Help: Builing a Street 408

[bobcowan]

A gear drive is more accurate than the gear/chain set up. BUT, only at higher rpm's, and only under a load. They're noisy, wear quickly, and are expensive. If you're building a high rpm drag race only motor, it's a good choice. Stick with what you already have, it's perfect.

It's very important that you check valve to piston clearance during assembly. You don't want to be checking that under power. You don't have to swap in checking springs. It's the easiest way, though.

The "problem" is the hydraulic lifter. Without oil pressure the lifter will collapse and you won't get full lift at the valve. Take the guts out of a hydraulic lifter, and replace the spring assembly with a stack of washers/shims. Then put it all together like final assembly. I set the rocker arms pretty loose to begin with; set it to zero lash and then back off 2-3 turns. That gives me plently of room.

Watch the rocker arm tip as it goes through it's range. That will tell you if your push rod length is OK. Checking push rods are pretty cheap at summit and jegs. They're a very valuable tool.

[donraye]

Originally Posted by bobcowan

A gear drive is more accurate than the gear/chain set up. BUT, only at higher rpm's, and only under a load. They're noisy, wear quickly, and are expensive. If you're building a high rpm drag race only motor, it's a good choice. Stick with what you already have, it's perfect.

It's very important that you check valve to piston clearance during assembly. You don't want to be checking that under power. You don't have to swap in checking springs. It's the easiest way, though.

The "problem" is the hydraulic lifter. Without oil pressure the lifter will collapse and you won't get full lift at the valve. Take the guts out of a hydraulic lifter, and replace the spring assembly with a stack of washers/shims. Then put it all together like final assembly. I set the rocker arms pretty loose to begin with; set it to zero lash and then back off 2-3 turns. That gives me plently of room.

Watch the rocker arm tip as it goes through it's range. That will tell you if your push rod length is OK. Checking push rods are pretty cheap at summit and jegs. They're a very valuable tool.

Thanks for the tips Bob. I gave the heads to my short block builder and he told me that I would have to have a cam lift of over .670 before there would be a clearance issue with the 16cc dish pistons he is using, but I'll double check it anyway to be sure. My cam lift is more in the .540-550 region.
Three more questions for you or anyone out there:
1: The valve spring compressors/removers I can buy reasonably cheaply at Summit look like slender pry bars about 10" long with a hole (I assume for the rocker stud ) a short distance from the flat forked end (which I assume goes around the valve stems to compress the springs). Can I use that same type of tool for putting the springs back in (if I take them out for the light pressure checking ones)?
2: You said you "set to zero lash and then back the adjuster off 2-3 turn to start with". What is the purpose of doing that? Everything I have read so far says to go to zero lash and then tighten the adjuster about 1/2 turn (street engine) to set the proper preload. What is the back off method for?
3: What is the big dis-advantage of simply leaving the real dual springs in the heads to set your rockers and push rods lengths up? I have a crankshaft socket and 1/2" breaker bar to rotate the engine assenbly. Is it that the springs are too beefy to easily rotate the assembly or?

I will for sure have the checking push rods to get the correct push rod length and your tip about the washers/shims in the lifters is a great one. Glad to know that one!

Thanks, Don