1.56" Intake Valves With Web 312a Cam & 4" Radius Followers

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Dan1950

Dan1950

1974 MK II Roadster
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After some input from fellow forum members familiar with this set-up and an email conversation with Jim Comstock it seems like valve clash will not be an issue running this combination.

Now I need to find a competent machinist that can do the work before spring of 2023.

Not looking for extensive porting, just open up the bowls a little and clean up the area around the guides.

Any suggestions on someone stateside that can do the work?
 
This is the set up I'm running, and JC did my headwork, though valve clash cannot be determined until assembly.

As for porting work, have a look at the videos on JS Motorsports website about this.
 
acadian said:
This is the set up I'm running, and JC did my headwork, though valve clash cannot be determined until assembly.

As for porting work, have a look at the videos on JS Motorsports website about this.
Click to expand...
I'm well aware that anytime you deviate from stock specifications clearances have to be checked.

When I put my 86 in Panhead together I had to take a mill file to the bottom of the piston skirts as they were just kissing each other at the bottom of the stroke.

If need be, the valves can be set into the seats.
 
Dan1950 said:
After some input from fellow forum members familiar with this set-up and an email conversation with Jim Comstock it seems like valve clash will not be an issue running this combination.

Now I need to find a competent machinist that can do the work before spring of 2023.

Not looking for extensive porting, just open up the bowls a little and clean up the area around the guides.

Any suggestions on someone stateside that can do the work?
Click to expand...
Was that combination Jim’s recommendation, or was your discussion with him only about the possibility of clash etc?

Why not ask him to do the head work ?
 
Fast Eddie said:
Was that combination Jim’s recommendation, or was your discussion with him only about the possibility of clash etc?

Why not ask him to do the head work ?
Click to expand...
I know a more than 1 forum member that had Jim do such a combination.

I have but he hasn't answered.
 
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I have that combo in my bike with no modification of the intake valve. It seemed to lack torque down low so I mentioned that to Jim and he recommended advancing the cam 5 degrees. (Info in the INOA manual) Now it pulls real hard from about 2500 rpm. It will pull from 2000 but pulls hard from 2500. Mine runs out of breath at about 5500 and makes maximum HP at 5300. (42 rear wheel HP on the dyno)
 
Dan1950 said:
After some input from fellow forum members familiar with this set-up and an email conversation with Jim Comstock it seems like valve clash will not be an issue running this combination.

Now I need to find a competent machinist that can do the work before spring of 2023.

Not looking for extensive porting, just open up the bowls a little and clean up the area around the guides.

Any suggestions on someone stateside that can do the work?
Click to expand...
Ask Kenny at NYC Norton for someone.

Herb Becker would probably be great, if he is still at it. I think he is outside Toronto. Mike Partridge at Walridge might be able to put you in touch.
 
motorson said:
I have that combo in my bike with no modification of the intake valve. It seemed to lack torque down low so I mentioned that to Jim and he recommended advancing the cam 5 degrees. (Info in the INOA manual) Now it pulls real hard from about 2500 rpm. It will pull from 2000 but pulls hard from 2500. Mine runs out of breath at about 5500 and makes maximum HP at 5300. (42 rear wheel HP on the dyno)
Click to expand...
I too ended up advancing mine by approx 5 degrees, can't remember what the precise LC figure was, but the RGM cam sprocket with 3 keyways worked a treat.
gortnipper said:
Herb Becker would probably be great, if he is still at it. I think he is outside Toronto. Mike Partridge at Walridge might be able to put you in touch.
Click to expand...

Unfortunately Herb isn't doing any more builds for general public
 
I know you can’t compare results from one dyno to the other but …
I worked at a shop with a Dynojet . After a good break in period I put my 1971 Commando to tune for timing and jetting. 43.3 rear wheel horsepower at the red line of 6000 rpm, 44.8 torque @ 4600
Stock rebuild including a base gasket, Megacycle cam and running a single Amal Concentric,
I would think that low 40’s is about average for a good running 750 and should pull right up to the red line ( or the crank explodes, whatever comes first).
motorson said:
Now it pulls real hard from about 2500 rpm. It will pull from 2000 but pulls hard from 2500. Mine runs out of breath at about 5500 and makes maximum HP at 5300. (42 rear wheel HP on the dyno)
Click to expand...
 
motorson said:
I have that combo in my bike with no modification of the intake valve. It seemed to lack torque down low so I mentioned that to Jim and he recommended advancing the cam 5 degrees. (Info in the INOA manual) Now it pulls real hard from about 2500 rpm. It will pull from 2000 but pulls hard from 2500. Mine runs out of breath at about 5500 and makes maximum HP at 5300. (42 rear wheel HP on the dyno)
Click to expand...
Is that a typo? Did you mean 6500 and 6300 ?
 
motorson said:
I have that combo in my bike with no modification of the intake valve. It seemed to lack torque down low so I mentioned that to Jim and he recommended advancing the cam 5 degrees. (Info in the INOA manual) Now it pulls real hard from about 2500 rpm. It will pull from 2000 but pulls hard from 2500. Mine runs out of breath at about 5500 and makes maximum HP at 5300. (42 rear wheel HP on the dyno)
Click to expand...
Fast Eddie said:
Is that a typo? Did you mean 6500 and 6300 ?
Click to expand...
I hope it is. What motorson describes is about how my bike runs currently. I would hope for some improvement.
 
acadian said:
This is the set up I'm running, and JC did my headwork, though valve clash cannot be determined until assembly.

As for porting work, have a look at the videos on JS Motorsports website about this.
Click to expand...

 
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Dan1950 said:
I hope it is. What motorson describes is about how my bike runs currently. I would hope for some improvement.
Click to expand...
Hope and money should get you some improvement.

Check out this page if you have not already -> Map Cycle long rods and pistons. I've not used these parts, but they would save some money over the high-priced spread and should help get you closer to the still pulling beyond 5800 RPM goal. MAP has been involved in British motorcycle upgrades a while. You don't need long rods to make the motor pull harder than it does, but they are a slight improvement with regard to reciprocating mass and rod strength when pushing to motor hard.

I used Jim's rods and pistons, and am happy with the results. I'm giving you another resource to check into.
 
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Fast Eddie said:
Was that combination Jim’s recommendation, or was your discussion with him only about the possibility of clash etc?

Why not ask him to do the head work ?
Click to expand...
Dan1950 said:
I know a more than 1 forum member that had Jim do such a combination.

I have but he hasn't answered.
Click to expand...
Jim has answered my email. It looks like we might be able to get together and have my heads ready for spring.
 
My RPM numbers are correct. Just under 42 HP and falling off after 5500 RPM. Incidentally, the mixture was quite lean at 18 something. I cannot seem to get it rich enough on the top. Maybe incorrect slides in my Amal Premiers? I know the engine is over carbureted and over ported. Combat head and 32mm Amals. I think the whole thing would wake up with a 30mm head and carby set up along with about a whole point more compression.
 
The Web 312A, IIRC, is specified by them for 3" radius, unless they changed the cam or the spec. Jim did the radius on my lifters, but the machining is readily available. I tried advancing the cam 5 degrees and spent a lot of time with a degree wheel and a piston stop. You'd think advancing the cam sprocket one one tooth (15 degrees) and retarding the crank pinion 2 tooth (-10 degrees) should be easy, but if you are infected with Perfectionpox , it can take a good portion of the day.

I didn't know wether or not I should be impressed so I put it back to stock cam timing, which took about an hour, and was impressed. While doing all this work my Ducati 1100 Hypermotard was laughing at me. At one point it told me, "wanna go fast and handle like a hot knife through butter? hop a board!"

A customer ask me once how much money to budget for building a hot Norton, I simply told him, "all of it". I have come to appreciate what a wonderful motorcycle a Norton is when ridden modestly.

Besst.
 
One benefit from a hot cam in an 850 might be the reduced torque load on the the transmission at 4- 4.5 k. The stocker sure has a lot of twist. Even non sporty riders make good use of the 850 mid range twist.
A older friend who rebuilds amc boxes noted that he really didn't see many problems with the boxes until the 850s showed up with their extra torque.
 
RoadScholar said:
The Web 312A, IIRC, is specified by them for 3" radius, unless they changed the cam or the spec. Jim did the radius on my lifters, but the machining is readily available. I tried advancing the cam 5 degrees and spent a lot of time with a degree wheel and a piston stop. You'd think advancing the cam sprocket one one tooth (15 degrees) and retarding the crank pinion 2 tooth (-10 degrees) should be easy, but if you are infected with Perfectionpox , it can take a good portion of the day.

I didn't know wether or not I should be impressed so I put it back to stock cam timing, which took about an hour, and was impressed. While doing all this work my Ducati 1100 Hypermotard was laughing at me. At one point it told me, "wanna go fast and handle like a hot knife through butter? hop a board!"

A customer ask me once how much money to budget for building a hot Norton, I simply told him, "all of it". I have come to appreciate what a wonderful motorcycle a Norton is when ridden modestly.

Besst.
Click to expand...
Jim did my lifters for the 312a - 4" radius.

Camshaft dialed in at 104.5 L/C inlet, 12 pins between idler and cam sprockets, Idler gear now 5 teeth counter clockwise from original marks.

Pretty spot on - I am not going to gripe about 0.5 degree. Here is the webcam 312a timing card.

webcamshafts.com

webcamshafts.com
webcamshafts.com webcamshafts.com
 
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