Questions and Answers
Valve Seat Leakage
Q. Dear Sir, I was browsing through the Auto Repair Guide and came across your question answer section. I found it very useful to understand the details of the problems. I have a query regarding the cylinder head of 4-stroke engine. If you don't mind, please help me out in this query.
I need information regarding the leakage through the valve seat and intake and exhaust valves of a engine. The question is how to check the leakage? What is the correct method and principle to check the leakage and what is acceptance criteria for the leakage as per international standards? (i.e. allowable rate of leak volume).
Thank you,
SachinA. There should be no leakage at all through the valve seats. Zero. Ziltch. Nada. Technicians have a few ways to test this. One is to hook up compressed air to the cylinders and see if there is any air coming either through the exhaust or intake. Any air coming through indicates a valve not sealing completely.
The other method requires the head to be off the car. The head is placed with the combustion chamber facing up. The area around the valves is filled with carburetor cleaner and the stem side is monitored to see if there is any leakage.
Another method is to lap the valves and see if there are any gaps in the seating surface of the valve or the valve seat.
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