Valve Lapping: Attempt 2

[DieselBoy]

Anyone lapped their used valves? how well did it work?

just curious

[DieselBoy]

also, how many of you have replaced your valves on your 400exs?

and what cost did you encur for the valves?

[GPracer2500]

On my last build I replaced both intake valves. I had two complete (used) heads. Among the 4 exhaust valves I had two that were still serviceable. All four of the intakes were not servicable. Between the two heads I was able to piece together a set of valve springs that where still in spec.

I think I paid $66 for a pair of intakes.

[DieselBoy]

valves i'm still learning about. but what sort of signs will verify whether a valve is servicable and not servicable?

i've heard many cases it's the seating of the valves that will be the problem, new or used...

[GPracer2500]

I'm not an expert on evaluating valves--so take my comments with a grain of salt. ;) I prefer to confer with my machinist/builder about the condition of valves and valve seats so I'm sure everything is as it should be. A professional opinion gives a lot of piece of mind.

But I can tell you that measurement and visual inspection of the valve seat faces and valve stem tells you about their condition. Things like ridges, edges, uneveness, as well as the width and the location of the face on the valve (as in too high or too low) indicates if they need refacing or replacement. You probably know, but just in case--the valve seat face is the part of the valve that actually contacts the valve seat. The face on the valve seat needs to be confirmed too.

If you don't have a service manual then I'd get one. It will have guidlines and specifications for whether or not a valve is servicable or not. It will explain what to look for a lot better than I can...

If the valves are currently assembled in the head and you're not sure you want to dissasemble them, then you can check for leakage through the valves using a liquid. But that doesn't necessarily tell you that the valves are still within spec. Plus, if your rebuilding the engine then you'll want to replace the valve stem seals and that will mean removing the valves/springs.

New or used the valves should be lapped. The lapping basically smooths the face on the valve and seat so they match-up and seal tightly.

Hope that gives you at least some info you may have been missing. I'll tell you what, your second engine rebuilding experience is twice as easy and half as confusing as the first!

[dunny_mark]

I lapped my own valves using lapping compound and a drill. The valves had a slight leak before I lapped them, after, no leaks at all. Actually worked very well.