In answer to Bluto - I think it would be fair to say that most of the failures that 650 Husaberg engines have can be traced to the crank or the surrounding components. Typical faults are main bearing flange failure, counter-balencer problems, even snapped big-end pins all have been seen here on the UHE.
All these problems can in one way or another be traced back to the counter-balencer arrangement that Husaberg currently use. The are 3 mains DESIGN faults with the OEM system I think:
1) The design chosen means that to accommodate the counter-balencer in the same space as the crank spins the face of the drive side crank web overhangs the inner edge of the bearing by 13mm, most cranks sit hard up against the bearings so the OEM Husaberg has a 13mm leaver with which to apply force to the mains.
2) The counter-balencer bearings are effectivly doing twice crank speed up to 20,000 rpm, which is F1 engine speed. Additionally the bearings are tacking an enormous oscillating load and passing it to the crank and the mains, additional to the load it sees from the piston and rod.
3) The mains are simply put to small for the capacity once you are up to 650.
The 750cc kit that we supply tries to address these problems, and our idea was to take 2 steps forwards in power by increasing the capacity to 750cc but 1 step back in the state of tune on the engine, to get more power with out a reliability sacrifice.
We did this by:
1) Removing the counter-balencer and billet machining a crank that is correctly weighted for the 105mm big-bore piston.
2) See the picture on the page
http://www.jbsracingpage.co.uk/750cckit.htm as you can see the drive side crank web has a 45 degree taper that fills the 13mm gap transferring the force to the inner edge of the bearing and making the crank much stiffer than OEM. Additionally we use a 4mm wider drive side crank web with longer tighter fit pin and make it all out of 4340 which is just about the best crank steel in the world.
3) We went for a longer skirt 3 rings piston rather than the mini-skirt slipper designs that are popular now with only 2 rings.
So as an answer to Bluto’s original question the reliability of the 750cc kit generally very good, it should out last your stock 650. Overhaul intervals depend entirely on how hard you ride the engine, as they do with any engine, so if you get 100 hours out of your 650 you should get at least that of the 750cc, if you are a GP rider and only get 8 hours engine life don’t expect to get hours much more than that. An overhaul the first time will generally consist of rings, de-glaze, mains and head-gasket, the second time you’d be looking at a new piston as well, a rod will do between 2-4 pistons, as will a liner.
