500cc CB77 Conversion - starting and reference points?

Ausracer · Post by **Ausracer** » Wed Dec 31, 2008 10:49 pm

Hi All,

New to this forum and thanks for the info so far. I am looking to build a 500cc CB77 or 72 for racing and am looking for some general direction on the major mods required. I am no newbie to honda twin engine building for racing, but know that the best way to start a build is armed with the right information!

Any info on piston types/diams, crank mods, case mods etc would be great to get me started? Maybe there are some old hands around on this forum that can help? I am happy to discuss offline if you don't want your secret tuning tips all over the web!

Thanks and Cheers.

Vince Lupo · Post by **Vince Lupo** » Fri Jan 02, 2009 12:23 pm

I was at Mid-Ohio two years ago, and there was a CB77 with a CB750 engine shoehorned into it, so I guess if that's possible then anything's possible.

Now, I'm definitely not a mechanic, and I know they make 350 kits for CB77's, but I'd be very doubtful that you could take a CB77 305 engine and turn it into a 500 (what's that, like 6.0 o/s???). Best thing might be to find a 500 twin Honda engine from the '70's (like a CB500T?), and see if would fit. Might be cheaper and less of a headache if you looked at going that route. Or just get a CB500T and trick that out...

Gun · Post by **Gun** » Fri Jan 02, 2009 12:31 pm

I think someone took the top end of a cb450, and slapped it together with a cb77 and probably squeezed 500cc's out of it that way.
looks like to fit those carbs, you'll need a custom tank.
probably would want more than 4speed too. I read a rumor on this forum that with a bit of work and a lot of money you can drop a cb350's 5speed in there.

but now we're pretty far away from being a cb77 at all.
I'd probably just try and fit a cb450KO engine in there with some welding,
or hell, i'd probably just buy me a cb45KO and cafe it.

Vince Lupo · Post by **Vince Lupo** » Fri Jan 02, 2009 12:40 pm

This is the thing I was wondering about as well (not that I should talk -- just look at my SuperHawk!). At what point do we get away from the SuperHawk's 'SuperHawkness' and it becomes something else?
I'd think that trying to put a bigger engine in that frame will really change the whole experience of riding that little bike -- for good or bad. Not to mention the skinny rimmed tires, the shortish wheelbase, blah blah blah. BUT, I'm not one to rain on anyone's parade.

It would be interesting to hear from someone who races CB77's or CB72's on the track....

(Neat tank on that race bike -- I love that little 'eyebrow' above the carbs!)

Gun · Post by **Gun** » Fri Jan 02, 2009 2:42 pm

if i had a cb450 engine on hand, and either the money or the know how to do it, sure i'd make me a little hybrid. but really, i can't imagine me riding along, and coming up to a stop light next to a guy on a 250-350cc bike from the 60's that wants to race.
so for me it's not super practicle. It would be nice as I do plan on some road trips for the superhawk, but if it gets to the point that i'm in need of more engine for a road trip, i'll just do something crazy like buy a 78 gl1000, put some chrome panels on the tank, and call it my CB1000 "godhawk".

I wish i knew more of the guys racing as well. I wonder what pros and cons there are to doing something like this.

Ausracer · Post by **Ausracer** » Fri Jan 02, 2009 3:32 pm

Hi All,

Thanks for the replys so far. There are a number of examples of people converting the 305 into a 500cc, through various means including modifications to stroke length and bore size. All are radical changes involving the manufacture of special parts. Very exciting stuff. There is one for sale on this site that looks the goods.... hoping to hear from the seller??

As the idea is to use it for vintage racing, the bike components must stay within period - this does not include the internals though!

Cheers.

Vince Lupo · Post by **Vince Lupo** » Fri Jan 02, 2009 3:46 pm

Ah yes, I see it now. Guess I shoulda kept my mouth shut.