View Full Version : Refacing a head

05-29-2010, 11:40 PM
Anyone here refaced an automotive cylinder head?

I have this 1978 Datsun 280Z. It's in great shape as far as sheet metal and frame goes. That's the original paint!
When I got it (380 miles ago), it ran poorly at startup which I thought was caused by a faulty injector. No, it was burning coolant. This has gotten significantly worse, now it seems as if the car thinks it's steam powered :D.

I hoped for a simple blown head gasket. I tore it apart and replaced the head gasket, it only took 8 hours :), but no dice. I checked the head and it was on the edge of acceptabe warpage, which is spec'd at 0.002" for a new head and 0.004 for a used head. Mine was 0.0035. The head appears to have been off recently (unless Datsun used Fel-Pro head gaskets as OEM), and it appears to have been rather poorly fly cut "flat" leaving a terrible surface finish, probably 64 RMS or worse (80 grit sandpaper). It looks as if it were done on a knee mill out of tram, as the center of the head is low everywhere.

I'm trying to get another head as a backup. I'm planning to machine this one. Help me select my weapon of choice.

The head's contact surface is about 5" wide and about 27" long. That's what happens with a ~4" bore six-in-line. I can use (a) my Bridgeport, which has 2HP and 33" X travel; or (b) my horizontal mill, which has 3HP and around 30" X travel; or my VMC which has 10 HP and 22" X travel so it would need 2 setups - I want to avoid this, perhaps I could set it up diagonally.
I would prefer to get the whole 5" width in one pass. I have a huge, 6" diameter, SECO face mill that I plan to use. I could also get/make a fly cutter. I might have a 5" wide slab cutter, but I think my biggest is only 4" wide.

What I'm thinking of doing is using the face mill in the horizontal mill. If the table droops a little it won't matter, as the cut is perpendicular to the ground. I can mount the head using the manifold flanges against the table, or I have some 12"x12" angle plates that could go against the cam cover mounting surface. Regardless, I'd indicate and shim until it's in the correct plane relative to the cutter.

The factory says the limit for machining is 0.008". As I said I think it's already been skimmed, and there's no real way to tell how much. The good news is that some people on ZCar.com have milled 0.080 off to raise compression with no real trouble, so there's no coolant or oil passages close to the surface to break into.

Any thoughts? Suggestions?

Optics Curmudgeon
05-29-2010, 11:49 PM
I would get it checked for cracks first.


05-30-2010, 12:13 AM
The L6 engine tends to break off the exhaust manifold studs on cylinders 1 and 6. So you need to carefully inspect the exhaust valve seats for those cylinders.

Personally, I consider the machine work on the cam side of those heads to be works of art. When mine drives its last mile, that head is going up over the mantle-piece in the living room.

05-30-2010, 12:23 AM
I worked as an auto mechanic and sometime auto machinist long ago (almost in a previous incarnation). My advise is to take to an automotive machine shop. They will have the specialized equipment to both test it for cracks and to machine it flat with the proper finish for good sealing. I also recommend that you have the valves ground and the guides checked. Believe me, you will be glad you did. The cost will likely be less than yet another set of head gaskets and the 8 hours of time you have already invested. As you have already discovered, there is more to surfacing a head than just facing it on a mill.

I know you are a good machinist and can do it properly but it will take time and attention to detail. Time which you could use for something else and you will likely also find that proper finish and flatness will require the purchase of some additional tooling.

You should be aware that many (most/all?) of these cars are subject to severe internal rusting of the fuel tank.

05-30-2010, 01:25 AM
I forgot to mention a few things.
This isn't my first 280Z. It's a replacement for my 1977 ("Early 77") 280Z which has terrible rust issues. I bought the 1977 Z in 1985 and drove it 135,000 miles over 10 years, then stored it at my dad's house for the last 15 years. He gave the '77 away 3 weeks ago :(. I did take the 5-speed and put it in the '78 car :). The '77 had the rear stud on the #6 cyl broken off when I got it. The heads are subtly different anyway, as I recall the '77 has an externally oiled cam while the '78 is internally oiled (it' s been 20+ years since I was inside the '77 engine).
The '78 had all the mainfold studs intact. I did check the head for cracks with dye penetrant. There was no sign of large quantities of coolant being burned - which I'd expect with a crack, all the pistons had an even layer of carbon on them.
The head was resurfaced at a "professional" auto machine shop before I got the car. Evidently 0.0035" out of flat and a surface finish like a phonograph record are a professional job. I may have a shop resurface this one, I don't know, there aren't any trustworthy shops around here unless you've got a Honda with a loud muffler. Around here people think you're nuts if your car is 4 years old.
I'm hoping to get another head. These L47 heads are not sought after by the power crazed crowd. They want L42 or S90 or something better.

Bob, I agree about the workmanship. I thought all heads were made with the same attention to detail. Certainly the VW VR6 head is. I also thought all rear wheel drive cars had independent rear suspension (all of mine have been so equipped). Perhaps I've been spoiled?

05-30-2010, 01:45 AM
When I was going to school I worked as a machinist in a car parts store. In addition to selling parts like everyone one else we had a machine shop including a large horizontal grinder for grinding heads and manifolds. Actually, anything that could be fitted to the cradle could be ground.

We always used our magnaflux tool to check for cracks. Most heads we examined were cracked. On 4-cyl heads (v-8 and inline 4) where exhaust valves were next to each other on 2 and 3 there was usually a crack in the webbing between cylinders. Exhaust ports would crack between ports frequently. Mercedez heads seemed to like to crack at the injectors.

I don't think I ever saw a 6-cyl head that wasn't cracked.

If your oil is not absolutely black then you have water in the pan. If that's the case I'd scrap the engine and drop a small block v-8 in there.

05-30-2010, 08:18 AM
I've successfully decked an inline six block on my 8x36 green milling machine.

292 Chevy with a window in one bore. Bought an old Kwikway bar to bore and sleeve it. Then set up on the mill with a fly cutter. Swung the turret one way, cut 1/2,then swung the turret around and cut the other 1/2. I had the mill under my chain fall and trolley with some tension to take most of the weight off the table. Dressed the transition between cuts a bit with some abrasive cloth and a flat block.

When I did this I still had the original milling head without a back gear. I took off the motor fan and installed a sheave in it's place. Mounted another motor next to it to give a double reduction to get the flycutter slow enough. I've since installed a vintage BP step pulley head on my mill so next time I should be good to go with the spindle speed.

Do I recommend this method? No. As others have said, an automotive machine shop has the right equipment for this. But what fun is that?

05-30-2010, 08:36 AM
As mentioned above, have head pressure checked and a valve job done while it's off. Find a shop the local racers use, hopefully one that is familiar with the z cars. While you're there, consider paying the $40 or so they'll charge to surface the head. Different types of gaskets require a different level of finish on the head. As for gasket choice, I prefer the oem nissan gasket, it's worked well for me. If you start to play with the power like I have on my turbo car that multilayer steel gasket from HKS is great( but over kill for a stock car). I'd ask the shop that would be surfacing the head what RA they're going to use. If they know what your talking about, the shop might be worth while. On a side note, be careful how much you shave off the head as it does affect cam timing. As you know, the guys that shave the head .080 are shimming the cam towers to bring everything back to proper height. Oh, and don't forget to check the block...it will warp too!

05-30-2010, 09:42 AM
The problem with warpage on the Z head is the cam piggybacked on the head. I don"t remember the numbers, but your .008 sounds good. The head would stand considerable more warpage being taken off of it, but the cam would break from the warpage. Check the back side of the head if it has been surfaced and see if the cam is being bent. There is a method of heating and drawing the head back into tollerance so it can be resurfaced. They also made cam tower shims to fix someone surfacing an overly warped head and just shimming the cam back to straight (this was not the best fix).

05-30-2010, 09:47 AM
Also the RA that the gasket manufacturers have wanted over the past 30 years has changed. For a while the manufacturers wanted a rough finish on aluminum heads. they now are back to wanting a smooth surface finish.

05-30-2010, 11:35 AM
well fasto you have hit the reasion i mill my own heads and bronze wall the guides. also grind my seats and valves. the pro shops around here and i had a different opinion of what was a good job. you want it done right do it your self or check it when you get it back.

05-30-2010, 12:52 PM
You have to be wary resurfacing ANY overhead cam engine cylinder head.

When the head warps, so do the camshaft bores. If memory serves, most OHC heads will only tolerate .007" warpage. Of course, resurfacing the gasket surface will make it seal better, but you're bending the camshaft,

I had a customer bring in an Isuzu four cylinder head, once. I checked it and found the head was curled up on the ends, and I told him to go find a better head, because this one was going to take a .0625" cut just to true it, and the camshaft bores would cause all manner of trouble. Well, he knew better than I did (apparently), and told he knew what he was doing...reface the gasket surface. Uh....Isuzu says never cut a head more than .007".

I did what he asked, and he installed it. The thing went like a rocket, until he was cruising on the Hollywood Freeway at 85mph, and the camshaft siezed in it's bores. Turned the little engine into swarf instantly. Nothing left but doorstop material. He came back and accused me of doing the job wrong, But, his case wasn't a strong one...especially when I found out his timing chain was too long, and he had to take a link out of it (Isuzus don't have master links, so I don't know how he managed that) to get the tensioners to work.

05-31-2010, 02:14 AM
I have done a few mini heads. I use a fly cutter . .003 doc and a real slow feed. Looks good imo


05-31-2010, 09:49 AM
When my uncle had a speed shop he had a stamp with a disclaimer when it was for street racing, track racing or a job he didn't think would work but the customer did. He would stamp the back of the invoice and require the customer and his witness and him and his top mechanic to all sign the invoice and he would notarize it. He would explain in detail the possible failures and causes and that there was no warranty on the back of the invoice where the signing took place.

If the speed work was for a teenager he would have the father there when all this happened.

He never lost a case.

The Fixer
05-31-2010, 10:23 AM
Most quality shops will straighten the head (with heat and a jig) to keep the cam bores in line. .004 on an inline 6 is nothing to worry about, esp if it's aluminum! You should verify where the coolant is getting in to the cyl as it could be MANY other things. Cracked cylinder, cracked head, valve guide pressed in thru a coolant passage. To home check for cracks just clean the head with hot soapy water and dry with comp air, flip it over and fill coolant passage with kerosene (block off thermostat housing etc.) the kerosene will find its way thru the most minute cracks and the stain will be quite visible. Done this lots and it works VERY well.

05-31-2010, 10:38 AM
Also the RA that the gasket manufacturers have wanted over the past 30 years has changed. For a while the manufacturers wanted a rough finish on aluminum heads. they now are back to wanting a smooth surface finish.

Very true. And the smooth surfaces are to be used with one of the newer gaskets that have a graphite or teflon surface. This is only true where the head and block are dissimilar metals, usually iron block, aluminum head. You want the surfaces to slide over the gasket as they expand and contract at different rates. The older rough finish and traditional gasket surface would cause microscopic tearing.

+1 on heating/bending. SOP for a long time now on aluminum heads, at least since the old 2600 Mitsubishis. A good machine shop will know where and how much to shim the head to preload it before heating. It comes out of the oven within a few thousandths. Then a light skim cut on the gasket surface as required, and the cam towers are within spec.

05-31-2010, 02:14 PM
Guys, thanks for all the info.
1) I found a replacement head, I think. Remains to be seen if it's any good.
2) These heads have removable cam towers. You can shim & realign the cam bores with ease. Most OHC heads aren't made like this.
3) Noted on the change in valve timing with head shaving. These engines are *very* sensitive to valve timing!

Facing OHC heads is prohibited in some cases. In particular VW L4 heads use the cam running in the aluminum cam tower - these can't be faced, they have to be heated and bent straight. The Datsun L28 engine uses bronze bearings in the cam towers so it is not as sensitive.

It's kinda tough to find a local expert on these engines around here. Remember they went out of production in 1983. Since it's New England, where road salt usage is measured in tons per lane-mile, most of the cars with these engines are long gone. I haven't seen a first generation Z-car other than mine in over 10 years. I did see a 280ZX around 4-5 years ago. I have to laugh at some of the posting on other forums where people say "just head to your nearest pick-a-part and get a few heads", not happening around here!

When I get the engine apart again I'll take some pics of the "professional" refacing job.

05-31-2010, 05:58 PM
I must have been lucky. Around my "neck-of-the-woods" the machine shop I used to use all of the time heat straightened ALL aluminum cylinder heads.
They only machined aluminum heads when the customer requested it. (local Junior Racing Experts) (Yeah, who else would want .125" shaved off of a Honda cylinder head, and then hang a turbocharger on it?) "It went like hell...for that long.."

Iron heads require care too. Especially on "Net build" engines where there is no provision for valve adjustment. Resurfacing has to be adjusted for by grinding the valve stems, or shimming the rocker arm stands. (BTW, I still have my valve stem height measuring tool, with it's dial indicator.)

Many times I've seen guys have their heads done, put 'em on, and wrestle with random misfires, from valves being too tight.

Way too many people don't pay any attention to stem height, valvetrain geometry, or correct clearances any more....Hence, not many good running engines are being built.

Gasket surfaces are of the utmost importance. When I worked fleet, we were always taking Crown Victorias to the dealer for warranty head gaskets. If the surface finish of the block on the engine in question wasn't finished to a certain value, they would junk the block. I still don't know how they judged which one was good and which one was bad.....but they put a lot of engines in those cruisers.

05-31-2010, 07:22 PM
If the head is bowed on the compression side it will be bowed on the cam side so the mounts for the cam towers will not be parallel, they will be on an arc and will have to be machined parallel to the comp chamber side. Then there is setting the cam towers to the right height and alignment.

06-01-2010, 12:42 AM
Most late model OHC engines have the bearing journals for the camshaft machined directly into the aluminum. A few Japanese engines have alloy babbit/bronze inserts pressed into the head. With very few exceptions, shimming or line boring the cam bearings of an OHC engine would be difficult, to say the least. The only thing I can see as feasible would be to line bore all of the cam bearing bores oversized, and either get or make oversized bearing inserts. A lot of work. This would be something to consider if the cylinder head was extremely rare (or expensive). BTW, 4.6L Ford OHC cylinder heads usually go for $1500 apiece, remanufactured. (I shudder to think what Ford would want for new ones)

There's a lot to be said for those old "pushrod" overhead valve engines...

06-01-2010, 11:38 AM
There's a lot to be said for those old "pushrod" overhead valve engines...

Unfortunately, due to the "Global Warming" Fairytale we are no longer allowed to have nice stuff....

06-01-2010, 12:24 PM
A real quick Google shows that Ford's 4.6 L new, not re-manufactured, performance heads going for less than $400.