6/1/1999
Performance Valve Jobs Are Easy With The Right Tools And Specifications
It is easy to do a performance three or four angle valve job, but it is very difficult to find a shop to properly do one for you. Well, I will explain to you the proper way to do a great performance valve job either using stones or pre-shaped three or four angle carbide cutters.
Always start with clean, carbon-free cylinder heads that have been magnafluxed or zygloed to make sure that you have a good head in which to grind your seats. The valve guides should be addressed first and repaired by using a .502" replaceable iron valve guide, bronze guide or a bronze valve guide liner. The only caution to take in this area is valve stem to valve guide clearance, especially if the heads you are doing have a large or dual heat riser crossover passage in the two center exhaust ports. This is predominant in some Mopar and nearly all Oldsmobile V8s produced between1964-’90.
I recommend an extra .0005" clearance on the exhaust valve guides with today’s unleaded gasoline which has absolutely no additives for upper cylinder lubrication. My recommended valve guide clearances for today’s unleaded fuel is .001" to .0015" for the intake valves and .0015" to .002" for the exhaust valves. If you have large heat riser crossover passages, add .0005" extra clearance to the exhaust valve guides. These clearances apply for either cast iron, bronze or bronze valve guide liners. The only exception to your valve guide clearances is if you are running aluminum cylinder heads. If so, you can tighten up these clearances about .0005".
The valve stem finish is very important and I recommend either polishing the stems so they are free of nicks and scratches, or use a flash-chromed or hard-chromed valve stem because these will outlast all of the valve stem finishes, especially on the exhaust valves. Once the valve guides have been broached, reamed and honed for final valve stem clearances, you are now ready to start your valve job.
Always check your valve guide clearances with ball mics or a dial bore gauge. If you are working with cast iron heads, install replaceable, hardened exhaust valve seats for today’s unleaded fuels. Do not trust induction heat-treated exhaust valve seats, especially if the heads are small block Chevy, Ford or Oldsmobile – or if they have over 100,000 miles on them. The unleaded fuels today with no lubrication in them are death on induction heat-treated exhaust valve seats. A stainless steel exhaust valve is also recommended for added longevity.
If you are going to install oversized valves, make sure your pocket porting is completed at this time before you start machining your valve seats. If you are using oversized or stock valves, reface them, even those that are new. Don’t ever assume that just because they are new that they are also concentric, because usually they are not.
You should use a valve face run-out gauge to check your valve refacing equipment and a valve seat run-out gauge to check the concentricity of your valve grinding or valve seating equipment. I recommend no more than .0005" to .001" run-out on either your valves or your valve seats.
If you are using a seat and guide machine, use a cutter with a minimum of three or four angles and try to use a primary valve seat width of .050" to .065" for the intake seats and .065" to .085" for the exhaust seats. If your customer is going to race, use .040" to .050" intake seat widths and .050" to .060" for the exhaust seat widths. If you prefer a wider primary exhaust seat use .080".
The angles I prefer to use will apply for popular small block and most big block Chevy heads with the exception of Oldsmobile and Pontiac heads with 30° intake and exhaust seat angles, and Chrysler Hemis. I have used these valve seat angles for over 40 years and they are real close to all of the high performance carbide cutters available from your suppliers.
I like 33° to 37° top cut angles, 45° primary cut, 58° to 62° undercut and 65° to 75° bottom bowl cut angles. If you have any radiused cutters starting below the 45° primary cut, I highly recommend that you use them.
Do not bury or cut your valve seats below the combustion chamber floor because this will affect fuel and air flow as the valves open. Always try to machine the intake and exhaust valve seats to the same depth for good rocker arm geometry and proper valve stem lengths for correct installed valve spring height measurements.
Always remember on non-adjustable valvetrains, like Mopar, Oldsmobile and some big and small block Fords, that valve stem lengths are what control the lifter pre-load dimension in these engines. Always refer to factory specs for valve stem lengths for these engines.
I make a valve stem height gauge for all Oldsmobile V8s produced between 1964-’90 to achieve the correct valve stem lengths (p/n HG-455). There are some other makes out there, but my gauge registers off the valve cover surface, not the spring seats and is very accurate.
If you are using the valve seat grinding stone method, always use general purpose grinding stones to rough in your valve seats. Measure the valve seat diameter on your valves with a pair of outside machinist dividers to obtain the primary valve seat O.D. dimension that you want. I like to be inside the margin of the valve on the valve face about .015" to .025" on both intake and exhaust valves.
Always rough in your primary 45° seats to where the dividers just contact the O.D. of the valve seat. Next use your topping stone, 33° to 37° depending on the shape and radiuses of your combustion chamber floor, until you have a 360° topping mark on top of the 45° primary valve seat.
If everything is concentric, use a 45° finishing stone and grind out the primary valve seat to its finished O.D. dimension. Using this procedure you eliminate burying the seats too deep in the combustion chamber floor. If you are grinding your valve seats to a specific depth for a non-adjustable valvetrain, check your measurement at this time.
Also remember that your valve stem tips can be shortened if needed, but do not remove more than .025" to .030" off the valve tip ends. You will usually grind through the valve tip hardness, or the valve tip will become too short causing rocker arm to valve spring retainer interference.
Once your primary valve seats are out to their final O.D. dimension you can narrow the seats to the width of your choice by using a 58° undercut roughing stone. Some machinists use Dykem on the 45° primary seat before narrowing it with the 58° undercut stone because it is easier to control the 45° valve seat width.
After you have undercut with your 58° stone, use a 65° to 70° stone to break the edge of the 58° undercut so you end up with a nice flowing valve bowl. The undercut widths in relation to one another should be .035" to .050".
When all the cuts have been made, use a smooth-dressed stone in an air or electric hand grinder to blend and roll the undercut angles up to the bottom of your 45° primary valve seat. This will complete your high performance valve job.
If your valve equipment is in tip-top condition, valve lapping will not be necessary. I use a very fine valve lapping compound to show me where my valve face contacts my finished primary valve seat so I can undercut my valves for maximum fuel and air flow. I undercut my valves .010" to .015" wider than my primary valve seat width impression made by the valve lapping compound. Valve bluing, Dykem and my VST-400 valve-scribing tool will also achieve this measurement.
Dykem the valve, measure the inside of your 45° primary valve seat with the VST-400 and set the tool. Next, slide the VST-400 over the valve stem and scribe the valve, then undercut it. I like to use a 16° to 24° undercut on intake valves and 16° to 28° undercut on exhaust valves. If the radius under the valve is larger, use any of the above undercut angles to achieve your final valve face width.
Make sure that you shorten your valve guide lengths on the spring seat side of the head short enough so when you install your valve seals, positive type or umbrella, that you do not have any valve spring retainer to valve seal interference problems which are usually caused from a higher than normal lift camshaft.
I like a minimum of .070" between the retainer and the valve seal and .080" to .100" between the valve spring coils before coil bind. I like metal teflon, viton and teflon valve seals over the umbrella or O-ring type for positive valve stem oil control.
I hope this will make your valve jobs easier and bring in a new type customer for you. I will share with you my valve seat angles for a 30° valve seat. Use the same widths mentioned in this article 15° to 21° top cut angle, 30° primary seat, 45° undercut, 65° undercut, and a 75° bowl cut.
My next article will be on porting, shaping and polishing combustion chambers, plus all the tools and abrasives on how to do them properly and faster. Always remember, we make horsepower, not promises.