View Full Version : Valve Lapping

08-01-2007, 11:12 PM
I recall a much heated debate about valve lapping back in the ctech days. The general idea was that lapping should not be done after the seats and valves have been ground.

Does anyone have any reference material on this?

08-02-2007, 05:20 AM
Just out of curiosity (and not to sound the newb) what is valve lapping?

08-02-2007, 12:59 PM
The process of taking a mild abrasive and applying it between the valve and the seat. Its then rotated to create a leakless seal between the two.

08-02-2007, 01:38 PM
Ah, I get it. :bigthumbu

08-02-2007, 01:59 PM
2 questions:

First, why is this necessary?
Second, why is it a bad/good thing?

Thanks in advance for sharing some knowledge :D

08-02-2007, 02:37 PM

It used to be a good idea, because it insured a good seal. As I understand it, it became unnecessary if your head was just redone by a good machine shop.

However, in my plane, I still have to pull the heads off and lap the valves as the seats get corroded by leaded fuel and moisture. Its not nearly as difficult as getting a toyota head off. I could do the whole process start to finish in four hours, for both heads.

Its now said to be bad because it impregnates the valve seats with the abrasive compound, shortening seat life.

Thats the 30k foot overview

08-02-2007, 02:41 PM
Ok, I understand now. Thanks Shmleff :bigthumbu

08-03-2007, 05:22 AM
Based on my admittedly limited knowledge, it seems you're presented a choice; better compression, or longer life. In your airplane, assuming you have the time and money to maintain the engine properly, I'd pick better compression. A little more power is a blessing on a hot, humid, low-pressure day.