Installing Rod Bolts on Steel Connecting Rods - Engine Builder Magazine

Installing Rod Bolts on Steel Connecting Rods

Do not use metal stamps to number the connecting rods. Metal stamps may disturb the roundness of the rod bore. Paint toolmaker’s layout dye on the rod and cap instead, and then inscribe numbers.

NEVER use bolts to draw the cap down on rod. Locate cap dowel sleeves into the counterbores of the rod. Then, CAREFULLY tap cap into place.

CLEARANCES vary, as to application. Measuring bearing surface at 12:00 o’clock and 6:00 o’clock, the general rule is approximately .001? clearance per 1.000? of crankpin diameter. Wrist pin clearance generally runs from .0007? to .0015?.

OIL PRESSURE: 10 Ibs of oil pressure for every 1,000 rpm is recommended. Thus, 7,000 rpm = 70 Ibs of oil pressure (hot).

Clean all parts thoroughly to remove all dirt and foreign oils. Spread bolt lube on threads and under ?ange of bolt and tighten per instructions below.

For any fastener to supply clamp loads high enough to keep the parts together, it must be stretched the proper amount. Torque does not measure or ensure proper bolt stretch, it measures friction. This is why most experts prefer the stretch method for tightening rod fasteners.

To use the stretch method, measure and note the free length of each bolt before tightening with a stretch gauge or a micrometer with ball end attachments. Then, using the chart below, tighten the bolt until the  proper stretch is achieved.

Bolt Type             Recommended Stretch              Torque & Angle

3/8? ARP 2000        .0052? to .0057?                         25 ft Ibs + 55 deg

As a ?nal check to make sure no bolts were missed: Set a torque wrench at 50 ft Ibs, and check all rod bolts. If any bolt turns before reaching the preset torque, it has not been properly tightened. You must loosen these bolts and tighten them properly.

When removed, if the bolt length changes more than 0.001? from pre-install length, it MUST BE REPLACED. A stretched bolt is worthless and will fail, resulting in engine damage.

–Tech Tip courtesy of Falicon Crankshaft Components, Inc.

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