Valve / Valve Seat Contact Width Questions

[Jocko_51_B3B]

 

I'm rebuilding my flathead so I had a machine shop resurface the valve seats. I also decided to replace all the valves. Out of curiosity I thought it would be a good idea to check the contact pattern and width of the new valves and the re-surfaced seats. I used a dry erase marker to mark each valve seat and then dropped the valves into their respective guides. I then pressed each valve down onto its seat and twisted the top of the valve back and forth five or six times. The shop manual calls for a 5/64 inch wide contact pattern (IOW a little bit more than 1/16), but my patterns are considerably larger - some are pretty close to 1/8 inch wide. It would seem to me that wider is not bad because it would allow for greater heat transfer out of the valve and into the seat, but Dodge must have had a reason for their 5/16 inch spec. I include photos of all twelve valves below showing the contact width patterns I saw and ask the opinions of the experts on this forum of whether the out of spec contact widths are a problem that needs fixing. By the way, I haven't lapped the valves and seats. The valves are straight out of the box. The one good thing (I suppose) is that the contact widths are pretty consistent all the way around all twelve valves....

[mechresto]

Your contact area is far too wide, also it appears that most are running off the top of the valve.....that alone will cause overheating and burning. 

The best advice I can give is to take the block back to the machine shop, they will recognize the error and redo the seat cutting if they're a decent shop.

Good luck 

[Dodgeb4ya]

The reason for a say .070" to .080" seat width is to prevent carbon build up on the seats. A narrow seat  contact chisels away possible carbon build up which will prevent valve burning and loss of compression.

The machine shop needed the valves so they could locate the seat contact area and width.

As mentioned those seats will transfer heat but are way too wide.

[Jocko_51_B3B]

Thanks for the solid advice. This block also has pitting in the #6 cylinder wall as well as on the top machined surface. So, decision time is fast approaching. Man, I hate to toss it away seeing as they don't make 'em anymore, but I'm not printing C-Notes in my basement either. I'll post my final decision once I make it. In the meantime, just for fun and to further my education, I'm going to check with several local machine shops to see what they'd charge me to fix these problems correctly. Thanks again, the advice I read on this forum is just super!

 

 

[Matt Wilson]

One other thing:  New out-of-the-box valves should receive a very light cut (skim cut) to make them true.  Valves often have a less-than-ideal surface finish on the sealing surface, so the skim cut addresses that.  Also, this surface is not always true relative to the stem, so good machine shop practice dictates the skim cut.  The cut should only remove a half-thousandth or so.  Then you should measure the edge margin (edge thickness) of the valve head afterward, to be sure it meets the required minimum.

[Fernando Mendes]

Hope this help.