327???

I am putting a 355 l98 sbc together with a comp magnum 270hr, oem replacement roller lifters, TFS 195's w/ the 1.46 dual valve spring option, and crane gold 1.6's.

My problem is that at the shortest recommended pushrod length(7.25") the rocker still rides on the outside of the valve stem, but when I shorten the pushrod to bring the travel to the center of the valve(6.9") the rocker is almost bottomed on the stud and the nut is so far down that i can't get the lock on.

the block is zero decked, the head gasket is not on now(should it be?) but is .041" thick, and the heads have not been milled. if you need any more info i will try to get it for you.

What should I do? Do I need longer valves?

I have pictures of how the rocker sits with the 7.25" pushrod if anyone wants.

Thanks!

five7kid

iTrader: (14)

Yes, it should be.

327???

ok, i thought so, but that won't solve the problem of the rocker basically bottoming out on the stud.

sofakingdom

iTrader: (1)

Of course it does. They're 1.6 ratio.

You do realize what "ratio" is, right? It's the length between the valve and stud, divided by the length between the push rod and the stud. You got 2 ways to increase that ratio above stock; lengthen the first distance, or shorten the second one. Most higher ratio rockers do some combo of the 2. You can't move the stud, and you can't move the valve itself; although you CAN move the CONTACT POINT outward, exactly as you observe, and you CAN offset the trunnion on the stud although that's not necessary on a SBC to get 1.6 ratio.

Don't worry about where on the valve stem the contact patch is. That's not what you set with push rod length.

Instead, choose your push rod length for the MINIMUM WIDTH pattern of the rocker tip on the valve stem. Least amount of sliding/rolling/side-load on the valve. That's the CORRECT way to select push rods.

327???

I was suggested lash caps on another board, but when i put an .080 spacer on top of the valve i still wasn't able to get the sweep right in the middle without a ridiculously short pushrod, right about then I began to think what you posted above.

sofakingdom

iTrader: (1)

Right...

Don't worry WHERE on the valve stem tip the rocker contacts; only on making the pattern AS NARROW AS POSSIBLE. That locates the half-lift point at the center of the rocker's arc; and minimizes side loading on the valve, which of course is what wears out the guides. It's usually better, if your "perfect" push rod length comes out in between 2 real-world lengths, to get the ones on the shorter side; that way, the extra side load occurs when all the forces are low, i.e. right as the valve comes off the seat; and when the forces are high, i.e. at full lift, the imperfection of the geometry is kept to a minimum.

327???

Thanks!

i'm going to go see what length i come up with using your method.

Edit: with your method the recommended 7.25" pushrod(w/headgasket on) is almost perfect, .060 in either direction and the sweep starts to get wider.

sofakingdom

iTrader: (1)

Sounds highly believable. Go for it!!