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Griffon 380 - QUB Piston inlet side cutaway

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  • Griffon 380 - QUB Piston inlet side cutaway

    Hi All,
    I got my new piston today from Simon (woopey) and it is better than his previous one - this one being forged not cast.

    My Old piston (also supplied by Simon - about 3 years ago - on the basis that the old piston her replaced already had this mod.....) though this one has a 3/16" cutaway on the back (inlet) side - which will raise the inlet port timing vs standard............The bike flies - so clearly I will look to replicate this on the new piston - but wondered whether any body else has had experience of such a mod on a 380 griffon.......before I make the 'snip' on what is a very expensive piece of hardware !!
    Cheers Kim

  • #2
    Originally posted by Kim275 View Post
    Hi All,
    I got my new piston today from Simon (woopey) and it is better than his previous one - this one being forged not cast.

    My Old piston (also supplied by Simon - about 3 years ago - on the basis that the old piston her replaced already had this mod.....) though this one has a 3/16" cutaway on the back (inlet) side - which will raise the inlet port timing vs standard............The bike flies - so clearly I will look to replicate this on the new piston - but wondered whether any body else has had experience of such a mod on a 380 griffon.......before I make the 'snip' on what is a very expensive piece of hardware !!
    Cheers Kim

    Hi Kim,

    This is a common mod on all piston-ported bikes, but 3/16" is quite a lot! Mine is only about 1.5 mm, but that is off the whole of the rear piston skirt. This is for an "ordinary" 380 Griffon, not a QUB, which may be different as standard anyway.
    If it worked fine before, then I can't see any reason why it wouldn't work again! Go for it!

    As a matter of interest, do you have somewhere near you for running-in purposes? Its just that your're not that far from me, and I have to drive 25 miles to my nearest practice track!

    Cheers,
    Andrew
    #190

    Comment


    • #3
      Originally posted by Andy Z View Post
      Hi Kim,

      This is a common mod on all piston-ported bikes, but 3/16" is quite a lot! Mine is only about 1.5 mm, but that is off the whole of the rear piston skirt. This is for an "ordinary" 380 Griffon, not a QUB, which may be different as standard anyway.
      If it worked fine before, then I can't see any reason why it wouldn't work again! Go for it!

      As a matter of interest, do you have somewhere near you for running-in purposes? Its just that your're not that far from me, and I have to drive 25 miles to my nearest practice track!

      Cheers,
      Andrew
      #190
      Hi Andy and Kim.

      Yep, same with me... Nick Nicholson told me this trick many years ago when those darn Honda Elsinore's came out and was pulling me bad on the straights.

      I think we raised the exhaust port a little too.

      regards,
      Kenny Sykes

      Comment


      • #4
        Thanks Kenny I will go for the 3/16 snip !!
        Andy my nearest practice is Gingers near lingfield now Churchill mx if you haven't tried this one then it is classic friendly .... They let me take the griffon on the main track in the kids session ....... Avoids getting beaten up by 450 fs but of course you have to watch out for quick kids on their 80cc's
        Where are you based?
        Cheers Kim

        Comment


        • #5
          Originally posted by Kim275 View Post
          Thanks Kenny I will go for the 3/16 snip !!
          Andy my nearest practice is Gingers near lingfield now Churchill mx if you haven't tried this one then it is classic friendly .... They let me take the griffon on the main track in the kids session ....... Avoids getting beaten up by 450 fs but of course you have to watch out for quick kids on their 80cc's
          Where are you based?
          Cheers Kim
          Hi Kim,

          I'm in Sevenoaks. Lingfield would be great, as I go to Harrietsham, which is not classic friendly at all! However, the people who run it are very friendly, and let you use the track whenever you want, even if nobody is there. You just put you £20 through the letterbox and ride!

          Lingfield is much closer, so I'll have to give it a go. I can't believe I've never heard of it. I've looked at it on the map, and I must have been past there about 50 times!

          Cheers,
          Andrew

          Comment


          • #6
            Originally posted by Kim275 View Post
            Thanks Kenny I will go for the 3/16 snip !!
            Andy my nearest practice is Gingers near lingfield now Churchill mx if you haven't tried this one then it is classic friendly .... They let me take the griffon on the main track in the kids session ....... Avoids getting beaten up by 450 fs but of course you have to watch out for quick kids on their 80cc's
            Where are you based?
            Cheers Kim
            Hi Kim,

            I think I did like Andy, about 1.5mm on my 250 Griffon.

            Wish I could go riding with you guys!

            Have fun!
            Kenny

            Comment


            • #7
              When I worked for Dave Rayner it was a common mod on DT175MX, 2mm off piston and 1.5 off top of exhaust port .

              Chris

              Comment


              • #8
                Originally posted by riflegreen View Post
                When I worked for Dave Rayner it was a common mod on DT175MX, 2mm off piston and 1.5 off top of exhaust port .

                Chris
                Chris,

                Nick wrote it down on a note for me visiting NNM one summer and my Dad did all the work... back in 72 if I recall...gained a little more on the top end.

                Kenny

                Comment


                • #9
                  griffon mod

                  i have 2 twinports did you say 1.5mm or 3/16 from th inlet side ? possibly 1mm from the exhaust ports ? then acording to rifle green in pecentage ?

                  good news for all us griffon nuts ! found out tallon make and sell front sprockets for the final drive ! £14 ?

                  and you saying the 250 as well take 1.5 mm off as well ?

                  Comment


                  • #10
                    Gary ,

                    Be carefull taking metal from the exhaust port , you can't put back what you have taken out .

                    Not sure what you mean by " then acording to rifle green in pecentage ? ".

                    And Gary check your PMs.

                    Chris
                    Last edited by riflegreen; 11/06/2011, 10:28 AM. Reason: Spelling

                    Comment


                    • #11
                      Originally posted by riflegreen View Post
                      Gary ,

                      Be carefull taking metal from the exhaust port , you can't put back what you have taken out .

                      Not sure what you mean by " then acording to rifle green in pecentage ? ".

                      And Gary check your PMs.

                      Chris
                      Hi Chris,

                      These days I leave the exhaust port alone, because you never know what was done before. I just clean and polish around the outlet a little.

                      Kenny

                      Comment


                      • #12
                        Originally posted by Bearingman View Post
                        Hi Kim,

                        I think I did like Andy, about 1.5mm on my 250 Griffon.

                        Wish I could go riding with you guys!

                        Have fun!
                        Kenny
                        hi Kenny .... Wish I could ride in CA !!! Thanks for your assistance ..... Andy I got big griff back together today do I will head over to Gingers (churchills mx ) tomorrow to run in the new piston and liner. Head over if you fancy a blast Cheers Kim
                        P.sGary for 380 3/16 th off inlet side of carb . No mods to exhaust port. And it flies !!

                        Comment


                        • #13
                          Originally posted by Kim275 View Post
                          hi Kenny .... Wish I could ride in CA !!! Thanks for your assistance ..... Andy I got big griff back together today do I will head over to Gingers (churchills mx ) tomorrow to run in the new piston and liner. Head over if you fancy a blast Cheers Kim
                          P.sGary for 380 3/16 th off inlet side of carb . No mods to exhaust port. And it flies !!
                          Hi Kim & Kenny
                          Yes, I was thinking how much I would rather be riding in CA too!!

                          I would love to go to the practice track tomorrow, but unfortunately I'm booked on a Family cycling day!

                          Good luck,

                          Cheers,
                          Andrew

                          Comment


                          • #14
                            Originally posted by kim275 View Post
                            hi kenny .... Wish i could ride in ca !!! Thanks for your assistance ..... Andy i got big griff back together today do i will head over to gingers (churchills mx ) tomorrow to run in the new piston and liner. Head over if you fancy a blast cheers kim
                            p.sgary for 380 3/16 th off inlet side of carb . No mods to exhaust port. And it flies !!
                            im gettin real curious to machining the piston ! And matching the exhaust ports in the triumph book it tells you to remove the nub on the inlet of the car as well and m/c a slot for better fuel supply

                            Comment


                            • #15
                              Hi All,
                              Tested the bike yesterday -and all went well (and yes Kenny - in true british fashion it rained!!! ) - gearbox slick after re-build (much quieter when it actually holds oil!!)

                              New barrel (slimline aka Arthur Browning) and piston from Simon worked well - especially on the mid to top end.....although on kicking I noticed less compression than my other QUB barrel...........still ran well though . When I got home I checked the head - and found out why..........It must have had some machining at some stage - and there was an additiona1 approx 1mm of space compared to my other head....so I removed a base paper gasket to adjust by 0.5 mm....and has more compression now - but probably still lower than I had before (which was set up by Simon at 12:1) .......When I get a chance I will get the ratio set correctly and head machined properly. Happy to stick with slightly lower compression until I can prove the reliability.....

                              re the piston cutaway.........difficult to tell because my old piston also had one......but It can still pull out of a corner on this oval track in 4th and hook up.....and by the mid range Bang away you go !! very impressive...in fact round the oval no other modern bike could get near me. I guess the answer is - if you want more top end - give it a go - but if you use more bottom to Mid - leave it as per standard....

                              Hoping to get a new exhaust next Staurday - in time for Marks Tey on Sunday where I will be hoping for a more relaible day mechanically than last time !! see you there
                              Thanks for all your assistance
                              Cheers Kim

                              p.s GAry - only work I have done (well actually Simon) on Carb inlet is matching to 36mm from the standard 34mm - as it has a 36 mm Amal Mk2

                              p.s Will post some pictures when I get the exhaust

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