Announcement

Collapse
No announcement yet.

Compression and spark plug reach

Collapse
X
Collapse
 
  • Page of 1
  • Filter
  • Time
  • Show
Clear All
new posts
Previous template Next
  • #1

    Compression and spark plug reach

    I've just re-read the article here on compression testing and I'm wondering how much the wrong length of tester (relating to spark plug reach) can throw off compression results?

    I have a 92 650SX and tested it with the stock head and a brand new compression tester and got a consistent 150psi reading off both cylinders. I then put on a new high comp. head and re-tesed with a consistent reading in both cylinders between 190-192psi.

    So first off...is 150psi about right for a stock 650SX?

    Second, could the wrong tester reach throw the results WAY off?

    Basically if my test is wrong then I may actually have lower compression and be able to stay with pump gas....if not I may have to pull the head cause I ain't payin for race gas ;)

    BTW...what exactly is the spark plug reach? the length of the threaded part of the plug?

    TIA

    Cheers

    [ February 24, 2004, 11:15 AM: Message edited by: ColdFusion ]
    Tags: None
  • #2
    Yes the reach is the threaded area. It makes about a 5psi differnce if you are too long or too short.
    SBT Tech Support is here to help with your problems.
    We try to answer each question quickly and accurately.
    Please do not use Private Messaging for Tech Support, use the forums.

    Comment

    • #3
      Great...thanks...one more piece of the puzzle ;)

      So is 150psi about right for a stock 92 650SX? If it is then I know I've tested right...if not then mabye I'm screwing something up ;)

      Cheers

      [ February 24, 2004, 12:05 PM: Message edited by: ColdFusion ]

      Comment

      • #4
        Yes 150psi is about right for a Kaw 650.
        Steve

        Comment

        • #5
          Just FYI - don't edit your post after people have replied - we don't see your additional questions!
          SBT Tech Support is here to help with your problems.
          We try to answer each question quickly and accurately.
          Please do not use Private Messaging for Tech Support, use the forums.

          Comment

          • #6
            hmmm...I edited it right after I posted it (my second message in this thread)...but yes...good advice ;)

            Thanks for the confirm on the stock psi...at least I know I tested it correctly with the stock head.

            Now I just have to sort out if I really need avgas or race fuel now that it's at 190psi. I sure wish there was some definitive way to know if any damgae is being caused with this new head (so many opinions).

            1) manufacturer says it should be fine with pump gas

            2) others say the worst is pre-iginition or detonation

            3) some even say the engine may seize (not sure why....heat mabye)

            4) I rode it and it seemed fine (faster though...and with 94 octane pump gas)...no loss of power at low/mid/top...no sputtering...just a bit rough at idle...simply nothing that made me say...hmmmmm...that's not right

            I've also heard that if I see silver dusting on the plugs that something is wrong (which I will check for next time out).

            Anyways....thanks for the advice...and if anyone can tell me what to look for...I'd be a really happy camper ;)

            Cheers

            Comment

            • #7
              To all following my compression issue!!

              I'm a complete fool ;)

              My original compression tests were done with the wrong adapter on the guage (too short of a reach). This threw off the results by 20 psi (not 5 as suggested above...just FYI)!!!

              So stock was about 135 psi and it is now 170 psi....pump gas it is (and perhaps a looksee at the old brain to make sure it's still firing on all cylinders)

              Thanks to all that have offered up advice [img]smile.gif[/img]

              Cheers

              Comment

              • #8
                Can't say I've seen either a 1/4" reach differnce make a 20psi compression reading differnce, OR a stoch 650 blow 170psi.

                If your first adaptor was cheap and had no schrader valve att he end, that could explain the 20 psi. The 170 stock compression? Got me.
                SBT Tech Support is here to help with your problems.
                We try to answer each question quickly and accurately.
                Please do not use Private Messaging for Tech Support, use the forums.

                Comment

                • #9
                  LOL...it was 135 psi stock...with the new head it is 170 psi ;)

                  The reach difference (between the 2 different reaches my gauge has) was more like 1/2" so that may explain things ;)

                  Thanks again

                  Comment

                  • #10
                    Then one of your adaptors is non-standard. The two sizes used on skis are 1/2" and 3/4".

                    It always pays to use quality equipment so you are sure of your readings.
                    SBT Tech Support is here to help with your problems.
                    We try to answer each question quickly and accurately.
                    Please do not use Private Messaging for Tech Support, use the forums.

                    Comment

                    • #11
                      Well it's not a ski specific gauge....for any Canadians reading...I got it at Canadian Tire ;)

                      I whipped up a quickie web page to show the gauge and what why it sucks...please check out this link:

                      http://142.179.101.53/clients/bryan/jetski/gauge/

                      Thanks again for all the help folks

                      Lucky for me I found Chester who is a jet ski mechanic on the mainland and actually used to race a 650...so he knows the ski and has lots of great advice.

                      Cheers

                      Comment

                      • #12
                        YOW talk about needing race gas! lol
                        SBT Tech Support is here to help with your problems.
                        We try to answer each question quickly and accurately.
                        Please do not use Private Messaging for Tech Support, use the forums.

                        Comment

                        Previous template Next
                        Working...
                        X