Worn valve guides are either replaced or repaired with K-Line bronze guide liners. These are installed using a centering cone clamped to the seat for boring the original guide, therefore much more concentric than replacing the whole guide, which usually install somewhat eccentric requiring more material to be removed from the seat to obtain concentricity. These are phosphorous bronze and have an interrupted spiral to retain oil and run less clearance(aids in creating a better valve to seat contact area) than conventional (looser fitting) guides. Liners are honed to size and checked using the Newen straight carbide pilots that are in increments of .0004″.
This is the only way to measure guide clearance correctly. Dial bore guages measure diameter at one spot but cannot tell if a guide is straight or banana shaped, which does occasionally occur in bronze guides. I offer this service for all sizes of guides from 5.5 – 9mm (except some Peugeot Diesels which use 8.5 mm)and 5/16, 11/32 and 3/8″
Cylinder head straightening
If an aluminum head engine overheats the head usually warps. When the head warps it’s not only the head gasket surface that warps but the entire head. The purpose of straightening heads, especially OHC heads is to straighten the cam bore. Aluminum OHC heads run .002-.004″ oil clearance between the cam and cam bore.If the head warps more than the oil clearance, there is no room for oil and the cam runs directly on the head material. Also, the cam is flexing as it’s turning, how long can that last? Theoretically, the cam should not touch the head but ride on a film of oil. Another benefit to straightening is that much less material is removed from the deck when resurfacing, therefore keeping the compression ratio where it should be.
This operation is done by bolting the head, using the center head bolt holes, to a piece of steel channel and shimming the ends of the heads. The trick to getting this right is knowing how much to tighten the bolts, or how much to straighten the head before it goes in the oven. Some heads warp more on the exhaust side than the intake side and I take this into account, trying to get both sides of the top of the head as straight as possible, especially critical on DOHC heads.
Pressure testing is done by sealing off all water passages and filling the head with compressed air to about 50-60 psi, then spraying the head with soapy water. I’ve found pin holes in ports, cracks that couldn’t be seen and porosity in chambers that leaked. Heads that are repaired by welding are always pressure tested after machine work is done.
I also pressure test cast iron heads that have had the exhaust seats replaced to make sure the counterbore for the new seat didn’t hit a water passage. This has happened.
I currently use a special machine for milling cylinder heads. It uses a CBN cutter for most heads and a PCD cutter for aluminum heads that use MLS head gaskets and require an ultra-smooth finish.
Valves are ground on a Sioux 2075 (variable speed) using an Accu-chuck. It uses collets instead of a ball-type chuck. These are very accurate but nothing is taken for granted. I use a dial indicator on the valve stem before I grind the face to make sure the stem is concentric with the face after grinding and check the valve on a valve face runout guage after I grind the valve.
Valve seat machining
The Newen Contour BB a world class machine. This machine is used by OE manufacturers, many well-known race teams as well as shops that insist on a perfect valve seat. Check out www.newen.com for all the info.
I’ve used many different methods for machining valve seats, stones with tapered pilots, Mira cutters, Neway blades, and, with my last machine, the Newen GII, the carbide form tools that Serdi created back in the 70’s. The carbide form tools are widely used today because they cut 1, 2, 3, up to 7 angles all at the same time. It sounds great in theory and works fine on some seats. But for the most part, cutting modern seats on late model engines properly with 3-angle form tools can be a challenge. Carbide needs to plow through material, it won’t cut skating accross the seat. The physics of maintaining proper pressure on three or more angles is impossible. The results are tiny chatter marks that leak compression and out-of-round seats caused from deflection(the cutter actually influenced by the variation of the width of the cut, the hardness of the seat, and the concentricity of the guide to the seat).
The Contour BB uses a single point cutter, like a brake lathe or a boring bar. It cuts, CNC contolled, on two axes. A cut profile is created by me on a computer screen with any angle, any length, any combination of angles and even radii. The machine cuts the profile starting at the bottom(in the bowl area) and then finishes with out the top of the profile, into the chamber. The optional CBN cutter cuts throught the hardest seats with no problem for a seat that looks like a bearing race on the most expensive Porsche or Mercedes-Benz.
Some of the most popular cars on the road today have some of the hardest seats. Honda, Chrysler, Mitsubishi and Chevrolet 350 Vortec ‘ 906’ casting(with hardened ex seats from the factory) are just a few. None of these seats is a challenge for the Contour BB, as they are to any other conventional method of cutting seats.
Enlarging valve seats for oversized valve is not a problem. I can enlarge the throat area below a seat to increase air flow. I can unshroud a valve by cutting the floor and wall of a combustion chamber in the same pass to help air flow.
The Contour BB also does a beautiful job of cutting counterbores for replacement seats. It will cut a bore for any size seat, not just the common sizes in 1/16th inch increments like a standard seat and guide machine uses. After the seat is installed, I can cut a profile that completely blends the seat with the chamber and bowl area. You almost cant tell there’s a new seat except for the chrome look of the new seat.
Checking the valve/seat. Ther are various methods for checking the valve job. There is vacuum checking, which pulls vacuum on the port showing how well the valve is seated. This works fine on larger stem valves, but on small stem valves the vacuum can actually flex the stem enough to make the valve appear to be seated. So a valve or seat with excessive runout can actually hold vacuum. An old, but widely used method is lapping with a gritty compound on the face of the valve and a lapping stick. Rubbing the compound between the valve and seat leaving a line on both components, appearing that they make good contact. The problem with this is that lapping compound has dimension. Rub a little on a micrometer or dial caliper and you will see a thickness of 2,3, even 5 thousandths of an inch. This means that a valve or seat with as much as .005″ runout will appear good using the lapping method.
I use a variety of methods for checking valve/seat contact, vacuum checking on larger stem valves, Prussian blue( a grease that shows a contact patch just by popping the valve on the seat once, not rubbing) and even pencil lead rubbed on face of valve and rubbed on the seat.
Every guide, valve and seat are checked these ways to ensure the highest quality valve job available.