Which CB350 engine to race

CanadianBacon

CanadianBacon

New Member
I'm looking to build a CB350 into a vintage racer, not looking to fully custom the thing but just do enough to get me on the track and have some fun.

I have two 350 engines to choose from. One off my '68 that's a K0 and running pretty good, the other is a K2 and is a spare that I haven't heard run but I don't mind tearing it apart and making it go.

I've heard the K0 is a good base to start from because of the higher RPM tolerance but I'm not really sure.

Anyone have any thoughts?

Any help would be great. I don't want to put all my energy into the wrong build.

cheers!
 
The K0 does rev higher, but the exhaust is harder to find (so don't rash it). Also, the oil pump in the K0 is made out of cast iron IIRC and will fall apart with a dirty look. So use a later model oil pump if possible.
 
had a k0 parts engine, oil pump looked to be aluminum, the higher lift earlier cams I picked through all seemed to fair worse than the later lower lift cams, could have just been my luck though... the 350 is such a great engine though, I put a year into building a hopped up 360 motor and went to a 350 later, was just amazed at how much more robust the design was. if you have a friend with a lathe and 4jaw, or bridgeport and boring head, they're super easy to convert to needle bearings in the cam too, and I've heard the plain bearings don't fare all that great under racing conditions.
 
Thanks for the replies. I do have a friend with a bridgeport so I might look into doing that. I guess it's not the worst thing to have a spare engine around though. I don't plan on racing super competitive but I would like to see what I can do with a near stock 350.
I'll take a look at both pumps and see what I find. I'm not in a rush either. I have a couple other projects going, this is sort of a "why the hell not" sort of a thing.

Any more tips would be appreciated. I'll post some pics when I get them apart a bit.

thanks again.
 
You may want to look at the period1&2 rules for guidance.

http://www.vrra.ca/wp-content/uploads/2011/08/VRRA-Rules-May-2011.pdf
 
Thanks Tripler but I'm in the USA. I've read through a few of the rules books down here and trying to decide which class I would like to be in.

Slightly modified stock is what I'm looking to do if anyone has any suggestions.

thanks.
 
If youre not looking to be highly competitive in a modified class, you really dont need to worry too much about the motor. Convert to electronic ignition, build a proper exhaust, upgrade the cam chain tensioner and valves, new pistons/rings, new gaskets and seals all around, etc... Youre real needs lie with the sub-par chassis and suspension. When racing in a vintage class, youre unlikely to use all of that motor very often, but you will use all of the suspension. Brace the frame accordingly (there are some great write ups floating around on this), upgrade the front end, buy new shocks out back, replace the shitty swinger bushings with brass, roller neck bearings and a steering damper, and so on. Its not always the most powerful bike on the track that wins... Its the one that has to slow down the least.
 
Sorry, the name fooled me. ;D Here is an example of what you would face up here. There are many guys come up for the Mosport Festival in August.

http://www.youtube.com/watch?v=N5BxW7Y3TVM&feature=player_embedded#!
 
If you're looking for robust, why not just switch the top end of the KO on to the later motor and then you'll have the good oil pump with the better cam? The exhaust and everything else should be a direct fitment.
 
Actually, the oil pump is an easy switch. It's behind the right side cover, and is held on by a couple bolts.

And Sean - I haven't been in very many 350 motors. The only K0 I opened up had the older style pump (which cracked after I dropped it). While searching around to be certain the later pump would work, I found out the early style were prone to cracking. But I'm glad to hear you haven't had that problem!
 
From memory/experience
Cast iron oil pump body isn't an issue if you don't drop it, check plunger and drive pin/arm.
Check eccentric on clutch basket as well as the parts already mentioned
You can always ream body and make new/better plunger
It's better to remove primary drive gears, oil pump bolts and clutch in more or less one unit (not removing properly cracks body at base of slot)
Top end will seize cam bearings at high rpm
They will probably last a complete season though (use full synthetic oil, they will last longer)
Carefully built and tuned 350 will make between 32~34bhp @11,500~12,000rpm with stock cam and heads (early or late engines)
At the wheel numbers, not at the crank as original Honda numbers (36bhp ::) )
Stock points 'bounce' around 10,500~11,000rpm and act as rev limiter, electronic ignition is better but can allow 13,500rpm or more
30mm carbs make better power than 32mm and are easier to tune, particularly with near stock motors
Bore Tech tensioner will last about 1~2 seasons then will be worn out
Stock clutch springs are crap, get heavy duty ones, stock plates then work fine
 
@ Crazypj- Can you sub in the CB500 clutch springs in place of HD springs, I seem to recall reading this somewhere and I know you've got a wealth of knowledge in modifying engines.
 
I've never tried it
For $15.00 it isn't worth pulling cover back off if they don't work.
I've found even stock 500/550 will slip clutch after a few thousand miles (it's designed to slip slightly to compensate for 'bad' gear-change technique)
 
I have the engine apart and my oil pump is aluminum. Perhaps a few slipped out of the factory with cast iron ones before they switched. Or it could have been switched out. This engine looks like it was taken apart at one point.
I'm upgrading the cam chain and tensioner, new rings, gaskets and oil seals. Giving the cylinder a fresh hone while it's open too. I'm leaving the bottom end as is for now. I'm only running in the Vintage Production class to start so until I move up a class and want to really upgrade the engine I don't want to get into it too much.
It's all in pieces now but I'll post some pics once the parts are all here and starting to come together.

Thanks for all the info!
 
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