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CYB racer

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Solanum Member
Posts: 1
Joined: Sun Apr 10, 2016 10:26 am
Location: Eau Claire, WI

CYB racer

Post by Solanum » Wed Mar 29, 2017 9:30 pm

Hi. My name is Nate and I have a Honda hoarding problem...

This is my first post here, so here's my introduction: I had a z50 as a kid that my neighbor gave me. I rode it every day and loved it. I bought my first "real" motorcycle in 2014 (a 1969 cd175), and it's been a slippery slope ever since.

Since that time I've bought 37 motorcycles, almost all Honda's. I re-sold some and parted out some really rough ones, but can't seem to let go of any 305's. There's just something about them - I'm sure this group understands the sentiment.

The only running 305 I've purchased to date was a cosmetically nice 1962 ca77 that would start right up and drive just fine, but was low on power and would leak oil out all the seals. It turns out the left oil ring was the only ring that was still intact. The fact that it ran was a real testament to how great these bikes are! This forum has been invaluable to a complete novice, such as my self. It seems like any question I've had, someone else has had. As a result, I've been coming to this forum for years, but have yet to post... until today.

As the title implies, I've started building a CYB style racer, so here's where my questions start. I've been researching race engines for some time now and have a general idea of where I'd like to go with mine, but the devil is in the details, so any advice is appreciated. I'm not out to bulld the world's fastest ticking time bomb, rather an engine with greater performance that stock that I can have fun with at track days (and occassionally on the street because I probably won't make it to a track more often that I'd like), without much fear of catastrophic failure. Here's my basic plan:

I have an aquaintence that has volunteered to teach my how to flow the head. He's an experinced race engine builder. His experince will be very valuable, but I'm not sure he has specific experince with a cb77 engine. Any specific advice in this regard, so I'm not starting from scratch?

I already have some performance springs that I aquired in a trade. I don't know who made them and have yet to measure the spring rate. Thoughts?

I will need a cam. Suggestions?

I am leaning toward making a cam chain tensioner out of a kz650 cam tensioner gear. Any suggestions in regard to the cam chain roller guide?

I plan on using a Cappellini oil filter and oil pump upgrade kit.

I bought some Kenig high compressoin pistons, but can't decide if I want to use them. I have some standard cb77 pistons and some cb350 pistons floating around too, so that's making the decision harder. I don't have sleeves or head gasket and I haven't modified the cb350 pistons yet, so I'm leaning toward 60mm pistons, at least initially.

I have a NOS ca77 crank that I'm thinking would be a good start to a race crank. It would need to have the flywheels turned down, the balancing holes opened up, and be re-clocked to 180 degrees and I'd like to have single roller cages. This is a major stumbling block currently. I've heard Cappellini had the single roller cages, but don't see them on their website. I work as an engineer, but my only formal education is as a machininst. I'd consider building the crank pressing jigs necessary to undertake this job if I need to, but I'd prefer to get some pricing from someone who could do this crank work for me, first. Any suggestions?

Primary drive: I'd consider buying a duplex conversion, because it's relatively affrodable and relatively easy to install, but I'm intrigued about a gear driven primary (and a gear driven cam, but I'll keep that on the back burner for now). The "how the hell does this happed?" post has some good pictures of what other's have done, and I've seen some more images online, but really know nothing about gearing. Because the teeth styles differ between chain drive and gear drive styles, I assume I need to calcuate the pitch diameter of the standard 15-47 chain sytem and the pitch diameter of the "race kit" 14-41 chain system and find spur gears that give an overall pitch diameter ratio similar to either of the chain drive systems. Any advice here is invaluable. If I use a cb500 clutch, are there readily available gears to use for the crank and idler? Is there a recommended method for attaching the idler to an idler plate?

Holy cow! Maybe I shouldn't have waited so long to post for the first time! Any way, I'll try to post some photos of the before and current state of this bike, and maybe a shot of my jam packed garage, if I can figure out how. ... ed-public/ ... ed-public/ ... ed-public/

teazer Member
Posts: 797
Joined: Mon Feb 08, 2010 10:32 pm
Location: Midwest US

Post by teazer » Fri Jan 26, 2018 1:18 pm

Welcome Nate.

There are as many ways to approach this as there are people on here. In my opinion, go to 350cc using either the 350 pistons you have or buy a set ready to go from one of the on-line stores.

The extra capacity really makes them easier to ride with the extra torque. Stock sized valves are adequate for all but crazy revs.

Crank can be run stock if its good. I like to shorten the alternator end to take a dyna on the end. You can lighten the crank by cutting down the OD and chamfering the sides of the crank wheels. I would not open up the balance holes.

For the ignition, you could also use a Motoplat or PVL etc. Somewhere here I have a brand new Motoplat set up that Todd Henning came up with for me that I never fitted that I should probably sell. I prefer to have the ignition crank mounted to avoid the cam chain fluctuations and resonance.

On a mild bike use a mild Megacycle cam and CB750 carbs. They are teh same diameter as CB77 but taller so they are like stock carbs at small throttle openings and like bigger carbs when wide open. They are fine to race with, but you could go to CR31 Keihins if your budget is open ended.

Duplex primary is a wise choice but stock chain is OK for a mild bike - just check it from time to time. The side plates do crack.

Gear primary and modern 6 speed is the way to go if you have access to a good welder and can machine the cases yourself. Use a CB360 6 speed transmission.

Next best is a NOVA 5 speed.

Last is a stock box. You can X 2nd and third for different gear spacing.

In the clutch, throw away any all fiber plates, thick steel plates and plate separation springs and fit a set of thinner modern clutch plates and check the stack height. I prefer longer lighter clutch springs but others use Barnett heavy duty springs.

Porting the head is not hard, but the ports are odd S shapes and the exhaust ports are not good and need a fair attention to detail.

Have fun

DJM Member
Posts: 534
Joined: Thu Oct 09, 2003 1:54 pm
Location: Chesterfield UK

CYB Race bike.

Post by DJM » Fri Jan 26, 2018 6:41 pm

All excellent advice, sorry I didn't respond myself but just too many questions in one post!

Just a small point about the Honda CYB Race kit primary drive set up, although the parts book details the front sprocket as being 14 teeth they are actually 15 teeth same as the standard one. If you count the teeth on the illustrations on the relevant pages in the parts book this will confirm 15 teeth
Honda Race Parts listing.jpg
Honda Race Parts listing.jpg (474.27 KiB) Viewed 1605 times
Honda Race Parts listing.jpg
Honda Race Parts listing.jpg (474.27 KiB) Viewed 1610 times

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