of the farmers up here use kubotas and cats, I rarely see any john deere.... are they better? no idea... easier to get? not really....

                          all I can think of is price or cost/effort to maintain, there's dealers for every name brand just outside the city so finding them isn't hard, getting qualified support and repairs is easy, toromont (cat) will even take in hitachi, toshiba and other "off" brands

                          Comment

                          Working...
                          X