Doug MacRae
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- Joined
- Jan 28, 2010
- Messages
- 216
Some pics of the short stroke motor Herb is building for my race bike.
It is a 763cc, 78 X 80.4mm stroke motor with a Fullauto big valve head and JS Motorsport lightweight pistons, long rods and beehive valve springs.
The Fullauto head has had big valves put in it, 42mm inlet (4 over) and 35mm exhaust (2 over). This head, generously provided by Fullauto, was an unfinished, unmachined blank without even holes for the valves (don't bother asking him for one). Thus a few extra mods were done to it aside from the big valves. Since there was no hole for the spark plug Herb was able to re-locate the plug about an 1/8" over from where it is normally- it is now directly in the centre between the big valves. If you look at the two Fullauto heads side by side below you can see the difference- the head on the right is a pre- finished customer head (also with a Herb big valve conversion) and the one on the left is the custom head. This also has a smaller 10mm spark plug hole for a smaller plug. If you compare the two heads pictured you can also see that the custom machined head has a smaller combustion chamber for more compression (12.5 to 1) and doesn't have the round recess for the piston top machined into it like any normal Norton head would have. The rocker pivot points in the head were not drilled so Herb opted to raise them a 1/16" to leave more room for the spring pocket.
The crank is a machined from billet piece with a Megacycle cam and there are Herb made pushrods in the there.
I laid out the bits and took a few pics;
The crank, JS long rods and lightweight pistons, beehive springs-
All the pieces laid out, 850 cases and barrels to start with. A base plate was made up to make the clearances correct with the combustion chamber and the long rods.
The custom, machined from an unfinished blank head with it's small combustion chamber, re-located smaller spark plugs-
The two Herb big valve Fullauto heads side by side- left is the custom, machined from a blank head, right is the customer head. Notice the spark plug hole and combustion chamber differences. The right head is for the bigger motor to race in Canada and is also going to be lent to a Canadian Bonneville speed record bike-
This is a solid, heavy steel adjustable jig Herb made to facilitate the delicate machining of the head-
Herb demonstrates his ultra simple tool for measuring port thickness when flowing the head. He has his own flow bench in the shop and could test each variation he tried for improvements in flow. Luckily there is lots of 'meat' in the Fullauto heads for doing exotic flow work to make the big valves work better. Head flow guru Tim Speigelberg helped to give some new ideas using his magic fingers to feel the port and say 'that's not right'-
Huge thanks to Fullauto, those heads are not just beautiful, they work great too.
Thanks also to Jim at JS Motorsport.
-Doug
It is a 763cc, 78 X 80.4mm stroke motor with a Fullauto big valve head and JS Motorsport lightweight pistons, long rods and beehive valve springs.
The Fullauto head has had big valves put in it, 42mm inlet (4 over) and 35mm exhaust (2 over). This head, generously provided by Fullauto, was an unfinished, unmachined blank without even holes for the valves (don't bother asking him for one). Thus a few extra mods were done to it aside from the big valves. Since there was no hole for the spark plug Herb was able to re-locate the plug about an 1/8" over from where it is normally- it is now directly in the centre between the big valves. If you look at the two Fullauto heads side by side below you can see the difference- the head on the right is a pre- finished customer head (also with a Herb big valve conversion) and the one on the left is the custom head. This also has a smaller 10mm spark plug hole for a smaller plug. If you compare the two heads pictured you can also see that the custom machined head has a smaller combustion chamber for more compression (12.5 to 1) and doesn't have the round recess for the piston top machined into it like any normal Norton head would have. The rocker pivot points in the head were not drilled so Herb opted to raise them a 1/16" to leave more room for the spring pocket.
The crank is a machined from billet piece with a Megacycle cam and there are Herb made pushrods in the there.
I laid out the bits and took a few pics;
The crank, JS long rods and lightweight pistons, beehive springs-
All the pieces laid out, 850 cases and barrels to start with. A base plate was made up to make the clearances correct with the combustion chamber and the long rods.
The custom, machined from an unfinished blank head with it's small combustion chamber, re-located smaller spark plugs-
The two Herb big valve Fullauto heads side by side- left is the custom, machined from a blank head, right is the customer head. Notice the spark plug hole and combustion chamber differences. The right head is for the bigger motor to race in Canada and is also going to be lent to a Canadian Bonneville speed record bike-
This is a solid, heavy steel adjustable jig Herb made to facilitate the delicate machining of the head-
Herb demonstrates his ultra simple tool for measuring port thickness when flowing the head. He has his own flow bench in the shop and could test each variation he tried for improvements in flow. Luckily there is lots of 'meat' in the Fullauto heads for doing exotic flow work to make the big valves work better. Head flow guru Tim Speigelberg helped to give some new ideas using his magic fingers to feel the port and say 'that's not right'-
Huge thanks to Fullauto, those heads are not just beautiful, they work great too.
Thanks also to Jim at JS Motorsport.
-Doug
