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Discussion Starter · #1 ·
Hey guys,

I have a 78 CB400t I have been working on for the past couple months. I am trying to turn it into a bike I can take to the flat track and spin some laps. When I rebuilt the motor I noticed the cam journals are aluminum an there are no bearings.

Is this common in bike motors, I always assumed there were bearings?? Haven't been into many motors so forgive my ignorance.

How do these heads hold up to abuse?

Should I expect failure if I am flogging on the bike?

Also was thinking about picking up an ebay head to try my hand at some porting. Are there gains to be had with this? Keep in mind I am doing this as a learning exercise. I do not expect to beat the best flow records out there I just want to try my hand.

Are there any performance cams out there?

Ryan
 

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SOHC Hondas typically run the camshaft directly on surfaces machined into the head. The head material is significantly harder than the typical babbit bearing material. The system works because the camshaft essentially floats on a layer of oil that's pumped under pressure to the lower cam journals. The heads hold up really well, as long as they've got a good supply of clean oil under pressure. Clog up an oil passageway or run low on oil, and you'll seize the camshaft to the head (if the con rod big end bearings don't go first). Flog away.

As far as porting goes, Honda's engineers are pretty damn good about optimizing shapes for good flow and broad power. Not sure about the air cooled twins, but the conventional wisdom with the inline air cooled fours was that doing anything more than smoothing out casting seams and roughness was a good way to get a bike that ran like garbage up until 8,000 rpm, then made insane but useless power. Hogging out the ports is a great way to ruin your engine.
 

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There's been mention of port work being done on these engines, no mention of using a flow bench while doing so and also no before or after dyno results.
Mega Cycle Cams does make a cam for these that also requires special valve springs. Only cam I know of.
If this is a literal toy bike built for racing purposes then I would loose the balancers first, use the 450 oil pressure fed rockers, loose the Honda CDI module and go with the Ignitech unit that you can program. You'll probably want an oil cooler so a 450 lower case would be in order there. Possibly you'd want to do ceramic coating to the pistons and head/valves.
 

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Discussion Starter · #4 ·
Thanks for the info guys. Sound like I should just pick up a complete 450 motor and sell the fresh 400. I will see how it does on the track and go from there.

And yes this will be a full on track toy.

Ryan

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The 450 is a six speed so you probably want to look at the gearing ratios for both transmissions. The weak spot IMO on the 450 is that the head oiling is taken from the center main bearing which is also serving the left rod, both balancers and the transmission whereas the 400 pulls oil from the outer mains to feed the head.
Also pistons are available for the 400, 450's are pretty scarce.
 
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