Modifying Roller Rocker Arms..

[djxib]

LT-1 with LT-4 Heads; RR; double springs; 7/16 Rocker studs

I am replacing some engine components after a head gasket blew. This question is about my Roller Rocker Setup...

So the ideal length pushrod for my setup (as far as roller against valve tip is concerned) causes the rockers to slightly rub against the base of the rocker studs. The original pushrods that I removed seemed too long; maybe the builder may have just been a little lazy.

Anyway - is there any guidance from the gurus out there; should I grind .150" from the base of each stud or take the same from the base of each rocker arm?

Any other bright ideas?

Oh - and I have measured it about 4 times using checking pushrods and valve check springs - and I have been careful not to preload the lifters for the measurements

 

[Hib Halverson]

Are the roller rockers the production LT4 rockers or aftermarket? If aftermarket, what kind are they?

Also, the 7/16 studs...are they aftermarket?

Why the dual springs?

Also, what camshaft is in the engine?

 

[djxib]

Are the roller rockers the production LT4 rockers or aftermarket? If aftermarket, what kind are they?

Also, the 7/16 studs...are they aftermarket?

Why the dual springs?

Also, what camshaft is in the engine?

Good questions - the build up was done well before I ever acquired the car and I have no information (I only discovered LT-4 heads after I blew the head gasket..)

RR are gold in color but have no obvious markings. I have to assume aftermarket. Also the studs - no clue, no obvious markings. Dual springs I assume because redline is about 6300. Also I have no idea on the Cam, I dont know if this helps but the engine is forged, supercharged (12psi) and also I have measured the valve to piston clearance using check springs and it is at least .250" at its closest point (measured at 5 degree intervals as the exhaust is closing).

 

[Hib Halverson]

The rockers are Cranes. You need to find out from Crane if the particular arm you have is compatible with the studs. I'm going to guess they're not. DO NOT modify the rockers or the studs for clearance. You need to either change the rockers or the studs to eliminate the problem.

If the cam is stock, dual Springs are not necessary if the engine's rpm range is like the OE LT4 but, if the engine is going to be run past the OE LT4 limiter or the cam is an aftermarket profile or the GM Hot Cam, they might. Nonetheless, the springs are probably not an issue as long as there is adequate clearance between the retainers and the rocker bodies.

How do you know the engine is "forged"? Neither the LT4 or the LT1 had forged steel crankshafts nor did they have forged pistons. If you're using stock pistons, with 12psi boost you want to make sure the tune on the engine is spot on because any detonation under boost and cast pistons won't live very long.

 

[djxib]

The rockers are Cranes. You need to find out from Crane if the particular arm you have is compatible with the studs. I'm going to guess they're not. DO NOT modify the rockers or the studs for clearance. You need to either change the rockers or the studs to eliminate the problem.

If the cam is stock, dual Springs are not necessary if the engine's rpm range is like the OE LT4 but, if the engine is going to be run past the OE LT4 limiter or the cam is an aftermarket profile or the GM Hot Cam, they might. Nonetheless, the springs are probably not an issue as long as there is adequate clearance between the retainers and the rocker bodies.

How do you know the engine is "forged"? Neither the LT4 or the LT1 had forged steel crankshafts nor did they have forged pistons. If you're using stock pistons, with 12psi boost you want to make sure the tune on the engine is spot on because any detonation under boost and cast pistons won't live very long.

The pistons are Probe LW40 (I have validated this from underneath), and when I bought the car I was told that it was an all forged 383. I agree on the tune - I am running a conservative tune and alcohol injection.

There is plenty of clearance between the rocker arms and the springs, and the rockers look like they are designed for 7/16 studs (the trunions are exact diameter). However I will call Crane to discuss the rockers - thanks for the advice!

 

[djxib]

We found the problem; whoever installed guide plates did not machine the head to keep the stud bases in the correct place. Since I only need a minor bevelling to the rocker slot, I will use that technique.

Thanks all for your comments