[Lefty]

I like to read as much on performance engine building as I can afford to. Sometimes a little info here or a tidbit there can help put together a previously cloudy subject. While paging through "Tuning for Speed", by Phil Irving, he says, "At slow speeds when valve inertia is low, almost the full spring pressure is acting on the cam nose, and since lubrication is often very scanty when starting up a cold engine, more wear can be caused by frequent starts or slogging around in top gear, than by hours of fast running when the valve inertia is almost balancing the spring-load on the cam nose".

This got me thinking about another article I saved off the internet detailing the building of Todd Hennings cb500 race bike, which to my knowledge is the pinnacle of these machines. In it, top race tuner, Kenny Augustine states, "There are some pressure angle problems in the geometry, which is why the valve train rockers wear out, especially on the short side radius on the exhausts. People think they just plain wear out, but there's more to it than that. It wears out on the closing side of the exhaust valve because the pressure angle is so rotten. Nobody can tell you what the pressure angle is except somebody who designs cam shafts".

So, slogging around in top gear causes more spring force over the nose and down the closing ramp which is especially bad news for this engine. I think when Honda designed this "Super Sport" bike, there were a lot of compromises made from the technology at the time. The oil pumps and four speed gear boxes were as good as it could be done and paired perfectly with the Super Sport Bike they gave us and expected us to use as such. The problems started when people insisted on cruising and parading, and not wanting to rev em too much for fear of damaging them. I try not to cruise below 3500-4000 on mine, and when in slow traffic, I'll fall behind and then rev it up to 7 or 8 and then let er slow enjoying the music the whole time.

 

[LiamG6]

Jensen always said these bikes were designed to rev, I think they are happiest in the 6-9k rpm range, ie high enough to get the oil pumping and keep the load on the engine at a reasonable level, which would extend to what you said about low rpm being bad for the valve train. That article with Kenny Augustine was the same one I read a few years back about the bad follower geometry in the bikes which got me thinking about how to shoe horn in a roller follower like some of the modern bikes have, Honda has a few models like that currently, remarkably similar to our setup but with a roller instead of a pad, I couldn't figure out what size roller to use to get everything to work correctly though, might need custom cams. It's also why I think the old trick of grinding a tooth off the torsion bar and cranking it around an extra tooth is a really bad thing to do because the added spring pressure just damages the valve train.

I'm happy I've gone with 17-41T gearing on my bike to keep the revs up, the bad vibration seems to be about the 5000rpm mark, some people try to gear the bike to cruise below that rpm but I tried to gear it so my cruising speed with that gearing and my tyre size is 6000rpm.

I wish Ari Henning had his fathers 450 to ride these days, he has the 350 but not the 450, or at least he doesn't ride the 450 if they do still have it.

 

[Lefty]

Yes, I'm always impressed when Jensen refers to these as "super sport" bikes, to be ridden as such. He really knows these bikes. And I bet the Honda engineers freaked when they were told to put a fifth gear in it. That Henning article really shows how real engineering companies were used building those bikes. I've got some drill rod chucked in the lathe now turning an offset pin to increase the torsion bar preload about 1mm at that point. It equates to about .065" extra lift at the valve. Good for about 25 extra pounds at that point I figure.(I'll know more when I get a spring scale) The torsion bar spline mod seems to be about 4 times that and if you look at the fsm chart where they actually bend, with a big cam it probably does. My plan seems more and more to use mild or even stock cams with a bigger valve. At first anyway 450's are sure a lot of fun.

 

[LiamG6]

That sounds like a good compromise lefty, just enough extra pressure to stop them floating and the extra lift is great but not so much pressure to cause issues especially if you ride it how it is supposed to be ridden. I've got two setups in my possession to test once I get my engine built, I have my ported head with 1mm larger valves and x11-12 cams which I'll use with the Keihin CR33 roundslides and some custom pipes and another stock unported head with stock valves and cams and I'll use it with stock carbs and pipes, or possibly VM30's. Both setups will be used with the 74mm pistons. I'm curious to see how different they both feel and which power delivery I prefer for street riding. I'd like to have a complete second engine so I can just drop them in to test them, I'll be going with the performance engine the first time so I'll see if I'm motivated to swap things out, or maybe I'll collect a few more parts and have the second engine spare and built up in case things go wrong, I'd probably go with those 71.5mm pistons from charlies place in the second engine if that was the case though. I sure enjoy messing around with these bikes

 

[tbpmusic]

.......The torsion bar spline mod seems to be about 4 times that and if you look at the fsm chart where they actually bend, with a big cam it probably does..........

My experiment with the spline mod showed preset torque increased from about 40 inch-pounds to 12 foot-pounds.......obviously WAY too much.
I've an old post about it somewhere here.

 

[Lefty]

My experiment with the spline mod showed preset torque increased from about 40 inch-pounds to 12 foot-pounds.......obviously WAY too much.
I've an old post about it somewhere here.

That's A lot! I was just eyeballing it and came with four times judging from my experiments. It does seem quite excessive though. I'm thinking about scaling the fsm chart up and drawing parallels to figure out inch pound readings at closed up to the limit. It would be useful for someone checking them with a tourque wrench.

 

[Lefty]

That sounds like a good compromise lefty, just enough extra pressure to stop them floating and the extra lift is great but not so much pressure to cause issues especially if you ride it how it is supposed to be ridden. I've got two setups in my possession to test once I get my engine built, I have my ported head with 1mm larger valves and x11-12 cams which I'll use with the Keihin CR33 roundslides and some custom pipes and another stock unported head with stock valves and cams and I'll use it with stock carbs and pipes, or possibly VM30's. Both setups will be used with the 74mm pistons. I'm curious to see how different they both feel and which power delivery I prefer for street riding. I'd like to have a complete second engine so I can just drop them in to test them, I'll be going with the performance engine the first time so I'll see if I'm motivated to swap things out, or maybe I'll collect a few more parts and have the second engine spare and built up in case things go wrong, I'd probably go with those 71.5mm pistons from charlies place in the second engine if that was the case though. I sure enjoy messing around with these bikes

Yes, how you intend to ride it is what final form should boil down too. The more I think about it the more an easy to ride, mild cam motor should fit my track riding inexperience, and be easier on the budget too. I didn't realize they had 71.5, good to know.

 

[LiamG6]

I believe Charlies Place has a 71.5mm 10.5:1 CR Wiseco Piston, may or may not be in stock though.

12 foots pounds, that's pretty insane for one spline extra. I wonder how many people actually use that method.

EDIT: Seem to be in stock, $350 for the pair with rings, wrist pin and clips. https://www.charlies-place.com/shop/custom-forged-pistons-for-cbcl-450s/ 1.5mm over or 1mm over. The dome looks like the compression has been bumped up, I recall 10.5:1 being the number I read in the past, might be 10:1 though. Good balance between performance and reliability.