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Buying used heads- what to look for?

3K views 9 replies 6 participants last post by  96slowbra 
#1 ·
#2 · (Edited)
On the simple end, you definitely at least want to know the casting number to get you started.

This will help with that part: http://www.terminator-cobra.com/castings.htm

A certain someone will probably chime in and provide everything else there is to know when looking at the good & bad in heads!
 
#3 · (Edited)
I believe the vast majority of the story is going to be on Joe's Terminator-Cobra site links that he pointed you to, Eric. Beyond the recognition process you want to check for worn valve guides and if possible try to find out how many miles are on the heads and what type of driving / use they have seen. The thing you are trying to get a sense of, is whether or not you will need to replace the OEM exhaust seats — that have a predisposition to loosen and fall out.

If you end up deciding to replace either the valve seats or the guides you ought to replace both to be safe. BTW if you are going to port the heads let the porter have them before you start to rebuild them. To get the knee in the port correct, the porting shop will prefer to work on the heads w/o the guides. If you go the porting route your porting shop will be able to properly replace the guides after the porting process. In addition he can do the seats before the bowl work so it blends properly to the new seats.

In addition you want to pressure test the heads to make sure there are no small cracks you might have missed. The pregnant question is how to do all this testing stuff remotely. If you live near you can go over to pick them up and test them. If you don't, then assume you will have to replace everything and price the heads accordingly.

Now about that guy Joe was speaking about, I've been looking for him all afternoon and I think he must have been beamed up by Klingons ... :)


Ed
 
#6 ·
A few more thoughts, Eric ...

Unless you find a set of virgin heads, just about every set you are going to find will have some level of performance usage. Even the street driven cars tended to work the heads because after all, why do people buy cars like Cobras. It is typically not for use as a Sunday go to meeting car.

That said as long as the heads are not cracked and as Tony pointed out do not have damage to the cam bores they are eminently rebuildable. One of the more tender points of the heads are the exhaust seats. They almost always loosen up. Turbo cars will see it sooner than PD blown cars but they will all do it. The good news is the exhaust seat replacement is a relatively straight forward job. Be sure to use a performance head shop to do the work. The run of the mill shop will install the new seats with the same press fit the OEM seats came with and they will loosen up just like the OEM seats will. You want a tighter than OEM press fit.

The second thing to keep near the top of mind in a repair effort is valve guides. Silicon bronze does a stunningly good job on a race only head but for street driven vehicles the porous quality of the OEM style iron guide is a blessing. The porosity allows the guide material to hold microscopic quantities of oil and aid in stem / guide lubrication that the silicon bronze will not be able to do.

Lastly the four thread heads can be as good or better than the 9 thread heads — when properly prepped. If you run into a set of nice 4 thread heads, the Lock-N-Stitch thread repair system will allow you to turn them into much superior 9 thread heads. The Lock-N-Stitch solution is as strong or stronger than the original OEM 9 thread solution. One of the specs that hints at the strength is their recommended sparkplug torque target. If I remember correctly it is 35 ft/lbs for a plug in a Lock-N-Stitch repaired plug hole! I don't recommend going that tight even with the L-N-S repair. The real message here is you give up nothing in terms of reliability with a L-N-S repaired head.

The other take away here is that everyone who has these heads knows about the 9 thread vs 4 thread issues. That means you can usually get a nice set of four thread heads less expensively than a not so nice set of 9 thread heads — something to think about.

The cam saddle issues that Tony pointed out are big time important and an oversight on my part for not mentioning. You need to pay special attention to this. Take a known good OEM cam, intake or exhaust doesn't matter for this test. You will want to take a sufficiently long straight edge and place it against the clean gasket surface of the head. Do this test parallel to the bores and also X'ed across the length of the head. Your straight edge will need to be as long or longer than the head. With the straight edge against the head you want to try to get a 0.0005" feeler gauge between the straight edge and the head. If you can not then the head is good and you can go to the next test. If you can you probably ought to avoid the heads.

The next test uses that straight OEM cam you brought along with you. Clean and oil the cam journals and also the corresponding cam saddles in the head wth a light oil like ATF. Place the cam in the cam saddles and put on the ladders tightening them down to spec. Now put the big exhaust cam gear on and try to turn the cams. After the initial stiction beaks free, the cams should turn effortlessly with the little finger of your hand. If they do not then the head should be avoided.


Ed
 
#8 ·
They are the same: Mach1, Aviator, Marauder, Terminator. Differences are between casting numbers based on the years (unless those listing them are oblivious to the model). All the info is in the link I posted.
 
#10 ·
Also worth considering is continental heads. While not identical as the later c heads, with porting they can be equal or better than untouched cobra heads. I bought the entire long block from a 2000 Lincoln continental at a local u pull it yard for $260 + tax. After selling some of the stuff of the motor and scraping all of the aluminum I netted around $50 positive on the heads. I did btr springs, fully threaded inserts, opened up and blended the bowls, new valve job, milled to cleanup and cleaned up the ports and came in well under the price of used heads before any work.
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