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  • 25SA Renovation

    As suggested in another post please see the photo of the 25SA I've been seeking gear ratio information upon recently. It is a '58 model and came to me with a 250 single engine fitted and sported a roadster two and a half gallon tank. The engine was returned to the previous owner while the tank went to another GRA member who was keen to use it on another more suitable project. Other than removing those parts and fitting engines plates that suit the twin, the bike is viewed as purchased and as it is today.
    Apart from the rear seat frame/mudguard loop, which is home made, the frame appears to be mostly original and all there. Unfortunately some brackets have been welded on to the bottom loop of the forks, so will require some careful removal. The rear wheel has an 18 x 400 rim and trials tyre attached and will be replaced with an original sized 19 x 3.75. I have a replacement rear seat frame, made to the factory drawing. Once the engine is finished and fitted in place then there will be the tricky task of fabricating the exhaust systems.
    I'm still seeking a petrol tank, so if anyone has a suitable item surplus to requirements that they are willing to part with then I'd be pleased to hear from you!
    With regard to the engine, modification of existing parts is being conducted, such as making the flywheels full circle and packing the crankcases to improve primary compression. Although options for the latter appear rather limited and certainly won't approach that achievable in the single. Providing the balance hasn't been too upset by making the flywheels full circle then I'm hoping to be able to dispense with the mag flywheel and use battery/coil/points igniton. Haven't yet decided what to do about carburation! With thanks to every one who has shown an interest in the project, I've appreciated all your reply's.
    Attached Files

  • #2
    The rolling chassis looks pretty good .

    Chris

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    • #3
      Looking forward to seeing this soon!

      Comment


      • #4
        Yeah, it looks like good clean bike to start from, apart from the link arm mod, by mr blobit the welder..
        That rear frame section & s/arm look very familiar, is this the same as the back end of my own bike, where the top shock mounts are not offset, a better design, than the later type, in my own humble opinion.
        But it has all the makings of a cracking project & it will be pleasure to see another variation of a greeves on the track soon (ish).
        i don`t envy you having to design an exhaust though, are you going to go for a underslung or high level system, or are you trying not to think about it for the minuite.....
        But good to see its all under way & hope you keep us posted on the progress, you & rob make. dave.

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        • #5
          i don`t envy you having to design an exhaust though, are you going to go for a underslung or high level system, or are you trying not to think about it for the minuite.....
          But good to see its all under way & hope you keep us posted on the progress, you & rob make. dave.
          Yes Dave we're defo trying not to think about it! Visions of 2 high level exhausts expanding to a diameter of around 6 inches each side of the bike has left us with sleepless nights , mind you if we could get get off the line quick no bugger would be able to pass I think a couple of maico up and overs would be just the ticket
          Punchy 336

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          • #6
            Maico up & overs maybe, but thats not really entering into the pre 60 spirit is it?
            Have you thought about increasing your horse riding lessons?.. dave.

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            • #7
              Originally posted by ADickerson View Post
              As suggested in another post please see the photo of the 25SA I've been seeking gear ratio information upon recently. It is a '58 model and came to me with a 250 single engine fitted and sported a roadster two and a half gallon tank. The engine was returned to the previous owner while the tank went to another GRA member who was keen to use it on another more suitable project. Other than removing those parts and fitting engines plates that suit the twin, the bike is viewed as purchased and as it is today.
              Apart from the rear seat frame/mudguard loop, which is home made, the frame appears to be mostly original and all there. Unfortunately some brackets have been welded on to the bottom loop of the forks, so will require some careful removal. The rear wheel has an 18 x 400 rim and trials tyre attached and will be replaced with an original sized 19 x 3.75. I have a replacement rear seat frame, made to the factory drawing. Once the engine is finished and fitted in place then there will be the tricky task of fabricating the exhaust systems.
              I'm still seeking a petrol tank, so if anyone has a suitable item surplus to requirements that they are willing to part with then I'd be pleased to hear from you!
              With regard to the engine, modification of existing parts is being conducted, such as making the flywheels full circle and packing the crankcases to improve primary compression. Although options for the latter appear rather limited and certainly won't approach that achievable in the single. Providing the balance hasn't been too upset by making the flywheels full circle then I'm hoping to be able to dispense with the mag flywheel and use battery/coil/points igniton. Haven't yet decided what to do about carburation! With thanks to every one who has shown an interest in the project, I've appreciated all your reply's.
              If my memory works I think Adrian Armson of Mansfield tried tuning up a 2T for vintage racing years ago.He might have some info for you.

              Comment


              • #8
                Originally posted by dave higgins View Post
                Maico up & overs maybe, but thats not really entering into the pre 60 spirit is it?
                Have you thought about increasing your horse riding lessons?.. dave.
                Nice one Dave, with an up and over system riding lessons(of any sort) might be beneficial, mind you it should keep the nether regions nicely warmed.
                Having seen some of the current modern systems fitted to Pre65 two stroke machines that look totally out of place, we'll be attempting something along more classic lines. The factory machines appear to have had stub exhausts fitted, which must have been deafening to anybody within a half mile of them. Thankfully we cannot use them in todays events so I hope a compromise system will eventually evolve, be it over or under.

                Comment


                • #9
                  I forgot the exhausts Adrian , yes they did have short stubs , marginally quieter than an MDS with a megga .

                  Also have vague idea of a pair of high pipes floating about , if I remember rightly they looked similar to the Mayfield exhausts .

                  Chris

                  Comment


                  • #10
                    OK, here's one for the technical bods, if a siamese system is used, will it need to be double the size of two single pipes?

                    Comment


                    • #11
                      Originally posted by Brian Catt View Post
                      OK, here's one for the technical bods, if a siamese system is used, will it need to be double the size of two single pipes?
                      On any two stroke seperate exhaust systems are more efficient than a siamese one, but if a siamese one is used the front pipes into the expansion chamber/silencer need to be of equal length not one short & one long as on the roadsters. The length of the exhaust system is critical so it may be advisable to design in an adjustable tail pipe that can be slid in or out to tune the system for optiman performance.
                      As for tuning the Villiers 2T (or 3T) the problem is the closeness of the cylinders resulting in a very narrow transfer port on the inner side of cylinders.
                      It also gives rise to overheating due to sparse finning. Tuning is therefore restricted to reshaping the outer transfer port & the inlet & exhaust ports, crankshaft & crankcase stuffers & heads. It is possible to fit 4T heads on the 2T barrels thus giving a central plug & higher comp ratio (8.75:1 as standard higher if skimmed). A larger carb should also help, but on a bigger manifold.

                      Comment


                      • #12
                        Originally posted by riflegreen View Post
                        I forgot the exhausts Adrian , yes they did have short stubs , marginally quieter than an MDS with a megga .

                        Also have vague idea of a pair of high pipes floating about , if I remember rightly they looked similar to the Mayfield exhausts .

                        Chris
                        Cheers for that Chris. Ernie Tull campaigned a 2T with high pipes in the mid eighties in Pre65 Club events, I remember seeing him at the Classicfest, Donnington park about '85, but can't remember seeing much of him, or it, after this time. Perhaps that one had survived from the factory and your memory for Ernie to ride.
                        Thanks too, Brian, for the question but I shall avoid a siamese system, if only based on Villiers advise to Bert, which he duly ignored. I see JW has stepped in to claim the title of "technical bod" and seems to have answered you quite comprehensively. I wonder what Primary compression ratio might result once all those crankshaft and crankcase stuffers have been applied?
                        Mayfield and CZ are two options worthy of consideration Marcelle, thankyou. I'm sure whatever we eventually end up with, it will be a compromise between a classic look, efficiency and the shear practicality of where it might fit. A very good friend of mine has supplied plans for the geometry based upon information gleaned from Rob Carricks tuning book involving lots of calculations. As to whether it could be made to fit the SA's contours or what the result might look like is another matter.

                        Comment


                        • #13
                          g/box

                          Hi adrian, did you have any joy in the end with info on a c/ratio box, or are you stuck with the standard cluster.
                          Is there any chance any of the A series g/box parts might be adapted? just a thought. dave.

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                          • #14
                            Hi Dave, apparently there are wider ratio gears available as JW pointed out, but not closer ratio. I haven't spent any time assessing whether the A series gears are interchangeable, but at first glance they don't appear to be so, the gears are individually wider as is the box so it looks unlikely. It's not a major concern though because apart from first gear the ratios are not much different to the A series box that I run in the Hawkstone. I only use first for getting off the line and even then not all the time, in wet conditions it'll take second OK, so that was most of last season.!
                            On another matter, I took the bottom loop off yesterday and had a pleasant surprise. It turns out that Mr Blobit the welder was indeed Mr Blobit the Brazer, so not too much harm done there then. It's definitely going to need new bushes as I think those in there are the originals!
                            Have assembled the crank into the cases this weekend so at last some assembly work has started and we also managed to get Robs built into the left side case too, so some progress made at last.

                            Comment


                            • #15
                              25SA scrambler fork bushes.

                              Hi Adrian, Good luck with the Hawkstone Twin. I hope to see you out on it this season.
                              Are there any decent fork rubber bushes about at the moment as the good ones seem to have been replaced with really stiff unyeilding ones that are no good for trials. They may be ok for scrambles but not for you as you are so light. Probably ok for a Tri-Greeves.
                              I do hope that you avoid the seizing problems that the twin suffered from, good idea to have a word with Simon Bateman as to clearances...John.

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