INSPECTION & LAPPING

Clean the valve stems with lacquer thinner. Clean the valve guides using solvent and an expanding wire type valve guide cleaning brush. Insert the valve into the guide it was removed from. With the valve slightly off of the valve seat, rock the valve face and stem back and forth. Excessive wobble means a worn guide, valve stem or both.

Measure the valve stems with a micrometer and compare the reading with the specifications to determine whether valve stem or guide wear is responsible for any excessive clearance. Replace or repair as necessary.

The valves should also be checked for proper seat contact.

1. Apply a thin coat of prussian blue (or white lead) to the valve face and place the valve in the head.
2. Apply light pressure to the valve, but do not rotate it.
3. Carefully remove the valve from the head then check the valve and seat. If blue appears 360 degrees around the valve seat, the seat and valve are concentric.
4. Check that the seat contact is in the middle of the valve face.
5. If the valve and seat are not concentric or the seat contact is not in the middle of the valve face, you should consult a reputable machine shop for proper refacing.
6. After machine work has been performed on valves/seats, it may be necessary to lap the valves to assure proper contact. For this, you should first consult your machine shop to determine if lapping is necessary. Some machine shops will perform this for you as part of the service, but the precision machining which is available today often makes lapping unnecessary. Additionally, the hardened valves/seats used in modern automobiles may make lapping difficult or impossible. If your machine shop recommends that you lap the valves proceed as follows:
   1. Coat the valve face and seat with a light coat of valve grinding compound. Attach the suction cup end of the valve grinding tool to the head of the valve (it helps to moisten it first).
   2. Rotate the tool between the palms, changing position and and lifting the tool often to prevent grooving. Lap in the valve until a smooth, evenly polished surface is evident on both the seat and face.
   3. Remove the valve from the head. Wipe away all traces of grinding compound from the surfaces. Clean out the valve guide with a solvent-soaked rag. Make sure there are NO traces of compound in or on the head.
   4. Proceed through the remaining valves, lapping them one at a time to their seats. Clean the area after each valve is done.
   5. When all the valves have been lapped, thoroughly clean or wash the head with solvent. There must be NO trace of grinding compound present.