Resolved Fixing a GT40P Valvetrain nightmare

[foxbodyclark]

I'll try to keep this concise, let's understand that I'm not a professional engine builder, but I'm a hands-on guy with good technical skills and have researched and followed the correct procedures for this.

A few months ago I installed remanufactured GT40P heads onto my Fox and paired them with Explorer upper and lower intake plus a 70mm TB.

I used Fel-Pro Head gaskets (unknown thickness). I don't know how much metal was taken off the heads, and I know I have a cam but not sure which one; likely a B cam or something mild like that.

That being said, I put stock length pushrods in (6.248") and the car had medium-loud valvetrain noise and ran strong until you tried to do a peel out or a burnout then it would start back firing and running incredibly rough. Not Ideal.

I bought the pushrod length checking tool and decided on the popular 6.300"... Even worse. No compression because they were too long and held the intake valve open, car couldn't even run.

OK, lets try shims. Set the shims up the best I could. Car is back to square one but worse. LOUD valvetrain, horrible idle, backfires at anything more than 60% throttle and feels like its at 70% power compared to the 6.248" pushrods.

So folks, I'm stumped. I must have some unicorn combo of cam and head that is causing me trouble. People online make it sound like you can carelessly rip some heads out of the junkyard, spray it with the hose, reuse your old parts, and zip it down without even considering a torque wrench and it'll run like a dream every time, clearly not the case

Any help is greatly appreciated and I can clarify any details necessary.

Thanks!

 

[General karthief]

Did you check piston to valve clearance?

 

[limp]

Has your engine timing been set correctly when you checked your pushrod length
Adjust intake valve as exhaust valve starts to open
Adjust your exhaust valve as the intake valve starts to close... A bit slower doing it this way but you address each cylinder and its valves at a time....
I do not like the " spin the pushrod" method, I just wiggle the pushrod up and down until there is solid contact.... I might do this 4 or 5 times on each valve until I feel good about its clearance...... Then its 1/2 to 1 full turn to torque ( 23 ft lbs).....
These are the stock GT40 head fulcrum lifters????

While you have your valve cover off, check your ELECTRICAL timing and find TOP DEAD Center... TDC
When your intake valve on #1 piston ( nearest one to the radiator on the passenger side of car) goes up and down, then hand crank your timing mark to 0 or you can set at at 10 degrees advanced.. That will be TDC.. then pull the cap and see if you have #1 wire in the right spot

Then make sure your spark plug wires are correctly run to the corrrect spark plug.... You do know there is a different firing order for HO cams? Make sure you know what your cam is....
Have you run the spark plug wires in the correct order on the cap?? Counter clockwise ( I think, someone confirm this) Don't laugh, I watched a guy who could not get his 911 porsche running.. He installed his new wires in the wrong direction....

Have you looked for vacuum leaks?? Block off the main vacuum source ( intake manifold I believe) and see what happens....You can search for the vacuum leak later....
Attached a pic of my gt 40 P heads..... Roller tip rockers are not stock

Basics here and ONLY time is involved no money...

 

[pindude80]

I put an Explorer longblock with GT40P heads in one of my cars about a year ago. I saw you mentioned your heads were remanufactured. Do you know if they upgraded the valve springs when they "remanufactured" the heads? The factory GT40P springs are pretty weak from what I read. My neighbor, who is a lifelong mechanic, setup my heads. He took his time, did them right and my car runs pretty dang good with the GT40P heads and a F cam.

 

[pindude80]

With the F cam we used Trick Flow Valve Spring Kit # TFS-2500100 and Comp Cams 6.350" pushrod length, part # 7753-16

Good luck and I hope you are to get it figured out. Let us know what you come up with.

 

[foxbodyclark]

Update:

Finally got the car running good

The answer was TFS 6.300" pushrods with 2 shims under every rocker which raises it by 0.090 total. This made every one click at 20ft/lbs with 1/2 to 3/8 turns past zero lash. Effective length of the pushrod would be 6.21 (6.30 - 0.09 shims).

Pushrods part # TFS-21406300
Shims part # Ford Racing M6529A302

I'm assuming the car wants shorter than stock pushrods because of the machine work done on the heads.

Here's the method I followed in case it can help anyone in the future

(you can go to TDC and do 1/4 turns on the crank bolt as you go to each cylinder in the firing order instead of watching the pushrods level out)

This video explains it well too

Here's the trick that finally got the car right:

"With a proper length pushrod, the rocker will have side to side play but should have none up and down" (on the top of the pushrod)

I had many rockers that felt wildly loose side to side but had literally nothing on the tip where it met the pushrod. It sure felt like it would cause a rattle but I trusted the science and once the car started it ran smooth and quiet.

Happy to have it running again for the summer

Take care, thanks for the help!

Clark

 

[nicholase]

Congrats!


That's pretty much how I find the base circle of the cam. As that states, watch the exhaust open and close, then watch the intake open and close. When the intake valve stops moving (closed) you are entering the compression stroke. When the intake valve stops moving I turn the crank additional 1/4 turn. This will be TDC on the compression stroke and right when the explosion happens. Set preload on both intake and exhaust for that cylinder. Repeat 7 more times.

You can practice on cyl#1 if you have the timing cover off. Watch the valves as mentioned. Give the crank a 1/4 turn after the intake valve stops moving and you'll see the timing marks on the cam and crank sprockets are perfectly lined up. It's an easy way to find the TDC of any cylinder. Well within a few degrees anyway which is plenty for rocker adjustment.

 

[limp]

With the F cam we used Trick Flow Valve Spring Kit # TFS-2500100 and Comp Cams 6.350" pushrod length, part # 7753-16

Good luck and I hope you are to get it figured out. Let us know what you come up with.

The heads in my above picture have Beehive springs from Alex's parts..... Alex's wanted to know what cam I had and recommended this set of beehives..