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]
looking for a stock seat
-
- Posts: 31
- Joined: Tue Jan 27, 2004 8:13 pm
valve spacing
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]
-
- Posts: 321
- Joined: Sun Jun 27, 2004 10:05 am
valve spacing
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.
-
- Posts: 204
- Joined: Sat Feb 14, 2004 11:26 pm
looking for a stock seat
If anyone has a stock seat they want to get rid of please drop me an
email.
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