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turbohead

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Posts posted by turbohead


  1. ....or you can cut it open along the edges, put a new perforated pipe in place with a few welds, pack the whole thing with hight temp insulation (or steel wool) and weld it up again. As you can tell by the weight of it, there is no need to worry about ultra-thin material, so welding (MIG, MAG or TIG) is easy.


  2. Interesting thoughts. Returning to trials from decades of enduro riding with lots of (small and medium) injuries over the years, I must admit I'm feeling a bit naked without a proper full face helmet and full body protection. But do I really need all that doing 2 mph on a 35 year old twinshock bike? Can't make up my mind and getting more and more used to the slow stuff nowadays....


  3. Thanks for your valuable input!

     

    I'll talk to Lorenzo at HFS regarding what can be done for my overhauled Foral forks, as that is what I am planning to use (straight from an Aprilia TXR312).

     

    Vielen Dank für Ihre wertvollen Kommentare. Vielleicht ist es Zeit, hier eine deutschsprachige Unterabteilung zu beginnen ...? Aber das wäre vielleicht unhöflich sein!


  4. Interesting!

     

    Could you please give a more detailed impression of riding behavior and so on compared to the original Marzocchi or Betor forks? And what about setting up and fine-tuning the front suspension for your riding style? Is it money well spent or not?

    • Like 1

  5. My old friends riding veteran mx and enduro on international level are using the Spanish developed HFS parts for their front forks with very good results. If you look at their web (www.suspensionhfs.com/en) there are some trials kits, too. Has anyone tried them out? 


  6. Interesting to read your comments, I very much appreciate your views. Thank you all!

     

     

    However, from a personal point of view, I have decided to go the mild cheating way. One of my TLs is going to get the TXR engine, at least while I rebuild the old one (the rest of the Aprilia will be left alone, waiting for a proper mono class or something). At the same time, that TL will get repositioned footrests, HFS inserts for the front forks, Powerdynamo electronic ignition, modified exhaust system, Öhlins modified shocks, steeper head angle and so on, but no new paint or plastics to be sure to not disturb every true, no-cheating SWM rider out there. As I return to trials after decades riding enduro, I am keen to keep a low profile, just learning again to keep my feet up as good as I can...

    post-9637-0-53107000-1466026423_thumb.jpg


  7. Dear all,

     

    I have just found an Aprilia TXR312 from ’88, used for competition for the first 5 years or so, then stored (or forgotten) for most of the 25 years until today. Is that Rotax engine an easy transplant to an early (1981) SWM 320? 

     

    If so, is such a transplant OK and within the spirit of modern twinshock rules, like electronic ignition, modern fork internals and so on…? 

     

    Or should this Aprilia better be stored for another couple of years, waiting for the hype of early air-cooled monoshock bikes …?

     

    Please, tell me what you think of all this!

     

    BTW, after draining the tank and transmission, giving it a little fresh pre-mix and transmission oil, the Aprilia started second kick. Good runner with minimal bad noise, excellent clutch, gearbox and general behavior. Couldn’t resist a quick run over the rocks behind my workshop, returning smiling like a child. 

    post-9637-0-47924600-1465669883_thumb.jpg


  8. You need to tell a bit more about your work and choice of engine, also the weight of the finished bike (if I remember it right, the old Rotax four stroke singles are a bit on the heavy side). A bit more detailed pics of the work done to the frame would also be interesting. How does it run, compared to a well sorted 276 cc twostroke?


  9. It depend on the ignition timing and RON fuel you are using plus fine tuning of the power delivery. On standard timing, ordinary pump gasoline at around RON 95 and a modern 2-stroke oil mix of 0,5-1% you can use anything between 0,5 - 1,5 mm. When these Rotax engines were used in mx and enduro bikes, squish around 0,8 mm was standard. The Rotax trials engines I have measured recently has had from around 1,2 mm to 1,75 mm. When rebuilding my Rotax 280 right now, I am aiming at around 1 mm.


  10. In the '80s some manufacturers tried this kind of solutions, but nowadays you don't see them at all as they simply destroy the low end torque of the engine. All later bikes rely on a design as outlined above and you can both keep the looks of your SWM and get better rideability by just modifying your silencer. If you don't care about that '80s look, just make a suitable mx silencer fit your bike or buy one of the aftermarket replacements for your SWM. Some welding is needed if you don't buy a replacement, but that is almost like therapy at this time of the year. It is easy to just cut off the end of your silencer and make that part detachable together with the new core tube when replacing the insulation.


  11. Of course, I will do a follow up on this later on. Right now we are having a taste of winter up here, -15C, clear skies and some snow, so it's enduro time on studded rubber. Maybe in a month or two, conditions are different and not so icy.

     

    I agree, the old Bosch system is (was) pretty good when set up right. State of the art 35-40 years ago, when we were used to service ignitions weekly, checking points, changing condensers and not knowing the exact timing for more than a couple of laps. But it was good enough back then.

     

    Having said that, I don't expect any miracles from the new Powerdynamo system, just easy starting in all conditions, consistent behavior and no need for any service at all other than a new plug sometime. The new flywheel is 2,5 kg, so it will be interesting to compare traction and low speed performance as well.

     


  12. I got tired of waiting for replies from a couple of sources for trials electronics and was surprised to see a mail in my inbox after almost no waiting at all. The guys at Powerdynamo in Berlin are of a different kind, both answering mails and getting things done (!). After sending my old parts to them, I got a nice, big box a couple of weeks later, old parts in return and a new system for my bike. I run a simple battery total loss set-up for lights when needed, so my new system is ignition only. 

     

    If you are interested, the system is now listed among Powerdynamo's other products, so you don't have to bother sending anything to Berlin (if you need power for your lights and so on, they can fix that, too).  Please, note the new flywheel has threaded holes just like the old one, so your old puller will work. Simply follow this link:

     

    http://www.powerdynamo.biz/eng/systems/7860/78605main.htm

    • Like 2

  13. I think you could be missing something in your life of motorbikes. As a keen enduro rider for lots of years, riding and racing in the dark is something very special IF you have light on your helmet and on your bike, lots of it! Today, in the time of LEDs, this is much easier than in the old days, so go for a ride at midnight and get surprised!

     

    In fact, some riders (including myself) even find it easier to get your bike where you want it during the dark hours, probably because your brain only recieve the information needed to do the riding, no more and no less.....


  14. Here are a couple of photos, before and some stages later. The main problem is cleaning, in my case even more so as the parts had been (badly) welded in the past, as can be seen from all the pores. I could have taken all those away by grinding, but I was afraid of warpage and post welding cracks and decided to leave it and repair the worst holes, broken lugs and cracks instead. Before welding, I used an industrial ultrasonic parts cleaner and lots of acetone. Then grinding, almost like your dentist, to clean all surfaces to be welded, from cracks to pores. Took some time.

     

    Before welding I pre-heat the parts for about 1 hr in an ordinary kitchen owen at 200 deg C. After welding I put the parts back for 1 hr in 250 deg C and then for 10-12 hrs in 200 deg C. Finally, slowly cooling off in room temperature.

     

    The welding job itself is rather like TIG-welding anything aluminium. The settings I used are the same as for cast Al of the same thickness, in this case 110A, 70% negative balance, 110 Hz, square wave. Shielding gas is Ar and the TIG-welder is a German EWM inverter with foot control and an air cooled torch. The (sharp pointed) tungsten is grey coded and the rod contents are minimum 90%Mg, 0,1%Si, 0,7%Zn and the rest Al. If the preparations are right, it is almost like welding Al. If not, there is a lot of splatter and smoke. When that occur (and it does), it is just a matter of starting all over with grinding and stainless brushes, then another pre-heating and so on.

     

    These photos show the parts after a first degreasing and brushing, then after the first stages of welding and rough grinding, but before final machine work and final filling/detail welding. If I had aimed for a perfect look, there would have been much more pre-grinding and more extensive welding before finishing, polishing and so on. However, in this case I have opted for function, not looks. Also, to show how relatively easy magnesium welding can be done with the right equipment and some patience.

     

    post-9637-0-11212000-1444726913_thumb.jpgpost-9637-0-19525600-1444726966_thumb.jpgpost-9637-0-19481700-1444727000_thumb.jpgpost-9637-0-66762900-1444727041_thumb.jpg

    • Like 2

  15. Thanks all for your replies to this. However, considering how hard it is to find certain parts when needed, I decided to have a go with my new TIG inverter. And the results are surprising, to say the least. No problems whatsoever, just clean and clean again, carefully set up all parameters involved and then careful welding, of course. Rather good results considering condition of the old parts, with old welds and so on. An hour or so of grinding and finally some paint. Not as new, but that was not my intention, just making useful parts out of badly damaged ones.

     

    I'll post some pics later and also some welding details if anybody is interested. Just remember: Magnesium is perfectly weldable with the right equipment and some practice!

     

    • Like 1

  16. Having recently made a typical barn find, a ´81 TL320, the need for magnesium repair is very obvious. I have done it before and I have the equipment, but when looking at the transmission case I and other parts, I still hesitate. This is not the best castings I have seen and after a long life soaked in oil, it will take some hours of cleaning, blasting, degreasing, grinding and so on before I even order the rods and take my TIG welder out. For example, state of the damage on the transmission side include sveral cracks, holes and worn out threads to deal with, previously "fixed" with bad epoxy and thick paint several years ago, making the welding a process in several steps and probably machining all surfaces after the case has cooled down.

     

    What have others done before me? Welding or better, modern epoxy?

     

    Is there any hope of new or used parts somewhere or do I have too make another barn find to be able to build one good bike out of parts...?


  17. I wonder if there are anyone here who has done more to their TXT 70/80 than just the obvious mods, for example as described on the US GasGas homepage.

    I have taken the engine apart, cleaned it, rebuilt it with new bearings, seals and so on. I have tried the mods to the standard Dellorto carb (raising the needle and grinding a 2mm nothch in the thottle) and I have tried taping off various parts of the airbox intake. And it works OK even if it has to be leaned out under certain conditions.

    Problem is, when the rider (my son) gets more experienced, he need a bit more power and crisper power delivery.

    I have been thinking of boring out the cylinder to the class limit (80 cc), ie a 10% increase in capacity. Also, doing some port work, perhaps another pipe and also changing the carb for a Keihin (I am used to tuning Keihins on our mx bikes and find them much more precise and easy to work on than the rather crude Dellorto on our GasGas). Has anyone tried any of this or perhaps other mods, like Boyesen reeds or something?

    Plese, let me know!

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