CB72 Vintage Racer

Stan Lipert · Post by **Stan Lipert** » Fri Oct 26, 2012 12:46 pm

Updating my CB72 that I built for myself in 1998:

GT750 brake, needs new megs and footrests.

Machining the stock stator mount for a RD 350 PVL ignition.

G-Man · Post by **G-Man** » Fri Oct 26, 2012 1:28 pm

Stan

Welcome to the forum and thanks for sharing those pics. I like the GT750 brake. What are the front forks? CB750?

G

Stan Lipert · Post by **Stan Lipert** » Fri Oct 26, 2012 4:56 pm

G-Man,
Forks are CL77, late? aluminum, including triples. Lower clamp has the CR style hydraulic damper, already!

The Buffalo brake required thinning of the backing plates to fit between the forks.

Stan

jerry · Post by **jerry** » Thu Nov 01, 2012 4:11 pm

Dear Stan,Your bike is looking good. Nice to see another Racer being built. All the best Jerry

Stan Lipert · Post by **Stan Lipert** » Mon Nov 05, 2012 3:27 pm

Jerry,
It is my honor. I've been a fan of your Honda's since your visit to Daytona with AHRMA 20-something years ago. You had a nice chat with my fellow CB77 racer friend John Early who was there. He was more than impressed by your kindness, generosity and technical brilliance!

Progress on my rebuild:

PVL ignition now mounted and tested on the dyno. The mounting plates and coils are a kit for a RD350 from
http://www.pentonracingproducts.com/index.htm
Here in Ohio. The stock stator plate has some simple lathe and mill work to mount the RD unit. Works in reverse rotor rotation, one simply needs to make some new timing marks.

Cleaning up a new spare 250 head:

Inspecting sludge in a crank pin. Still needs to come apart!

Teazer:
Thanks for your input and advice, I value what you have to say! What has been your history racing with the stock primary chain? (before duplex chain sets were available) I'm looking for someone that has actually broke one!

Cheers,
Stan

teazer · Post by **teazer** » Thu Nov 08, 2012 12:16 am

Stan,

I have been very lucky to have never broken a primary chain. I have removed one with a cracked sideplate. Interestingly enough I don't recall anyone I raced with back in the day ever breaking one completely.

Maybe we were not making enough power :-(
I ran a stock first gear which is really low so maybe that helped to reduce stress coming off the line.

When I built that bike I was able to get my hands on a pile of new chains so that was never a worry. Of course that stash is basically long gone now. Down to my last two chains but to be honest I'm not a fan of duplex chains. Big heavy things that remind me of my T100 unit motor or the Rocket 3 - though that I think was triplex.

What I did break were cam chain wheels, followed a nano second later by bent valves and broken rocker arms. That was probably my own fault because I had machined a huge amount off the barrels and head to get compression up without a large lumpy piston and that really screws with cam chain geometry. I was tempted to remove a little more to see if I could shorten the cam chain.. Probably not possible.

I bought a VFR can train at one point to see if I could slip that in unnoticed and go to a gear drive. The one on the bench I'm looking at using a CBR600 tensioner blade if I can work out how to locate the bottom end.

That's a long crank end. They scare me. I have them shortened and fit a DYNA on the end of the lightened crank.

I still have a complete Motoplat system that Todd Henning sold me some years ago that I never got around to fitting.

Stan Lipert · Post by **Stan Lipert** » Thu Nov 08, 2012 9:31 am

Teazer, thanks for the reply. I am using a stock primary chain in my 250, although I will consider a hard mounted teflon shoe to eliminate chain slack when I get the engine apart soon. Ken Miller has designed and makes the slider tensioners for the CB350K and CB750 that are sold by Todd henning Racing, Bore Tech and M3. They work perfectly well, perhaps it is time to make a CB72/77 version? Ken's hard slider for the 750 primary eliminates breakage.

Before Ken made his sliders, I had a batch of case hardened rollers made for the CB350K and 72/77:

The top is for the 350, bottom for the 72/77. Since I use the heavy chain in my 350s, there is a taller center ridge so that the chain rides on the center pins, not on the side links. The 72/77 rollers are for the stock chain, and the side plates and center pins touch together.
This eliminated the rubber rollers from disintegrating, but in racing applications, it moves more shock loading to the tensioner arm push rod, in other words, I have had a cracked shoe in a couple 350s.

I still have some movable/top rollers if anyone wants to buy some ($50):

No more bottom rollers. (OKay, I'm saving one! ) The center bore is finished honed for the stock bearing, as a press fit. The outer ridge diameter is 41.6mm, 38.86mm for the main diameter.

Stan