cam opening and closing time

When a valve is opening is there another valve closing at the time? Does not have to be the same cylinder, so it could be 2 intakes or 1 then an exhaust? Is there 1 or 2 or... doing this.

There's always several valves opening and closing at the same time. I don't really understand your question

Now on the same cylinder, depending on how much overlap, your exhaust valve will be closing as your intake valve opens so in this case both valves are open for a short period of time or degrees of rotation.

toooo much thinking...lol but then why double pin your cam? If you get the same amount of pressure on either side of the cam then the timing chain dosen`t know what weight springs you have? One is opening and another is closing its the same amount of pressure put on the timing chain with 100lb spring or 500lb

Good point however the crank is yanking on the chain which is turning the cam. Double pin is like added insurance. I've run single and double pins. A good bolt with service removable loc-tite and a hardened washer is also mandatory.

Give this little experiment a try next time you are assembling an engine. Leave the timing chain off, and try to roll the camshaft with the gear installed. I'll bet you will answer your question.

nitro717 wrote:When a valve is opening is there another valve closing at the time? Does not have to be the same cylinder, so it could be 2 intakes or 1 then an exhaust? Is there 1 or 2 or... doing this.

Typically in our performance engines, the exhaust valve may not be fully closed as the intake valve begins to open (anticipating the next downstroke of the piston). So an any given cylinder of your 385 Series engine, both valves are likely open at the same time during some point of the engine cycle (exhaust cycle-to-intake cycle).

Paul

I think what nitro717 is saying is that the torque required to turn the cam shouldn't rise dramatically with a rise in valve spring rate, because while one spring is RESISTING cam rotation (opening), another one is ASSISTING rotation (closing). That makes some sense, but I'd guess that the heavier springs would also multiply the FRICTIONAL LOADS at every component in the valve rain, from the cam bearings to the lifters to the pushrods to the rockers to the valve itself. Sounds like good reasons for stuff like roller bearings, roller lifters, roller rockers, etc. I guess that's why the old sled type rockers are among the first things to hit the scrap pile with performance upgrades. It's about minimizing frictional loads and losses.

I know this hasn't settled all debate so I'll just say this: I have broken a cam pin and hurt a motor, so I'll keep using double pins.

What Gets me is Why the Cam Co.'s don't just go ahead and either DP the cam/gear or at least have the holes there we can do it if we desire, especially when the cam gets to the size that it needs the big spring pressures. They could tack the xtra money on w/price of the cam.

bbf-falcon wrote:What Gets me is Why the Cam Co.'s don't just go ahead and either DP the cam/gear or at least have the holes there we can do it if we desire, especially when the cam gets to the size that it needs the big spring pressures. They could tack the xtra money on w/price of the cam.

I think at the point of needing a double pin most people go with a custom grind. With a custom cam the option to have it double pinned is offered when having it speced. I would bet that most people who buy a catalog cam dont want, know about, or know how to drill a 2nd pin. Thats why its not offered.

I just put a cam in and noticed this push/pull of valves opening and closing as I spun the motor with a wrench, it wasn't constant there were times that it was noticably stiffer and then further in the rotation it actually pulled the wrench!
My cam & gear are now double pinned, such a good feeling...

IF you don't have the cam nose below the surface of the timing gear, a HARD, THICK washer, a long enough grade 8 or 9 bolt...with enough torque AND Locktite on it...all the pins in the world aint gonna help.