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601 Posts
hi all
just wanted to quiz you on how this is done? if it is by measuring the packed valve spring length - can anyone describe the process for us?


You can measure it that way if you know the original working
height of the spring. Of course you know that valve seat
recession is the process where the valve actual pounds the
valve seat into the head. On old iron heads it was excessive
seat wear caused by the use of the wrong fuel. Lead vs no
leaded fuel. This of course proved to be a big myth with a
dash of truth in it like most myths.

The big myth part was that lead was needed in order to lube
the valve and seat. However, fuel is backward complyant,
as it has to meet guideline for lubercation, amount of acid
levels and so forth. So in the end lead was not need to
combat valve seat recession.

Now for the dash of truth, it all has to do with the iron itself
in most cases. The iron needs to have a high nickle content.
Most American made iron has this, so do the Japanese blends
of various iron compounds. British iron it depens on the decade
it was made. Some of the older cars do suffer from valve
set recession, but not all, it varies from foundary to foundary.
Something like a valve seat insert would most likely have a higher
nickle content. So this is why most British bikes do not suffer
from the problem.

What does suffer, I know of one good example, Mexico. The
iron they produce is just about scrap metal. Some of the lowest
nickle levels out there. That is way hot rodders pass by Chevy
blocks made in Mexico.

The other cause of valve seat recession is right back to fuel
again, however, it has nothing to do with lead. Running something
like LPG or Propane as the main fuel can also lead to this

So back to the question, valve seat recession will take up the
clearance of the valve adjuster. And will show up as a longer
spring length in the end. However, it should be noted for fullness
of this discussion that there is another type of valve problem
that will give the same effects above and will also add another
effect to the mix. The valve will also kiss the pistion.

The problem is called "necking". Major causes are too high of
a valve spring pressure, or metal failure in the stem of the valve.
The result is a streching of the base of the valve stem at the
joint of the stem to the tulip of the valve. Easy to check just
compair valves to each other. Usually only one valve will become
necked at a time.

I hope this is the answer you were wanting,


796 Posts
I had this same question. Not sure if you can tell from the pics but I tried to show what may be seat wear. I have no clue. If it is too worn what is the fix?


Super Moderator
14,020 Posts
Kev - the bottom cylinder looks to be unevenly cut, maybe enough to warrant replacing the head.

You can get a set of hardened seats and have a machinist replace them, then cut them all down to match new valves with new guides. you are going this far, go all the way (on the head, at least).
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