Head Swaps


This guide was written with the small block Chevy in mind, but most it applies to any engine.

For the first part of the head swap process, follow the 2QuickNovas Guide to Intake Manifold Swaps . It will guide you through the removal the carb and intake manifold.

If you didn't totally drain the coolant, go ahead and do so now so that no coolant will seep into the crankcase when the heads are removed.

If there is a temperature sending unit in the heads, remove the wire (if it an electrical gage). If it is a mechanical gauge or if you plan on using the same sending unit in the new heads, remove it now while the head is still torqued down.

You may need to disconnect the exhaust system from the manifolds/headers. If you have manifolds and will be using headers with the new heads, you can probably leave them attached to the heads, but the heads are heavy enough by themselves, so you will probably want to remove the manifolds now.

Remove any accessories that bolt to the front of the heads. If the alternator needs to be removed, unhook the battery before doing so.

Remove the valve covers if you haven't already. Loosen the rocker arm nuts. With stock rockers, you can just loosen them enough to allow the push rods to be removed. If you totally remove the rockers, balls, and nuts and plan on using them again, use a twist tie to keep them together as a set. If you will be reusing your pushrods, make sure to get them back in the same place they came from to avoid unnecessary wear.

Now that the heads are free of the rockers and push rods, you can loosen the head bolts. Start on the outside and spiral in towards the middle. This keeps the heads from being torqued on one end and not on the other, which could lead to cracking. Don't forget the bolts below the exhaust ports.

Clean up the decks of the block, and if you feel really ambitious, you can clean up the tops of the pistons. While you are this deep into the motor, you might as well take a look at the cylinder wear (indicated by a ridge in the top of each cylinder). Also, wipe a piston down enough to see if its a standard bore or if its a over-sized replacement. This information will give you a better idea of whether or not the engine has been rebuilt before and what will be necessary when the time comes for the next rebuild. Also take note of any excessive carbon build up in any of the cylinders, which can be an indicator of oil burning. An overly rich air/fuel ratio can also lead to carbon build up, but that would most likely show in all the cylinders. Some carbon will be there, so don't panic when you see black pistons.

Once everything is clean, you are ready to check the condition of the decks. Lay a straight edge across the decks and measure any gaps with a feeler gage. A few thousandths is OK, but if you are getting over .010"-.012", you will most likely need to deck the block (which requires removal of the block and taking it to a reputable machine shop). If you only find that the decks and heads are only a few thousandths out of flatness, you can skip the machine work.

Head gasket thickness plays a significant role in determining compression ratio. If you're working with a stock short block with dished pistons, you may want to consider thinner gaskets to help improve the combustion chamber efficiency. If you've experienced some problems with detonation or pre-ignition, thicker ones may help. But beware that overly thick head gaskets can lead to poor quench in a wedge-head (non-hemi) engine. That can actually make detonation worse.

Now that you've determined what gaskets you are going to use, you are ready to button the motor back up. I've had good luck putting gaskets on dry. Some people like to use a thin coat of a special spray sealer on shim gaskets. I recommend following the gasket manufacter's recommendations.

Slip the gaskets over the dowel pins and set the heads on the block. The dowel pins will keep the heads in place while you thread in the bolts. Use some thread sealer with Teflon on the threads. Many of the head bolt holes are open to the water jackets and you will get seepage if you don't use some sealer. The sealer also acts as a lubricant for the threads, which promotes more accurate torque readings.

Torque the bolts from the middle towards the ends in a spiral pattern (reverse pattern of what you used when you removed the heads). Sneak up on the final torque value. Start by torquing all the bolts to about 25 ft-lbs. Then go on up in increments of 15-20 ft-lbs until you reach 70. Keep going through the pattern until all bolts are torqued to 70 ft-lbs. You need to do this since as you tighten one bolt, an adjacent bolt will loose tension as the head gasket compresses.

You are now ready to put the pushrods and rockers back in. Just tighten the rockers enough to take up most of the slack in the pushrods.

Bolt the exhaust manifolds/headers on, hook up the exhaust and install any temperature sending units.

Following the 2QuickNovas Guide to Intake Manifold Swaps, reinstall the intake, carb, distributor, etc. Reinstall all accessories.

To set the valves, follow the 2QuickNovas Guide to Setting Valves. Reinstall the valve covers using new gaskets (you'd hate to get those pretty new heads all dirty).

These are the basic steps to swapping heads on a small block Chevy (or other similar engine). Once the engine has gone through a few heating and cooling cycles, go back and retorque the heads, headers, and intake manifold.

If you have any questions or comments please click the "Contact Craig" link and let him know.

Copyright 2009 Bruce Johnson and Craig Watson