Thrust Washers
A Critical Adjustment During Engine Rebuild

by Ed Barnard

This month I was asked many questions about setting up an engine by an individual who was doing his own rebuild. I be-gan to realize that what may seem very obvious to me after play-ing with these cars for so many years, might not be obvious to a person rebuilding his first tractor engine. I would like to start doing a series of short articles, each dealing with a different step in the rebuilding process.

One of the most critical measurements and adjustments to make during the rebuilding process is the measuring and ad-justment of the thrust washer clearance. The thrust washers are placed on the middle journal of the TR2-4A engine, and on the rear journal of the TR6 and Spitfire engines. They limit the for-ward and rearward movement of the crankshaft within the block. The crankshaft actually moves front to rear as the engine speed varies, and as you step in and out of the clutch. They are sold in sets measured much like pistons; standard, +. 005, +. 010. They can be mixed and matched to set the clearance to what is desired.

The prescribed method for checking their clearance is to assemble the crank in the block in the normal fashion with the bearings installed and lubricated and the thrust washers installed. Orient the thrust washers correctly; with the oil notches toward the crank surface. With a plastic mallet hit the front of the crank until it moves rearward to its limit. Mount a dial indicator to the front of the block to measure the front to back movement of the crank and zero it. Hit the rear of the crank with your mallet and observe the amount of movement on the dial indicator. Check this against the specification given in your workshop manual. This clearance varies between engine types. If the measured clearance is too great use a larger thrust washer. If the clearance is too small use thinner thrust washers. There may even be a time when the sizes available to you do not get you within the clear-ance window. If necessary you can sand the flat surface of the thrust washer with emery cloth on a flat surface until you get the clearance you need. In between measurements reset the crank rearward, and measure the amount of forward travel when you strike the back of the crank.

 
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