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Perspective On Using CBN Versus Polycrystalline Diamond (PCD) Cutters

In your June Shop Line you offered Jerry Lawson's of DCM Tech, Inc., perspective on using CBN versus poly crystalline diamond (PCD) cutters. Have any other manufacturers voiced their opinions?

In PERA's May 1996 Current Concerns publication, Andy Rottler of Rottler Manufacturing made the following observations on CBN versus PCD cutters:Rottler says that due to differences in porosity, generally for a given feed rate and rpm, aluminum will show a smoother finish than cast iron. Cast iron yields a rougher finish because of its higher porosity.Rottler says that CBN was designed for use on cast iron and hardened steels, and that there is no advantage to use CBN over PCD, coated carbide or uncoated carbide when cutting aluminum. CBN does not yield a longer tool life than PCD or carbides when cutting aluminum.Due to the higher cost of CBN cutters, other cutting materials are far less expensive on a per head basis when it comes to expendable tooling cost. Rottler says that PCD, coated carbide or uncoated carbide will cut aluminum better than CBN will. He says that PCD will produce the best quality finish in aluminum, and that PCD can't be used on cast iron.It is important to look at the mix of cast iron and aluminum heads to determine if inserts should be changed to maximize the cutting performance of each material. If, for example, your shop machines 10 cast iron heads, then one aluminum, then several more cast iron, it probably doesn't make sense to change inserts. However, if you are machining 10 aluminum heads, then one cast iron, then several more aluminum, it makes sense to change to an aluminum head insert. There is middle ground where it is cost effective to change inserts.(Automotive Rebuilder does not endorse the use of one particular type of surfacing material or equipment over another. It is our experience that machine shops and engine rebuilders across the country use a variety of materials and equipment with varying degrees of success. We, however, would be happy to publish any machining requirements, etc., that provide optimum performance for use of specific surfacing materials).

What's the proper procedure for installing rear main oil seals on 1995 2.0L Chrysler engines?

According to a technical bulletin released by the Automotive Engine Rebuilders Association (AERA) in May, engine oil leaks will occur on 1995 2.0L VIN C or Y and 2.4L VIN X Chrysler (these engines are manufactured by Chrysler not Mitsubishi) engines as a result of mislocated rear main oil seals.AERA notes that if the rear main seal is installed below flush with the rear block surface, it may place the seal's sealing lip beyond the sealing surface on the crankshaft. To properly locate and install the seal, Chrysler now offers a tool - p/n C-4681. See Figure 1. The seal should be installed dry, positioning it and the tool over the crankshaft. Lightly tap the tool until the seal is flush with the rear of the block. The seal - p/n 4667904 - currently is only available through Chrysler.

Any ideas about what could cause an oscillating type noise on 2.5L Probe engines? The noise seems to occur after the engine reaches normal operating temperatures.

The noise you speak of may be caused by the friction gear spring on the camshaft losing its tension. This can result in an oscillating noise coming from the engine about every five seconds.Ford suggests replacing the camshaft friction gear spring with a new friction gear spring which has more spring tension. The recommended replacement friction spring carries p/n F42Z-6278-A.

Any ideas for causes of engine stalls after startup on SOHC (LKO) Saturn engines?

If this vehicle is equipped with an automatic transaxle, the engine may stall after the vehicle is initially started, or stall or stumble when first shifted into gear.If the vehicle is equipped with a manual transaxle, the engine may stall after the vehicle is initially started, when the vehicle is at a complete stop and the steering is turned to its maximum left or right position, or during launch when the engine is cold.The cause of these conditions may be caused by loss of fuel pressure, throttle body injector unit gasket protruding into the throttle bore (1991-1992 through VIN NZ 151498) and/or engine calibration.Possible causes for the loss of the fuel pressure include the TBI fuel pressure regulator assembly valve not seating due to debris, or leaking fuel pump check valve, fuel line or injector. This condition can cause the engine to stall immediately after start, usually within 15 seconds.The gasket between the TBI unit (all 1991 and 1992 engines built before and including VIN NZ151498) and intake manifold can protrude into the throttle body bore causing fuel to puddle on it.The engine calibration (1991-1992 vehicles only) can cause a start/stall condition due to the calibration supplying a lean startup fuel mixture, if the ambient temperatures are between 2-56° C (68-133° F). This condition can occur during initial start and/or after the engine has been operated for one minute or more.NOTE: New engine calibration must only be installed if the vehicle's TBI unit gasket has been replaced, fuel and/or engine electronic control system are found to be operating properly.If the fuel system will not hold pressure, the TBI unit must be cleaned with air pressure to eliminate debris that may cause an intermittent start/stall condition. After the start/stall calibration has been installed, there may be slight vehicle hesitation on initial launch, if the engine is allowed to idle for more than 90 seconds. This slight hesitation goes away when the coolant temperature warms up a few degrees or the vehicle is driven immediately after initial engine start.

What is the white, waxy film that often is seen on new CV boots?

It is basically a protective material which is used to enhance the ozone protection characteristics of the boot. What you are likely seeing is this waxy material immigrating its way to the surface of the boot.

What is the appropriate cylinder pressure for gas octane used in two-valve, wedge cylinder heads?

Provided you have good gas and good quench, 160 psi should work well. You usually figure one-half point compression advantage with an aluminum head. Running a cooler spark plug will also help to reduce the chances for detonation.

What is the maximum oversize that the Chrysler 5.9L engine should be bored to?

Chrysler says that its 1977 and later 5.9L engines should not be bored more than .040" (1.02 mm) oversize. In a March technical service bulletin, AERA reported that beginning in 1977, the 5.9L block design was changed to a lightweight casting, consequently resulting in reduced cylinder wall thickness.AERA noted that the 5.9L blocks prior to 1977 were the same casting as a 5.5L (340 cid) engine, which has a 4.040" (1.02.62 mm) bore. The 5.9L engine has a smaller 4.00" (100.0) mm bore, and those blocks from 1971-'76 may safely be bored to .080" (2.03 mm) oversize.

Can you provide any information on how to identify cylinder heads on Mack E6 and E7 diesel engines?

The Automotive Engine Rebuilders Association (AERA) published a July 1996 technical bulletin providing the following identification information. AERA says that machinists can't completely rely on casting numbers and sometimes those numbers are illegible. These heads are not interchangeable and identifying them before installation can save time and labor.There is a significant difference on the head gasket surface of these heads which is easily observed. The E6 heads have additional small, water by-pass holes between the head bolt holes. Those holes are located on the intake manifold side. Those holes are not machined on the E7 heads.The cylinder head gaskets are also different. The one you use must match the engine being worked on. The standard head gasket, p/n 57GC189A, should be used for the E6 engine, and p/n 57GC2115A should be used for the E7.There is one other difference that would be apparent when the wrong head is being installed; one head bolt hole will not line up completely with the block threads.

Can you supply the cylinder block deck height dimensions for Mitsubishi 4D31 engines found on 1995 models?

See Chart 1 on page 20 for engine model and cylinder block deck height dimensions on these engines. Mitsubishi cautions that if deck height is not within specifications, the following problems can occur: interference between piston and cylinder head; cylinder liner projection will be increased, which can cause coolant leak problems. Deck height is affected by machining the deck and line boring the crankshaft journals. Main bearing bore diameter, connecting rod bore diameters and connecting rod length dimensions are found in Charts 2, 3 and 4.

We're looking for engine specifications for the 1994 Mack E7-250 engine. Can you help?

The bore and stroke of this engine is 4.875" x 6.500" (124 mm x 165 mm). This six cylinder engine displaces 728 cubic inches (12 liters).Mack says that maximum horsepower is 250 at 1,950 rpm. Torque at 1,200 rpm is 975 lb. ft. (1,322 Nm).Operating range rpm is 1,200 - 1,950. Compression ratio pressure at 1,000 rpm (hot) is 16.9:1 (625 psi). Cranking motor at 100 rpm (cold) is 465 psi. Lubricating oil pressure at idle (600 rpm) should be 10 - 30 psi. See Charts 5 and 6.Engine piston assembly with injection pump p/n 313GC5212P6 is 240GC2249 (re-entrant bowl). With injection pump p/n 313GC5188P6 is 240GC2246A. Cylinder head is p/n 732GB533M; exhaust valve (Pyromet) is p/n 688GC2389; and camshaft is p/n 454GC5142.