higher compression requires better head sealing

Discussion in 'Performance Mods' started by jaguar, Nov 2, 2016.

  1. jaguar

    jaguar Well-Known Member

    Jennings wrote:
    "stock aluminum gaskets are almost certain to fail, being a bit weak at ambient temperatures anyway -and impossibly frail at the temperatures to which they will be subjected. Copper is a better material, for while it is nearly as soft as aluminum at ambient, its hot-strength properties are better. Copper is soft enough to make a good gasket in the annealed state, but hardens in use, and must be re-annealed frequently to keep it soft and thus retain its properties as a gasket."

    I believe that the stock aluminum gasket is only barely adequate with the low cranking pressure of 90psi (given the head is not the slant plug head) and that higher cranking pressures need a better gasket. I had good luck just cutting out my own gasket from hi temp gasket material. I'm sure there are plenty of people who think their aluminum gasket works just fine but I'm sure they completely ignore the fact that upon disassembly they can see that blackened areas of the gasket was telling then that they were losing compression, and therefore losing power.
    Also I believe that every time the head is removed that a new gasket needs to be installed if the gasket is aluminum. That is because it conforms only once to the irregularities of the surfaces.
     

  2. HeadSmess

    HeadSmess Well-Known Member

    keep preaching.

    teflon is far superior in all regards, costs sweet F all, and well...it works. no cutting, no trimming, just twist some tape up, and tighten down. of course, it is absolutely useless if you have a warped head/sealing surface...

    even cranks the CR up a few points by removing 1mm of material between head and cylinder. bonus.
     
  3. Steve Best

    Steve Best Active Member

    I strongly agree with both of you.
    I easily got 5 uses out of stock aluminum headgaskets, especially at stock pressures.
    I was careful to not over-torque it and filed and sanded both surfaces smooth.
    My largest problem is with the stock head warping in a front-back axis.
    I have to sand the stock head a few thou every time to assure flat.

    The teflon tape trick has been a godsend Headsmess, eternally thankful.
    Be careful of your squish gap when you do it folks, and it needs to be flat.
    Here is what a blown headgaasket looks like:
    [​IMG]
    Note that it happened in the fore/aft axis.
    Most of mine are.
     
  4. gary55

    gary55 Active Member

    I remember when I was a wrench fetching kid seeing the older wrench turners paint head gaskets. They said it helped them seal better. Makes me wonder if maybe some VHT might help. Also seems like wrapping a exhaust gasket with tef. tape could save a lota scraping at replacement time.
     
  5. Steve Best

    Steve Best Active Member

    Yup, silver paint I bet.
    The aluminum (or lead in other colours) acted as a filler and sealant.
    It was messy and of negligible help in difficult situations.
    I like the teflon exhaust gasket idea. Count on me to try it.

    Been steady rain here. I am getting bicycle withdrawal.

    Steve
     
  6. gary55

    gary55 Active Member

    Since first speaking of how I build my engines, and listening to the feed back to the point that I had to test the heads myself IE volumes and compression at different deck heights my school of thought has completely changed. Now the only ones I deck are those getting performance heads. I still haven't done the solder test. I did check the radius of the piston and degree cut of the perf. heads and think with the jug decked to where the piston is just noticeably below the deck the .7mm head gasket gets very close to the sought squish.
     
    Last edited: Feb 15, 2017 at 6:58 PM
  7. gary55

    gary55 Active Member

    What do you think about spraying down the mag. coil with flex seal to water proof it?
     
  8. Street Ryderz

    Street Ryderz Active Member

    Teflon tape?the plumbing type?
     
  9. gary55

    gary55 Active Member

    That's what their talkin about. I suppose if you got it to seal the head with no alum. gasket a guessed boost of 20 to 25 lbs. of extra compression pending on how much the tape squishes down.
     
  10. Street Ryderz

    Street Ryderz Active Member

  11. Street Ryderz

    Street Ryderz Active Member

    The first two pics are of my old 6cc head that the same as steve said warped fore and aft but a little more in the front. sorry didnt mean for doubles. the last pic is my current one.I am curious if the teflon tape stays in with higher cr
     
  12. Street Ryderz

    Street Ryderz Active Member

    when that head is decked just over half a mm it might be closer to 5.5cc just a guess.
     
  13. gary55

    gary55 Active Member

    A little over .5 mm off the 66 cc slant plug engine head should be real close to a 5cc head and 155+ lbs. of compression with a stock head gasket. She'll be fast, but don't think she'll last. For my own bikes I just stick with the aftermarket heads. No warping no constant re torquing. Can't wait to see where this goes.
     
  14. Street Ryderz

    Street Ryderz Active Member

    I agree it wont last!but its fun and it will still give me a couple hundred passes before it cant be trued anymore and go through a couple jugs but at 40 bucks for whole top end money well spent to me!I also use the after market heads when traveling long distances or even just cruise speeds for longer periods.they wick away heat much better i have rode non stop for over two hours with no over heat from Hamilton to Toronto and back .
     
  15. Street Ryderz

    Street Ryderz Active Member

    For that I have always had good luck with high heat silicon filling the rubber grommet from inside as the last bit of wire is pushed through until it oozes out and is sealed around the wires then thinly coat each side of cover gasket and sealed pretty much waterproof!
     
  16. Street Ryderz

    Street Ryderz Active Member

    Gary do you know or anyone know whats best to seal a tank with? I would like to use this tank its all welded up and dressed but im sure there is pin holes (porosity)in the welds and its hard not to blow through, the thin filler neck was not fun but its done and rather than grind it and subject it to more possible f**k up's im hopeing that sealing it will work. 2016-11-03 23.03.11.jpg 2016-11-03 23.01.39.jpg
     
  17. skyash

    skyash Active Member

    It depends how you want to go there is expensive motorbike fuel tank sealers or you can use fiberglass which is not affected by petrol I have made full tanks out of cardboard covered in fiberglass and a bit of fibre or old clothing .fiberglass is only $10 for 500 mls $4 for a little bottle of hardener you put 20 drops to 100 mls of fibreglass resin in a cup it does smell strong give it a stir and paint it on whatever you like it should harden within an hour or two but the thinner the coating of fibreglass the more like glass it is ..easy to break that's where the fibre comes in...here is a tank the top and sides are balsa wood and bottom is a tea towel you can see in the red circle blue Red pattern lol .I put on the frame then covered in fibreglass to get the shape the top cap is a stock one cut off a tank and fibreglassd in....My mate has a peewee tank old and Rusty so we put rust converter in it then got it all out then put 100mls of fibreglass in and kept rotating the tank till dry .
     

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  18. jaguar

    jaguar Well-Known Member

    On my Suzuki 100 it was getting too hot running 150psi compression so I reduced it to 135 and there was too small a difference in power to have any regrets. So now it runs cooler and it doesn't have the power loss at peak operating temperature like it did before.

    Heads-a-mess, how do you get the two ends of the teflon tape to join together?
     
  19. skyash

    skyash Active Member

    What about brass or bronze gaskets? Or stainless Steel ?
     
  20. skyash

    skyash Active Member

    Evon nylon? I make sprockets out of it and gear's its pretty strong just don't know it's melting point
     
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