[68grandprix]

I'm thinking about buying a used cb750 sohc big bore kit. One of the sleeves is cracked, but it comes with another jug with three good sleeves, and the guy says a sleeve can be pressed out of the one jug and put in the other. Is this true? Also, he says the pistons measure 66.5mm and the bores measure 67.15mm. Is this within spec? It sounds a little worn to me , but I don't know what the clearance should be. Finally, assuming the kit is usable, can I get rings for this? Thanks, Jimmy.

 

[jbranson]

68,
Those measurements would give you a piston/cylinder clearance of about .025"....way out of spec. Typical on a fresh engine would be .003"...worn engine about .006"

If CB750 jugs are like other Honda jugs...yes you can "press" out the sleeves...although you don't want to actually press them out...you heat the jugs up to a 200-300 degrees and usually the liners will just about fall out. If you press them out and in with the jugs cold it shaves off too much aluminum and you end up with loose fitting liners.
Sounds like the used kit is a very used piece of crap.
JohnnyB

 

[68grandprix]

Thanks for the reply. I guess I won't be buying that kit. I'm trying to make my bike run with my friend's 94 fzr600. I figured it might be possible with 900ccs, cam, carbs, exhaust, headwork, some lightening, etc. I'd be content to kick my other friend's 2001 Sportster 1200's ass. My bike has 46,000mi, and he kicked my ass the last time we raced. I felt pretty bad losing to a Harley. Any one have a cheap cb750 big bore kit? Help me put the fear of HONDA into my friends. Jimmy

 

[jbranson]

I'm no CB750 expert but I'd imagine at that mileage your present motor is getting a bit tired. Even going with 1 or 2mm oversize OEM pistons and a basic rebuild should pep it up quite a bit. Probably looking at another 20cc with the oversize pistons and a bit more compression. Add a valve job to that, exhaust, some free flowing filters and you'd probably see a considerable improvement.
Light is right with the older bikes...take off 50 lbs of weight and you'll keep up with the sportster.
JohnnyB

PS. I have a 68 GTO ....it's kind of spread out at the moment



Edited by - jbranson on Mar 30 2006 06:29:59 AM

 

[68grandprix]

There is a 3rd oversize NOS piston set on Ebay I've been thinking about buying that would take me to around 755ccs. It's a lot cheaper than the 836 kits. Right now I have an aftermarket 4-2 exhaust that weighs about as much as one of the stock pipes (and doesn't look too bad either) . I just bought a Dyna ignition, but one of my coils crapped out, so I'm buying some Dyna 3 ohm coils.

My 68 Grand Prix is out in the driveway on jackstands right now. A couple years ago I had a 455 built and soon after I lost second gear in the th400. Now, a couple weeks ago my spider gears chunked up and took out the pinion, so I'm looking for a replacement carrier. Jimmy

 

[UngaWunga]

http://www.wiseco.com/Catalogs/Motorcycle.aspx

Wiseco makes an 836cc kit for the CB750...

 

[68grandprix]

Can't afford it.