Rebuilding 327 Heads
Article by Mark Trotta
Gen-One small-block Chevy heads are known for faster-than-usual valve guide wear, so it's essential to check the valves and guides when rebuilding.
Before I bought this car, the heads had been rebuilt at a machine shop. After taking the heads off the engine, I still removed the valves to check.
Tools and Supplies
Once the heads are off the engine, a valve spring compressor tool is required to remove the valves, locks, retainers, and springs. The common ones are hand-operated with an extendable arm.
Most valve spring compressors will work on a variety of cylinder head designs, so if other engine rebuilds are in your plans, it's a good investment.
Supplies included new valve stem seals, a little engine oil, and a couple small containers to keep parts in.
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Remove Valves and Springs
After compressing the springs with the valve spring compressor tool, carefully remove the two small keepers with either a small flat-blade or needle-nose pliers.
Release the valve spring compressor slowly, then remove the metal shield and valve spring.
If the head has been rebuilt before, there may be a shim underneath the spring. Make a note of where and how many shims there are.
Remove the O-ring from the groove and slide the valve out. It's a good idea to keep each valve, spring, and shield together.
After disassembly, here's what I found--the valves were new, the seats had a fresh cut, and the guides had been knurled.
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What Is Valve Guide Knurling?
From the factory, cast-iron Chevy heads were fitted with cast-iron valve guides.
As an alternative to replacing, renewing the guide is sometimes done by knurling. The process is done by passing a tool down the guide, which rolls a spiral of material into the spaces of the tool. When the tool is run through an old guide, it displaces the metal and makes the diameter of the hole a little smaller.
The rolling method does not remove metal, but rather raises it up in rings. The guide then gets reamed to the proper size.
Some will argue that the rings left by knurling process hold extra oil, which increases lubrication over non-knurled guides. But a knurled surface will always wear quicker than a new guide because of the missing surface area.
It's hard to say how many miles knurled guides will last before the engine starts burning a little oil and blowing out blue smoke. Perhaps 10k, maybe 20k miles, but for an old car that doesn't get driven regularly, knurling valve guides is always an option.
Related Article: How To Measure Valve Guide Wear
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Oil Control
From the mid-fifties thru the mid-eighties, small-block Chevy's used an O-ring combined with the metal shield over the spring. When the engine is fresh, this works very well, but as it ages the stem to guide clearance increases and allows oil consumption. GM used this design until emission concerns came along.
Some who don't understand this design will use the O-ring, but discard the metal shield as unnecessary weight. The shield was intended to direct oil onto the valve spring and away from the stem. Taking away the shield renders the o-ring useless.
NOTE: when reinstalling, do not put the O-ring on the valve before the metal shield. This will push the O-ring down the stem of the valve and do nothing to help oil control.
Upon reassembly, I lapped the valves to confirm that the seats were airtight.
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Valve Springs
After 50k miles, SBC valve springs often begin to lose pressure. If yours are worn slightly, a spacer washer (shim) can be placed under the spring to compensate for the loss of strength.
Shims should not be used to increase pressure, as they may bind. Heavy-duty springs should be used, but only if recommended for the cam you're using.
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Paint Cylinder Heads
Here's what I did before painting--spray the heads with brake parts cleaner (leaves no residue), wipe down with shop towels, then scuff with a Scotch-brite pad.
After taping them up, I sprayed them with a few coats of Chevy Orange Engine Paint. No primer was needed.
That's an old set of old valve covers I installed while painting.
Read: Spray Paint Engine Block And Parts
Before reinstalling, both cylinder head surfaces were cleaned before setting the heads back onto the block. The block should have two dowel pins for each cylinder head to align onto.
Re-use or Replace Head Bolts?
Although the head bolts on this Chevy 327 are over 50 years-old, they were OK to re-use. I can't think of the last time I heard of a SBC head bolt failure.
Head bolts should be cleaned before re-installing heads (a wire brush works well). Also, chasing the threads in the block is a good idea.
Install Head Bolts
Some techs like to put a small dab of Permatex Ultra Black on all head bolt threads (on the bottom 1/4"), and a smaller dab of engine assembly lube underneath the top bolt-heads. The sealant takes up the remainder of the space between the threads to prevent any leaks. Lubricating underneath the bolt-head gives more consistent torquing.
NOTE: Felpro head gaskets are installed dry.
Last step is to torque the bolts, which is done in steps. First, snug them with a 3/8" ratchet, then torque to 40, 50, 60, and then 65.
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