Bushmechanic frame Build pics and Stuff

some of the ideas in here viewtopic.php?f=8&t=13017 need to be tested

the pics still truncate, you can open the links below to see more

frame design looks easy in photoshop



adjustable mythbusters "Adams rig" style to check geometry



another jig to hold the head still and locate shock mount while I cut out the heavy mid section

mid section removed, weighs about 7 kgs



putting stuff back in, idea is to add less than I removed



all tacked up so check alignment and angles before welding . checking the alignment and deciding what to do are the tricky bits, just making the thing is fast by comparison



total weight is 6kgs so far but another 3 or 4 still left to add. FWIW the stock subframe weighs 2kgs

the twin tube or perimiter design is NOT the lightest strongest or cleverest way to build a frame becasue the 2x 1" tubes weigh the same as a single 2" centre spar and Im still to add another 2 sets of tubes to triangulate it

the advantage of the perimiter setup is you have more room for a forward mount air filter if you wanted one and the tanks don't have to be load bearing. every bike ive had with a tank you sit on has eventually given me grief in some way or another. so the choice is between a heavy loadbearing tank thats a PITA to make or a heavy perimeiter frame to protect some lightweight tanks. the perimiter frame can also be stiffer torsionally if that were an advantage.

so with the hindsights switched on the easiest way to lighten a stock frame is to cut out the airbox and replace it with a damaged 48mm fork lower tube. I'm mostly doing this to change the geometry and get betterer ergonomicals, it will still be lighter than stock but a single spar frame could be 2-3 kgs lighter again.

more botching pics soon

tis a long way from the front wheel to the engine

the "problem" starts with the output shaft location in the cases, its 40mm to low so in order to lower the COG without ruining the swingarm angle I had to cant the engine forward. then if i want 28 - 30 deg rake the headstock needs to be right where it is or the wheel hits the frame. the once piece radiator makes this about 30mm "worse" than a 2 radiator setup.

its about 50mm further from the front wheel to the COM than I had before which is about 50mm further than stock. that 50mm extension was an improvement, 100mm further than stock may make it hard to turn but then I'll just make the swingarm longer. the idea is not really to increase stability its mass centralisation lower COG and increasing the trail for sand. the new bergs have an extra 160mm between the wheel and the crank...........

from what ive seen shorter bikes don't nescesarilly turn any better 3rd gear and above, the hayabusa hillclimber in my gallery has a 1700mm wheelbase.

my berg at 1520mm wheel base is 30-40mm longer but still has higher front wheel loading than the japper MX bikes and still turns inside them.

not sure what will really work in the end but its fun this stuff. the film on any sunday sublty points out that a great deal of the enjoyment of motorcycling can be found in tinkering, working on and improving the bike. its sad to see how many dirtbike riders miss out on that bit.

30% off sale on chemical alis argon racegas and special 5 viscosity blend red bottle forker oil

personally, i like yamaha's idea of low crank & gearbox height for a low c.o.g ,then the barrel & head on a lean back to get weight central.

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me too, if the dreaded husaberg mains would fail or even just look a little tiny bit worn :twisted: Id make my own set of cases with bigger mains, the crank down low output shaft up high and the cylinder leaned back, would be BT i reckon.

or we could spin the engine 90 deg in the hrozontal plane use a Guzzi style carbon driveshaft instead of a drivechain

should be able to put the crank well back 8O

all good ideas great stuff lads ideas are cheap :cheers: :cheers: chromoly tube is not

next bike I build will be more conventional ; the old burnt 550 engine with lightened crank, angular contact mains estart and in an 85 bigwheel chassis, perfect tight track enduro weapon for a light rider.

pretty sure this big one is gonna work fine though, the wheel 100mm forward from stock puts the engine closer to the geometrical centre of the bike, well the engine stays put but the geometrical centre moves.

downside is perhaps not enough weight on the front but the engine is canted forward, its not much really, the front of the rocker cover is only 15mm further forward. so both concerns work together really and with a nicer seat ill be able to get my weight 200mm further forward on corner entry.

almost got another 3/4" tube fitted today after work, blasted work :evil:

ahh.... well see the front wheel is where I want it 8)

everyone else wants me to have it closer to the engine. if I wanted to do that I could easily have picked up a rolling jap chassis cheap and just squeezed my engine in like enginehardware did.

the other way to do this is like Taffy hints at is steeper rake and reduced offset or simply go this way and extend the swingarm if needed

yes something like that only with 550 or 570cc

how come it took you 7 months to figure me for a nutter ?

seriously though there are some sandy bits here that make my 700 feel like a PW50, the 85s wheelbase is around 1300mm, 100mm extension at the swingarm and a 50mm at the head with a bit more rake .... nice

I can't stand small engines, you give em a handfull and they grumble then couple seconds later and some clutch work then they get going, uncontrolled agression :evil: extrapolating this behaviour into the bigger ccs where the "i bet thats a handful" comment comes from

but it doesn't have to be like that, with a bigger more responsive engine and a nice flat tourque curve i find it goes when you want it to go just exactly how much you want it to go, ie give it a handfull you get a handful, if you can't hang on just give it less

any expected dry weight figures for a 550/85?

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somewhere between 80 and 90kgs + me at around 75kgs with gear and a paddle tyre should go pretty good :twisted:

FWIW the Cr500 engine is the same weight as my 700