| DISK BRAKE REFINISHING |
Disc Brake Refinishing
Brake discs can be refinished if precision equipment is a available and a few simple rules are followed. The first thing to do is to determine which of the following will need to be done. Resurface-Recondition or Replace.
Resurface with a flat sanding disc (with disc rotating) if scoring is light or if the disc surface has severe rust scale.
Recondition if scoring is deep or if runout, thickness variation flatness and parallelism are out of specification. Scoring of the brake disc surfaces not exceeding .015 in depth, which may result from normal use, is not detrimental to brake operation.
Note: Both sides of the disc must be treated in the same manner. If one side
needs resurfacing or reconditioning the opposite side should be
treated in the same manner.
Replace if the disc cannot be reconditioned to bring it within specifications and meet the minimum thickness specification after reconditioning.
Remember: The number cast into the brake hub is a discard dimension not a refinish dimension. Note the following chart for each vehicle line:
Minimum Thickness Discard
Model After Reconditioning Thickness*
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Chevrolet 1.230 1.215
Monte Carlo & .980 .965
Chevelle
Camaro .980 .965
Nova .980 .965
Corvette 1.230 1.215
Vega .470 .440
Truck C-K-P 1.230 1.215
10-30 Series
* This dimension is past into the hub surface. Following is a picture story of the specifications as printed in the 1971 Chevrolet Shop Manuals.
All specifications are important and should be held even though must customer complaints will result from specifications as shown in Figures 6 & 7 not being within limits.
The AERA Technical Committee |
| VALVE CROSSHEAD CLEARANCE |
Valve Crosshead To Rocker Lever Clearance On
NH, NT & V-1710 Series Cummins Engines
Valve crosshead nose to rocker lever clearance on the subject engines must be checked during engine rebuild and at any time valve crossheads are replaced on engines using crossheads No. 123416 & 3000326. A minimum of .020 (.51 mm) clearance must be present as illustrated in Fig. 1, on the cylinder being checked with valves completely closed and crosshead in the upmost position. After installing rocker lever assemblies, check crosshead to rocker lever clearance as follows:
1. Turn crankshaft slowly in direction of rotation until the valves are closed on the cylinder being checked. With rocker lever held firmly against the stellite pad of the crosshead, a .020 (.51 mm) wire type feeler gauge must pass between the crosshead nose and the lower beam section of the rocker lever.
2. If the feeler gauge does not pass through:
a. Remove the rocker lever and/or crosshead and grind the nose of the crosshead or rocker lever beam in the area circled in Fig. 1 until enough clearance is obtained.
b. If the rocker is ground, grinding should cover the complete area illustrated in Fig. 2 in a continuous arc. Do NOT grind just the contact area.
Caution: A sharp depression in this area will cause a stress riser and eventual failure of the lever. Grind only enough material to achieve the required clearance. If grinding enters the oil passage, the rocker lever must be junked.
c. Grind sharp edges smooth.
The AERA Technical Committee |
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| CRANKSHAFTS INDUSTRIAL |
Crankshafts Used In Industrial Applications On
GM (Chevrolet) 5.7L (350 CID) Engines
When the GM (Chevrolet) 5.7L (350 CID) industrial engine is used in some applications such as lift trucks, the only crankshaft that is applicable has the forging number 1182. Dimension A of the rear flange is slightly smaller than that of other crankshafts used in General Motors 5.7L (350 CID) engines.
The larger flange crankshafts will not pass through the center hole of the bell housing. This is very critical when an oil clutch system is used.
The AERA Technical Committee |
| BURNED EXHAUST VALVES |
Burned Exhaust Valves, Low Power & Hard Starting On
Cummins NH & NT Engines With Jacobs Brake 25B & 30
Cummins Engine Co. reported that if the following complaints are experienced in the NH and NT engines equipped with Jacobs brakes, the slave piston clearance should be checked:
A. Exhaust valve burning
B. Low engine power when at operating temperature
C. Engine hard to start or will not start at operating temperature
A standard slave piston adjustment of .018 +/- .001 has been established. The .018 clearance setting is a cold setting which results in zero slave piston to crosshead clearance when the engine is at operating temperature.
Should the slave piston clearance setting be less than .018, the following conditions outlined in A, B or C above may result as well as affect breaking power.
If the slave piston clearance is greater than .018 +/- .001, the following problems may occur:
1. Engine injector train component problems
2. Injector carboning
3. Bent injector push rods
4. Worn injector adjusting screws
5. Decreased camshaft life
6. Cam follower and follower shaft failure
7. Delay in breaking action
If the above problems are experienced and the engine is equipped with a Jacobs brake, the slave piston clearance should be checked with the latest Cummins specifications.
The AERA Technical Committee |
| NEW CYLINDER LINER O-RINGS |
New Cylinder Liner O-Ring Seals On
Cummins NH/NT 6 Cylinder Engines
Cummins Engine Company has released new O-ring seals for the cylinder liners in NH/NT 6 cylinder engines. The new seals are made of an EP material and have a smaller diameter cross-section.
The new seal replaces both the old center seal #3008998 and the old lower seal #183049. The new seal carries Cummins part #3032874 and is black in color with one blue dot.
The new O-ring seals are not to be intermixed with the former seals on the same liner. Cylinder liner deformation will result. You can use the former seals and new seals in the same engine as long as they are used in the correct combinations on each liner. The illustration below shows the correct combinations.
The AERA Technical Committee |
| OIL IN COOLANT |
Oil in Cooling System on
VW 1.5L & 1.6L Diesel Engines
AERA members have reported instances of engine oil in the cooling system on VW 1.5L diesel engines. According to AERA sources, the problem is related to a crack in the cylinder head bolt hole located near the oil gallery feeding the cylinder head.
The oil feed gallery in the block is located on one side of the center head bolt hole and a coolant jacket is on the opposite side of the bolt hole. Pressurized engine oil is diverted through a slot in the head gasket and is feed up the side of the head bolt to the cylinder head. The oil also follows the bolt back down to the bottom of the bolt hole. Should the crack in the head bolt hole extend to the coolant jacket, oil can mix with engine coolant.
This problem is generally found on engines equipped with 11mm head bolt holes. Later design engines utilize 12mm head bolts and do not exhibit this defect. At the time of this writing no successful repair procedure is available.
The AERA Technical Committee |
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| CYLINDER HEAD SPECS |
Cylinder Head Specifications on
Case 207 Diesel Engines
The following cylinder head specifications should be considered when remanufacturing Case Model 207 diesel engine cylinder heads.
The minimum cylinder head thickness has been established at 3.968 with a new head measuring 4.000 +/- .005. Heads are measured from the deck surface to the rocker cover rail.
Valve recession should be checked and adjusted if necessary to a maximum recession of .015, below the deck surface, for both intake and exhaust valves. Valves on new cylinder heads are generally flush with a +/- .005 tolerance.
The AERA Technical Committee |
