Here's an entry of mine from a while back on crankcase/barrel/piston/head configurations using components available to me at the time. I've since bought 750 and 850 bikes and a nearly complete 750 engine--my engine work since this original message has confirmed the relative merits outlined below:
Many thanks to Rip et al. for empirical, compelling evidence making the argument for using 850 cases where feasible. If I wanted to leave the 850 bottom end undisturbed I could probably use my almost clapped-out spare 750 barrel with .060" or .080" oversize forged pistons to compensate somewhat for the heavier 850 crank in terms of the balance factor. Potential combinations that would make sense for me:
1. 750 crank and Combat cam in original 750 cases wth Combat head (on bike at present)
2. 850 crank and standard cam in 850 cases with RH10 850 head (current spare engine)
3. 850 crank and Combat cam in 850 cases with skimmed-down RH4 850 head (and cam tunnel opened up)
4. 850 or 750 crank and Combat cam in 850 cases with bored-out 750 barrel, heavier pistons and pins and Combat or spare 750 head
All I need is a second Combat cam and oversize pistons to cobble together any of the above configurations over a long weekend. If someone has experience running 750 barrels on 850 cases please let me know. Given that the Combat bottom end has been practically bulletproof since I put in Superblends in '72, the current inventory may just suffice for the rest of my miserable little life. Thanks again to everyone who weighed in on this.
Tim Kraakevik
kraakevik@voyager.net
'72 Combatkraakevik
Posts: 92
Joined: Mon Oct 12, 2009 7:33 am
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