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CB72 Vintage Racer

CYP77 - Police | Race Bikes | Choppers, Bobbers and Mods
Stan Lipert Member
Posts: 32
Joined: Fri Oct 26, 2012 9:00 am
Location: Cleveland

Post by Stan Lipert » Thu Nov 08, 2012 9:41 am

I know it was talked about in another thread, but I also made rollers in teflon and fiber reinforced Delrin. Both compressed and loosened in the center bore right away!

The PVL rotor is mostly aluminum with magnet inserts, very lightweight. I had Dyna S's mounted on several CB350s, and have had a high failure rate, I'm guessing from heat. I won't use them anymore!


jerry Member
Posts: 173
Joined: Tue Feb 19, 2008 2:33 pm
Location: australia

Post by jerry » Thu Nov 08, 2012 2:44 pm

Dear Stan, I am also using steel rollers and the heavy cam chains. I have never broken a chain but because of valve lift, very strong springs and up to 13500rpm the chain life is limited to 2 race meetings. I have been using the analogue PVL ignitions for over 6 years with no problems. Make sure you use Non Resistor spark plugs and caps. In my case I shorten the crankshafts approx. 12mm for the ignitions to suit my purposes and have had no problems. All the best Jerry

Posts: 150
Joined: Wed Oct 27, 2010 12:36 pm
Location: edinburgh scotland

primary / cam drives

Post by GORDON BROWN » Thu Nov 08, 2012 5:04 pm

Hello Stan

I hope this might be of intrest. While like Teaser have never broken a std. primary chain myself, possibly because most of my use has been as a 250 but I do know people who have.
The people two know both broke them going down the box, not accelerating ( there's mabey more "whip" then causing the breakage, I dont know ) I have seen final drive chains do this and wrap arround the front sprocket.
The damage caused by the primary drive going destroyed the oil filter and the L/H casing etc. breaking out at the front.
I think it was after this happened to John Davidson ( he was running one of the quickest 77's in the UK at the time ) that he and some friends developed the duplex setup.
I have heard of both belt drives and gear drives with offset idlers being used ( this is with Std. type indirect gearbox's ),both with some problems. The short run and sprocket size diffrence making the belts try to lift of at the front and the gear drives needing cases reinforced etc. and actualy adding weight. ( riderless they do run to the left anyway, dont ask ! ).
The duplex chains are actualy not much heavier, approx 6 grams, the newer clutch sprockets are alloy I think but even the steel ones are about the same as Std. once a few holes have been drilled. The other good thing with the duplex chain is available and reasonably priced, more than can be said for NOS Std. ones.
The race kit primary chains are lighter than Std. but have another strange pitch again and only fit the lower geared special sprockets, probably this is to speed up the fairly frail 5 speed box ?.

Teaser, somewhere I have a article in a Japanese Clubman magazine showing a CL72 with a gear cam drive conversion, have you seen it ?. ( the picture of the drive is quite small but I will see if I can get it on the site ).
After running slippers in the 350K's for years I though to try one in the 72 ( it has Yoshimura style steel tooth tensioner / steel bottom roller ) but so far I have only got to milling a slot in the crankcase mating face for a locating pin, there's a lot more space in the K's.

Hope this all makes sense and is accurate, better get into the garage now and actualy put something together rather than write about it.



jerry Member
Posts: 173
Joined: Tue Feb 19, 2008 2:33 pm
Location: australia

Post by jerry » Thu Nov 08, 2012 5:43 pm

Dear Stan, Made correctly the idler gear primary drive will not give any problems. I made 3 sets in the early eighties which were run for appro. 5 seasons trouble free. All the best Jerry

Posts: 150
Joined: Wed Oct 27, 2010 12:36 pm
Location: edinburgh scotland

race stuff

Post by GORDON BROWN » Thu Nov 08, 2012 7:21 pm

Hello Racers

Stan, just realised you had posted some pictures of the "stronger" RSC K pistons, that one almost seems usable ! LOL

Jerry, I am sorry if I made out that the idler gear drives did not work, that's not the case, I know of a couple that have ran for a long time, the first one I think I saw over here was built by George Flick ? from Holland and that would be in the 80's , mind you my memory's pretty poor. The thing with the duplex setup is just that its race proven and a easy fit.

Actualy after I first read about your bikes in Classic Bike, like others, judging by the posts on this site, I dreamed about 6 speed boxes, short strokes,etc. for a while. Later seeing the pictures of your conversion and the amount of work you put into them I know why there are not many out there ! and I thought the G50 was modified.
If its OK to ask, did your 250cc bikes also run the 6 speed direct boxes ?



jerry Member
Posts: 173
Joined: Tue Feb 19, 2008 2:33 pm
Location: australia

Post by jerry » Thu Nov 08, 2012 7:57 pm

Dear Gordon, It is funny how I myself dreamed about a 6 speed box and gear primary drive for my own race bike when I was young. It is also interesting that I havent ridden a motorcycle for 31 years and therefore never got to try the machines that I built. Obviously the oppertunity was there but the inclination was gone. I never built a 250 version of any bike. I have always had a passion for 350s but seem to spend more time with the 500s. I always looked at the G50 as a big single cylinder 305. Some of the Brit bke lovers didnt like that thought but all well and done they are all mechanical marvels or monstrocities. I love them all. All the best Jerry

jensey Member
Posts: 384
Joined: Sun Jun 17, 2012 3:34 am
Location: Netherlands

Post by jensey » Fri Nov 09, 2012 1:31 am


Correct, I visited George Flick once, amazing what he has achieved.

assembly of Japanese motorcycles requires great peace of mind (Pirsig)

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