Straightening Connecting Rods

If a rod is in perfect alignment, piston bottom will rest squarely on plate with flywheels turned so that crank pin is in either forward or rear position. Keep in mind that this check, to be accurate, depends upon checking with crank pin in both forward and rear positions. It. is the change of rod angle, resulting from changing crank pin from one position to the other, that influences the seat of piston on squaring plate and thus indicates whether or not rod is in alignment.

Insert narrow strips of very thin paper of equal thickness underneath piston, one on each side, below piston pin, as shown in Fig. 3C-25. Press piston down lightly with fingertips resting on center of piston head and pull first one paper, then the other, partially from underneath piston. If piston is perfectly square (rod in alignment), both will have the same amount of drag.

If rod proves to be out of alignment, it can be straightened by means of a bar inserted through piston pin, as shown in Fig. 3C-26. Use a bar with a diameter as close to the hole diameter in the piston pin as possible. The manner in which piston seats on squaring plate indicates as follows:

1. Piston high on same side, both crank pin position; rod is bent.

In refitting and reassembling connecting rods, and finally fitting pistons, rods may possibly be bent or twisted, throwing upper bearing and lower bearing out of alignment with each other to some extent. Therefore, after pistons have been installed, rods must be checked and re-aligned as may be necessary. If a rod is left bent, or twisted, piston has a "cocked" relation to cylinder bore and the result is excessive noise and rapid wear.

Check rod alignment by means of Piston Squaring Plate, Part No. «6181-26, as shown in Fig. 3C-25. Be sure crankcase face is clean and free from burrs so that squaring plate seats fully.

2. Piston high on opposite sides as crank pin position is changed; rod is twisted.

3. Piston square or nearly square with crank pin in one position and high on one side with crank pin in other position; rod is bent and twisted.

Correct as follows:

1. To straighten a bent rod, insert straightening bar through piston pin hole on low side of piston and apply upward force.

2. To straighten a twisted rod, insert straightening

Figure 3C-27. Inserting Piston Pin Lock Ring in Tool

Figure 3C-26. Straightening Connecting Rod

Figure 3C-27. Inserting Piston Pin Lock Ring in Tool bar through piston pin hole on high side of piston, and if crank pin position is to front, apply force to rear --if crank pin position is to rear, apply force to front.

3. To straighten a bent and twisted rod (combination of a bend and twist), remove bend first and then remove twist. See above paragraphs, Nos. 4 and 5.

After rods have been aligned, check to see that pistons center in crankcase cylinder opening, without side pressure on upper rod ends. If further realigning is necessary to center pistons, correct by dressing off end of rod bushing on interfering side with a file. This allows the piston to shift slightly on rod to find a more suitable alignment of rod, piston and cylinder.


When connecting rod is true, remove squaring plate and attach piston so web on piston pin boss inside piston skirt is to right side of engine. Be sure left side piston pin lock ring is in place. If the piston is heated the piston pin may be inserted into piston with a slip or light press fit.

After pin is in place, install new piston pin lock ring using special Lock Ring Tool, Part No. 96780-58A, as shown in Fig. 3C-27 and 3C-28. Make sure ring groove is clean and that ring seats firmly in groove. If it doesn't, discard the ring and install a new one. A lock

Figure 3C-29. Installing Cylinder on Piston

ring loosely installed will rapidly loosen further in service and finally will come out of piston groove, resulting in both piston and cylinder soon being damaged beyond repair. Never install a used lock ring or a new one if it has been installed and then removed for any reason, always use a new lock ring.

Lubricate cylinder walls, pistons, pins and rod bushings with engine oil. Space ring gaps about equidistant around rear piston. Turn engine until crank pin is at bottom center. Install new cylinder base gasket. Position Piston Inserter Ring Tool, Part No. 96331-57, on rear piston and slip rear cylinder down over piston as shown in Fig. 3C-29. Install flat washers and nuts and pull them down tight. Repeat process to assemble front cylinder.

Figure 3C-28. Installing Piston Pin Lock Ring in Piston

Assemble cylinder head and remaining parts of motorcycle as indicated in "Installing Cylinder Head Assembly," Section 3B.

0 0

Post a comment