Big bore question

Bert96 · Post by **Bert96** » Sat Sep 09, 2017 8:50 pm

I recently bought a cb77 1965 and i plan to restore it.I would like your thought about the big bore kit(358cc)
Is it a good kit,anyone bought this kit?

Bert

Merz64cb77 · Post by **Merz64cb77** » Sat Sep 09, 2017 10:13 pm

Hi Bert
I am currently restoring a 67 CB77 but went with 61 mm pistons as I'm not looking to push the bike hard but I assume you want more power.

I've never heard of anyone going to 65 mm but hopefully someone will be able to help. I've also heard that aftermarket pistons like wiseco and i assume the ones that you would be using are going to forged as oppose to oem cast. Racers like forged as the Sunday driver and honda purist may prefer cast.

Merz

Bert96 · Post by **Bert96** » Sun Sep 10, 2017 5:19 am

Its this kit that i'm talking about,

https://bore-tech.com/product/358cc-big-bore-kit

davomoto · Post by **davomoto** » Tue Sep 12, 2017 3:21 pm

I'm using that kit with Harmon Collins cam and roller rockers. Nice power gain for sure. I'm sure you can run it with stock cams, Vince Lupo installed that kit in his stocker.

davo

CharlesM · Post by **CharlesM** » Tue Sep 12, 2017 3:39 pm

You can use CB350 standard pistons, they are 64mm. I have not used them, but just melted my ASSO 64mm ones so might have to. To go that big you need to shorten and fit CB750 liners and open up the crankcase. You also need an oversize head gasket, I get them from America, but I have used CB77 standard gaskets.

I am tempted to try the Boretech kit.

I would recommend 1mm oversize valves, a duplex primary chain (Moore Performance Engineering) and a high lift cam (Phil Joy). Valves are available from the US and I am having some fitted this year.

G-Man · Post by **G-Man** » Tue Sep 12, 2017 3:42 pm

You have to machine the crown of CB350 pistons to match the combustion chamber profile.

G

CharlesM wrote:You can use CB350 standard pistons, they are 64mm. I have not used them, but just melted my ASSO 64mm ones so might have to. To go that big you need to shorten and fit CB750 liners and open up the crankcase. You also need an oversize head gasket, I get them from America, but I have used CB77 standard gaskets.

I am tempted to try the Boretech kit.

I would recommend 1mm oversize valves, a duplex primary chain (Moore Performance Engineering) and a high lift cam (Phil Joy). Valves are available from the US and I am having some fitted this year.

CharlesM · Post by **CharlesM** » Tue Sep 12, 2017 3:50 pm

Sorry. Yes. Thank you G-Man. Forgot to add that the crown needs to be machined, I don't know how much but given there are almost certainly no ASSO pistons about I might move to CB350 ones as the supply is cheap and readily available.

I've spoken to those who used to race the CB72/77 in the 90s and i'm told just taking the crown down a little will suffice. Compression won't be as good as the ASSO, but for a road bike then maybe that's ok.