Thnx, but no thnx terry.
Good overbore 61mm slugs can be found, my 'fav happens to be a 2 year run of pistons only.
The '77/'78 F pistons with the higher dome is a REALLY nice overbore for the cb650...
Got a set in my '79cb650!
Luvin 'em every time I ride!
They are fairly easily modified, and fairly cheap. Even when you count in the $$ of rings.
Not only that, but the stock head gasket will accommodate the 61mm pistons.
A serious boon for those wanting a overbore on the cheap.
Anyone wanting a low compression cb650 with a 61mm overbore(only 1.2mm bigger than stock) would be looking at the stocker K '69-76 cb750 pistons.
Turbo comes to mind for that application.
You could easily machine them easily to get 8:1 or lower I think.
64mm(810 kit for the cb750) pistons are a option as well.
Paulages proved that with his 550/650 hybrid 718cc bike.
Not that any of those are a drop in unfortunately, they all require some extent of machining to make them work.
As far as larger liners, I could easily drop in 750 liners(or DOHC 750 liners) and get up to 65mm, but unfortunately I am going to have to source something a tad bigger for these 66mm pistons.
Untested waters are interesting to me, always have been.
The more the challenge it seems the more I am drawn to try.(even if it's pointless... me putting on a dyna2000 on a cb650 proves that point pretty well....
)
And as far as larger studs...
I am not sure what I am going to do.
I COULD go with studs, sounds tempting, until I mocked up 2 studs in a "mock up" motor I have in my spare parts project '82 cb650 frame, and tried to remove the head.
Ran into a snag there.
The head will no longer come off with the motor in frame using studs.
I have been tempted to helicoil the block and run with stocker bolts and go with 10-15lbs more torque holding it all down....
But with a extra 130+cc's AND higher compression.... I really think I need a HD set of bolts, and tap the block to accept the new bigger threads.(mabey helicoil them as well!)
Unfortunately my work does little threading, and we are limited to single point cutters.
No tooling to roll threads, so I am forced to buy them from someplace that either happens to carry the threads, and lengths of bolts I want, or have them custom made.
So far I have not found any place that sells bolts the exact lengths I need.
I found some studs that are close enough I could trim them to the lengths I need.
But I would like to avoid studs, being able to take the head off with the motor in the frame is REALLY NICE!!!
I am leaning towards having them custom made, as I will then be able to choose the material used.
However, $$ quoted to me so far has run about $300+ for a full set....
But mind you thats bolts made of Inconel718 with rolled threads to my specs.
The loss of strength in single point cutting them makes me want to do it myself....
At least I have access to material at a good cost if I go that way.
No one said power was cheap....
But I got time.(more so than money)
I might just end up buying the tooling to roll the threads I want and going that way.
Haven't looked into that yet, but will soon!
l8r
