Wilsons Sandbox

Hey all, I think I might have overrun my "healthy" period for valve spacing. Last time I ran my A12, I felt smtg was ever so slightly different. A little less power than what I'm used to maybe. It's hard to define, but there was stmg. So I've got to quetsions abotu valve spacing: 1 - does the feel of the engine change if maintenance is overdue (long overdue maybe, I'll know when I opne it up tonight)? 2 - What causes the spacing between the shim and the cam to reduce over time and usage? I know the spacing narrows, but I don't know why! Thanks! JP Granger [Non-text portions of this message have been removed]

Hey all, I think I might have overrun my "healthy" period for valve spacing. Last time I ran my A12, I felt smtg was ever so slightly different. A little less power than what I'm used to maybe. It's hard to define, but there was stmg. So I've got to quetsions abotu valve spacing: 1 - does the feel of the engine change if maintenance is overdue (long overdue maybe, I'll know when I opne it up tonight)? 2 - What causes the spacing between the shim and the cam to reduce over time and usage? I know the spacing narrows, but I don't know why! Thanks! JP Granger [Non-text portions of this message have been removed]

Some engines increase valve clearance (the clearance between the tip of the valve stem and the camshaft or rocker arm or push rod) while some decrease clearance as a result of operation. IME most cam and bucket overhead cam engines tend to see a decrease in valve clearance while it is 50/50 with push rod (cam in block) engines. Valve clearance changes because of wear in some aspect of the valve train. The KLR seems to decrease clearance and this will be because of valve seat recession. In other words, the valve seat is wearing or eroding such that the valve seats deeper into the head as time goes on. As the valve seats deeper into the head the tip of the stem moves toward the camshaft which decreases clearance between the tip of the valve stem and the camshaft (the fact that the valve retainer and shim are in there is incidental. Typically there is much more wear to the valve seat than to the face (sealing surface) of the valve. In the 1970's we saw huge problems with valve recession due to valve seat wear. This was because of the low quality seat material which was no longer being lubricated by lead from the fuel. One Ford V8 which comes to mind had over 1/4" of valve recession which moved the valves upward until the hydraulic lifters could no longer adjust and several valves remained partially open. Some other engines experience more wear on the camshaft + lifter + push rod + rocker arm than they do valve recession and so these tend to see an increase in valve clearance. These engines tend to get nosier valves as time goes on while engines like KLRs which decrease valve clearance tend to burn valves if neglected long enough. HIH Norm P.S. This brings a question to mind: Has anyone experienced a burned valve? In the time I've been reading from this list no one has mentioned one..... Just wondering.

If anyone has a stock seat they want to get rid of please drop me an email.