Valve Face Condition

[Matt Wilson]

Getting closer to assembling my 251-turned-265 and I was cleaning the valves this evening in preparation for bagging them to keep dust off till I install them.  I noticed one had a rust patch on the valve face.  The photo is after I polished on it with some scotchbrite.  If you zoom in, you can see It well, but it looks a little worse in the pic than in real life, I think.  I worked on it for a few minutes and this was the best I could do without going to something more abrasive, which I'm hesitant to do.

 

I think I know the answer, but I feel like I should ask....is this anything to worry about?  It looks like it's right where the valve will contact the seat.  My first thought was to take it to a machine shop to have them grind it a bit, but the edge thickness of the valve head (the margin) is already right at the minimum allowed per one of my manuals, so any grinding will no doubt violate the minimum.  I suppose I could chuck it up in my lathe and do some hand polishing with some 400-grit or 600-grit sandpaper, but not sure how well that will work.

 

A few of the other valves have tiny dings on their faces (they were all in the same plastic bag for years and no doubt bumped into each other as they got moved from one spot in my garage to another).  All those valves are right at the minimum for edge margin too.

 

I wonder if lapping would clean them up.  I don't really care for the idea of lapping, but I'd consider it to avoid buying new valves and getting them ground to true them up.

 

Thoughts?

[MBF]

I'd lap them (always do) and look at the pattern on the face when you're done just to make sure the seat and valve face are going to seat properly and are making contact around the entire circumference of the face.  I think its referenced in the service manual what the contact area is supposed to look like.

[47 dodge 1.5 ton]

When it comes to valves and seats, I like to remove the least amount of material necessary even if it cost time. I would lap and verify if the rust is removed, re-grind if needed.   Please explain your thoughts on not lapping? 

[Matt Wilson]

23 minutes ago, 47 dodge 1.5 ton said:

When it comes to valves and seats, I like to remove the least amount of material necessary even if it cost time. I would lap and verify if the rust is removed, re-grind if needed.   Please explain your thoughts on not lapping? 

The main reason I am hesitant to lap is because, when my machinist was first doing the valve and seat work (more than four years ago), I mentioned something about lapping to him, and he said that's really not the preferred way to do things anymore.  He said modern equipment and techniques achieve significantly better results than lapping.  He's an old timer, but he has kept up with changes in technology.

 

Having said that, lapping has served many people very well for many years, so it's probably fine.

 

I suppose another reason is that I'm concerned about lapping is that the seat comtact widths for all the valves are pefect right now, and if I lap enough to remove the pitting on this valve (and nicks and dents on the other valves), I'm concerned about accidentally lapping too much of the seat material away so that I exceed the allowable contact width specified in my manual.

 

In any case, I don't see anyone saying that this pitting and the nicks and dents are ok to leave (I doubt they are).

[kencombs]

I'd remove the rust with chemicals, not abrasives.  Evap-O-Rust works and is safe to use.  Once the rust is gone you can evaluate the pitting.  I suspect you will have none.  Nicks/dents are another matter and it depends if they are actually in the seating area, if not no problem leaving them.   This is where a light lap can positively identify whether or not they need attention

[John-T-53]

Matt - If you have rust pits and dings/nicks on the sealing face, have them all retouched in a valve grinding machine. Don't mess around. If the rust pits lead to removing too much material (looking at the photo, probably will not), just replace that one valve. The sealing surface has to be absolutely perfect. 

 

If the seats have been cut with a seat and guide machine, then lap the valves before assembly to check sealing contact area. If they have been cut with a stone (hand held grinder), no need to lap. 

[RobertKB]

No one else will say it, so I will. If you are this concerned about the rust, dents, and nicks, why don’t you just replace with new valves. It sounds like the old valves have been resurfaced maybe more than once and the edge thickness is already minimal. New valves are not that expensive and the peace of mind they would offer would certainly be worth it. 

Edited December 8, 2021 by RobertKB

[Matt Wilson]

3 hours ago, kencombs said:

I'd remove the rust with chemicals, not abrasives.  Evap-O-Rust works and is safe to use.  Once the rust is gone you can evaluate the pitting.  I suspect you will have none.  Nicks/dents are another matter and it depends if they are actually in the seating area, if not no problem leaving them.   This is where a light lap can positively identify whether or not they need attention

I happen to have some Evaporust, so I'll try that on the one rusted valve.

 

Some of the valves have nicks in the region where they contact the seat, so those will need attention.  Actually, after looking closer at the valves this morning, I see that nearly all of them have tiny nicks and dings on the faces (usually just two or three) and I think most of those are in the region where they contact the faces, but I'll check more closely to verify.  If it turns out to be too many, then that will be more than I want to spend to replace them and have them ground true when these are otherwise new, so I'll probably try a light lapping to get rid of the nicks. 

 

If any pits remain after soaking the one valve in Evaporust, then I'll try a light lap of that valve. 

 

If any valves don't clean up adequately after lapping, then I'll break down and buy new ones to replace only those that don't clean up, and I'll have those ground true.

 

I've never lapped valves so it'll be another learning experience. 

[Matt Wilson]

2 hours ago, John-T-53 said:

Matt - If you have rust pits and dings/nicks on the sealing face, have them all retouched in a valve grinding machine. Don't mess around. If the rust pits lead to removing too much material (looking at the photo, probably will not), just replace that one valve. The sealing surface has to be absolutely perfect. 

 

If the seats have been cut with a seat and guide machine, then lap the valves before assembly to check sealing contact area. If they have been cut with a stone (hand held grinder), no need to lap. 

I don't think there's any room to grind without violating the minimum edge margin.  I'm hoping lapping will be enough on most, but I suspect I'll end up replacing the pitted one.

[Matt Wilson]

1 hour ago, RobertKB said:

No one else will say it, so I will. If you are this concerned about the rust, dents, and nicks, why don’t you just replace with new valves. It sounds like the old valves have been resurfaced maybe more than once and the edge thickness is already minimal. New valves are not that expensive and the peace of mind they would offer would certainly be worth it. 

Actually these were new valves, made of 21-4N alloy, which is supposed to be very good stuff.  They are what Vintage Power Wagons sells.  I had them ground because it is not uncommon for the faces of new valves to run non-concentric with the valve stem, or to be slightly out of round.  Two machine shops have advised me to have new valves lightly ground to correct this.

 

I'm leaning toward trying the lapping and I'll check for proper sealing by filling the ports with solvent and seeing if the solvent leaks past the closed valves (under spring pressure).  If no leaks for several minutes or an hour, then they should be good, I think.  I may change my mind, though, and buy new ones.  Still thinking about it.  Gotta do some research on valve lapping to see if it seems risky or if it requires a particular level of skill or practice.

[John-T-53]

Evaporust only removed the rust, not the pits. The pits (voids) are what remains in the metal when the rust is gone. 

 

Valves are ground and reused all the time. Since these are already new valves you won't be hurting them but touching them up on a grinder. 

 

Keep in mind that even a human hair will prevent a valve from sealing. 

[Matt Wilson]

3 hours ago, John-T-53 said:

Evaporust only removed the rust, not the pits. The pits (voids) are what remains in the metal when the rust is gone. 

 

Valves are ground and reused all the time. Since these are already new valves you won't be hurting them but touching them up on a grinder. 

 

Keep in mind that even a human hair will prevent a valve from sealing. 

Thanks, John.  I figure it won't hurt to try the Evaporust, but I suspect I'll still have pits.

 

Maybe I can get a shop to just kiss the faces and not go below the minimum edge margin.

[Matt Wilson]

I took a closer look at the valves tonight, under greater magnification, held up next to my Starrett 6" scale as I rotated the valve to see the entire circumference.  Most of them look like they still have a little meat left - maybe enough to allow a cleanup by grinding.  So now I'm leaning toward taking them to the machinist to see if he can take off just a slight amount to clean them up.

[JBNeal]

I recall reading in an old machine rebuild book about lapping valves by hand, and using progressive grits, like sandpaper on bodywork, to achieve the best results.  The reason given was to finish the valve and seat so that they wear into each other to remove the highest points first, achieving improved sealing.  It's a slow tedious process but after a few I could actually feel and hear when the valve and seal were optimized.