- Jul 8, 2011
I am with you on this one Jim. What I see as the big challenges are valve spring pocket to valve seat distance; there is only so much real estate between the two on a Norton head. There are a few tricks that can be played out (including offset and/or raised rocker shafts, different springs, welding up and raising the spring pockets) but those are chump change compared to the real estate the XR head has to work with between the valve seat and spring pocket. Take a close look at the molds you show and you will see it.jseng1 said:Using the XR 750 port specs, intake & exhaust lengths etc on a de stroked Nort could bring new HP levels - possibly enough to blow off the 8 valve weslakes. Centered cam bearing has been engineered to eliminate flex and I think someone has even worked up roller lifters. Maybe use a 270 deg crank. It would take someone with deep pockets and a lot of ambition.
If I find out more I'll post it.
As for the middle bearing cam support, are you referring to what I showed you with Herb Becker's handy work or is there another arrangement out there?
Finally, cam loading, cam drive loading and rocker ratios are all challenges to overcome when trying to emulate an XR750. Not saying it should not be tried but there are certainly some challenges there. I know with the ultra short stroke 750 (75mm stroke) we are not far off the mark. With Rob McClendon of D&D cycle as a pilot of the Seeley Norton Rob beat Jay Springsteen on a factory XR 750 at Mid Ohio a few years back.
What would be really handy is if someone has valve lift/crank angle data for one or more of the HD XR750 cams. I have the service manual for all models but it lacks that detail.
So this is fun and interesting but I really need to get back to dreaming.