CB77 Race Pistons.
CB77 Race Pistons.Hi all,
I'm looking for a proper race piston for Cb77's, any leads?  High compression 250 pistons still available, as are the nice Italian Kenig. Bill Moeller at bore Tech sells a nice conversion package to install modified CB350 pistons, including oversize sleeves. John Early had Forged pistons in the early 90's. Stan,
Kenig are not good. They seem to have metallurgical issues that result in crown failures. We always used machined CB350 in CB750 liners. They require shorter barrels and a machined head to make the squish band work, and then the cast iron skull may leak around the edges. That worked for several engines we built over the years. Not a perfect solution but reasonable cost compared to other solutions. Les Barker of Vintage Advantage sells a nice set of pistons but they don't match what I like to do to our heads. That's not his fault though :-) Stan
This is a Forged True 64mm which is the same weight as a standard CB77 piston but looks a little fragile. I'm either going to use these or some machined CB350 pistons in my conversion... Hepolite made some copies of these at one time. G
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F
Thanks for the replies.
Teazer, Yes, it seems that Les Barker want's you to extend the squish band in the head, (mill down the ridge step), to match the squish in his pistons, a very reasonable procedure, in my opinion. Makes for a very large squish band much like the CB350's. His price is near what Wiseco charges for a batch of four custom pistons.  Is your experience with Kenig first hand, street or race, or something that you've read? I've seen your "teazer" handle in a thousand posts, yet don't frankly know who you are. I've been building vintage road racer's since the early 80's, and racing for the past 20 years. Do you own a shop? race? Putting a real person behind your advice would lend more credibility. G-man, Good luck with your conversion project. One of the thinnest pistons that I've seen is the CB350 race kit piston, I would guess that they were meant to be replaced every race event! The stock CB350 piston is trustworthy and reliable, currently being raced in a couple dozen "stock spec" bikes. Stan
CB77 race pistons etc.Hello Stan
I have attached some pictures of the Italian ASSO race pistons just for intrest, these were brought in to the UK by Dennis Murfin over a number of years, unfortunately I think he stopped importing them when the demand for CB77 race stuff slowed up here. They generaly have to race with the 350K's etc. now and even with a lot of time and money I dont think they can be compeditive (no doubt the short stroke,6 speed ones would be but that's another pile of time money altogether ! not to mention engineering skill) Anyway the one in the pictures is of the later type, the earlier ones used 350K rings these use thinner( Kawasaki 600?) ones and have some other detail changes, the downside with them is they are a bit old fashioned ,tall dome etc. the up side is they fit well with a little squish work on a 72 head, have all the correct valve angles etc. already there. By the way they are a lot stronger than the CYB350K ones that you mentioned I have only seen a few of these (with and without the holes in the sides) and they were all cracked ! Good to see the pictures of your 77 racer are you keeping the Honda footrest plates or are you planning make " loops" to mount them on ? you see a lot of broken /cracked std. ones. I still have a set with the serrations milled off which I used on my CYB kit bike at one time. I did try to put the race parts list on this site a while ago on the race machine only section, on page 11, but my copies were so poor (or possibly my ability to work a computer ) that I gave up in the end, do you have any of the other pages ? Last question, are you allowed to run a oversize on the 77, I see all the K pistons advertised for the USA seem to be OS and if it's OK that might give more possibilities for you. Gordon SAFOJ
Gordon,
Thanks for the photos of the Asso, nice looking pistons, but I agree, they do look like the RSC? piston, (I'll post photo) with the large radius squish area. I have had great success with tuning the 350K's, and other bikes, by closely matching the head squish to the piston squish. Better combustion through turbulence, reduced ignition timing, and no need for twin plugs in the combustion chamber. All tested on the dyno. It is relatively easy and affordable to have Wiseco Pistons make a custom piston. The basic procedure would be to build up a 64mm 350K piston with metalized epoxy, machine to your own specs, and have the dome replicated onto one of their existing forgings. Wiseco would select an appropriate ring set from their catalog. For example, the Todd Henning Racing pistons use a forging and ring set for a CBR600. (At least the last that I heard) All of the race classes use a formula that allows a piston diameter to be at the class limit, plus an overbore of .020", .040", etc. from WERA: "Engine: Aspiration will be natural. Make and model of carburetor is unrestricted provided that the design and operating principle was in use prior to the cutoff date. Internal engine components may be modified, altered or changed as per Chapter 9. Cylinders may be bored to a maximum of .080” singles, .060” twins, and .040” three and more cylinders from the class limit. No turbo charging or supercharging are permitted in any vintage racing machine. Any machine with a displacement limit following it in the class rules cannot use these overbores, the listed displacement is absolute. If there is no class limit then stock bore is the limit." Since the beginning of vintage/classic racing here in the States and Canada, in the early 80's, the CB350K was always classed higher than the CB72/77, Ducati's, and period Brit bikes. The racing club organizers, such as Bob Coy (USCRA) and Rob Ianucci (AHRMA), knew that the Honda would clean up the competition. Curiously, in the 90's, Coy had the brilliant idea to let the CB350K race in the "GP" class, but only with a stock engine. For the past 15 years or so, this "stocker" 350 has become the most popular bike at the races in the Eastern US. The CB72/77 is not very popular, most people go with a Ducati in the 250GP and 350GP classes. Racing has become (always was?), expensive, and there are more people that have a budget to race a 350K than anything else. In fact, it may cheaper to race an off the shelf older CBR than a full tilt 350K or 72/77. It is a heavy blow to the 72/77 to have to race against the 350K! I usually get 46-47HP on my Dynojet 250i. I'd like to keep my 72 "period", and I'm happy with the stock alloy foot peg hangers. I have spares! Yes, Yosh had loop hangers on his early bikes, I guess I like the look of the stockers. I have the full catalog and will post the other pages, same photocopy quality. You can check out my other bike projects @ http://s606.photobucket.com/albums/tt146/vintagestan/ Stan
Race pistons etc.Hello Stan
Just a couple of pictures of a well used ( two welds and at crack ) RSC / CYB 350K piston so everyone can see how fragile they look and are. I better not post more K stuff or I will get thrown of the 305 site ! Its good to see all the CB77 racers on this site as I said there are hardly any out in the UK now and although the K's are faster ( I have a 69 Drixton type one that had the RSC kit stuff on it originaly) I perfer the "period" look of the 72/77, older pictures of my CYB and racer are on the Race bike only thread but both are undergoing surgery at present seeing the latest posts makes me want to get on with them. Thanks for sharing your photos. Gordon SAFOJ
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