GT40 Heads Issues

PonyGTrider

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Feb 27, 2019
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Hi all,
I’m helping a friend of mine with his 94 GT. Long story short, his 5.0 was spitting oil out of both exhaust pipes so he decided to do a rebuild using a set of GT40 heads, GT40 intakes, E303 cam, and 1.7 rockers. I have the short block assembled at the machine shop with with new rings bearings and stock like pistons 0.030” over. The heads were refurbished with a new set of trick flow springs and valve seats and valves were machined to match their seats. They were also resurfaced very lightly.

The height of the heads is unknown and I’m having PV clearance issues being ~ 0.025” with a 0.047” compressed HG n the intake valve. With a 0.068” gasket it bumps the clearance to ~ 0.093” My stock pushrods are about 0.015” shorter.

I’ve red many instances where some people claim they did the same upgrades using the same pushrods and no PV issues. So what gaskets height are you using? Obviously every engine is different and the heads height completely changes the dimensions. Just need a little help with these issues.

Have to mention that I’ve done all my measurements were done torquing a head straight to the block without a head gasket and then adding the gasket thickness to all the related measurements like PV height (using clay) and pushrod length. It is funny that with the head torqued straight to the deck without a gasket the stock pushrods length gave the exact lifter preload of 1/4 to 3/4 of a turn @25 ft/pound. Once I get the pushrod length checker will verify all of those results.

Thank you all for any help given to me
 
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AeroCoupe

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An E cam with 1.7 rockers has about 0.530" lift. I know its tight on most stock 5.0 motors but most have success with running them. Assuming the pistons are fly cut for the valves? Really you are not concerned with max lift as that only happens when the piston is on the down stroke pulling air into the cylinder. What you are concerned with is when the intake valve is just opening and the piston is passing through TDC on the intake stroke and when the exhaust valve is just closing and the piston is approaching TDC on the exhaust stroke. The higher ratio rockers change the lift only by about .004" at the small valve openings when the pistons and valves are close.

Are you sure you have the valve geometry correct on the top of the head? This has to do with push rod length more than anything.

I will be the first to admit I know just enough about this to get myself into trouble so I rely on a guy that makes his living working on cylinder heads and building motors.
 
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Mustang5L5

Put lubricant all over the balls
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Cam duration and lobe centerlines is usually what comes into play with regards to PTV.

Did you degree the camshaft when installing to make sure the timing events are correct?
 
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PonyGTrider

Active Member
Feb 27, 2019
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An E cam with 1.7 rockers has about 0.530" lift. I know its tight on most stock 5.0 motors but most have success with running them. Assuming the pistons are fly cut for the valves? Really you are not concerned with max lift as that only happens when the piston is on the down stroke pulling air into the cylinder. What you are concerned with is when the intake valve is just opening and the piston is passing through TDC on the intake stroke and when the exhaust valve is just closing and the piston is approaching TDC on the exhaust stroke. The higher ratio rockers change the lift only by about .004" at the small valve openings when the pistons and valves are close.

Are you sure you have the valve geometry correct on the top of the head? This has to do with push rod length more than anything.

I will be the first to admit I know just enough about this to get myself into trouble so I rely on a guy that makes his living working on cylinder heads and building motors.
Thank you for your help here.
To start the pistons were not fly cut. The stock like pistons have four eyebrows valve reliefs but they seem too small for the GT40 head valves. DO I HAVE TO TAKE THEM OVER TO BE FLY-CUT?

On the valvetrain geometry like I said that I made all the mock up and measurements were not made with the required precision because I don't have yet the pushrod length checker. So once it is here I will do the correct measurements. The measurements I made were done torquing the head without the gasket and using the stock pushrods which gave me the correct preload on the lifters and the rockers left a centered contact mark on the valve tip. to those measurements I added the gasket thickness for a theoretical values.

Thank you
 

Mustang5L5

Put lubricant all over the balls
Mod Dude
Feb 18, 2001
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Thank you for your help here
Unfortunately I don't have a degreeing wheel... :(


You can print them out.



You should degree it to verify your cam is not advanced or retarded, which would have an effect on PTV. In some brief searching, I have found a lot of folks running an E303 with 1.7's and claiming it works fine.

I don't necessarily think you need 1.7 RR's on a GT40 head however. It's .498" with the 1.6 vs .528" with 1.7. This video shows a ported GT40 head and beyond 0.400" of lift, there's not a whole lot of improvement. Really, if this seems questionable i wouldn't even bother with the 1.7's.


View: https://youtu.be/cAWn_S2y_rU
 
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AeroCoupe

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Degree the cam first...cannot stress this enough. Advancing the cam from its as-ground position decreases intake valveto piston clearance and increases exhaust valve to piston clearance; retarding the cam increases intake valve clearance and decreases exhaust valve clearance.

I have seen the pistons fly cut in the motor with an old head and old valves like in this video:


View: https://www.youtube.com/watch?v=XV5IKmxpQLE


There are a lot of things that can go wrong doing it this way so not something I would recommend. Biggest thing I saw that this guy should have used was a positive stop device on the valve stem. Bring the piston up to TDC, drop the valve down so the cutters or sand paper touch the existing relief, use a set of calipers to set the positive stop devices on the valve to the desired depth to cut to and then proceed to cut the relief.

I will caution anyone doing this themselves to understand a few things:

1) This will affect that balance of the motor. You be the judge of how much you are willing to risk whether it be a stock short block or a build Dart block motor.
2) Cannot stress this enough but you have to get all the shavings cleaned out.
3) You should not use the head(s) that will be used on the motor.
4) You should also check your radial clearance as mentioned in the video which may necessitate the use of a larger diameter valve to gain the clearance needed. Remember the cutter "valve" does not need to seat in the head it just needs to fit the valve guide.

Anyhow, my recommendation is pull the slugs and take them to a quality machine/engine shop and get the reliefs cut professionally.
 
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PonyGTrider

Active Member
Feb 27, 2019
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You can print them out.



You should degree it to verify your cam is not advanced or retarded, which would have an effect on PTV. In some brief searching, I have found a lot of folks running an E303 with 1.7's and claiming it works fine.

I don't necessarily think you need 1.7 RR's on a GT40 head however. It's .498" with the 1.6 vs .528" with 1.7. This video shows a ported GT40 head and beyond 0.400" of lift, there's not a whole lot of improvement. Really, if this seems questionable i wouldn't even bother with the 1.7's.


View: https://youtu.be/cAWn_S2y_rU

Thank you for sharing, That's an interesting video. Well I will try to get a hold of a degreeing wheel if possible.
Thank you
 

PonyGTrider

Active Member
Feb 27, 2019
173
32
38
Mexico
Degree the cam first...cannot stress this enough. Advancing the cam from its as-ground position decreases intake valveto piston clearance and increases exhaust valve to piston clearance; retarding the cam increases intake valve clearance and decreases exhaust valve clearance.

I have seen the pistons fly cut in the motor with an old head and old valves like in this video:


View: https://www.youtube.com/watch?v=XV5IKmxpQLE


There are a lot of things that can go wrong doing it this way so not something I would recommend. Biggest thing I saw that this guy should have used was a positive stop device on the valve stem. Bring the piston up to TDC, drop the valve down so the cutters or sand paper touch the existing relief, use a set of calipers to set the positive stop devices on the valve to the desired depth to cut to and then proceed to cut the relief.

I will caution anyone doing this themselves to understand a few things:

1) This will affect that balance of the motor. You be the judge of how much you are willing to risk whether it be a stock short block or a build Dart block motor.
2) Cannot stress this enough but you have to get all the shavings cleaned out.
3) You should not use the head(s) that will be used on the motor.
4) You should also check your radial clearance as mentioned in the video which may necessitate the use of a larger diameter valve to gain the clearance needed. Remember the cutter "valve" does not need to seat in the head it just needs to fit the valve guide.

Anyhow, my recommendation is pull the slugs and take them to a quality machine/engine shop and get the reliefs cut professionally.

Thank you for sharing.
I will seriously look into degreeing that cam
I think I will take the short block to the machine shop to have them fly cut the valves reliefs.
That's a great video. I might make a jig to myself to do that cutting in the future.
Thank you
 

Rcdgl

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Feb 19, 2018
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Ran Iron GT40 heads, the original ones, on two 302s. Both had TRW L2482 forged replacement pistons and I had adequate vavle clearance with my cams. With the stock GT40 valve sizes. Stock bolt down rockers one one engine and Comp adjustable on the the other engine. Went to some AFR185s, did the clay check on the valves and had interference. Did the cutting with a Dremel on all 8 pistons. Works. Not recommended.
 
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manicmechanic007

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You need at least .090 clearance
I am with 5L5 on this one and would just run the stock rocker ratio
To fly cut the pistons, the machine shop needs them out of the block and off the rods most likely
And they are liable to say that the pistons are too thin or otherwise they don't want to do it
So, that combined with the balance issue, means to me it's better to go with 1.6 rockers and solve both issues
 
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PonyGTrider

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Feb 27, 2019
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You need at least .090 clearance
I am with 5L5 on this one and would just run the stock rocker ratio
To fly cut the pistons, the machine shop needs them out of the block and off the rods most likely
And they are liable to say that the pistons are too thin or otherwise they don't want to do it
So, that combined with the balance issue, means to me it's better to go with 1.6 rockers and solve both issues
Thank you for sharing this information.
The guy is on a budget and more likely will have to use the rockers he already has. To do that I will take measurements and use head gaskets accordingly with the P2V clearance. When I disassembled the engine it had really thick head gaskets 0.068” compressed I have no idea why they used those gaskets on a stock cam, heads, and pistons.
Since those old gaskets are in really good shape I will use them to find the correct P2V clearance and pushrod length.
I will use the clay method because I want to make sure my radial clearance is safe too.
The pistons will not be touch at least for now unless my static CR is too low, then will have to use thinner head gaskets.

Thank you
 

manicmechanic007

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I was wondering myself where you found a .068 gasket
Most compress to .030 or .040
A fan of steel shim myself at around .010 and copper coat
That's my 302 chev, talking. I'm not sure you can get a steel gasket for a sbf
 
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PonyGTrider

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Thank you for your comments,
TF Victor is the brand of those head gaskets, below are some pics.
I’m using felpro 0.039” compressed on my 306. Never used steel or copper gaskets but there are a whole bunch of gaskets out there from 0.030” to up to 0.090” thick for the 302-352 Fords.
 

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manicmechanic007

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Steel is where you go right before o-rings for high compression
The steel is coated but you recoat them with copper coat is what I mean (spray can of sticky copper stuff)
I sucked a valve on my 302 chev after putting 205 angle plug fuelies on it. No fun!
306 how?
352 takes the same head gasket? as 302
Good on you for using clay. That's the best method IMO
 
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PonyGTrider

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Thanks for sharing,
I’ve never used a steel/copper head gaskets on my Stang. I used and even reused old gaskets on Tacomas rebuilds with proper cleaning and permatex copper spray and never had any issues.
Reinventing valve angles doesn’t worth the subsequent troubles.

A 302 ci engine overbored 0.030” makes it a 306 ci.

Sorry that was a typo, I meant to say 351.

It would be nice to verify the cam events by degreeing it but since I don’t have a degree wheel I will just verify my true TDC, use clay to get P2V and radial clearances, and determinate pushrod length with an adjustable one.

Thank you
 

PonyGTrider

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I was just playing on finding TDC using the piston stop method and found a couple interesting things.
I installed a piston stop and turn the crank CW until the piston hit the stop, I then made a mark where a wire pointer pointed on the damper. I then rotated the crank CCW until the piston hit the stop and made a mark on the balancer. I measured from this mark to the previous one, divided by two and set that as my TDC or zero. Found out that this TDC mark is off from the zero mark on the damper by 12 degrees and the marks on the sprockets are dot to dot perfectly aligned, but if I install the stamped timing pointer my TDC mark on the damper is off by 6 degrees. Could this means that the damper outer ring has spanned six degrees?
I used this same method on my 306 and after using the piston stop CW and then CCW and divided that difference my piston 1 TDC position matched right on the damper TDC mark.

By the way I made myself a nice pistón stop for different sizes of spark plugs, different engines 809AA38A-6A60-4EB9-A9F0-A121D2394B43.jpeg
 
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AeroCoupe

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That is a tried and true method of finding TDC. The cam timing has nothing to do with it cam timing but I’m guessing the cam timing comment was just you verifying they were lined up with motor at true TDC.

What brand of damper is it?
 
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PonyGTrider

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That is a tried and true method of finding TDC. The cam timing has nothing to do with it cam timing but I’m guessing the cam timing comment was just you verifying they were lined up with motor at true TDC.

What brand of damper is it?
Thank you for interacting,
That’s correct the timing sprockets dots mentioned was just to make sure things lined up properly. I don’t even have the pushrods installed yet.

That damper is a stock one and will ask my friend to buy a new one for himself to prevent future problems.

Thank you
 
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