Cylinder Head, Pushrod and Muffler

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

| March 2006

  • Finished Head
    Finished cylinder head with new valve seats and repaired exhaust thread. The original repair to the rocker pivot was left unchanged.
  • Cylinder Head
    Cylinder head shown with the two valve seats that had broken off and one of the rusty valves. The damage can be seen to the exhaust, where part of the thread has broken off.
  • Valve Seats
    The cylinder head with the two valve seats in the middle being machined to give square faces for the new seats, then bored out for the stems of the new valve seats.
  • Igniter
    The igniter in place on the engine, the bare metal showing on the extension piece fitted on the trip finger.
  • Rocker Arm
    The repaired exhaust rocker arm mounted on its pivot. The repair to the tip, with the tongue into the old metal, is visible. A new pivot screw and an adjustment bolt were made.
  • Pushrod
    The old pushrod and the replacement, fitted with the original catchplate and roller. The new pivot pin and components of the igniter trip are also shown.
  • valves
    The two replacement valve seats, which had to be tapered to match the originals as well as the two new valves. Their stems were cut to length after lapping the ports in the head.
  • Pride and Joy
    More Pride and Joy – Another of Peter Rooke’s Amanco eng-ines: This engine is all original including the planks it is mounted on. It has been on a local farm near Notts, England, since 1914. It even has the nameplate of a local supplier! This is slightly earlier than the Hired Man in this series, as the magneto is parallel to the gears rather than at a 90-degree angle with a beveled gear wheel.

  • Finished Head
  • Cylinder Head
  • Valve Seats
  • Igniter
  • Rocker Arm
  • Pushrod
  • valves
  • Pride and Joy

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.