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Valve Question

  • Thread starter Thread starter almarconi
  • Start date Start date
A

almarconi

Guest
In the process of cleaning up and measuring an 8 valve head.

If the valve margin is out of spec (too small) on a particular valve, and the valve is replaced with one that is within spec, does the valve seat need to be re cut? Will lapping the valve be sufficient?


There are many measurements to take and I am just trying to get a feel for which ones are critical and which one you have some leeway with. For example, if the installed valve height and seat width are in spec but the valve margin is out of spec would this be a passable situation.

I suppose the most important test is once the valves are assembled that the valves create a positive seal and the combustion chamber does not leak.

Attached is a labeled valve diagram
 
I would lap the valve and inspect the seating area. If it appears to be sufficient, leave it at that.

.
 
Also probably worth removing the stem seal and checking the valve in the guide for excesive wear, you will be putting new stem seals?
 
Bearing blue is a good way to test after the lapping that STEVE just mentioned. Just the lightest dab on one spot on the seat contact area of the valve then insert it and spin it arround and you should have one thin line all the way round the valve face.
 
Also probably worth removing the stem seal and checking the valve in the guide for excesive wear, you will be putting new stem seals?
Click to expand...

Yes new seals. I've got the head torn down completely, been soaking in the parts washer for the past week to get all the crud off it. I've got lots of measuring to do, valve to guide clearance is at the top of the list. Will replace components that are not in spec.
 
Bearing blue is a good way to test after the lapping that STEVE just mentioned. Just the lightest dab on one spot on the seat contact area of the valve then insert it and spin it arround and you should have one thin line all the way round the valve face.
Click to expand...

I've got clover brand lapping compound and prussian blue on my shopping list. Lots of cleaning and measuring before I'm ready to start reassembly.
 
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