Nice link on bevels and such

[00weel]

http://translate.google.com/translate?h ... .com&twu=1

[Garnet]

Very cool stuff.

I was in the south of France on holiday in Oct of 82. I saw a group of riders, a couple of them on airheads and three or four unrecocnizable bikes of some sort. I thought at the time it must be some new model of Jap bike, but they had flat paint jobs and where not very attractive. It was not till the next year when I was at the MOA rally did I hear rummors of the soon to come K bikes. I allways wonder if I saw early road tests, or just had too much red wine.

[Zombie Master]

http://translate.google.com/translate?h ... .com&twu=1

Now that's a post!

[gspd]

No bevelheads for me thank you. I see complexity of design as a weakness, not an art. sorry.
When it comes to MY ride, I want pure mechanical simplicity.
Stuff I can fix in the dark. Nothing else will do.

BlLAST FROM MY PAST
If you scroll to the bottom of chuey's link,
you'll see Frank Romanelli's 6 valve heads.
I was hangin' with him in his machine shop/foundry back then.
Those heads were all in-house cast and machined 5 minutes from here!
I built some prototype 5 valve Harley heads with/for him.
He designed and we built those heads way before Yam came out with the 5 valvers.
All were eventually proven to be a waste of time.

Nice guy, Frank, but wacko italiano!
He was a mechanical genius but was not around when god was handing out the social skills.
We had a lot in common.
He's also the guy that sponsored my Guzzi racer.

[Zombie Master]

[quote="gspd"]No bevelheads for me thank you. I see complexity of design as a weakness, not an art. sorry.

I built some prototype 5 valve Harley heads with/for him.
He designed and we built those heads way before Yam came out with the 5 valvers.
All were eventually proven to be a waste of time.

The 5 valve Yamaha engine is still being sold today in the FZ1. I also remember reading there are current 5 valve Yamaha dirt bikes as well.

My nine year ownership of the XTZ 750 10 valve twin gives me some insight on the benefits of this design.
First of all the spread of torque was everywhere in the operating range of the engine. I found throttle response to be exceptional for a 750 parallel twin. Not only did it pull strong and smooth in the lower rpm range, it also had a nice bump at 6000 to red line. I often rode with a friend on a GS1100 who had no power advantage. The first valve inspection wasn't due till 42,000 KLMs. When I checked them at that mileage, only two were slightly tight. What other motorcycle engine goes that far between major services? None that I know of.

Is a 10 valve twin as complicated as a 16 valve four? It may very well be that there is no maximum power advantage with a 5 valve per cylinder engine. From my experience the real advantage is in throttle response. That engine never ceased to amaze me with its tractability and power. IMO the only reason this design will disappear is the cost to manufacture, and the ignorance of the public who only care about maximum power output numbers.

[gspd]

The 5 valve Yamaha engine is still being sold today in the FZ1. I also remember reading there are current 5 valve Yamaha dirt bikes as well.

OOPS!
I thought they all eventually went back to a maximum of 4 valves per head.