jaan Posted July 27, 2008 Report Share Posted July 27, 2008 I'm planning to convert a Hiro 125 engine from the end of the 70's into a trial engine. Why? Who knows! The engine has six speeds and a reed valve. It's from an Ancillotti 125 moto cross bike. I have the Ancillotti frame too but it's too heavy and wide to converted into a trial frame. So the frame would be some monoshock (or twinshock) trial frame. Any opinions, advices, ideas etc.? Quote Link to comment Share on other sites More sharing options...
lee harris Posted July 27, 2008 Report Share Posted July 27, 2008 why not sell it and buy a used 125 trial motor. Less hassel and better resulkt Quote Link to comment Share on other sites More sharing options...
jaan Posted July 27, 2008 Author Report Share Posted July 27, 2008 why not sell it and buy a used 125 trial motor. Less hassel and better resulkt Undoubtedly that would be rational! But in that case the world will perhaps miss the one and only Hiro 125 trial bike. Quote Link to comment Share on other sites More sharing options...
jaylael Posted July 27, 2008 Report Share Posted July 27, 2008 You will need to find a way to lower the exhaust port height to trials specs. As engines become race tuned this height gets raised. The higher it goes, the less low end torque and the engine becomes pipey to ride. Also you will need to accomplish very low gearing, perhaps with a big rear sprocket and add a fair amount of flywheel weight. Usually this is done by attaching a disc shaped, thick metal plate to the engine's magneto flywheel. This must be done perfectly to avoid run out vibrations and crakshaft twisting could also require welding the crank pin. These are just the first points to address of course there is also carberation and exhaust which effect the trials performance. Good luck with your project. Please post pics of it. Jay Quote Link to comment Share on other sites More sharing options...
swooshdave Posted July 27, 2008 Report Share Posted July 27, 2008 I tried a Sammy Miller-framed Sherpa T M92 this weekend. It had a Pursang top end and had "plenty" of power. I don't know the porting specs for that bike but Jay probably does. I think the Sherpa T lower end (with flywheel, et al) and the Pursang top end worked well. It had more power than you would need in a typical AHRMA event, which are typically very low speed and moderate climbs that a stock bike can easily handle. But it would probably be ideal for ITSA and other Twinshock events. Quote Link to comment Share on other sites More sharing options...
lee harris Posted July 28, 2008 Report Share Posted July 28, 2008 Jaan, you are trying to achieve the impossible. A MX motor makes most of its power above 6000rpm. A trial motor rarely revs above this. A MX motor has very low torque, a trial bike motor lives on torque. It not just the exhaust port height either. The scavanging ports or transfer ports are far too big on an mx motor. The speed of gas flow at low revs is not enough due to the large area. It will never run. Also inertia. The flywheel on my 249 engine is comparible to a 4 bedroomed house in size. Also the motor internals add to the inertia. A trial motor has weights also on the opposite side of the flywheel. Put it another way, my 125 cabalerro motor has a fly wheel the size of a skateboard wheel. Low weight and small diameter=low inertia. This means revs quickly but stalls quickly. Big flywheel weight and larger daimer means more inertia and more torque. The gear ratios will be all wrong....its is a wast of time and effort and a good mx motor. PM me if you want a tip for a good trial motor supplier lee Quote Link to comment Share on other sites More sharing options...
feetupfun Posted July 28, 2008 Report Share Posted July 28, 2008 I tried a Sammy Miller-framed Sherpa T M92 this weekend. Dave what did you think of the handling and steering of the Miller framed bike compared with your M92? Quote Link to comment Share on other sites More sharing options...
swooshdave Posted July 28, 2008 Report Share Posted July 28, 2008 (edited) Dave what did you think of the handling and steering of the Miller framed bike compared with your M92? I thought it was insane. Now remember, I have never nor will I ride a new bike so all I have to compare it to is other vintage ones. But the steering was quicker (I'm coming from the M49 which takes days to turn, then to the M92, which I'm still getting use to), it's way higher off the ground and with the engine mods this one had, there was no shortage of power. I think the suspension on my bike is a little better. The owner said he's not happy his setup. But the bike never gets ridden so it hasn't been addressed. Also nice was the one finger clutch (!). Apparently he had a 250 clutch and the rear brake arm mod. The bike was ridden well into the 80s in the Expert class which says a lot for the rider and bike. If I ever get a chance to buy the bike I will. There was an identical one that sold here several months ago. Apparently several of the bikes were bought new at the same time. So there a couple in the area. If you could make it as light as some of the pre-65s they are making now it would be a perfect bike. I need to check to see how much titanium fasteners are... I may break down and get a Mukuni one of these days, but only as a last resort. Edited July 28, 2008 by swooshdave Quote Link to comment Share on other sites More sharing options...
jaan Posted July 28, 2008 Author Report Share Posted July 28, 2008 Jaan, you are trying to achieve the impossible. --- It will never run. Perhaps it's best to build up a walker with Hiro 125 engine! http://www.hs.fi/omaelama/artikkeli/Rohkea...50926SI1TL03s7n Quote Link to comment Share on other sites More sharing options...
swooshdave Posted July 28, 2008 Report Share Posted July 28, 2008 Perhaps it's best to build up a walker with Hiro 125 engine!http://www.hs.fi/omaelama/artikkeli/Rohkea...50926SI1TL03s7n Now to be fair (and I'm very sorry to have clicked on that link) no one ever said that it couldn't be done. There is plenty of evidence on this site alone of odd trials bikes. Heck, if Jay's endeavors aren't proof of that I don't know what is. I mean just recently there were pictures of a Guzzi trials bike and even a CZ trials bike. I'm pretty sure they didn't leave the factory that way. So, can it be done? Of course. Will it be easy or cheap? Not really. But if those two obstacles aren't a problem, go for it. Quote Link to comment Share on other sites More sharing options...
peterb Posted July 30, 2008 Report Share Posted July 30, 2008 Hi Jaan, If you don't mind spending a lot of time working on the Ancilloti to achieve something close to a trial motor then I think it is a good idea. I like the involvement in building a special and the learning that goes with it, lots of fun. I also don't think the motor is a good choice but if it's all you have got........ As detailed earlier, you need more flywheel weight, is there room in the mag casing for a larger outside diameter flywheel? Gearing may be a problem, tend to have close gear ratios in MX bikes back then. Porting is the biggest issue. trial transfer ports tend to be wide and flat though accommodating a large volume. Maybe you can find a cylinder/head/piston from another motor that can be adapted to fit, you can always re-drill the cylinder for through bolts or different stud bolts, and maybe there is room to re-locate the existing cylinder studs in the crankcase. Maybe an older Japanese 125 cylinder/piston & head could be made to fit, that would save the original set up. Good luck with this one, PeterB. Quote Link to comment Share on other sites More sharing options...
jse Posted July 30, 2008 Report Share Posted July 30, 2008 (edited) Hi Jaan,If you don't mind spending a lot of time working on the Ancilloti to achieve something close to a trial motor then I think it is a good idea. I like the involvement in building a special and the learning that goes with it, lots of fun. I also don't think the motor is a good choice but if it's all you have got........ As detailed earlier, you need more flywheel weight, is there room in the mag casing for a larger outside diameter flywheel? Gearing may be a problem, tend to have close gear ratios in MX bikes back then. Porting is the biggest issue. trial transfer ports tend to be wide and flat though accommodating a large volume. Maybe you can find a cylinder/head/piston from another motor that can be adapted to fit, you can always re-drill the cylinder for through bolts or different stud bolts, and maybe there is room to re-locate the existing cylinder studs in the crankcase. Maybe an older Japanese 125 cylinder/piston & head could be made to fit, that would save the original set up. Good luck with this one, PeterB. I like off-beat projects too and even if they are not practical, they can be a lot of fun. As long as you can accept the possibility that it may not work, you can always learn something from them. Porting can be modified to a certain degree. The cylinder base can be machined to lower the cylinder in the case, which will reduce the port/time area of all the ports and then you can modify the ports as necessary, say, to change the "blow down" time (the time that the exhaust and transfers are open at the same time), or stagger the transfer ports (open the rear boost port first, secondary transfer next and front primary ports last to increase low RPM scavenging) etc. Cutting the cylinder base will raise the piston crown a little above the cylinder, but you will need to machine the head anyway as the combustion chamber shape and squish band will need to be modified. MX heads tend to have a narrower squishband width and higher volume for higher RPM operation. Port angle and width are easily modified to increase velocity and direction if you so desire. There are a lot of other "tricks" (porting and otherwise) that can be done and you will need to decide what your time and resources are and how far you want to take your project. As mentioned before, it may not end up working as well as you wanted (but sometimes better) and as long as you have fun doing it, I can't see any reason why not. Jon Edited August 7, 2008 by JSE Quote Link to comment Share on other sites More sharing options...
martinm Posted October 29, 2008 Report Share Posted October 29, 2008 Converting a Hiro MX motor to trials use has been done before......take a look at this Fournales mono here Martin Quote Link to comment Share on other sites More sharing options...
hop blip and a jump Posted December 24, 2008 Report Share Posted December 24, 2008 Converting a Hiro MX motor to trials use has been done before......take a look at this Fournales mono hereMartin Now thats what i like to see, thinking outside the box!!! Nice engineering! thanks for that link. Quote Link to comment Share on other sites More sharing options...
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