Deburr Process For 3500 Connecting Rods Improves Reusability And Decreases Rod To Crankshaft Wear Caterpillar

Deburr Process For 3500 Connecting Rods Improves Reusability And Decreases Rod To Crankshaft Wear

Usage:

ENGINES3500 FAMILY OF ENGINES;
CATERPILLAR MACHIENS POWERED BY 3500 DIESEL ENGINES

Problem:

Normal wear at the parting line between the connecting rod and the rod cap can cause the potential for the rod and cap to become misaligned during reassembly of a used connecting rod. Misalignment may cause the rod cap to present a cutting edge that can remove material from the crankshaft. This problem has not caused a crankshaft to fail or break, but if allowed to progress, a crankshaft will not be reusable at the next overhaul. Indications of this problem are usually iron in the oil filters and not in the oil samples. Illustration 1 identifies the areas of possible misalignment that can result in a cutting edge.

Illustration 1.

Areas of possible misalignment that can result in a cutting edge.

Solution:

There are two main procedures that must be followed in order to reduce or eliminate this problem. These are, proper Tightening Procedure for Connecting Rod Bolts and Manual Deburr of Sharp Edges On Connecting Rod Cap.

Tightening Procedure for Connecting Rod Bolts

Illlustration 2.

Reference for tightening connecting rod bolts.

1. Side of connecting rod with chamfer.

2. Rod bolts.

3. Pin.

NOTE: Bolts (A) and (B) are on the same end of the rod cap that has the bearing tabs and locating pin (3).

Tighten the connecting rod bolts as follows:

1. Put 6V-4876 Molykote Paste on the bolt threads, shank, and the area under the head of each bolt.

2. Tighten bolts (A) and (B) to 90 ± 5 N·m (65 ± 4 lb ft).

3. Tighten bolts (C) and (D) to 90 ± 5 N·m (65 ± 4 lb ft).

4. Tighten bolts (A) and (B) again to 90 ± 5 N·m (65 ± 4 lb ft).

5. Tighten bolts (C) and (D) again to 90 ± 5 N·m (65 ± 4 lb ft).

6. Tighten each bolt an additional 90 ± 5 degrees.

Manual Deburr of Sharp Edges On Connecting Rod Cap

The purpose of this deburr process is to remove the sharp edges on the rod cap that can present a cutting edge to the crankshaft if the cap is assembled misaligned.

Illustration 3.

Rod Cap

Remove sharp edge from Point A to Point B.

Use a pencil grinder or hand held grinder with circular grinding wheel (Grit size - A80, Diameter - 2 inches, Width - 1/2 inch). Carefully grind the area shown in Illustration 3 from Point A to Point B. The object of the deburr is only to remove the sharp edge and not to remove large amounts of material. Be careful to only deburr the sharp edges and DO NOT deburr any of the shot peened areas. If the shot peening is touched by the grinder, that area must be re-peened using a needle peen. Failure to re-peen the area can result in a failure of the rod cap. Illustration 4 shows what the completed deburr should look like. Notice that the shot peen area has not been touched with the grinder.

Illustration 4.