Informazione Technici

Cylinder Head Installation Tips
by Terry N. Terezakis
August 2001

In my last article we looked at general practices to help make sure that your head gets a good rebuild. Now we'll look at making sure that head gets installed properly the first time. If you are installing a used head that is not rebuilt, you should review a copy of the last article on rebuild tips to help check over your used head.

There are several things that need to be checked out here before you place that head on the block. By this time you should have already inspected all of the threaded locations in the cylinder head, so now its time to clean up the threaded holes in the block. Here again, a thread forming tap is best to use if you have one.

Each hole should be tapped out. Putting a small amount of grease in the flutes of the tap will help to collect the shavings and keep them from falling into the water jacket. These particles could chew up your water pump and pump seals over time. You'll want to clean off the tap after each hole and reapply more grease. If you don't use the grease be sure to get a few drops of oil into the female threads before chasing them with the tap.

You should also check the tops of the threads to make sure that they have not pulled up from prior over-tightening. These areas can keep the gasket from seating properly, so you should re-establish a chamfer with a countersink if needed. You might as well double check the holes on the intake/exhaust gasket surfaces for this problem as well.

The next step should be to inspect the condition of the two dowels at diagonal ends of the block surface. Make sure they are round and in good condition. If you've lost them, get replacements since they locate the head in the proper location on the block.

Use one loose dowel and make sure it will easily insert into the two dowel holes in the head. This is especially important if the head has been cut, because you'll have lost some of the chamfer around the hole. The location may need to be cleaned up with a countersink.

While you have the dowels out its a good time to inspect the deck, or top surface of the block for damage. You can use a medium grit sharpening stone, app. 2" x 6" in size, to look for any high spots. First rotate the engine until all the pistons are about half way down in the bores, and then place rags in each cylinder bore to catch any debris. Cover the surface of the stone with WD-40, and gently run over the deck surface in a circular motion. Any high spots will show up as shiny, so just take them down carefully.

If you have heavy carbon deposits on the piston crowns this would be the time for a little cleanup. Carefully remove the rags from the bores being careful to catch any debris, and vacuum out the top of the piston bores. Rotate the engine until a pair of pistons are at the top of the block. In order to keep deposits from getting into the top ring land, use your finger to smear a little grease between the bore and the top of the piston. Then, place rags in the other two bores.

There may be solvent-based cleaners to loosen up the carbon but I stay away from them because I don't want the deposits to make their way into the piston rings, which is why I prefer mechanical cleaning.

You can get cleaning discs from MSC Industrial, Goodway, or K-Line. These use replaceable Scotch-Brite pads and are turned by a power drill. They really make cleaning up the top of the pistons a snap. But don't use a wire wheel, as it can damage the top of the piston.

Once the first pair is cleaned up, rotate the engine 180 degrees so that the next pair reaches the top. You'll now be able to clean up any grease/carbon residue from the top of the bores you just worked on. Be sure to clean up the tops of the second pair of bores when you're done with them as well.

Now we should take a look at the head bolts. The difference in the thermal expansion rates between the cast iron block and the aluminum head increased the frequency of head gasket leaks, so Fiat and other manufacturers started to use "Yield-type" head bolts around 1983.

You'll be able to tell if they are Yield-type head bolts because the shank of the bolt (unthreaded portion) will be reduced to a diameter smaller than the thread root (minimum) diameter.

Yield-type bolts should be thrown out when removed, and replaced with new counterparts. Here's why. Standard bolts stretch a little bit when tightened properly, but return to their original length when the load is removed from them. That little stretch is called "elastic deformation" and as long as standard bolts are properly tightened, they will always return to their original length.

Yield-type bolts are specifically designed to yield, that is, stretch in length beyond the elastic limit by a small amount during tightening. The shank lengthens a little and reduces in diameter at the same time by a smaller amount (research Poisson's Ratio for more information on this relationship). Therefore, since the diameter has been reduced, the bolt will never again achieve the design-clamping load, and you'll be inviting a head gasket leak.

The older conventional style head bolts are fine to reuse multiple times, but only after passing an inspection. Since the root-diameter of the threads is the smallest diameter, this is where any material yielding will have occurred as a result of over-tightening.

You should first clean up the threads on the wire wheel of your bench grinder to remove any sealant and dirt. Then obtain a 10mm x 1.25 nut, and try to run the nut down the threads of the bolt, by hand. Do not run the nut down with a socket, and do not clean up the threads with a die. The nut should thread down rather easily. Period. If not, then some portion of the thread has Yielded and the fastener should be pitched because the design torque value will not provide sufficient clamping force to prevent leakage.

I know this section has gotten a little more technical than some would like, but the science of fasteners has subtleties that lead to problems if overlooked. The best practice is to replace these items as recommended, so that you don't run into trouble. This is not to say that corners can't be cut, but the results may be questionable.

Now back to the head to install any studs on the intake and exhaust sides. Since the top two locations on each side of the head are drilled through to the oil drains, these studs should be properly sealed to prevent oil leakage. Clean the male and female thread fits with brake cleaner to remove any oil residue, and use a Teflon paste thread sealant (Pro Lock P/N 82000 or equivalent) on the male threads of the stud. Install the studs and snug them up.

Any additional studs installed should be cleaned as well, and treated to some medium-strength Loctite (P/N 27100). This will help prevent the studs from backing out during disassembly in the future. Resist the temptation to use the high-strength Loctite, as it can only be released by heating to over 350 degrees F. Yes. Been there, done that, and sheared off a few studs trying to extract them. Then it was Heli-Coil time.

Well we're almost there, so this would be a good time to clean up the two mating gasket surfaces. I use brake-cleaner or electronic parts cleaner to remove any oil residue. Install the two dowel pins to their locations in the block, and tap gently with a bronze or plastic hammer to make sure they seat fully.

If you plan on running an aftermarket intake manifold, this may be a good time to attach it to the head so that you can check for clearance. I've seen where the bottom of the manifold runs into the top of the block, and would have led to certain leaks. If this is found to be the case, the bottom of the manifold should be relieved with a grinder.

Now without the gasket, carefully set the head down on the deck, over the dowels. A shop hoist is handy here, but if you're installing this manually you may want to place a 2 x 4 over the fender guard to rest your elbow on. This will prevent dimpling the sheet metal with your elbow. Don't ask how I know that can happen.

Check for any rocking at all, and use a mirror along each side of the block to make sure the head is fully seated. If not, find out why and correct.

Once you have verified that the head will seat properly to the block, remove it, and install the gasket over the two dowel pins. I've noticed in the last three years or so, that most gaskets seem to have some trouble getting over the dowels, almost like the center-to-center distance has been changed on the gaskets. So make sure that the gasket seats fully to the deck. You can use the smallest socket that will fit over the dowel, and gently tap the gasket flush to the deck. Be sure the word "Alto" for up, is looking at you from the gasket.

Complete the head preparation by installing your cam wheels and adjust the valve lash to specs if you've not already done so. Line up the cam timing wheels, and the auxiliary shaft to their respective timing marks at the front of the cam boxes, and set the crank pulley to Top-Dead-Center.

Once the gasket is in place, gently set the head over the dowel pins, and again, use a mirror to check both sides of the block to verify that the head has seated properly. Do not rely on the head bolts to seat the head.

Use the torque table from the factory manual to verify the proper tightening sequence and specified torque for the bolts. Apply engine oil to the bolt threads and install with washers hand tight. Many use a lower torque value the first time around, and then increase to the specified value the second time around.

After you've made all of your connections, including the ground at the rear of the exhaust cam box, you should change the oil to remove any contamination that may have been introduced. Filling the oil filter and the two cam boxes with oil will help provide lubrication to the critical parts of your motor sooner. It's also a good idea to keep the spark plugs out, disconnect the distributor trigger wire, and crank the motor over until the low oil pressure light goes out. This assures you that you have oil pressure, and that the engine will be lubricated as soon as it starts.

There are different schools of thought on the need to re-torque the head gasket. I'm a firm believer in taking that extra step. I warm the engine slowly, bring it up to operating temperature, and let it idle for an hour or so. Resisting the urge of the test drive, I shut the motor down and let it cool overnight. Then I go through and re-torque all of the head bolts to the specified value. You'll be surprised at how many bolts actually do have room to be taken up. After this kind of re-torque, I've never had to re-tighten the fasteners.

Hopefully you'll benefit from this review of head installation tips. If you still have unanswered questions or need clarification, please feel free to contact me.

Sincerely,

Terry Terezakis
MotoComp Engine Development
Easthampton, MA 01027
terry.zak@comcast.net