Roller cam newbie Once you start going down the rabbit hole!
Alright, it seems I have a heck of a lot to learn. Valve stem positive seals - Do we need to machine heads for this? Valve springs for camshafts, what pushes the need for springs, the duration, lift or rpm.?
I am looking at getting a roller cam with these specs, DUR @ .050 218INT/224EXH Intake lift .535 Exhaust lift .531 (1.5 Ratio). So I will need a spring upgrade I was going to get Melling 466463 the specs say coil bind is at 1.025. So .535 X 1.5 = .8025 lift for coil bind.? (But the way of my thinking is if the lift is .535 with 1.5 Rockers then is that not the max lift? & if so a coil bind of 1.025 seems EXTREME!) Am I reading/doing this correct? Or are the other specs like installed load & height (112 @ 1.687) & open load and height (290 @ 1.187) factor into the math of figuring out maximum lift for these springs? Also will I need positive valve stem seals. Will I need to machine the heads for these valve springs? I was also looking at Hughes 1110P springs. Anyone using the Hughes or Melling springs I mentioned? If so what lift are you running and did you need to do any additional machine work for these springs? Thanks guys and gals.
OK, one at a time;
1: positive valve seals. Generally yes you need to machine the tops of the guides to fit the seals. When using a higher lift cam you also need to check retainer to seal clearance and may need to machine a bit off the height of the guide.
2: Springs: lift and RPM are the determining factors on new springs. It is a matter of inertia of the valvetrain components. Now duration does also affect this, but getting high lift requires lifting the lifter, valve and everything between at a higher rate. Of course higher RPM increases that rate also, imparting more momentum into the parts.
3: Lift. The lift of the lifter × rocker ratio gives the design valve lift. Bottom line.
4: Coil bind. This is a spec the spring manufacturer gives or you can measure. It is the length of the spring when all the coils are compressed on eachother and it can not be compressed more. Not something you want in a running engine.
5: Installed height. This is the length of the spring as installed and ready to run. The installed height gives the seat load the spring imparts to hold the valve on the seat.
6: The stuff that is also important. Installed height minus the valve lift gives the spring length at max lift.
OK, so if you have an installed height of 1.8", you subtract the 0.535" lift to get 1.265". So if your coil bind height is 1.025", you have 0.245" extra room. Springs work better to stay out of surge if run closer to the coil bind spec. For conventional springs probably 0.050" to 0.750". Beehive springs can be run down to 0.025" to 0.030".
You have to check retainer to seal clearance at max lift. This is easier to do with checking springs. You can get a couple at your local hardware store. Use these instead of the valve springs with the retainer and keepers installed. Use a dial indicator on the edge of the retainer to measure max lift. It should be the same as listed on the cam card. Using the numbers you have supplied the intake lift should read 0.535". You should then be able to push the valve open at least 0.050" before the retainer touches the seal.
I hope this clears up the situation.
Also remember you have to check piston to valve clearance on any new build. 0.080" minimum on the intake and 0.100" minimum on the exhaust. Strips on modeling clay in 1/4" diameter strips across an intake and exhaust valve with the engine turned through two complete revolutions and remove the head. You can do it without a head gasket and just snug a couple of bolts on the cylinder being checked. When you put the gasket in the clearance will only increase.
