JBS 700 Kit on welded 80mm Crank

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thanks Spanner, ive only tried the chitty gaskets I got with the kit so far, I'm pretty sure a bit of bushmechanic botching will sort this out.

re the piston weight I too thought it would suck and wanted to go to a Ti pin.... but tried it anyway and the balance turned out better :? FWIW under load in sand with a paddle (when it counts for me) I find the 700 engine revs up quicker and feels more responsive than the 628 becasue it makes more grunt, I have a few tricks in the head though and have ended up with 1.1 mm squish instead of the 1.8 its suposed to have.

what I'd like to do if/when I'm sick of the 700 is go nuts with a 100mm piston and a Ti pin/ Ti conrod and lighten the crank.

Spanner I had a Ti pin made by trick titanium about a year ago before I bought the 700 kit, its a lovely peice the pin but i had it dimensioned for my old rod bush and being only Ti-17 I'm reluctant to put it on the 105mm piston.

a Ti conrod would need a hardended steel insert for the Big end to run in but i think it could be quite affordable.
 
There must be a difference between my 05 and your 08 Bushie as mine had a 1.05 squish height standard ie,
compressed gasket 1.3mm, Piston at TDC +.25mm
I remember measuring it quite well as the piston tends to rock a bit and you can easily get the size wrong.
Not sure it they used a different piston in the later bikes.
I am still keen on the composite rod and considering going back to the a 82mm stroke crank, and maybe a 102mm
piston.
JBS have a high volume oil pump and with increased pressure ( restrict oil to rollers may be necessary ) to the big end it my work.

Heavy piston and flywheel will of coarse help with low end slogging power ideal for sand I would think. A bit like my farther`s old BSA M20 I first learn to ride on.

Cheers spanner
 
had to shave a bit off the block in an effort to get it nice and smooth for the MLS, also the compressed thickness of the JBS fibre gaskets is 0.9mm with 70N.m tourque

the oil pump impellor off an LC4 is sposed to fit in an rfs its 15mm wide instead of 10 don't know if it will fit ours. iv'e got 30psi and pretty sure more could come out of the stock setup.

dunno how exactly but under load it revs up to 7500 quicker than the 628, doesn't feel like a heavy engine at all.

thumper racing in the USA has done 102mm berg builds, perhaps another source for pistons/liners

anyone know where I can get 0.25 or 0.3mm thick soft tin? the fire rings that are failing are 0.2mm thick.

delo400 drum bottom is 0.4mm olive oil tin 0.2mm buscuit tin 0.15mm.. :D
 
Hammering the delo tin may not be consistant so maybe roll the delo tin out some?
Two layers of biccy tin shold do it.....
wotabout some shim stock?
sorry.... boring nite at work.
 
tried the outer 2 crinkly layers of the MLS either side of some soft alloy, lasted about 30 min not enough crush at the bore to seal the combustion pressure it would probably have worked with a steel ring in the liner. I tried to put a 0.2mm stainless wire in but it was so flimsy I gave up and went without it.

the easiest way to get a steel ring in there seemed to be the SCE copper ICS Titan idea since I could leave the engine in the bike and leave it together. ended up with a 0.5mm thick bronze wire inserted into a rolled groove on the ID of the fire ring, then rolled the groove closed over the wire, copper nominal thickness 1.2mm and the finished wire ring bit rolled to 1.8mm thick. annealed it and scrubbed off the gunk.

for the water sealing off problem I gouged grooves in the surface of the copper to hold some 3bond 1207B in the same patern as the OEM fibre gasket runs its silicone. some light coats of hylomar over the top and bolted it up till there was a 0.08mm gap between the head and the gasket, left overnight and then tourqued down to 70N.m ran some heat cycles with the radiator cap off and drained the water, tried to retourque but it didn't need any. the big test is tomorrow.

first pic shows both a copper and an alloy gasket with the rolled groove and bronze wire inserted into the groove, stainless would be better I think.

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the 1207B looks messy but its only just enough to fill the gouges about 1/2 a ml each side.

pics of roughly how I rolled the groove the plywood face plate has another bit that clamps the gasket in place.

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and the roller

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the rolling of the groove is fast. the time consuming bit is cutting out the rest of the gasket and gouging the 1207b grooves and all the goo tricks associated with it.

after all that I worked out that if the embedded wire idea doesn't leak then the quickest way to make a gasket is probably to take a 100mm fibre gasket, cut out the bore bigger and then make a solid copper "fire ring" about 4mm wide with a wire ring embedded at the ID and cut a lap join to squash into the fibre. then you'd have a copper and wire ring "fire ring" and then a fibre gasket for the water passages. be quicker and easier than making jigs to roll flimsy bits of tin onto a fibre one.

be nice if this idea of SCE's can solve a few issues from their blog it looks like JBS has been trying to get this gasket thingy sorted since 2002 or 2005. i beleive in the mass produced fibre gaskets but the fire ring needs to be thicker than 0.2mm if its going to be made of thin rolled sheet.

ultimately I still like the idea of a fully closed block and head with external water junctions but if its not needed then good!
 

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2 hours so far so good, if it makes 10 its an improvement :D

X-2 cam has been back in for the last 2 headgaskets and together with the head porting and OS valves is very nice, beautifly smooth and incredible off idle tourque. a tad more lift and a tad more lobe seperation might be worth a go but I need to bore my spare carb to 43mm and try that first.

this time I took the auto decomp off and the balance weight off the cam gear then put lobes sticking out 180deg to usual in relation to the gear, seems good, easier to kick start and harder to stall.
 
I once made the mistake of reversing the sprocket with the ADC still fitted. customer wasn't happy. the sprocket is defanitely balanced to match the ADC and not the lobes!

the best thing you can do is to bore the lobes through their 'hearts'.

regards

taffy
 
a note on the Hylomar for bergsmlerg

its seriously gunky stuff even though i put on a tiny amount Ive done 2 oil change since and there are blue globs showing up on the oil screen

I'd not use it anywhere normally in contact with oil if at all possible.
 
12 hrs on the copper gasket

works good, it still lifts under WOT for extended runs but its not really a problem, the water stays in, just have to let a bit of gas out the bleed bolt every now and then.

I think the 4mm wide copper fire ring/ fibre gasket will give a tighter clamping force at the bore, thats the next thing to try.

FWIW i have 34 hrs on these mains under the 105mm piston so far no problems
 
yep all 1st gear single trail 14/48 gearing and a bridgestone 110/80 rear, 6 radiator fans and a high padded seat :twisted:

I just need a set of Taffmeisters fluffy dice to hang of the bars 8O
 
40 hour update

mains are fine, the 2206 is looking more worn than the 206, 206 looks brand new

piston liner rings look good, bit of wear but nothing unusual

found 1 dog off the slider that engages for 3rd gear jaming up a fork. no missed shift this time, got stuck in 3rd after a quick blast up a sand hill, so opened it up to see... the dogs look new its just broken under the strain

also found the cases are cracked at rear between the swingarm mount and output shaft

so 700 kit still gets the thumbs up,

case design around the output shaft and weak 3rd/4th gear design thumbs down.

mains being an issue with the 700 kit... myth busted IMHO. if there is enough power/tourque to break gears and cases then the extra load on the mains isn't an issue. if you're increasing RPM and crank mass yes then the mains will be more stessed axially like the 550 engine.

Taffy do the sidecar guys weld their cases back up or chuck em?
 
i've welded two sets and they are fine. one team raced intermittently this season with their one engine while the other set are on a rotation but the engine is on over 20 hours without a rebuild.

regards

Taffy
 
cool, ill weld it and see what happens.

if the welds break Taffy I reckon the best thing to do is make up a large section out of 6061 to weld in place so the welds are located elsewhere and in compression rather than shear and the part that cracks can be made stronger, grind a little (1mm) off the swingarm end then can add 2mm to the thickness from outside and there is enough clearence between 2cnd gear and the case to add 2mm inside.
 
Hi Guys,

On the subject of welding cranks does anyone know the material
they are made off ?
Have they been hardened?
I would suspect they are made from 4340 or something similar.
 
Ive been told by the guy who does/did most of the katoomtalk RFS strokers they test rockwell 50+ 8O 8O the material is "known" as unobtanium making stroker crank filler rod difficult and expensive.

re welding the pin I have used 316 ss filler rod with good success but will try the E70S2 next

trick is to be quick so the filler doesn't suffer enbrittlement

Have read GWR uses little or no filler so the weld does not protrude
 

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