Re: Valve jobs every few 1000 miles?

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In Reply to: Re: Valve jobs every few 1000 miles? posted by Roger Karlsson on March 16, 2002 at 04:35:30:


Hi Karl,

But today's fuel has no lead of course- and many folks find no trouble with valve seat recession. The low speeds, the low tempertures, the low valve seating pressures must be the help.

Reasons that valve jobs were so often needed in the old days (there may be more if you can add in)

-Fuel in US was half kerosene, and kerosene builds up carbon deposits because it is too non-volatile to fully vaporize.

-Head had to come off to remedy carbon knock. Made sense to lap in the valves at that time since they'd be needing it soon enough anyway

-Valves were cast iron heads. While factory work left the valve seat with a radius profile for a hairline seat, when valves were lapped in the usual method was with cutting compound and the valve seat was made full contact. Hence, low seating pressure and greater opportuninty for a flying bit of carbon to unseat the valve, and that lead to leaking and valve seat erosion.

Can anyone think of other reasons for frequent valve jobs. Not every driver had this much trouble. A well tuned car fed clean air and oil and good gasoline probably went double or triple the miles before needing a valve job. Especially if the job was done with interference angles precision ground.

Regards, Reid