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  • milling 650 head

    I purchased a 650 engine from SBT last year. It has been a great engine...thanks a million. My question is this: the warranty is about to run out and I was thinking of having the head milled and taping a second cooling line into the head. Is this a wise move or not? I do not want to screw up a good thing, but always could use a tad more performance.
    I know the engines are bored 1 over and brought back down to stock compression, but I do not know what affects milling the head will have on it. I do want reliability and want to continue using pump gas.
    What is recommended? How much should it be milled if it should be?
    Thanks,
    Brian
    Brian

  • #2
    Hi Brian;
    Sure, increasing the compression ratio of your 650 is a good mod if you're looking for more low end "snap". The only real consequence is the need to run high octane fuel. You can either send your OEM head out to a reputable PWC machine shop, or look around for a used Westcoast head with a set of pump gas compatible domes, which is the only aftermarket head I would recommend for the 650. I can check my old notebook, but I seem to remember running Westcoast 29 and 30 CC domes on premium pump fuel in my 650 X-2. You might luck out and find new Westcoast parts, but they are out of production.

    If you modify your OEM head, both the sealing surface and the "squish" band on the head will need attention from the machinist, and it's best to employ an experienced PWC machine shop for such work. Be sure to specify your engine's current bore size, your desire to burn 92 octane fuel, and any other cylinder pressure enhancing mods like an aftermarket pipe, or ignition timing advance. After an OEM head has been milled, I also recommend thicker or additional SS washers under the head-retaining acorn nuts to prevent the cylinder studs from bottoming out inside the nuts.

    A second cooling water "out" line is a good idea, since it allows you to balance your front and rear cylinder temps, but keep in mind that you should also modify your head gasket as well by opening up the restricted hole on the carb side of the gasket so that the front and rear diameters are the same.

    Dan

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    • #3
      Ok, I am ready to mill my head, and have looked around since the last post and have not seen any Westcoast heads for sale; therefore, I am just going to have my stock head milled.

      What is a safe level for this ski?

      I checked compression last night and it was 120 on rear and 110 on front. What does SBT put them at from the factory? I know they say they put it back to the OEM setting. What is that? Bryan??? The manual says stock is anywhere from 125 to low 190's. That seems like a big jump, what should it be stock?

      Who do you recommend doing this mod?
      Brian

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      • #4
        I don't have any experience with that mod of that engine, but I can tell you we set them up to 145ish coming out of there. From the details in your email I'd say get a working gauge to test by, and if you still have those readings, you have damage.

        Comment


        • #5
          Posted by Brian:
          Ok, I got a new, good compression tester last night and checked my compression. It is reading 100psi +/- 1 or 2 psi on both cylinders.

          I had the ski at the lake Tuesday night and it seems to run good. There are a few times when it seemed sluggish on the low end, but overall it ran pretty good.

          I figured maybe the head bolts needed to be retorqued and there was one or two that were loose and one that just spun when I tried torqueing it. I pulled the head off, so that I could fix the stripped bolt, which I will do tonight after getting a heli coil kit. It is of course the one I do not yet have.

          The head looked great and so did the top of the pistons and the cylinder walls. What should I look for or test. Is it likely that the stripped bolt caused the poor compression? It is the #2 bolt (outside on exhaust side) if I remember correctly on the 650 kawi engine.

          Also, are the gaskets reuseable if I put new gasket sealer on or should I get a new one every time I pull the head off? What is the rule of thumb? The gasket looks good, except the black sealent has come off.
          Thanks,
          --------------------
          Brian

          Comment


          • #6
            OK, first of all, your readings at this point are moot, as you have been reusing your head gasket, and totally screwing up the compression. You MUST use a new gasket everytime you pull the head for correct compression, every time.

            Second, get new gaskets (get more than one at a time if you know you'll be pulling heads), and treat them with Permatex Copper-Spray-A-Gasket. What 'black sealer' were you using?

            Then take new readings.

            Comment


            • #7
              OK...I have not been reuseing head gaskets...the black sealer is the film that cover the gasket when new. It is SBT's gasket...this is the 1st time I pulled this head, since having this ski.

              This said, the readings are right on and should mean something. I pulled the head after taking the readings and have not had a chance to put it back on as I have not fixed the stripped out stud yet. I plan on fixing that and putting the head back on. That is why I was asking if it is alright to reuse or if I should buy a new one (gasket that is).

              I am asking this question because I want to know if I should check anything else while the head is off. I do not mind putting the head on and off, but (and not trying to be tight) do not really want to throw away $27 (cost of head gasket) every time I put the head on and take it off...if I am trouble shooting.
              Brian

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              • #8
                If you got readings of 110 and 120, then used a different gauge and got 100-100, something is wrong with that second gauge or your test procedure. Normally when that happens, it means teh head was pulled and reasembled using the now-leaking head gasket.

                Did you add oil to the combustion chambers on that first test or something? Make sure you are following the instructions in this article when you do the test.

                Comment


                • #9
                  Hi Brian;
                  As Bryan mentioned, you can reuse undamaged OEM steel shim head gaskets if you carefully clean off the sealer (use a solvent such as acetone and fine steel wool) then spray both sides of the gasket with Permatex (or similar) "Copper Coat", which you can find at most auto parts stores.

                  Since you're near sea level in Wichita, 100 PSI of cranking compression is somewhat low. The good news is that since both cylinder readings appear to be within 10% of each other, I suspect that the engine is fine and your test gauge or proceedure may be at fault.

                  What type of compression gauge are you using for your tests? Not one of those K-Mart specials I hope. Is there a Schrader (tire valve) built into the screw-in adapter? Are you using an adapter that has the same 3/4" reach dimensions as your sparkplug? If the gauge sparkplug adapter doesn't occupy the same chamber volume as a sparkplug, your readings will be low.

                  Dan

                  Comment


                  • #10
                    The compression tester I used before, I do not trust...as it had been sitting in a tool box with wet life jackets and such and had moisture in the lense area and the o-rings did not seat well.

                    The one I bought I got from Harbor freight and was told it was good. I have looked around and do not seem to have much to choose from. I attached the link of the exact gauge I have if you want to give an opinion, as I admit I am trying to learn. "http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=39224" It was not their cheapy, but the only other one they had was for diesels. The person I spoke with said he used that guage on his race car. (may or may not mean anything, but he recommeded it.)

                    I am not sure the reach was 3/4" it may have been 1/2" it was the only one that fit and I did not realize that mattered, nor did I know 3/4" was the one to use. I will go out and buy a 3/4" reach tonight when I go to get the heli-coil kit. How much diffence would that make? ...a few PSI, or 10-20?

                    I tried the test with one plug in and one out and with both plugs out and got the same readings. (plugs were grounded on the head)

                    The head had not been pulled, but may have been leaky as I mentioned the #2 bolt was not tight and stripped easily when I tried to torque it. I think 2 other bolts in that area were only about 110ft lbs tight...manual called for 122ft lbs. All others were at least 122ft lbs. I tightened what I could and still got the 100lbs of compresion.

                    Is cleaning up the gasket and spraying good enough to get a good test reading? I do not mind buying a gasket if it reads good and I know I am not going to be pulling the head right back off. (I will buy the gasket if need be for the test though. I am not trying to be cheap, but also do not like throwing money away...kind of suprising I love to jet ski!!!)

                    Sorry about the start of a new thread, I guess I did not really think about it!

                    Also, the ski did diesel (rev'd real high while on trailer and did not turn off when I hit the stop button. I knew how to stop it with the throttle at WOT and it did not have a chance to get to hot to touch)on me the other day! I did not think about it earlier because I had been told it was fairly common, but could the two be connected?
                    Brian

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                    • #11
                      The compression tester I used before, I do not trust...as it had been sitting in a tool box with wet life jackets and such and had moisture in the lense area and the o-rings did not seat well.
                      Throw that gauge out.

                      The one I bought I got from Harbor freight and was told it was good.
                      At $19, you don't get good. You might get something to give you a ball-park reading in some situations, but it's not any kind of precision gauge. As long as the hose has a valve at the end of it, AND at the gauge base, AND you use the correct 3/4" reach adptor, AND everything is sealed right, it should give you a good reading for this test though.

                      I will go out and buy a 3/4" reach tonight when I go to get the heli-coil kit. How much diffence would that make? ...a few PSI, or 10-20?
                      It makes a huge difference, as it adds several cc's with too short of a reach. 10-20 would be on the low side.

                      The head had not been pulled, but may have been leaky as I mentioned the #2 bolt was not tight and stripped easily when I tried to torque it. I think 2 other bolts in that area were only about 110ft lbs tight...manual called for 122ft lbs. All others were at least 122ft lbs. I tightened what I could and still got the 100lbs of compresion.
                      I hope that was a series of type-o's - the head torque should be 22, not 122.

                      Is cleaning up the gasket and spraying good enough to get a good test reading?
                      *Maybe* once, but not gauranteed, and I would personally not actually run it on a gasket that has been compressed even once, and removed.

                      Also, the ski did diesel (rev'd real high while on trailer and did not turn off when I hit the stop button.
                      This can and does certainly do damage, the severety of which is not known until you get a good compression reading and tear it down for inspection is needed. You are basically running it to the point of ring float, with no lubrication after a few seconds of it starting.

                      Comment


                      • #12
                        Originally posted by Bryan Glynn:
                        [
                        Throw that gauge out.

                        It is not my guage, and the guy who's it is does not understand why I think it is not accurate...his response is, well it reads consistant. Don't ask!!!


                        [/QUOTE]It makes a huge difference, as it adds several cc's with too short of a reach. 10-20 would be on the low side.

                        Maybe, the bad bolt and that is my problem, like I said, this ski runs great...

                        [/QUOTE]I hope that was a series of type-o's - the head torque should be 22, not 122.

                        Let's say it was a memory lapse...I read the reading right out of the Kawi owner's manual. I am sure it was 22 not the 122. I know I did it right. I suppose 122 would be awfully tight...

                        [/QUOTE]*Maybe* once, but not gauranteed, and I would personally not actually run it on a gasket that has been compressed even once, and removed.

                        Do you guys sell just the head gaskets? How much? I think my shop is ripping me off...and when I called I told them Kawi 650sx and they were sure I was speaking of Yamaha. They immediately think motorcylce. I suppose that is why I do not like them much, but they are good for the little stuff...

                        [/Quote], the severety of which is not known until you get a good compression reading and tear it down for inspection is needed. You are basically running it to the point of ring float, with no lubrication after a few seconds of it starting.[/QB][/QUOTE]

                        Not to make guesses, but it did not run for more than a sec or two...just long enough to start to yank the hood, then think throttle and act. My friend was shocked at how quickly I got it to stop. I was immediately able to put my hand on the block without even starting to burn it or be unconfortable.
                        Brian

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                        • #13
                          I would not suspect any damage from your runaway.

                          Yes we have the head gaskets for $25.

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                          • #14
                            I will get the 3/4" reach for my guage and clean up the gasket real good and spray the sealer on it, fix the thread and try it again. If all looks good, then I will buy a new gasket and go from there. If not I will let you know what I find. If there is wear on either the piston or the rings, is it possible to go bigger yet? ..or is 1 over the most I can safely go? I honestly think the pistons and rings are fine, but I have put a bunch of hours on this engine.

                            Thanks,
                            Brian

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                            • #15
                              you can go 1.5mm.

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