JBS 700 Kit on welded 80mm Crank

I got a 700 Kit off Ben last year. The plan was to put it in when I wore out the stock 100mm ELKO piston.

With 210 Hard hours on it and showing only 0.02mm wear on the piston and 0.01mm wear on the liner I decided I would grow old boring and very slow before I wore out the mighty berg 628 piston/liner so I put the JBS 700 kit in.

There are plenty of people wanting to know the details, heres what I got:

My 105mm piston weighed 328gm and has an 80gm pin.

Just for comparison the 100mm ELKO out of my bike weighs 272gm and has a 70gm pin

The 105mm piston to cast iron liner clearance is 5 – 5.5 thou and in line with the clearance used by the KTMtalk big bore RFS builders doing 102 – 104mm pistons in cast liners.

Ring end gap was 0.6mm

Squish with a 1.4mm head gasket measured 1.8mm and comp ratio 11.32 :1

The fibre JBS 105mm gaskets were too small in ID so Ben sent me some replacements. In the meantime I used a 105mm gasket on a 100mm build and it came out 1mm thick, on the 628 that gave 1mm squish and 11.8 :1 comp ratio, very nice smooth tourquy engine. If you’re looking for a thinner head gasket try a JBS 105mm on your 100mm bore. It retards the cam timing, which is just what I wanted to do to the X-2 profile to make it rev more.

The gasket I used on the 105mm build was a bigger diameter and also came out 1mm thick, taking the squish down to 1.4mm and the CR up to 11.8.

All the JBS liners are checked in a set of 650 cases to see if they turn freely by hand. This is something you need to check even on the 100mm liners. Assemble the cases around the liner without o-rings and bolt them up the liner should turn easily and move freely up and down. This is not in the DOC or the manuals AFAIK.

My cases have always come out being out of round and the liners won’t turn freely till I correct the localised deformation of the cases near the joins and squash them overall back into round in my press. I really need to get a mill so I can machine this sort of problem out.

Ok so first issue I had is the JBS liner would not turn freely in my cases and doing up the cases squashed it out of round, I could have assembled it like that without knowing but I don’t think it would have lasted very long.


My cases are different to every one else’s it seems. [attachment=2:2qht87t5]piston 004.jpg[/attachment:2qht87t5]


See in the middle of the pic where the OD of the liner was contacting the water jacket, normally this cast area is further away from the liner than the machined bit above it. So I needed to take out the water jacket area with the die grinder to get about 0.5mm clearance. I also took 0.5mm off the liner and put grooves in it like the pics of the Thumper-racing ones I have seen.

[attachment=0:2qht87t5]feb 016.jpg[/attachment:2qht87t5][attachment=1:2qht87t5]feb 008.jpg[/attachment:2qht87t5]

In hindsight I could have added some o-ring grooves but the RTV method works very well, I used threebond 1207B. it’s a bit messy but this 3bond stuff is very good better than most o-rings.

The nuts and washers in the head stud kit don’t fit in/on the head. I made them smaller to fit but It would be better to machine the head to keep bigger washers and spread out the load as much as possible.

That’s The JBS 700 part of the engine taken care of. Just a stud kit, gasket, piston and a liner, pretty simple compared to the crank.

Many thanks to Ben for sticking his neck out and making this stuff available to the public, He's offered good support and answered most of my odd questions.

The 650 is a great platform for a proper big bore and It’s a shame there are not more people providing quality gear for us to pop in for some extra grunt. The 700 weighed in at 28kgs on my new scales, still lighter than a Jap 450.

I set up the crank with 0.65mm axial play, NJ206 ema c4 16mm wide rollway bearing on the RHS. I run without the counter balancer and use an NJ2206 ema c4 20mm wide rollway on the drive side with a steel spacer like weeds. I retained the bearings by heating the cases to 100 deg and installing the bearings with loctite 609 to get some crush and adhesion happening. Resulting radial play measured 0.02mm.

My main bearing tunnel in my cases is worn to 0.03mm interference fit which does not hold the bearing outers when hot. You need 0.05mm or more as in the KTM technical bulletin in the doc. Problem is that I think this bulletin was released when they used NTN specials with nearly C4 clearance. Then they went to C3 SKFs and needed to reduce the crush so the bearings had some radial play. Wandering end float is the result. Also drilled an oil gallery and dam for the LHS bearing

Replaced the stupid stock sintered metal silver plated big end cage with a steel caged big end bearing I got from Max Nightingale at Alpha bearings in the UK. I was having issues with my nice Moreys oil stabiliser corroding the silver plating. I set the big end axial play to 0.62mm as 0.5mm was too tight for my heavier balanced crank. There were signs of spalling on the sides of the rod and the crank. I did 0.6mm the first time and had no problems but closed it up to stock spec; blooday specs L gut feeling was right in this instance and I should have stuck with it. Lineaweaver recommended 0.8 in a thread for Dr-C and the KTM rfs engine guys use 0.62 to 0.78 on smaller engines. I over trued the crank (anti spread) to 0.05mm between centres and welded the pin.

I was expecting it to vibrate very badly since my nice balance factor of 0.75 was mucked up by the 66gm heavier piston but its smoother than before at all RPM. Very surprising. I think the BF is now 0.55 or so.

Initially I found it made a lot of very nice smooth bottom end torque but didn’t rev out the jetting was way rich, after run in I went down to a 150 main with 165 MAJ. It’s a freaking monster engine, never thought id say it but it’s a tad too much till I do some training. With the 150 main WOT peak power was spot on but WOT peak torque was down and the delivery quite aggressive mid RPM so I’ve stuck a 155 in till I can do some more press ups. I prefer to use low RPM and bottom end torque to ride smoothly mostly just above idle and keep the minimum corner speed up.

There’s a lot of potential or possible improvements or alterations with the cam/exhaust/jetting but overall I’m very impressed. 20 thumbs up for the JBS 700 kit.

Will update more when there’s something interesting to add. and try to fix the pics, they get truncated if I put them in the page

ah yes the unobtainable 1mm thick headgasket that everyone wants.

I got some JBS 100mm fibre gaskets too off someone else but these only compress to 1.2mm and the ID is around 98-99mm this may have been fixed by now but its something to watch for if your piston comes up to the top of the bore like the 628 engines.

the ring end gap is large, the bore is at the max diam for their spec from the MNFR but like you said Dr-C there is very little oil or any airflow from the case vent. there are some fancy rings you can get from the US called pro seal or something that work with no end gap, interesting stuff.

Ive always thought perhaps the husaberg wet liner is cooled more than the piston compared with other bikes and maybe this means we need larger pist/liner clearences with iron liners. in any case with the grooves it runs cooler than stock for the same loads. bit of piston slap till its warm then its fine.

my cam is a taffy tourque cam or x-2 grind so top useful rpm is about 8000. with the 150 main its scary 5-8k. pretty sure you could tailor the tourque and output to whatever you want by just playing with the cam. it certainly doesn't have an issue reving its head off if that was a concern.

the HBERG case ovality thing probaby doesn't matter that much as its surely some weird shape when its hot anyway. It worries me though because ive seen a 550 engine rip the nikasil off the liner front and back at 20 hrs, cases were ovalised about 0.2mm out of round.

a billet head on top of this thing surely be interesting Dr-C! nice twincam model BTW. FWIW Im a single overhead fan, so is weed and we're both interested in some expensive alloy

sounds good Steve, let me know i'll stock up on DELO400 and beer,

could meet you out on the nullabor and ride in along the cliffs this side of the bight, I'll bring a sand spec front tyre up for your DR

yes the BF thing is very interesting now im wishing I'd tried the same factor with the little ELKO piston

I wonder Taffy how 0.4 or 0.3 would feel ?

would be lighter and a lighter crank would surely be better for some things

Dr-C the EFI thing is something ive always wanted to have a go at just for the hell of it, great stuff!

twincams lets us play with the overlap, be nice if that was made nice and simple just by slotting the drive gear or something. i like the husaberg camchain too with the rollers instead of the nasty plate teeth the jap chains are made of. gears seem to last longer with the rollers

this 700 build needs a bigger MAJ to smooth out the fuel curve, nearly done piddling with jets

vid for taffy

http://www.youtube.com/watch?v=3byv8WMd ... -main-area

I think about the 2 engined bike all the time, I have some vids of it handles quite well.

youd get a 56kg 1386cc parallelish but very very wide twin with around 150hp. I would prefer an 1150 folan V twin at 44kg.

nearest good dyno is 700km from me. if i had around 68hp from the 628 as you supposedly get from a bit of head work, exhaust and squish etc then the 700 makes around 5 or 7 more HP in a low state of tune with a tourque cam.

Thomas of engine hardware has some of these engines too so he may have a figure for you

nice Dr C, the jap 450s missed a big oppourtinuty there with their rediculous cam gear mount system

the best threads are the hijacked ones, and we find out with this one who is interested in more from the 650 ... not many

the canines would be very dissapointed in us

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.