Honda HR17, HR173, HR194, HR195PXA, HR195PDA JOB AID FAILURE ANALYSIS

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This job aid was extracted from the Online University.

INTRODUCTION

When we’re trying to determine the cause of a failure, we have to treat the product and the process just like any good detective would. We have to have a plan. We have to be systematic. And we have to be careful that we do not destroy any delicate evidence.

In this job aid we’re going to look at a plan that will help you get to the right answer quicker, and we’re going to look at a couple of common situations.

• First we ask questions so that we can understand the situation.

• Then we make observations—things that you can and should do with the customer standing right there.

• Third, we examine the evidence very carefully.

JOB AID

FAILURE ANALYSIS

• And finally, we develop conclusions.

We do these four steps. And we do them in this order, every time.

ASK QUESTIONS

We start with the questions. When a customer says it’s not working, and maybe even gives you his opinion about what happened, we need to get all the facts.

• How was the engine being used just before it failed?

• Were there any noises at the time of the failure?

• Did you attempt to restart the engine? If you did, what happened?

• And — when was it last serviced?

You probably ask most of these questions when you’re writing up a repair order. But now you might want more detail.

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MAKE OBSERVATIONS

This is where the detective work really begins. You start to look for clues. These are all quick checks that you should do with the customer right there—and you don’t need anything more than a spark plug wrench.

First, we examine the outside of the engine.

• Is the cooling air inlet obstructed?

• Are the cooling fins clogged?

• Is there a hole in the crankcase?

• Are there signs of oil leaks? This is all very quick and can be done in about the time it

takes to talk about it.

Next, check the oil.

• How much oil is there?

• What does it look like—fresh and clean, or old and dirty. What you’re looking for may not be as obvious as you might

think. Certainly you need to see if the oil level on the stick is within normal operating range. All engines consume some oil and air cooled engines typically use more than water cooled engines.

There’s always the possibility that the owner never checked or added oil to the engine. You will have to drain the oil to fully understand its condition.

If the oil is black and a lot thicker than fresh oil, you may be dealing with an engine that’s never really had an oil change. The owner added some, but never drained the old oil. Or you may be dealing with an engine that has been badly overheated.

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If you see sparkling metal particles in the oil, save them. They may be a clue to the failure. You’ll want to check to see if they are attracted by a magnet.

Fresh, clean oil may not be entirely good news. It may have been added after the failure. Too late to do any good. If it was added after the failure, it will float on top of the old, burned oil.

If you see fresh, clean oil on the dipstick, make a mental note to watch the color of the oil carefully when you drain the engine.

Next, take a close look at the air filter.

• Are the elements clogged or damaged?

• Do you see any dirt trails around the seals and down the carburetor throat indicating that dirt was bypassing the filter?

• Is the oil breather connected to the air cleaner?

A “yes” answer to any of these is an important clue. If dirt gets into the engine through damaged filter elements, a damaged or incorrectly installed seal, or a disconnected oil breather, it’s like running sandpaper on the engine parts. Abrasive damage will occur to the cylinder, piston, and bearing surfaces.

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Dirt can be a problem even if it doesn’t get into the engine. If it clogs the air cleaner elements, the fuel mixture becomes too rich and can foul the spark plug, wash the oil from the cylinder walls, and dilute the oil. Sometimes it will dilute the oil so much that the engine seizes from lubrication failure.

Next, check out the carburetor. You want to make sure that it’s secure to the manifold. See if the governor linkage shows signs of damage or tampering. Is the carburetor throat clean?

If the carburetor is loose, it may offer another path for dirt to enter the engine. At the very least it will allow additional unfiltered air into the engine, making the mixture leaner. Since a too-lean mixture raises the temperature of combustion, it can cause overheating, detonation, and subsequent failure.

If the governor linkage is out of spec, either because its been damaged or because someone has tampered with it, you can suspect overspeed damage. And there’s another problem to check for: black oil deposits indicate excessive blowby through the breather.

The last step in your quick check is to examine the spark plug.

• Is it fouled with oil or soot?

• Are there signs of overheating or detonation?

• Is there mechanical damage? Just like the eyes are the window of the soul, the spark plug

is your window into the combustion chamber.

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EXAMINE THE EVIDENCE

Now it’s time to get inside the engine. Before you even turn a bolt, remind yourself to be careful so that you don’t destroy any evidence.

Normally, when you’re tearing down an engine, you take the parts straight to the parts washer. If you do that, valuable information literally goes down the drain. Try to keep everything just as it was when the engine failed.

Now examine the oil and engine very carefully. First, we drain the oil into a clean container. Look at the oil as

it drains; it can tell you a lot. If it starts our black and thick and then turns cleaner, it’s likely

that fresh oil was added after the engine failed.

Often it’s a good idea to strain the oil through some sort of filter; you can use anything from cheesecloth to a clean shop towel.

Look for things that shouldn’t be there;

• small metal flakes

• gasoline smell

• condensation in the oil

Any of these are clues to the probable cause of engine failure.

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Once you’ve drained and examined the oil, start disassembling the engine. Examine each piece as you remove it.

You’re looking for things like broken pieces in the crankcase, cylinder, and rocker box when you open them.

Look at the oil on the parts for signs of coking or overheating.

You’ll usually need to clean the oil from the components for a closer look. Do it carefully; use clean solvent and a soft paintbrush to remove the oil—not a rag or stiff parts brush.

Remember, what you’re trying to do is remove the oil and not the evidence.

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DEVELOP CONCLUSIONS

DIRT INGESTION

There are only a few causes for failure of a Honda engine. The most common are oil starvation and dirt ingestion or both.

For instance, dirt ingestion typically leads to high oil consumption which, in turn, can lead to oil starvation and engine failure.

Dirt ingestion is usually very obvious—think of constantly blasting an abrasive on all of the wear surfaces of the engine. Instead of the polished, burnished finish, engine components will have a satin finish.

This is what it looks like when the engine fails due to dirt ingestion. Dirt makes an engine old very fast. Look for wear on the cylinder walls, valve stems, and bearings.

You might also see dirt tracks down the carburetor and through the intake. Keep in mind that, although the carburetor is the usual entry point, the dirt may have come in through the crankcase breather.

The point is that we don’t overlook any suspect.

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OIL STARVATION

The first phase of oil starvation is aluminum rod material transferring to the crank. Rod bearing material may seize to the crank and spin in the rod.

Here is a crankshaft that failed due to oil starvation. You can find clear signs of overheating.

The crankshaft journal should be a silver color with a sheen of oil. This blue color means that the journal got hot enough to take the temper out. The only way you get that kind of heat is when there is no lubrication.

Here’s another clue. Aluminum from the connecting rod has actually welded itself to the crank pin.

After enough metal transfer or removal, the rod will pound on the crank journal, and the rod bolts will lose torque and begin to loosen.

Eventually the rod fails, sometimes right through the block as shown.

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Valve faces will become dished from wearing on the hardened seat. Ring end-gaps will increase, increasing oil consumption and blowby. You can see the oil deposits in the carburetor if the breather hose is still connected.

This is what happens when a good part goes bad. The idea is to investigate thoroughly and determine the problem so you can fix it properly.

It’s not always as easy as it seems, nor is the obvious answer always the right one. Remember the process.

• First, we ask questions.

• Next, we make observations.

• Then we examine the evidence.

• And finally we develop conclusions.

Four important steps.

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EXAMPLE CASE

A customer comes in and says his engine failed due to a loose rod bolt. The customer says that the engine has 200 hours on it.

Here is what an actual loose bolt failure looks like. This is a GC160 engine with the rod bolts intentionally left

finger tight. The engine was run for an hour and then cooled for 30 minutes.

The engine was started again and ran for 11 minutes before self destructing.

You can see that there has been a parts explosion, but look at the journals. They are bright and shiny with no discoloration or metal transfer. Just what you’d expect from an engine that had plenty of clean oil.

You don’t get rod-bolt failure on an engine that’s been running fine for hundreds of hours.

Then why are the rod bolts loose?

Simple. Without oil, the rotating parts generate enough heat to take the temper out of a crankshaft and melt aluminum from the rod onto the crankshaft. That heat will expand the aluminum rod more than the steel bolt.

The aluminum compresses before the bolt stretches and the result is no more tension on the bolt threads.

Yes, you have a loose rod bolt, but it didn’t cause the problem, it was caused by the problem.

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Honda HR17, HR173, HR194, HR195PXA, HR195PDA JOB AID FAILURE ANALYSIS

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