Topic: cb750 pistons, rings, and valves, (rebuild kit??)

[nexsolo]

I have her all apart, and the valves are in really rough shape. The couple of valves that were open when it sat are pretty rusty, and the top of the pistons are hugely corroded. I think a new set of valves, pistons, and rings are in order. Does anyone know a reasonable complete set, and where to purchase? I would entertain a new cam as well, if the price is right.

This Forum is my new addiction btw. 

[Bodi]

You're opening a big can of worms!
There's no "kit" I know of. You have a lot of decisions to make about what you want to do.
Valves: you can get stock valves from Honda maybe, not cheap. You can maybe get stock valve guides, keepers, and springs too. Many parts are no longer available from Honda though! You can get replacement stock size valves from a few aftermarket suppliers. You can get guides, springs, and such as well. You can install slightly larger valves if you want to. You can have the head worked on to improve flow (and eventually power) and have new guides and valves installed and seated properly: this can get expensive... member mreick is getting quite a good reputation for head work.
Pistons: If the bores are rusty then you will want to rebore to a larger size and install oversize pistons and rings. There are several "steps" of oversize stock pistones: as far as i know few are available now. The cost, if available, will be high. The option is to go for an aftermarket overbore kit, these use pistons quite a bit bigger than the stock ones, up to and over the maximum size possible in the stock cylinder sleeves. 836cc is a poular size and is about the largets size that usues the stock sleeves - bigger requires new sleeves and the cylinder block bored out to fit them, plus some machine work on the upper engine case to fit the bigger bores.
Cam: many choices again. there are mild cams that improve midrange and top end power while keeping a decent idle and driveability. There are full race cams that do not idle well, have poor low rpm power (and are a chore to street) plus require stronger valvesprings and modified pistons to avoid damage to valves and pistons. Plus a lot of choices in between.
Overbore kits, "hot" cams, and headwork plus a new exhaust pipe all mean carburetor rejetting work as well, of course.
Best bet is to establish what you want from the engine at the end of the process. Check out the options and come up with a basic budget accordingly. It will end up costing between 1.5x and 2x your budget.

[nexsolo]

Good info for one. That was really good reads, thanks... I would love to take your valve advice, so I think I will buy new oem valves (which appear to be the value). I dont know that I want to get too fancy with the pistons. So, I am thinking a ring set only. The cylinder walls are in good shape, so I dont know that new sleeves are necessary. Are you telling me that 836cc is available in the stock sleeves, or is this a common upgrade to stock? If this is the stock sleve, I would really like to know the ring sizes.

Thanks agn.

[Griz]

You might also try Cycle Exchange. Ken, the owner, is a great guy and very helpful, he also has alot of NOS parts available for 750's.

http://www.cyclexchange.net/Honda%20Page.htm

[754]

F or K..

[nexsolo]

It's a K I am pretty sure. Is there an easy indicator somewhere?

[rhos1355]

erm, I might be talking out of my backside here but I'll copy what the parts manual says. Corresponds to my bike no. (K2) so I reckon it's accurate

Check the engine & Frame Nos. and see which category it falls under below.


Model               CB 750                 CB750K1                   CB750K2

U.S.A.            CB750-1000001~     CB750-1044650~      CB750-2000001~
England          CB750-1010369~     CB750-1066912~      CB750-2004779~

I'm assuming you live in one of the 2 above listed countries so I won't write all the frame/engine numbers.

Hope it helps

[nexsolo]

I will take a look tonight. Thanks!