........where you have that done makes a difference.

If...... The performance of the motor matters to you.

Let me back up a bit here........

I had sold a roller cam to a customer a few years ago..... Car ran what it should.....several races are won...... But as things usually go....... The desire for better ET's inevitably rears its head.
The original cam was a basic bracket type cam, easy on parts, reliable.
The new cam is a big step up in ramp speed, but not much of a change to the overall theme of the cam(seat timing, lsa, etc).
It should have made a definite improvement in performance...... Not a huge difference...... But a definitely noticeable difference.
Well....... Whatever difference there might have been, it was much less than I would have expected. Only now we're wearing out springs faster than before.

I don't recall if that was run for one or two seasons, but eventually there was a major engine failure....... And now a new bottom needs to be built.
Since there's a bunch of bent valves, the heads now need to be gone through as well.

I get a call about whether it would be worth having the heads come to me of if they could just be gone through locally.
I put forth the proposition that if the local shop he plans on using is known for their high quality head porting and cylinder head prep they should be fine, but if not...... It's probably worth the trip here.

When I get them here and apart I can tell right away they don't have the valve job that was done on them when they left the original porting shop.
I make a call and learn that, no..... That isn't the valve job they came from the porting shop with. They got freshened once before...... Done by the local shop...... Just prior to the new cam going in the motor.
The light bulb came on at that moment as to why(more than likely) the new cam didn't show any gains.

If the first valve job is done so the contact area between the valve and the seat is such that the area of interface is way out on the edge of the valve....... Then the next valve job is done with a 3 angle cutter that's set up to cut to the very inside of the valve........ Then you're going to have to sink the valve until the seat angle is reestablished in its new location. This is never the hot ticket for flow.
Even if the valve seat concentricity is perfect, and the valve job is functionally 100%...... This will almost always result in less flow, and less power.

Basically........ It looks like this:

There are two ways to go about correcting this situation .
1- replace the seats
2- install a bigger valve so you can get out onto new material.

Well.....3...... Just recut the seat and blend away the ridge on top, which will get you back some of what you lost.

Depending on what size valves are already in the heads, and how far the current valves are sunk will usually steer the decision.

In this case, since the heads still had the std valve size in them, it was a better option to just install bigger valves(in part since new valves were needed anyway).

I recut the seats for 2.055 valves, up from the std 2.02, and placed the contact point at the outer edge of the valve........ Added a bottom cut, and reblended the valve job into the bowl.

This is what it looked like after recutting the seat, but prior to reblending the bowl:

So........ What difference does it make???

Lift---before/after---difference
.100---58.5/67.2-----8.7
.200--123.6/146.4--22.8
.300--184.0/206.8--22.8
.400--235.6/246.8--11.2
.500--262.5/273.7--11.2
.550--273.0/275.6--2.6
.600--273.0/276.7--3.7
.650--268.1/277.5--9.4
.700--270.0/278.6--8.6

Keep in mind those gains are with a zero increase in runner volume or added cross section.

Another "nice" touch with the previous freshening was the way in which the valves were cleaned.
They were cleaned in what's known as a "tumbler", which is just what it sounds like.
Parts are put into the machines basket, which also has some sort of metal shot/media, and the basket rotates around and around, and the interaction of the media and parts removes the deposits from the parts.
The problem occurs when you put several valves in the basket at one time, and they bang and crash into each other, leaving little nicks and stress risers over the entire surface of the valve.

Tumblers are fine for cleaning certain things...... Valves aren't one of them IMO.

The exhaust seats weren't sunken as badly, so the std valve size was retained there.
Careful blending of the top angle into the chamber, and reblending the bowl after the seats were cut resulted in this:

Lift---before/after
.100---48.8/48.8
.200---98.8/99.3
.300--140.3/155.4
.400--172.5/193.9
.500--190.0/209.1
.550--200.0/212.7
.600--204.9/213.9
.650--208.6/215.9
.700--209.8/215.9

Dwayne how often do you recommend refreshing the heads?
A number of runs would be helpful to me because some YEARS I haven't run many races do to work.

I always try to pick the best shops for my work and I figure that is who should refresh them or I would've picked a different shop in the first place!

Thanks, Don

Interesting stuff, thank you for sharing the pictures and details.

+1!

You are one of the old timers here as you have been sharing your knowledge from likely the beginning of MOPARTS.I know so many people that you have touched their heads which in turn touched their lives.
Thanks!
I just has to bring my heads back to the machine shop as the seats were good,but recently tigged the o-rings and had the heads milled true.They volunteered to touch the seats,,,,,and messed them up.Only 40 thou was touching the seat up high.Thrashing to make carlisle.

Good info Thanks Dwayne

Very nice upgrade. Would like to see the performance difference now with the heads corrected.

Don, with a motor combo like yours, the heads really should have no problem lasting as long as your freshen up schedule for the short block.
If I had to put a number on it.......somewhere around 500 runs, and then you're really only making sure the springs aren't going away.
But basically, just have them gone through when you're doing the bottom end.

I see stuff like this in the shop pretty often, and most of the time I think how it would be a "fun" dyno session to "before and after" test something like this.
As is often the case, the heads aren't the only thing that gets done/changed when the motor comes apart, so how much difference the work on the heads themselves makes isn't easily determined.

As in the case with this set of heads, it's a new bottom end combo, with more cubes, so not really apples to apples.

this kind of info is the reason that when my trick flow's need a little pep talk that you are the guy I want to have do them, the guy that did my 408 was good at porting ,valve job's and such as he fixed up the mess that I had with the 408 but he is not doing much anymore,so this post has piqued my interest.

Thanks for the. Post, Dwayne. It points out one area to look at for why my motor doesn't put out as much steam as it used to.

Thanks for sharing Dwayne. I learn a lot from you.

Thanks for sharing

Thanks for posting Dwayne !!!

Great info and I would concur, not all shops are the created equal for sure. I just sent my stuff to Slawko to get touched up and look for any improvements that can be had. The heads off the heads up are get sent back there every year for improvements or just a freshen up.

Thanks Dewayne. Very useful info. I to appreciate your input and knowledge. Jim

An absolute asset, we are lucky to have you Dwayne.

Thanks for the props guys!!!

I'm just trying to do my part to keep it interesting.

My phone has a hard time with real close up pics, so I can't capture a decent image of the valve stem with all the little nicks and dings in it from being tumbled with other valves, but you can see in this pic how the banging around raised a lip on the outer edge of the valve.
I would think they would have had to be in the tumbler for a while to get this to happen.
It was all the way around every valve.
They were Manley valves, so no........ They didn't come like that.