Whats Going On With My Iron Gt-40's???

[carbed87]

ok, this is the last time i'll post this, i know you guys are probably getting pissed...

ok, around mid August i installed my cast iron gt40's, and ever since, they've been making a bunch of noise, my heads include as follows:

rebuilt around 10k ago with all new hardware
(possibly milled)
minor head work
and crane 1:6 roller rockers

here's what i've done so far:

when i first put them on, i just tourqued the roller rockers down to 14lbs. with stock legnth pushrods.

they ticked like a mofo and the car had NO power.
next, i put the stock stamped rockers on, and they quieted down some, but they still made noise and had no power
after that i decided to pull off the lower plenum and watch each lifter preload as i continuisaly (sp) rolled the motor and adjusted them.

when i did that, i had a stock legnth pushrod with a small valve lash cap on it, but i don't think the lifter preload on the valves were consistant, so when i put it back together, it still made noise, but i did have power.

and thats where im at right now, i checked each rocker arm after running it a bit, and a few of them have a bit of play back and forth.
as far as the pushrod, it CAN rotate back and forth but can't go up and down.

do you think i have too short of a pushrod?

i dont know what to do anymore, im getting pissed, they just sit there and make a bunch of noise...

sorry for the long post, but i need youre help...PLEASE! HELP ME!

 

[carbed87]

any one... please

 

[-=Red5.0GT=-]

idk if this will help but its a copy of Michael Younts install post:
Here is the proper installation procedure --

To install pedestal mount rockers:

1) For each pair (int/exh) be sure you rotate the engine so the lifters are on the base circle of the cam - this is very important. When you install the rockers, both valves must remain closed. Neither lifter can be on any part of the cam lobe - they MUST be on the base circle.
2) Install the rocker and bolt it down to zero lash. Zero lash is reached just when you eliminate the gap between the pushrod and the rocker and the valve stem and the rocker. Tighten with one hand and 'rock' the rocker with the other hand. Just when you reach the point that you can't rock the rocker anymore you're at zero lash.
3) Now - put your torque wrench on it and tighten to 18-20 ft-lbs. while counting the number of turns it takes to reach that torque. It should occur between 1/4 turns and 1 turn. If it takes more than one turn, use a shim to raise the rocker. For each .030" shim you use, you'll reduce the number of turns to torque by about 1/4. If it takes less than 1/4 turn, or you have trouble reaching zero lash even with the bolt torqued all the way to 18-20, then you need longer pushrods.
4) If all goes well on the install, crank it up. If some make noise let the car warm up completely. Then (unfortunately) go back through the install procedure with the components warm. That will usually quiet them down.

Mine has 11 with no shims at all, 4 with one .030" shim, and one with 2 .030" shims. And I had to do the final install with it hot to get them quiet. That approach has them all hitting the required torque within 1/2 to 3/4 turns.

I have a Buddy Rawls custom cam with steeper than stock ramp rates, 1.7 roller rockers (pedestal Cobra type), and stock lifters. It runs just about as quiet as it did stock.

 

[302RollinHard]

i am 100% with Red. That Yount guy knows his stuff. If you torque them down while any part of the lifter is on the cam lobes, it will add that much play when you run it. Just follow that procedure and you should be fine.

 

[carbed87]

well thats what i thought, so when i re-adjusted them i did it a diff. way, but no matter how tight the rockers are they still have a tiny bit 'o' play.

 

[carbed87]

any other ideas

 

[8950HO]

any other ideas

Hey Grease Monkey,just change the oil and everything will be OK.j/k.

Seriously though,going by what you`ve said it sounds like you just installed both sets of rockers blindly without going through the proper procedure to get the correct preload on each lifter.

You can`t just bolt them down without checking for the proper preload,especially when you`ve installed different heads or rocker arms as
production tolerances can vary in these situations.

I`ve posted in the past for a few others how to do it properly,but don`t feel like typing it out when someone here posted the Yount instructions.

But basically,make sure the valve you`re adjusting is closed,then find your zero lash point by hand,(not with the ratchet on the socket/allen bolt).

Once you get zero lash,start to tighten the rocker bolt counting the number of turns until you feel the bolt snug down to the head and stop.(this is your preload amount).This differs a little from the Yount/Crane Cam method,because once you feel the bolt snug down by hand,theres no more preload after that point,but you`re not at the final torque spec,so you`re counting of the number of turns will be a little more than it actually is if you count by using the torque wrench method.
(try it both ways and you`ll see what I mean)

Adjusting the proper preload takes a bit of skill and the right feel,but it`s not that hard once you know how to do it properly.

Don`t worry about some rockers feeling/getting loose during the procedure.That`s normal because when you`re rotating the engine over by hand other valves start opening and valve spring pressure bleeds down the lifters creating that "loose" rocker even though it has the correct preload.

I hope what I just said makes sense.

Oh,for a street engine 1/2-3/4 of a turn after zero lash is ideal.If you get a 1/4 turn or less,longer pushrods are necessary.If you you get more than 3/4 of a turn you can use shims under the rocker pedestal.

Don`t be surprised if some rockers may need a shim or two and some don`t.

Years ago I was setting the preload on a 351C-4V and some rockers needed a shim and some didn`t,but this is not uncommon at all even with a 5.0L.