porting

Discussion in '2 smokers' started by willis 2000, Jul 21, 2012.

  1. willis 2000

    willis 2000 neo-quixote

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    Maybe, but not just yet. Leave your power tools alone.
    You have some old Spanish stuff, and the casting work was inept. Look at the ports and you'll likely see some hasty factory attempt at curing the worst of it. Could you finish their work and make it better?
    How does the base gasket fit the transfer ports? One mm there will make more difference than your exhaust port. How does that base gasket fit the crankcase?
    #41
  2. anotherguy

    anotherguy unsympathetic

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    Before raising the exhaust I'd widen to the maximum allowable and profile for ring life. How many transfers in the cylinder we're talking about? Boost port? And the first question should have been what bike and what is your end goal?

    If you really want to learn about porting Rick has a good article here.
    #42
  3. Twin-shocker

    Twin-shocker Long timer

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    Any sort of tuning work on any bike is relative to end use, and of course what bike its being carried out on. In most cases optimising the stock set up will be the sensible way to go, and while hacking away at ports may well mean gains in some areas in nearly all cases they will also mean losses in others.
    #43
  4. willis 2000

    willis 2000 neo-quixote

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    Not necessarily true. My advice is balance left-to-right first. It requires caps, DO NOT touch the cylinder openings. Get the transfer ports working correctly first. Read a bit on fluid dynamics, ok, here it gets weird, but think of runny jell-o running through your ports. A mismatch or a sharp edge will cause a turbulent flow, The polish is inconsequential as the boundary layer is at least .010". On these old air-cooled bikes, first concentrate on getting the transfer ports evenly matched, use your fingers as gauges and a base gasket as measurement. Y'all might be surprised how many of these old motors need the crankcase portion of the transfer ports modified to get even flow.
    #44
  5. Twin-shocker

    Twin-shocker Long timer

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    An awful lot of people seem to think that things such as OE squish clearance of 2mm, and less than ideal exhaust and induction systems make no difference at all. Contrary to popular belief though, without sorting out these basic areas first, any other work carried out wont work anywhere near as well as with the basics done first, and is a bit like fitting a 40mm carb to a bog stock 125cc scooter.
    #45
  6. Shocktower

    Shocktower Long timer

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    How can my squish be determined, to what it should be :ear.

    A little about my bike 1979 RD 400 with new TM 28mm carbs Moto Carerra Millinum pipes, stock porting :D
    #46
  7. stainlesscycle

    stainlesscycle Long timer

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    #47
  8. Shocktower

    Shocktower Long timer

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    :lol3 That guy is local I may need to take my bike parts there :evil
    #48
  9. stainlesscycle

    stainlesscycle Long timer

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    do it. he's excellent.
    #49
  10. supershaft

    supershaft because I can

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    That's exactly how I measure it. Way better than clay. You can do it through the spark plug hole on some engines.
    #50
  11. willis 2000

    willis 2000 neo-quixote

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    To lessen the squish clearance, wouldn't it work better to machine the head gasket surface of the cylinder?
    Or the base gasket surface if one wanted to tone down a hard-to-ride power delivery?
    #51
  12. Twin-shocker

    Twin-shocker Long timer

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    In some cases there is no need for any sort of machining at all. Removing head and base gaskets is all you will need. I would be very cautious over using someone offering to machine heads on the basis of solder, for the simple reason that if the solder test isnt done perfectly then neither will the head machining. Taking the motor to someone who knows exactly what they are doing is the only real option for this type of work, but in most cases closing the clearance by the 1mm that will be provided by removing the gaskets, will be all thats needed on roadgoing motors.
    #52
  13. willis 2000

    willis 2000 neo-quixote

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    What will be used to seal the cylinder? I imagine machining will be required to square up the contact points.
    #53
  14. stainlesscycle

    stainlesscycle Long timer

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    if you remove the base gasket you change exhaust port height and to a lesser effect intake/boost port height.. machining the head (or removing head gasket/using thinner head gasket) is the only way to modify squish without affecting port timing. most water cooled motors (and many air cooled) don't have head gasket, so head machining is the way. you can modify squish by changing the base gasket stack, but it will effect port timing, sometimes enough to have a drastic effect on the top end rpm - not always in a good way.. you can easily lose massive top end hp if your exhaust port doesn't open all the way due to no base gasket.

    solder check works fine. there is a reason he asks for 3 solder samples. repeatability. it's kinda hard to do it wrong.


    also, most are not just decking the head. the head gets reshaped to get better squish, and optimum combustion chamber volume. there's more to it than just turning off some of the head to cylinder mating surface.
    #54
  15. stainlesscycle

    stainlesscycle Long timer

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    jetting and ignition timing ( and power valve adjustment - if it's got one) can adjust hard to ride power delivery. and it's reversable...
    #55
  16. Twin-shocker

    Twin-shocker Long timer

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    Running without a base gasket tends to improve mid range torque and low end pick up, but the effects of this are likely to be hard to detect on road going motors. On air cooled 2T bikes which have head gaskets, in most cases its possible to run without, after lapping the head to the cylinder using fine grinding paste, and using high temperature silicone sealer on both top and bottom deck faces when building.

    The main thing in favour of seeing how a bike runs without the gaskets, is that it costs very little to do, and unlike bodged machining jobs, is not going to mean a need for new parts, if there is a need to go back to stock set up.

    Whether someone provides 3 or 300 pieces of crushed solder to indicate what squish clearance they might have, isnt going to alter the fact that if measuring using this method hasnt been done properly, the results are going to be far from accurate, which kind of gets away from the point of adjusting the clearance in the first place.
    #56
  17. stainlesscycle

    stainlesscycle Long timer

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    there are so many wrong statements in your post, i'm not gonna bother.
    #57
  18. Strong Bad

    Strong Bad n00balicious

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    For sealing a head without a gasket. EC Birt's solution back in the day was to go to a paint store for a can of silver paint, he would reach back and get the one that has been sitting undisturbed for the longest time. Without disturbing the paint he would drain off all of the can's contents but the gooey residue paste at the bottom. He would "paint" the gasket surface with this goo to create the seal.
    #58
  19. Twin-shocker

    Twin-shocker Long timer

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    Seems to work very well in the real world, so glad you didnt bother to reply from the perspective of a Google Gary.....................
    #59
  20. stainlesscycle

    stainlesscycle Long timer

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    i don't google shit about tuning. so much bad info out there.
    #60