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Old 06-17-2014, 03:57 AM
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J-Mech J-Mech is offline
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Default Technical Tuesday June 17, 2014: Listen to the parts, Part 3

I just can't seem to find time to do these weekly. Sorry guys.

I also want to say again, that not all the pictures I use are mine. If you recognize a pic as one you uploaded to the site, thanks! Because I stole it!

In the last two in this series I discussed how you can "listen" to what the parts of your engine are telling you about it's condition. We discussed spark plus, then head gaskets. Now, lets look at valves.

After head removal it's a great time to check your valves. You can do a visual check by just the color, and by rolling the engine over and looking at the valve seat, and the seat contact point on the valve, which is called the valve face.

Visual check:

On a motor with any kind of "run time" on it, the valves should be different colors. This is because the intake valve runs quite a bit cooler than the exhaust valve. The reason is simple. The intake valve has cool outside air flowing across it at all times, whereas the exhaust valve has very hot, just burned gas flowing across it. In a good running engine, that is well tuned and not been overloaded, or overheated, the intake should be slightly black, while the exhaust should be a tannish grey. Now, understand that if you accidently spill oil, gas or in the case of a liquid cooled engine, antifreeze on the valves during disassembly, that may change the color. But, if you know what your looking for, it won't change it so much that you can't tell. This is about the best looking engine I had here in the shop as an almost perfect "text book" example.


Now, if the motor has been running rich, or is burning oil, or even if it has low compression, it starts to change cylinder temps which in turn changes the color of the valves. The exhaust will no longer be grey, it will turn black just like the intake. Then carbon can also start to build up on both the valves, leaving a black hard crust on them along with the top of the piston and the head. Tell tale signs of oil consumption will be the presence of heavy carbon. If it's just a rich fuel condition, the hard carbon should be minimal, but it will be black with soot. If it is running lean, the intake valve can start to turn white-ish grey and the exhaust can turn almost pure white.

too lean.jpgrich, oil consumption 2.jpg

Valve Seats/ Valve Margin:

While your in there, go ahead and roll the engine over and open the valves one at a time and take a look at the seat and the valve face. The face is the area of the valve head that contacts the seat. It's the "angled" part of the valve.
If the valve is rotating properly, and a good seal is present, the intake valve face and seat should be shiny for the entire circumference of both. No black spots, cracks, or carbon build up. The exhaust valve can be this way also, but usually as a result of the heat, and just normal soot, it isn't unusual for the seat and face to be somewhat darker than the intake valve. As long as there is good contact area is smooth, with no pits, or dark "spots" in it, I don't worry too much about it. But, if there is pitting, erosion, or if you can see a nice shiny area part way around the circumference of the seat or valve face, then there is a problem and a valve job is in order. (I won't go into the specifics of the problem or the repair procedure in this article.)

In this example the intake valve on the right was seating well. Note the shiny area on the valve face. The exhaust valve on the left, however, shows signs of pitting on the face and no overall seal to the seat.

valve face margin.jpg

In this pic, you can see both the intake and exhaust valve seats have a "shiny" look to them where both valves contacted them.


If you find signs of bad valves, or if you find that your engine is running lean, don't wait to fix it. The result can be catastrophic to your engine, and your wallet!!


When it comes to valves, this information only scratches the surface. There is so much more to look at in terms of wear and condition. But, if you are able to recognize the beginning signs, then the other conditions are more obvious. Plus, most do-it-your-selfers aren't going to have the equipment to do a valve job, and a good engine machinist will know what needs done to correct the problem, and will inform you of such.

I get a lot of feedback on these articles, and I want you to know, I enjoy doing them. Drop me a line (PM, text, e-mail) if there is a topic you'd like to see discussed here on Technical Tuesday. I have no idea what I'm going to do the next article on.
"They say money doesn't buy happiness....... but it does buy Cub Cadets, and Cub Cadets make me VERY happy!"

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