Technical Tuesday June 3, 2014: Listen to the parts, Part 2

[J-Mech]

I know, I know.... It's Wednesday again. Give me credit, I wrote it Tuesday night.

Before I begin, I'd like to apologize for missing last week. I just didn't have time to write an article. I also want to thank Jimbob, and Sawdustdad, as I stole pics from their threads for this edition. (And the next one.)

Last time, we discussed how spark plugs can tell you a lot about the condition of your engine. This week, I'm going to show you how to read the condition of the head gasket, and the how well it is sealing on the deck and head surfaces. Remember, although the look of the components may change, this information is true of almost every engine.


Head Gasket:

If you already know that your head gasket is blown, because you can see it without head removal, or you hear it, then you probably expect to find something when you take the head off. But what about that engine you just got, and your just taking it apart to "look things over". What kinds of things should you look at? What are the tell-tale signs of future problems? Is there an issue now?

When you pull a head, your going to look at the surface of the head, and the block. The section on the block that the head gasket seats on is referred to as the "deck". If you have a "K" series Kohler, looking the sealing surface over is really pretty easy. The "KT's" are a little different, but only because they use a different gasket.

A good surface:
The sealing ring on the head gasket is the very small area that runs around the inside of the gasket. It is a thin ring, that when compressed, seals the combustion chamber. It is the area between the two arrows.

HGSS1.jpg

This surface, when doing it's job, should leave a "ring" all the way around both the deck, and the head surface. When looking at the deck or head, there should be a bare metal ring all the way around with no discolorations, or exiting carbon trails. The arrows point to this ring all the way around both the head and the deck on these pics.

DSS.jpgHSS.jpg

Get the idea?
Ok, now when a head gasket starts to blow out, that compression ring can no longer do it's job. Either the gasket has just gotten old, expanded and contracted to the point that it is wore out, or the head bolts have worked loose.... whatever the case may be, compression/combustion gasses start escaping the inside of the motor. When that happens, there is a carbon trail left from that escaping exhaust gas. When that happens, you get this.....

BHG.jpgBHG1.jpg

So, if you see this kind of black soot that looks like it was "seeping" out of the gasket surface, you know you did the right thing pulling the head. If left unchecked long enough, MAJOR head or deck failure can occur. Remember, the temp of that gas escaping is HOT! It will eventually work just like a blow-torch eroding the metal. Most likely from the head, as they are aluminum.

On these engines, when the head gasket starts to leak, it usually leaks on both the deck, and head side. However, that is not always the case. Look at both sides of the gasket, and at the deck and the head, as it can be leaking on only one side. Usually, this condition happens on larger motors that have a much larger sealing surface. Also, when there is a head gasket leak, as I said, metal can erode, or the head can become warped in the area of the leak. That is why, you should ALWAYS plane the head before re-installation. If the head isn't flat, in time, it WILL develop a leak in the exact same spot. It is a good idea to check the deck for damage as well, however a bad, or non-flat deck surface is rare. It is a difficult thing for a do-it-yourselfer to check the deck, as the best way is with a perfect straight edge and a feeler gauge. Here at my shop, I have a piece of metal with a machined perfect edge for checking a deck or a head. It's not something that you should worry about, as it is rare that this happens. It's just something that you should know so that if you have a continued head gasket problem, even though you planed the head, you may need to have the block checked. In all my years, I have only seen one, maybe two engines with a bad deck.

Stay tuned for the next edition on TT! (Even though, it seems to be landing on Wednesday.... LOL)