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  1. #1
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    Pressure Testing Two Stroke Engines

    What is pressure testing?

    Pressure testing is a test performed on a two stroke engine to ensure that the engine has no air leaks. An air leak in a two stroke engine can cause a lean condition in your engines air-fuel mixture. This in turn can result in serious engine damage. For example: Piston seizure, detonation, etc.

    Note: There is absolutely no way to ensure that your engine doesnít have an air leak without performing the following test.

    To pressure test your engine you will need a few special items. See below for instructions on building your own pressure test device. To test the engine: cylinder, head, reed cage, intake manifold and spark plug must all be installed and properly torqued. Exhaust pipe and carb must not be installed.

    Here is a pic of a typical Mikuni Pressure Test Kit than can be found at many places on the iternet.


    A steel or aluminum plate must be bolted onto the exhaust side of the cylinder using a piece of rubber as a gasket.
    A round fitting with pressure gage attached should be clamped into the intake manifold on the cylinder.
    With equipment in place, use a hand pump to fill the sealed engine with 6-8 lbs of air pressure.
    Once 6 lbs of pressure is pumped into the engine. Set a timer for 6 minutes.
    Engine must hold a full 6 lbs of pressure for 6 minutes without any loss.
    A tight motor should be able to hold this setting for more than 10 minutes without losing any air.

    Rule of Thumb The normal bleed-down pressure loss is 1 psi per minute.


    If gauge shows a loss of pressure, squirt all gasket surfaces with a water based soapy solution (Windex, 409, etc.) If there is a leak at any surface you will see soap bubbles. Re-torque any areas that leak.

    If you cannot locate the leak by looking externally, consult a qualified two stroke mechanic.

    If after 6 minutes the gauge shows no loss in pressure, remove testing equipment and continue assembly of machine.

    Building your own pressure testing device. All parts can be found at any good hardware store. total cost should be around $15.


    Below are some pics that GPR Veteran Fernando Delgado (Fercho) posted on his web page
    http://www.hydrotoys.com/gpr/tuners/fernando/









    References:

    http://www.off-road.com/atv/ptester.htm

    http://www.macdizzy.com/thread_spread.htm

    http://www.off-road.com/dirtbike/aug99/gorr/


  2. #2

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    As usual - great information to have. Simply awsome Billy!

  3. #3
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    for those that like the fancy ones, here is one by Motion Pro

    http://www.off-road.com/dunes/produc...pro/july_2000/


    [/list]

  4. #4

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    !!! THIS IS NOT COMPRESSION TESTING YOUR CYLINDERS !!!

    This is more than just a standard "Billy's Great Post."

    This is the ONE post that everyone should get to understand.
    A ton of tuning differences, as well as siezed pistons and trashed engines can be directly related to leaky cases on two strokes.

    Areas of concern:
    Rear seal.
    Reed cage area.
    cylinder base.
    case halves.
    head gasket or oring.
    front seal.
    Pulse lines.
    Cracks in the assembly.
    Intake/carb mounting.

  5. #5
    WE DONT DIAL 911
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    hey guys i was reading through this and something caught my eye... does the rule of thumb (1 psi loss for every minute) only apply after the completed 6lbs for 6min?? should you expect a loss of pressure after the alloted time?

  6. #6
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    Lowell Horning has a nice custom made pressure test kit for sale.
    http://www.2-stroke-porting.com/

  7. #7

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    I purchased my kit from Lowell.

    Well worth the ninty bucks. The first time I put it together there was
    a leak in the head that lasted 15 mins.

  8. #8

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    Quote Originally Posted by mtrager View Post
    I purchased my kit from Lowell.

    Well worth the ninty bucks. The first time I put it together there was
    a leak in the head that lasted 15 mins.

    hi mark,do i ask lowell for a efi test kit or is there a few to choose from...

    paul

  9. #9

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    Quote Originally Posted by RDH View Post
    hey guys i was reading through this and something caught my eye... does the rule of thumb (1 psi loss for every minute) only apply after the completed 6lbs for 6min?? should you expect a loss of pressure after the alloted time?
    It's capable of getting below 1psi a minute. I've had plenty hold pressure for a very long time. You do have to refill it the first time, to get all the crevices filled with pressure.

  10. #10
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    Quote Originally Posted by Hydrotherapy View Post
    hi mark,do i ask lowell for a efi test kit or is there a few to choose from...

    paul
    Paul test is done with intake plugged. so you have to remove carbs, EFI.
    I leave my reeds installed as the VF III's are more challenging to seal.

    I will never build a motor again without pressure testing before use.

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