Rebuilding vintage cylinder heads with today’s durability.
Jim Smart - October 18, 2012 10:00 AM
For Your Information
JGM Performance Engineering
Summit Racing Equipment
1 JGM Performance Engineering in Valencia, California, has an environmentally responsible cleaning process that gets iron and aluminum like new. There’s a high-heat cooking process, a metal shot blasting process followed by shakeout tumbling to remove all debris. Like-new castings emerge ready for magnetic particle inspection and machine work.
2 For a valve job that will take you 200,000 miles, opt for all new parts without exception. It’s a good idea to go with hardened intake and exhaust valve seats if you can afford it. This sets your heads up for life with steel seats for both valves.
3 Valve guides don’t always have to be completely replaced, but instead renewed with bronze inserts. Valve guides are measured, reamed, and readied for new bronze inserts.
4 The bronze insert, which acts as a valve stem bearing, is driven into the factory valve guide. Bronze inserts are an economical high-wear answer to valve job life because they wear well and control oil flow to the valve stem.
5 The valve stem is measured in preparation for valve guide honing to proper size.
6 Valve guides are honed at least two ways that we’re aware of — a conventional or ball hone, which dresses the bronze guide, like honing a cylinder bore for piston rings.
7 The lubricated valve stem is test fitted. Any resistance is unacceptable. If it binds cold, thermal expansion will only make things worse.
8 Steel valve guide inserts are replaced when worn so severely the guide cannot be salvaged. Here, JGM Performance Engineering reams out the old steel guide.
9 A new steel guide with bronze insert is driven into the head casting where it will be machined to proper length, then honed to valve stem size.
10 Valve faces receive a dye, which serves as a guide for grinding and lapping purposes. Valve faces are then ground to the proper angle.
11 Until the early 1970s, this was your typical exhaust valve seat in machined cast iron. Aluminum heads, of course, received steel intake and exhaust valve seat inserts. This iron seat is pitted from heat and wear.
12 New steel exhaust valve seat is measured for both the head valve pocket and cutter.
13 Iron seat is reamed out, creating a void for the steel seat/insert.
14 Steel exhaust valve seat is driven into place and will be machined to match the valve face.
15 Valve seat is machined to match valve face angle. For most, a standard 30/45/60-degree three-angle valve job works fine. This allows good airflow and comfortable valve-to-seat contact for cooling.
16 New steel exhaust valve seat is ground to the proper angle. Machine shops can perform three cuts or use a single three-angle cutter.
17 Once guides and seats are done, it’s time to mill the deck surface. Minimum milling necessary prevents changes to manifold/block/head angle, which can cause manifold/head leakage.
18 Heads get a bath to remove all machining debris.
19 JGM uses Viton valve seals, which perform better and last longer than Teflon and umbrella seals on street engines.
20 Valve spring pressures and installed height are checked to confirm cam compatibility and function. Then, retainers and keepers are installed.
21 JGM performs a vacuum check on each port to ascertain proper sealing. If the vacuum holds, these heads are good to go.
When driving a classic car on a regular basis, you’re more concerned with reliability than those who trailer or drive their occasional rides.
Daily use is better for an automobile versus sitting in a garage because it keeps everything fresh, lubricated, and functional. A driven car is a happy car because that’s what automobiles were designed to do. However, daily use takes a different kind of toll in terms of wear and tear.
Old cast iron engines have soft iron valve seats that performed well when there was tetraethyl lead in gasoline. Lead was a cheap way to boost octane and provide lubrication for valves and seats. However, it also polluted the air with toxic lead. In the 1980s, Washington began a mandated phase-out of lead in automotive fuels to reduce air pollution, which caused quite a panic with classic car buffs, fearful it would put an end to the classic car hobby. The sky didn’t fall.
We’ve found ways to get along without lead in automotive fuels, which has actually been a positive turn of events because engines run and burn cleaner today than they ever did in the old days. Engines last longer between rebuilds and valve jobs because lead is gone from fuel. When there was lead in fuel, engines sludged up and accumulated heavy combustion chamber deposits. It also fouled spark plugs, mandating tune-ups every 12,000 miles.
Because lead was a good lubricant for valves and seats, we didn’t have to sweat out valve and seat wear with iron heads. However, in truth, lead was never a good thing for internal combustion engines and exhaust systems because it caused engine and exhaust system deterioration due to its corrosive personality. It also hindered heat transfer from exhaust valves to seats, which caused them to run hotter and fail. Beginning in 1971, automakers began installing hardened steel exhaust valve seats in new cars to improve durability with low-lead and no-lead fuels. Little by little, the air became cleaner and engines started lasting longer.
There’s everything to be gained from the use of unleaded fuel if you prepare beforehand. Preparation includes a blueprint valve job that includes new valves, guides, hardened seats, valve springs, and Viton seals, and most of all — solid craftsmanship by a competent machinist. Begin a valve job with guides that are all in parallel to ensure a solid foundation. This is where all valve jobs must begin.
When you have guides out of parallel, nothing’s going to line up from then on. Valves and seats are next. And lastly, a perfect mating surface for block and head. If you’re working with an engine with stud-mounted rocker arms, consider the installation of screw-in studs and guide plates for durability. You also want rocker arms, keepers, and retainers that are in good mechanical condition.