JBS 700 Kit on welded 80mm Crank

bushmechanic said:

if you have the 80mm (bell or pork chop) crank then running without the counterbalancer with the 328gm piston would give a balance factor of around 0.45 or less I think but ive not done the calculations on it.

I have no idea how that would behave the only thing i can say is mine is super smooth and i have welded a 35gms weight to each crank half

running without the balancer allows you to use 0.6mm or more for the rod big end axial play and still have enough room for the mains to run at 0.6- 0.7mm endfloat.

you also have the chance to run a 20mm wide roller on the drive side to reduce the span of the crank. ie the LHS bearing supports the crank closer to the flywheel.

IMHO the counterbalancer belongs in the bin, a clattering peice of junk lineaweaver called it. in conjunction with the 80mm crank and stock piston the counterbalancer makes a very nasty vibration at 7500rpm. so really you should rebalance the crank in the stock engine even if using the CB.

the advantage of the CB is you can supposedly have a lighter crank but if there is no need to add weight to the crank then the CB has no advantage at all.

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so if you use stock 80mm bell crank + no weight + stock piston and no counter balancer you should be ok?

if you use a 20mm wide roller on the LHS and larger axial floats the engine will be stronger

but i have no idea what the vibrations would be like. you'd have to try it


I think someone must have done that allready though? just not me...

bushmechanic said:

if you use a 20mm wide roller on the LHS and larger axial floats the engine will be stronger

but i have no idea what the vibrations would be like. you'd have to try it


I think someone must have done that allready though? just not me...

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i guess the sidecarcross teams over here run that set-up fromk JBS and i can ask them on sunday at the first round of the british championship.

regards

Taffy

hi, i'm very curious to know the lifespan of the mains bearings (NJ 206)...i would like to try the 700cc kit but i don't want to worry about the reliability of my motor.

Johnyberg you have the 82mm crank ? maybe worry about the rod?

its roughly a 10% increase in power over the 628 im sure a bit of work to a stock 644 could nett the same result. if you tuned this 700 up a bit it should make 80-85hp easy but mains would last about 2 hrs I think.

as is its not tuned much currently i think they will go at least 100hrs, will definately let you know, there needs to be more information put up from other 105mm piston users to help build confidence or not... whatever the trend is, i'm not sure.

I run an 8 paddle on the rear with 4 bolts in each paddle, 16/40 gearing and mostly ride in sand 3rd/4thgear WOT out of every corner, broke 2 stock hubs in 6 months, 2 gearboxes in 2 years and never give the engine much rest once it running :twisted:

so if I can build a bottom end that lasts with the JBS 105mm piston I think most people should have no problems at all. 10 hrs so far, everythings still fine

had to change the MAJ from 160-165 with the 628 to 170-175 and raise the DL needle a clip, 6/7, 155 main, 40-42 pilot, paj to suit. not perfect but works OK for what i'm doing.

I'm used to the power now, could use another 10-15 HP easy without lengthening the swingarm.

bushmechanic i think if i weld the crank pin i won't have a problem, the problem is the mains! i think you use the NJ2206 without the balancer? why don't you ask Ben, he uses bigger mains but you must machine the cases.

sorry i don't understand how welding the pin will help with your rod ?

you're right the big problem with using the 82mm crank with smaller pin is supposesdly the mains and welding the pin helps the mains, I know about the bigger spherical roller mains/machining the cases and yes mate i did ask Ben quite a number of things, roughly the gist of it was that mains wise tuning up the 105mm beyond how they come makes for a more agressive and faster combustion explosion that can overstress the mains.

Ask him about his latest on the mains, the blog hasn't been updated for quite a while, hes always trying new stuff, not for me to spill the beans and say what he is up to but you guys might be able to work something out.

I allready explained why I think the mains will be ok in this build, how to build a strong bottom end in our cases, which mains to use and how its going on the 80mm crank, and so far the mains are fine, If we're not on the same page by now I'm not sure if I can help. in your other thread you said you have an 11 000 rpm 644 with the 82mm stroke without the CB and stock NJ206's ? if thats right you have a piston speed of nearly 6000 Fpm :shock: so I think you know a thing or two, just give it a go.

the 82mm cranks are proving very strong when supported by roller bearings. far from the so called flexible crank knocking the mains out - the mains have made the crank behave.

as for the 'below the little end' being weak lets try it like this: a tree is thinner at the top. the bottom of a tree supports all of it but a metre up doesn't support the bottom metre and so on up the tree. Thus rods are always weaker under the neck of the little end. It's not rocket science!

so guess which bit will look stressed first under the microscope....

regards

Taffy

my previous motor had no c/b, bigger roller(left) nj2206/c3, stock roller(nj206/c3) on the right, high compression piston(wossner), 82mm crank, 10,200 rev limit and titanim oversised valves. Now i use an elko piston with c/b and a ballbearing at the left of the crank.

I would try it on an 82mm crank johnyberg why not? and given you can set up the mains in a heap of different configurations I think any feedback I give with the 80mm crank on rollers is only relevant to the exact configuration I'm running. I know some guys are running this 105mm piston on the 82mm crank they don't seem to share any info publicly though.

if you don't like the idea of rollers you could use a 20mm wide spherical roller on the LHS retained by a plate screwed into the cases and lock the crank over to the left with a collar then use a nj206 roller on the rhs with 1 or 2mm axial clearence like the jap bikes run.

the "problem" with running the ball left and roller right is that the crank isn't locked over to one side.. nor is the bearing retained in the case but both fits are quite tight so if anything moves it can lock the axial clearence at zero. I have seen this type of setup fail in a 550 at 20 hrs because of that.

interestingly the guys who build 600cc + KTM RFS big bores go for a loose slip fit between the crank and the ID of Ball mains with lightened cranks. lighter crank means less deflection. instead of making the crank behave with rollers they let it go with balls and reduce the problem by lightening the crank.

FWIW they are getting similar HP numbers to us from smaller engines and having them last a rediculous amount of miles. Johnnyberg those weird full circle cranks you have would be ideal for cutting right down into light 82mm stroke pork chops.

mines going well, i believe a big part of that is NOT using the SKF nj206s, the roller end radius on them is very very sharp 3 or more times sharper than the other makes.

it is possible with some work to get 70- 72 RWHP from a 644 and Dr-C has a little more than that I think, GWR builds 660's from the new ktoom engines with 82hp, bigger mains though. so this "big bore" kit is just a quicker way to get a little more. my ony critisism is that the piston is 328gm. I like lighter parts.

we will see how the mains last, can't do anything else

Taffy the tree would bend and snap off at the top if you dropped a truck on it

bushie rods snap coz they stretch not because they compress!

regards

Taffy

think I read the same book

I have seen both, fortunately neither in a berg

the tree analagy is weird unless you hook a helicopter up to the top of the tree

AKra slip on muffler gave noticable gain across the range over the stock setup with endcap mod

this is with the X2 cam profile, and collector 2 into one junction tidied up a lot, see simons gallery
I didn't like the akra previously with the 08 cam and the 628cc 100mm piston because it lost bottom end

balance factor of this build is very nice, will work out exactly what it is and post it

Man I bet that thing would be a torque monster ! Does it stretch your arms ?

the torque from idle to 3000 rpm makes throttle appplication soo smooth it makes a cr500 seem like a really really stupid idea.

sure there is a lot of peak tourque and it also makes a fair bit of power but its all controlable, just dial in however much you need.

its not that powerful or tourquey really compared to that hayabusa rmz with 19 paddle rear, extended swingarm, 160 rwhp and 12000 useful rpm.

problem I had with the 628 was that it only made enough useful tourque from just under 4000 to just over 8000 rpm so I was always banging the tranny like a stud rabbit. it didn't have enough tourque or power to gear it up enough to run in a higher gear. with only 3/4 the rev range of a 450 you need say 40% more tourque to be able to gear up and carry a gear for as long. 450s had an advantage in that they could rev to 11500 and carry a gear for longer, their valves and pistons suffer but that was an advantage.

with all the mods I did to the 628 it did have enough useable tourque down low to ride without changing gear all the time, in deep sand tracks I was running the whole track in 3rd while most 450 guys where using 2cnd through 4th and fiddling teh clutch the 700 is just like a little more of everything. :twisted: :twisted:

Sounds like it would be a heap easier to ride faster for longer on it now, the 450 guys wouldn't be too happy about it I would imagine 8)

bit of a disclaimer I didn't actually measure the balance factor just calculated it from the numbers I have on the 628 build but it works out 0.58 for this 105mm piston with my rebalanced pork chop crank. its very very good but the full circle 644 crank will likely behave a lot differently.

FWIW if you remove the CB from the stock 628 you get about that with the 100mm elko, who said the factory doesn't know much ... i think i did a couple times

if i can get a lighter decent chassis organised for it then yes it will be miles easier than a 450 to ride. ATM its par for the course, engine kicks ar$$%se but the seat/frame/tank ergos are all out of whack.

did some beach runs yestdy ooh nice love the grunt of this one, smooth tourque beewdy will happily sit on 130-140 in really soft deep n nasty sand

get some vibes through the bars at 3000rpm as with the 100mm elko and 0.75 BF but much less. 3500 or so and its gone, be a reasonably nice touring bike.

endfloat is wandering again, RHS main loose in case .... again, have drilled a hole in the ign cover to slap teh crank when I stop.

I will make a retaining plate for the RHS bearing. 32mm exhaust valves comming from taffy and some porting to do so will have it open soon for a look about 30 hrs runtime.

Ben seems mighty busy, i need some more headgaskets

quick update

fibre head gasket leaking, pushing coolant out got slowly worse to 15 hrs retourqued and was good for 2 hrs now worse again.

Ben said there are some new "better" ones being made, might take a while till i see them, will have a go at making my own from 2 layers soft alloy and a stainless wire ring. works on drag engines.

will post some pics of the innards when its apart

Had an idea for the cheap frame, drag race said 450's on that nasty sand, shouldn't take long.