Oh choice, it's got a slimline seamless...and a unit engine with the gearbox chopped off....what a wonderful idea. Pistons from 7.5 to 11:1, and camshafs with the profile of a matchbox.
Yeah, but its got a pre-bent frame. Saves having to crash it to get the cool bends in the frame.
Some days are diamonds, some days are duds. Took the head into my new second best friend ' Gary the head man ' to get him to open out the ports for the 32mm carbs. Some numpty has already taken to the inlet side around the valves , the port volume in that area is way to big so the air in effect stalls on its way into the cylinder, hence a lack of oompf. He can open out the ports for the 32 mm carbs but it still will be far from ideal, reckons I'm better to start off with another unbutchered head. Put a call into British Spares, they will have a look for something on Monday, Tardme had one listed the other day but it is no longer there & I am kind of wary of something I can't be sure has not been butchered . If any one knows of a suitable head, you can be my third best friend. At least I now know some of the reason for the lack of performance. Such is life.
So its a 10 stud 750 head...? oh and keen on Sunday too....give the Norton a spin.
The Americans were the ones who developed the Triumph engine and got power out of them. I remember something Jerry Branch wrote about Triumph heads...he said the ports and valves were too big. Compare a Triumph head to a Norton head, the Norton has smaller valves and breathes better.
....apart from the Combat which they hogged out....described on the Norton forum and 'ruined"........oh well...
Pretty much what I was told yesterday. I'd been keen on a 7mm valve conversion for better flow but my man reckons they are way over valved anyway , the only advantage would be a weight saving . Cool that is US$ 650 saved. He does like the profile of the Kibblewhite valves & reckons he can machine up something better. I wondered out loud why Triumph would overvalve the motor , ' They did not understand this shit back then , just assumed bigger was better ' . Somewhere way back in time I lent my copy of 'Tuning for Speed' to someone, can you still get it ?. EDIT . Google says I can download it.
We had better quality air back in the day . Thicker, more goodness in it. So they had to have bigger valves, to let enough of the thick air in. Nowadays, the air is all thinned out and weak. Proof ( for anyone factious enough to cavil) is that if you look at the specifications for old bikes, you'll likely see the tyre pressures as around 26 or 28 psi. Whereas nowadays bikes have to have pressures of 40 psi or so. Proof that the air is 50% weaker now.
Ah ,, but if you had thicker air that was so much betterer surely you would have needed smaller valves to restrict the amount of goodness that was consumed. Me thinks you were fuller of shit back in the day.
The Triumph was designed to have about 6:1 compression with flat top pistons, that's why the combustion chamber is so huge. Makes sense to fill it up with valves. By the time better fuel enabled compression of 9:1 and more the combustion chamber was a very bad shape with a high dome piston...it's just a bad design getting worse as performance went up. They also had fat pipes...in the mid '60's when they were getting good power out of the 650, the header pipes were reduced in size, you can see the big step down at the exhaust clamp end. The smaller dia pipe gives higher gas speeds. Rickman and Westlake made 8 valve heads for Triumphs , that's the way around it.
Already had the lecture about the pipes being tooo big. Bugger me, this was supposed to be low tech , low bucks It's always darkest before the dawn, yeah right , wat ever
It all become clear to me now. Thicker air explains the (lack of) top speed on those old Blitish bikes. Or the pea soup fog as seen in those old films.
Purchased another head & delivered it to ' Gary the man ', he thinks will put smaller exhaust valves in it as it is still over valved. At least it is progress. He is still keen on titanium keepers etc, every bit of weight saved on the end of the valve means quicker & higher revs & less stress on the valve train.
