Cam/Valves

[Edwin Spangler]

What would you guys put together regarding cam, springs, pushrods, and valves? Gonna bite it and get a billet flywheel for my 420. Im hitting well into the 50s for speed and I just dont feel comfortable with the stock flywheel anymore. Not a matter of safety, I have the scatter shield but I dont want to ruin the engine now.

High rpm is not really necessary although my goal is to hit into the 70s.

Is this just wishful thinking? If need be, I would rather lower my speed goal than sacrafice low end power.

 

[Master Hack]

my goal is to hit into the 70s.

With a little luck ya could hit 80 or 90, but dont buy into this golden years BS.
70’s aren’t for sissies, be prepared.

 

[Whitetrashrocker]

Buy once, cry once.

 

[Sparkwizard]

We have a 420 with ARC flywheel and rod, stock cam, 22 pound springs and 1.2:1 rocker arms. I think it has a .010 head gasket, too, but don't remember for sure.
We have been abusing it on a mud mower for about 10 years. It revs pretty good and has some pure pulling power. Top speed is not comparable to a kart. We have seen 5600 RPM coming out of mud holes. That is where the coil stops the revs.

I suggest leaving the stock cam in it if you like the torque. But you knew that.

 

[Edwin Spangler]

We have a 420 with ARC flywheel and rod, stock cam, 22 pound springs and 1.2:1 rocker arms. I think it has a .010 head gasket, too, but don't remember for sure.
We have been abusing it on a mud mower for about 10 years. It revs pretty good and has some pure pulling power. Top speed is not comparable to a kart. We have seen 5600 RPM coming out of mud holes. That is where the coil stops the revs.

I suggest leaving the stock cam in it if you like the torque. But you knew that.

For sure. What my concern is, is that Ive read the stock cam shouldnt take the abuse of heavier springs. Disregard that?

 

[Sparkwizard]

Ten years since I installed the springs. 10W40 with MMO once a year.No problems to report.
We don't rev the whee out of it every time.

 

[Whitetrashrocker]

Im not sure about cam abuse, but the heavy springs are more about the valves following the cam on the closing side of the lobe.

And I'll second keeping the stock cam for the low end torque curve.

 

[Edwin Spangler]

Alllright, keeping stock. No despair in that.

 

[Edwin Spangler]

With a little luck ya could hit 80 or 90, but dont buy into this golden years BS.
70’s aren’t for sissies, be prepared.

Lol I get what youre saying but thats not for off-road.

 

[Sparkwizard]

Without DOT approved tires, I limit my shenanigans to 40 MPH.

 

[Whitetrashrocker]

What was this engine going on Ed?
I think 50+ in a street race kart would be fine. I get close to 50 in El Chingon and I back off cause its getting squirly.

Another thing about stiffer spring, the stock valves dont hold up to the real high rate springs. They will tend to cup. Then you have to move up to the stainless.

Sparky looks to have a solid build.
The more wild the build the less longevity it will have.

 

[Sparkwizard]

Mine is still governed, but with a HEAVY spring and a Tillotson bored, blueprinted stock carb. Stepson was racing it and stock appearance was important.