Cylinder Head, Pushrod and Muffler

Part three in a five-part series: Restoring an Amanco 2-1/4 HP Hired Man

| March 2006

The first repair was the exhaust rocker arm, but before starting, it was necessary to drill out the pivot screw, which had completely seized, even after trying to free it with heat. 

The broken end of the rocker was filed square and then a 1/4-inch slot was cut 1/2-inch deep into the middle of the good metal. A replacement for the broken end was cut and roughly shaped oversized from a piece of steel, making a tongue that precisely fit in the slot. The new tip was then brazed to the old body, and then it was finish-filed for a seamless join. At the same time, a new pivot screw was made together with an adjusting bolt and lock nut for the exhaust valve.

Fortunately, the cylinder head was not warped and did not need truing. The head was clamped on to the milling machine table and the broken valve seats were machined flat. In order to retain as much of the original metal as possible, they were finished to different heights. Each of the old valve stem holes was used as a reference point to set up the head for boring out the hole for the new seat. The holes were then bored out to a diameter of 5/8-inch to provide a shoulder for the replacement seat.

New seats were machined from cast iron. First they were individually taper-turned to marry up with the remainder of the old seat, then shoulder-cut and under-sized holes were drilled for the new valve stems reaming 3/8-inch. 

The method of fitting the valve seats was the next decision. I did not want to use heat on the cylinder head any more than necessary, therefore I decided to press-fit the seats which were made 0.002-inch larger than the bored hole for the last 50 percent of the stem. For good measure some industrial adhesive was used, but this was not really necessary. There was no real pressure on the repaired seats, and the press fit proved adequate. Once the valve seats were in position, the oil holes were drilled and the exterior finish was filed.

New valve stems were made from 3/8-inch silver steel, the ends of which were reduced to 5/16-inch to provide a seat for the old retained valve heads.


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