How much compression do you have with standard head and RockSolidEngines Billet Head

Discussion in '2-Stroke Engines' started by Fabian, Nov 23, 2009.

  1. Fabian

    Fabian Well-Known Member

    G'day all

    I'm curious if people who have bought the Rock Solid Engines, billet cylinder head, can do a compression test and give the compression reading in PSI.

    If you have a standard cylinder head, do the same thing and let me know what reading you are getting.

    If you don't know, the correct way to measure engine compression is to screw your compression gauge into the sparkplug hole and hold the throttle in the wide open position (full throttle) whilst pedaling the engine over quickly or just ride and drop the clutch if you have a single speed drive system.

    Cheers Fabian
    Last edited: Nov 23, 2009

  2. Al.Fisherman

    Al.Fisherman Active Member

    If you have installed a compression tester, you would be hard pressed to start the engine without a spark plug, hence you wouldn't need to press the kill switch.
  3. Fabian

    Fabian Well-Known Member

    point taken.
  4. gothicguy64

    gothicguy64 Member

    hi mate .
    1 i ride a full rocksolid chainless an 50cc hp1 with billett head ...
    my compression is much higher than standard 48..
    top of 64kmh with 44 tooth rear ..
    added a poo poo goes 55 kmh but much quicker at take off .
    if u need help with tech ask tony at rocksolid
    an u need a race piston for nos i have1 fitted ......
  5. 210061741

    210061741 Guest


    Hows that racing piston working out.
    Is it one of the ceramic coated ones from RockSolid.
    I been looking at thoose.

    Wouldn't mind having one.

    Any input?
  6. AussieSteve

    AussieSteve Active Member

    Test-rode mine today. Works well, starts better.
    I have a compression gauge, but it's the type with a rubber tip, for holding against the plug hole - no thread. I'll enlist the help of the next visitor through the door to hold the gauge while I lift the rear wheel and try to spin it hard enough. I'll let you know how I go.
    ... Steve
  7. Fabian

    Fabian Well-Known Member

    Hi AussieSteve

    I'll get myself a screw-in compression gauge and do a test on my Rock Solid Engine with Billet Head and post the results.

    Be interesting to see how large or how small the compression variation is between engines and compression increase with the billet head over a standard head.

    Last edited: Nov 24, 2009
  8. AussieSteve

    AussieSteve Active Member

    I'll have a look for a screw-in type myself in the morning at SCA. They sound easier to use than mine.
    Something I just thought of, though. My engine isn't fully run in yet, 290km so far, so compression might not be up to max. The top ring appears about half bedded in, but the bottom one looks like it has just been fitted. (Don't know if it'll make much difference.)
    I've attached a pic with the head fitted for anyone who hasn't seen them yet.
    ... Steve


    Attached Files:

  9. 210061741

    210061741 Guest

    That head looks sweet.
    I love it.
  10. clay

    clay Member

    mine made 125psi, but it was a stock head that was welded up.
  11. AussieSteve

    AussieSteve Active Member

    So do I. After a second ride, same opinion. Starts better, idles better, a bit more power all through the rev range. The engine seems to like it, like it should have been standard.
    Also, RSE's billet head is much meatier than the stock head, with roughly double thickness fins etc.

    Hello Clay, I read the threads on your mods with interest, a couple of weeks ago. Good job. Be interested to see how mine and Fabian's compressions compare with yours.

    Fabian, I didn't get a chance to look for a screw-in comp gauge today. Had to catch up on a few chores. Tomorrow.

    ... Steve
    Last edited: Nov 24, 2009
  12. AussieSteve

    AussieSteve Active Member

    Here's mountain80's stock compression. (Not sure about the 160psi, though. If the only mod was 50 thou off the head, that sounds high.):-

    Thread Title: Compression Numbers
    ... Steve
  13. AussieSteve

    AussieSteve Active Member

    Sorry to hog the thread. Got a screw-in tester today. (SuperCheapAuto, Product #12556, $45AU)
    Result: 135psi with RSE billet head.
    Tested twice, WOT, normal starting speed.
    A bit of extra advice. CDI units don't like being charged without firing. When doing tests of this sort, it's a good idea to stick a plug in the cap and hang it on the head to allow the CDI to discharge. They can otherwise build up higher than normal voltages and fail (prematurely).
    ... Steve
    Last edited: Nov 25, 2009
  14. Fabian

    Fabian Well-Known Member


    I've done a compression test on my Rock Solid Engine with Billet Cylinder Head.
    The compression does not seem to have changed (either increased or decreased from brand new) since i've installed it in my bike.

    I've done approx 80 kilometers of distance on the engine.
    I'm getting a repeatable 90 PSI or 600 Kpa from a high quality, professional grade, compression gauge.

    How much compression does a standard, non angled plug, cylinder head have on a 70cc engine - very curious to know the figure.

    Last edited: Nov 26, 2009
  15. AussieSteve

    AussieSteve Active Member

    You're kidding? Only 90psi? That sounds pretty low to me. Are you sure the gauge isn't sticking or something? (Even 'high quality, professional grade, compression gauge's can be faulty.)
    My new gauge is only a cheapie at $45, but I doubt if the error could be 45psi.
    Mine's a stock, (except for the billet head), new series ZBox 66cc, did 290km before fitting the new head and about 20km after, before the comp. test.
    Have you talked compression with Tony Ciccio at RSE?
    ... Steve
  16. Fabian

    Fabian Well-Known Member

    Tony is aware of my situation and is in the process of sending me another cylinder and a set of piston rings.
    He went as far as saying that he would refund my money and also pay for the postage costs, and then run the engine to it's limits on his dyno to find out if and why there might be a problem.

    For some unknown reason my engine is seriously down on compression, despite the leak-down test on my engine being perfect when it left his factory.

    It's quite strange as his other customers have reported a significant increase in compression and power, which would stand to reason.
    My engine just isn't doing what it should be doing and yet, i know that it should be doing quite a bit more than what it's doing.

  17. Fabian

    Fabian Well-Known Member

    As i have a SickBikeParts shift kit, it's a pain, to keep changing over engines and the quality of castings of the Rock Solid Engine are much better than the standard Chinese engine as is the sealing method of magneto wires exiting the engine.
    The quality of chrome on the cylinder bore is also much better on the Rock Solid Engine, not to mention a quality set of bearings installed in the engine.

    In saying that, it's easier for me to keep the engine in the frame.
    Tony is sending me another cylinder and a set of piston rings.

    I knew something wasn't right as the bike didn't seem to have any more compression than a standard engine, from the first test run.

    We compared compression gauges by using another gauge from an auto repair shop a few doors down.
    90 PSI is all i'm getting.

    I am still confident that everything will work out well as Tony stands behind his product and services.

    Last edited: Nov 26, 2009
  18. AussieSteve

    AussieSteve Active Member

    Out of sheer curiosity, I'll bolt the stock, (unmodified), head back on tomorrow and do the same test, for comparison with the billet head's compression. I have a spare head gasket sitting here doing nothing.

    Another thought, Fabian. Are you running the recommended oil ratio or somewhere near it? These engine's need a lot to seal well, I'm told. I'm still running 16:1 for now.

    ... Steve
    Last edited: Nov 26, 2009
  19. Fabian

    Fabian Well-Known Member

    20:1 is what i'm using with 98 octane fuel
  20. mountain80

    mountain80 Member

    Hey Aussie steve....Yes it is 160 psi with 50 thou off the head, im an ex motorcycle mechanic among other things and the smaller the combustion chamber the more psi you get when shaving the head. The intake timing and duration has been changed and the pressure was checked with proffesional tools NOT backyard mechanic quality.