Fixing other shops work
Below are pictures from a set of heads that a customer brought in. He asked me to check over the heads, flow them and determine if the ports could be improved upon. They had been previously ported and had a fresh valve job and refaced valves. The original port work was not bad, but the machining was not good! I lapped the valves with very fine lapping compound to verify valve seat widths and locations. Half of the valves needed to be refaced as the valve face, sealing (seat) surface was not concentric with the valve stem (only 1/2 of the valve seat was making contact).
XXThese 4 valves came from the same set of heads.
The 4 valves pictured above show various valve seat widths and locations. (Light gray/Dull marking on valve face is actual area where the valve and valve seat are in contact. The valve on the left has a very wide seat, as you look at each valve to the right the seat keeps getting smaller in OD, until the last valve that is barely making contact. Not only would the valve on the right probably leak, it is restricting the intake port flow by reducing the cross section area of the throat and the excess valve diameter (shiny area) is restricting/blocking the flow path into the chamber.
XXBelow are close up photos of the above valves.
(Note: Valve seat mating surfaces should all have the same OD and widths)
Valve #1 from photo above | Valve #3 from photo above | Valve #4 from photo above |
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This valve was the best of the bunch, valve seat OD is good, although seat is very wide. | This valve seat is too small in OD for a performance application . | This valve seat is way too small, barely seating on the valve face. |
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.002" cut on head reveals trouble
After refacing all the valves and machining new valve seats (at the proper diameter and widths) the heads were placed on GHP's CBN surfacer to straighten the deck surface. The initial pass on GHP's machine took off just .002". The marks you see (shiny/newly machined) are the high spots on the head that were just cut down. The head must of been surfaced on an old or worn machine. You can clearly see that when the other shops cutter had a larger cutting surface, it pushed up on the worn cutter. When cutting over the chamber (less cutting surface) the worn cutter head moved downward giving the deck a wavy/not flat surface.
Luckily these heads were fixable. Some heads require new valve seats installed to correct past "rebuilding" goof-ups. Shops the don't maintain their machines, won't care about the quality of the work their doing for you either. Isn't it better to spend a few dollars in shipping the heads to GHP and be assured it will be done right the first time? GHP takes pride in their machines, tooling and workmanship.
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