Divya Auto Head Repairing & Engg. Works
Heads give trouble in two basic ways: valves can stop sealing (burned or sticking) and head gaskets can fail.
In the case of a burned valve, the cylinder will no longer fire. If it’s a burned intake valve, the engine will backfire through the intake manifold. A burned exhaust valve is less noticeable. The exhaust sometimes will have a “putt-putt” sound to it. An old trick is to hold a dollar bill so it flaps over the exhaust pipe: if the bill gets “sucked in” every so often it can be a burned exhaust valve. A compression test or leakdown test will tell you if you have a bad valve.
Normally head gasket failure is from overheating. Often a engine will blow a hose or water pump and overheat. Several months later the head gasket will fail. Of course if you get an engine hot enough the head gasket will fail immediately.
Head gaskets commonly fail in two ways: a combustion leak between two cylinders or a combustion leak into the water jacket (cooling system). If a compression test shows two cylinders with low but equal compression, and the two cylinders are next to each other, the gasket is probably blown between those cylinders. If you have bubbles blowing out of your radiator or coolant recovery tank (the plastic tank usually on the fender that has a cap saying “engine coolant” on it) the head gasket has probably failed between a cylinder and a passage in the water jacket.
To repair any of these problems requires removing the cylinder head. To do it right, I send the head to an auto machine shop. If the gasket is blown, I have them pressure test the head to make sure it is not cracked. If it tests good I will have them do a valve job on it while it is off. This involves resurfacing the valves and the valve seats and brings the head back to a “like new” condition. They will also resurface the head, providing a smooth surface for the new head gasket.
If a valve is burned but the head gasket was still good the pressure test is unnecessary: the head just needs the valve job.
The pictures below show a 350 Chevrolet V-8 head and gaskets. This head gasket failed between two cylinders. The customer complained of lack of power along with pinging (spark knock) . When I checked the compression I found two adjacent cylinders with 60 pounds of compression. The other cylinders had 150 pounds of compression. Incidently, I had put a water pump on that vehicle about 3 months before I did this work!