cb72 350cc ?

Rookhill · Post by **Rookhill** » Wed Mar 30, 2011 2:21 pm

Hello, I've just been looking through the "bikes for sale" and came across a 1962 cb72 with a
WEBCO 350cc KIT - HARMAN/COLLINS DRAG CAM & SPRINGS - 305 CARBS.
If you bore out to 350cc do you use the barrels of a bigger CB or is it a resleeve of the original CB72 barrels.
Also what kind of gain is achieved as I have a 1963 CB72 that needs a complete restoration. I intend to use it for the road and the odd track day. Not racing though.
Any information is much appreciated.
Thanks H.

davomoto · Post by **davomoto** » Wed Mar 30, 2011 3:10 pm

There are different ways to do it. No matter which way, the engine cases need to be bored on a 250 lower end. The stock 305 sleeves can be bored 4mm, but they are left quite thin. There's a seller on ebay that sells a kit that has oversized sleeves, cylinder must be bored to accept them. I have 2 and 3mm overbore kits for the CL72, you can stil use stock liners, no need to bore cases. Megacycle still offers a few different re-grinds for the cams, and hard facing for the rockers. It adds up to a lot of money for a little gain IMHO

Davo

teazer · Post by **teazer** » Wed Mar 30, 2011 9:46 pm

With a Cb72, the replacement liners often are larger than the barrel muff and it's possible to machine right through the base of the fins at the front and back.

That's less of a problem with Cb77 barrels which have more metal in the middle for the larger liners.

A Webco 350 kit with H&C cam and light port clean up is a significantly faster bike that a stock CB77 and much more so than a stock 250 - according to tests from the time.

Drag cams typically have a lot of lift but not much duration and are excellent for those of us that "point and squirt" our way around a track. Great acceleration as a rule.

If the motor is not worn out or rusted solid it would be a great track motor in all probability.

Rookhill · Post by **Rookhill** » Thu Mar 31, 2011 12:53 pm

Thanks guys. If I've got this right, dont bother boring out the CB72 barrels use CB77 barrels instead.
Does that mean I use the CB77 head as well or does the CB72 engine need replacing with a complete CB77 engine. Then bore/tune the CB77 engine. If so do they bolt straight in?
Thanks H.

davomoto · Post by **davomoto** » Thu Mar 31, 2011 1:04 pm

Yes, the 305 barrel and head as the 250 head doesn't have clearance for the bigger piston. Cases need to be bored as well.

Sorry about the ambiguety on the cams. As Teazer stated the entire package will make a big difference in performance. The cams and hard facing of the rockers less so on thier own.

I have a CL77 that I bored 3mm over into the stock lining, and that made a really big improvement on it's own!

Davo

Rookhill · Post by **Rookhill** » Sat Apr 02, 2011 7:51 am

Again, thanks guys. I will now start looking for CB77 and tuning parts. I'm in Texas visiting the in-laws in August so I have plenty of time to fill their garage with bits !
Regards H.

LOUD MOUSE · Post by **LOUD MOUSE** » Sat Apr 02, 2011 8:52 am

What area of TEXAS?. ...........lm

Rookhill wrote:Again, thanks guys. I will now start looking for CB77 and tuning parts. I'm in Texas visiting the in-laws in August so I have plenty of time to fill their garage with bits !
Regards H.

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cb72 350cc ?

cb72 350cc ?