Big Bore Expectations

[Finnigan]

Been going over the options for my cb450 engine. Team Hansen has 4mm overbore pistons with high compression and Weisco has a 1mm overbore with higher than stock compression. My main question is that with an engine that produces more compression is it harder to tune? Are there reliability issues with simply increasing the cc's? If anyone has actually done this and could give me their impressions I'd appreciate it.

 

[Tim]

I've only done a big-bore on my XS650. It was coupled with an engine rephase, hot cam and ported heads/enlarged valves. With all of that, it's still deadly reliable.

A simple CC increase won't do anything to the reliability of your engine - just needs more stuff to burn.

 

[Tim]

Oh, but also don't expect to be pulling wheelies with 4 extra mm on a 450. Unless you need to replace the pistons, I'm not sure I'd bother.

 

[Finnigan]

Thanks for the reply, I think I need to get the cylinders deglazed or honed so I figured if I was spending the time and money on machining and rings to just get bigger pistons too, 444 to 498 sounds tempting...

 

[joevirus563]

I've made the same upgrade to my cb450. I had to open the engine anyway so I haven't run a stock 450. Hers what I have on mine
Dyna coil and ignition
New valve
Piston kit with Cooper gasket
Head And deck milled
520 chain conversion kit with aluminum sprocket
Mikuni vm32

Would I do it again?
No.
Why?
For sure you have power a torque and but after killing the head I had to go t a thicker gasket to prevent piston slap. So I'm losing a little bit there. My biggest issue is that I had to open up the engine a year ago and after 500km found a crack on the cylinder sleeve. Just to overbore the sleeve cost me 250$ so I had to buy another one to over bore it and install it again and might see the sleeve crack again.

A lot of person I talked to told be they had no problems with crack on the extreme overbore like this. If the sleeve is cracked open you'll need a new engine. Thr told me that it doesn't happen, I don't know what to think but still of the reliability of you wanna ride the bike a little I'd go with a stock overbore... But that's me.

 

[cxman]

hmm

honda tried to bore that engine out to 500 and they had to de rate the horsepower to make it reliable

and then they discontinued it

1975 and 76 cb500t 34 bhp (25 kW) @ 8,500 rpm

1973-4 cb450 43 hp (32 kW) @ 8500 rpm

that motor is not happy as a 500 !!

 

[joevirus563]

Well... I can say that it's a lot of fun to ride! And people likes the sound too. Thr use those piston kit in racing and guess what... They are pretty fast... Faster than any other stock 450.

 

[Finnigan]

That might be why Weisco only has a standard overbore