Heat Affected Valve Seat

[Vintagewrench]

hot.jpg

After stripping a couple of Volvo B20 heads for inspection before rebuilding, the colors visible on this intake valve seat came to light. The colors vary and it is blue, purple, and a light tannish color in different locations. It is the only seat on the head thats appears this way, and its service history is not known.

We want to rebuild this head, which is going on our '68 station wagon and are concerned that the heat may have affected the seat, port, and the combustion chamber enough to weaken it, cause it to crack, or cause other problems when pressed back in service?

[PRH]

If it mag tests good...... I’d use it.

[modok]

The oxide color being a record of the temperature really only works in a normal air environment.

The combustion chamber can develop all sorts of colors, especially with odd fuels or fuel additives.
If the colors do mean anything, or not, I don't really know.
What means more to me is wear. If it has worn rapidly then that's bad, if it hasn't...it's good, as far as the seat material.

Heat damage and warpage also go hand in hand.
Although it varies with different head designs, after becoming familiar with how they warp, you can gauge how much it has warped, and from that tell exactly how much HEAT it has suffered, especially true with iron. Although can be different with aluminum. With aluminum the metal can become harder or softer depending more on how rapidly it cooled, in addition to how hot it was.

[Vintagewrench]

Tempering_standards_used_in_blacksmithing.JPG

This chart shows the colors that steel turn to when heating it for tempering. Even though the head is cast iron, within reason I believe it can also be used as a guide for how hot the seat has been.

By comparing the blue and purple colors of the valve seat to the chart shows that it has been as hot as 590 degrees in spots which is the reason for wondering if it will cause trouble down the road?

I'm assuming the intake valve was stuck partially open and the cylinder was still firing and thats when the seat was subjected to the heat. None of the other valve seats on the head show any color.

[modok]

I understand what you think, and I'm saying it's silly.
What makes cast iron valve seats work in the first place?
isn't because it's hardened, it isn't hardened,
what HAPPENS to a valve seat in service is it gets coated in carbon and hammered....again and again, and that makes it work, and the carbon acts as a lubricant as well as keeping the hot gas from burning the carbon out of the metal.
It'll work, just as it did before.

[modok]

I think it developed the color while it wasn't running.
If it was running it would have worn the color off.

[MadBill]

I suggest lapping the valve into the affected seat just to see if it makes concentric contact. If it does, you could be pretty sure that the insert hadn't come loose at temperature and it would be safe to carry on as per a normal valve job. Seat inserts are normally a better material than cast iron heads and heat effects should not be an issue.

[ProPower engines]

hot.jpg


After stripping a couple of Volvo B20 heads for inspection before rebuilding, the colors visible on this intake valve seat came to light. The colors vary and it is blue, purple, and a light tannish color in different locations. It is the only seat on the head thats appears this way, and its service history is not known.

We want to rebuild this head, which is going on our '68 station wagon and are concerned that the heat may have affected the seat, port, and the combustion chamber enough to weaken it, cause it to crack, or cause other problems when pressed back in service?

You really only have 2 clear choices.
1 is to search out a new casting and start from scratch or
2 rebuild it as a good core if its not cracked. Give it the full meal deal and install new seats guides etc and build it again.

It looks like any other old hard to get head and till you fully clean and test it you will not really know what you have.
Those engines were real common in marine applications and they would get worked harder then a car and most times
it came down to how much effort was to be put into an older design to salvage it compared to locating a suitable core from a wrecker and just doing a basic rebuild with no seats installed.

[jake197000]

Use a concentriciticy gauge or die to check it.lapping will only tell you where on the valve the seat contact is and how wide it is.kind of.

[Tom Walker]

Looking at the picture makes me wonder if some of the heat from the exhaust seat made the intake seat warp or bow out some and create at situation where the intake valve was leaking hot combustion gases some.

[ProPower engines]

Wat too much over thinking here.
Guides wear and valve seats mush off to the side. The concentricity goes away and the seat and valve wear increases like every other cast head ever made.
It don't look like the intake seal was too bad but they always leak when they get beat up with time.
Clean it mag it pressure test it and if all is good at that point rebuild it completely and run it for another 40 years or so.

[Dave Koehler]

^^^ what ProPower said.^^^^

[Vintagewrench]

I think it developed the color while it wasn't running.
If it was running it would have worn the color off.

We think the intake valve was stuck open and the intake seat was overheated by the heat of combustion. In over 40-years of professionally rebuilding engines I've never seen a seat that was colored like this.

This is a hard to find Canadian-European 1974 big valve (44mm intake) carb head without valve seat inserts and after a clean-up and mag we will surface it, and install new bronze guides an EX seats.

These heads apparently were cast using the same foundry cores the normal 42mm intake valve heads and whenever you try to bore these intake seats for an insert there is a good chance the cutter will break thru. So the intake seats will only be resurfaced and narrowed.

The color of the seat is brighter in person and apparently has been as hot as 600 degrees judging by heat color charts. That is the reason why we are asking if this overheating may have harmed the cast iron intake seat and surrounding area and cause trouble later?

Thanks for all of your replies.