engine guru's; installing gt40 heads on 351w, ?'s

[SDlivin]

Okay,

Got the gt40 heads to install, have a few questions on the install;

-What spark plugs to use (the previous 351w heads used a larger dia spark plug)?
-Re-use existing mounting bolts? I read to use a dab of oil, but no threadlocker?
-Fulcrum style rockers with U channel, do I just hit TDC on each cylinder then torque the rocker bolts down to spec?

That's all I can think of for now, but I am sure once I get into it, more ?'s will follow.
As always, thanks for the advice!

 

[broncnaz]

Id get plugs for the year of heads you have so if they are 1996 heads ask for plugs for a 1996 5.8 f250 you should be fine although I really wouldnt bother using platiunum plugs for a carbed engine.
You can reuse the exisiting bolts would be better to use new ones but I've reused bolts a lot with no issues yet.
Thats probably the best way to torque down the rockers. although some repair manuals(chiltons) show that you can use TDC and make 2 other marks on the balancer and torque down all the valves with just 3 positions.

 

[SDlivin]

Okay thanks.

So in checking for pushrod length with hydraulic lifters.
How much preload should be on the lifters?
Using an adjustable pushrod and when I get the rocker snug, can still spin pushrod with fingers, rocker still moves a little bit, but is solid. At this position the hydraulic lifter is about 1/16th loaded.

Does this sound about right?

 

[DirtDonk]

By that you mean it's pushed in about 1/16 of it's full piston travel? A 16th of a turn on the nut?
Seems to me it should be approximately half it's travel, or for an adjustable setup, 1 full turn of the nut. But I'm sure not sure about that, so maybe broncnaz will clear that up.

Paul

 

[KyleQ]

I did this on my build - 96' 351W with 96' GT40 heads. I used 96 F250 pushrods and the correct 96 Explorer spark plug (they want the expensive ones)

IIRC the rocker arm torque was in ft.lbs. - so start with that.

 

[SDlivin]

So these are the NON-adjustable rocker arms, fulcrum style that use a bolt that you just torque to spec, not a nut.
My understanding is the ONLY way to adjust these are with the correct length push rods.
In using the adjustable pushrods the check for pushrod length. To get the valve train taught enough so the rockers don't have a lot of movement (still have a little) and can still spin the pushrods by finger. I end up collapsing or loading the hydraulic lifter center (piston?) by about 1/16th - 1/8th.

If I should be in the halfway range of the hydraulic lifter piston travel, how far down would that be? Or am I good where it is at?

 

[Viperwolf1]

No real adjustment, pushrod length is critical to setup. Crane also sells shims that can be used under the pedestal for fine tuning.

Pushrods will probably still spin even after the lifter is collapsed some. Total lifter inner travel is just a little over 1/8" so 1/16" is pretty good estimate for center.

Are you checking valve stem tip contact?

 

[SDlivin]

Okay, that matches what I just found on crane cams website, below.

http://www.cranecams.com/uploads/instructions/151g_.pdf

If your engine has non-adjustable rocker arms, a lifter preload
of .020 to .060 must be maintained. To check preload on engines with non-adjustable rocker arms that have bolts or
bottleneck studs, i.e. some Ford, Oldsmobile, Pontiac, and AMC. Turn the engine until the engine is at top dead center firing on the cylinder you are adjusting. At this time, both lifters will be on the base circle of the cam lobe and both valves will be closed. Install the rocker arms, or loosen the rocker arms if that is the case. Turn down the bolt or nut until it makes contact with the fulcrum of the rocker arm with no airspace between the rocker arm and the pushrod or valve and no preload in the lifter.
Using a torque wrench on the bolt or nut, torque the bolt or nut to factory specifications, counting the torque wrench movement after zero lash. For the correct preload, the torque wrench movement must be between 1/2 and 1 turn. If you have less than 1/2 turn, you will need to purchase longer pushrods. If the torque wrench movement was more than one turn, you will be able to use shims as shown in Figure 1 or 2.
If the adjustment procedures are followed correctly for hydraulic lifter cams, no further adjustment is necessary for the life of the cam.
Maintain a recommended lifter preload of between .020”minimum and .060”maximum for proper lifter operation.