Join Date: Nov 2001
Location: Huntertown, Indiana
New valves in not-new heads
Bit of history here. Back some 20 years ago, I bought a set of rebuilt heads from eBay. They cam assembled, and everything looked really good. I bolted them to my engine, and thought nothing of it. Since then I have probably 15-16k miles on these heads. No issues. These are 1971 351-2V heads (not my originals obviously).
Fast forward to today. I am rebuilding these heads with all new components - new single piece stainless valves with single groove locks, new retainers, and new springs. I have taken these heads apart to find a) the guides have been replaced, and they are in great shape, and b) the valve seats all look great. I have checked the install height for the springs, and I am finding that all the install heights are at 1.795-1.800", exactly where I want them, and very consistent, meaning (hopefully) that all seats were ground to the same depth. My plan was to blue the valves, and if minor lapping was needed, lap them in, and leave it at that.
Now, someone has asked me why I dont have the heads machined and the valves lightly ground to ensure a quality seal. My response is, because as far as I can see they don't need it. My position is that if the blue and lapping proves to show a good seal, that I dont need to worry about machining the seats, that the valves will seal just fine. Since the guides are nice and tight, and all the valves were in like new condition (save some carbon build up), nothing points me towards thinking I need to do any machine work.
But I kick the question to a larger audience... in this scenario, is lapping the valves in a good option (meaning a reasonable life span of normal performance)? This is a street machine with under 5000 miles annually. No racing, just spirited stupid driving.