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Diagnosing Oil Consumption;

 

There has been a rise in oil consumption complaints on 2005 - 06 model year vehicles.

 This might help you determine if there is an actual oil consumption issue and more

accurately diagnose the root cause.

 

1. First, determine if there is excessive oil consumption by analyzing the complaint

and vehicle condition.

Many times fuel delivery related issues cause smoking complaints and may even

gas wash cylinders leading you to believe you have an "oil burner" on your hands.

Is the vehicle modified and what is its state of tune?

Does the EFI calibration match the actual components on the vehicle?

Is there fuel stand off in the air cleaner or manifold?

 

2. What is excessive consumption?

You may not realize that all engines have some normal rate of oil consumption,

and air cooled engines are more prone to use some oil in the course of normal

operation. It would not be unusual for a Twin Cam engine to use one quart

of oil in 1500 miles or a middleweight powertrain to use one quart of oil in

1000 miles.

Oil consumption is impacted by engine condition, mileage, duty cycle (how the

vehicle is operated and in what environmental conditions), and accessories.

Is the vehicle through its break-in period? Remember rings must seat before they

will begin to seal the cylinder to piston clearance.

After a little investigation of the complaint and a brief inspection of the vehicle

you should be able to determine if you are dealing with a rich condition, oil

consumption complaint, or a misperception.

 

3. Determine the real rate of consumption.

To determine the rate of oil consumption bring the oil level to the full line following

the "Checking With Warm Engine" procedures outlined in the service manual.

Ride the vehicle and inspect the level at 500-mile intervals to determine the actual

rate of consumption. Be careful not to overfill the tank, as that will provide a false

indication of consumption.

If the rate of consumption exceeds the norm, you will need to review duty cycle

and then begin your inspection of the engine's state-of-tune accordingly.

 

4. Verify the system before you tear it down.

Don't overlook the obvious items before disassembly. How are the oil hoses (tight

clamps, routings, etc.)?

Verify breather operation, this might be a carry-over situation. If you blow lightly into

the breather snorkels, there should be some resistance if the umbrella valves are

closing properly.

Verify oil pressure and oil return functions. You might be dealing with an oiling

system issue and/or a wet-sumped lower end.

Take a compression reading and perform a leakdown test. Remember to write down

the numbers.

If leak down exceeds 10%, determine where it is leaking by.

Into the lower end, out the exhaust or intake port, or through a head gasket?

 

5. Now begin your disassembly based on your findings, and keep both eyes open

as you take things apart for clues to the root cause.

If the leakage was primarily into the crankcase, then you are chasing a piston to

cylinder sealing issues. To rule out a barreled or tapered cylinder re-check leak

down in three places (top - middle - bottom) in the stroke once the rocker arm

support plate is removed.

By the way how did those umbrellas look, and was the rocker box fairly well

scavenged? No clogged return passages right? No signs of leakage at the head

gasket oil returns? Good gasket surfaces?

Check the piston crown for carbon build up. Washed areas on the edges of the

piston crown are a good indication of an "oil pumper" (bad rings or piston to

cylinder fit). Solid carbon build up across the piston crown generally indicated it

is coming from above.

With the cylinders off you will be able to more closely examine (and take note of)

ring end gap locations. Do they match the service manual recommendations or

are they lined up? Also, check the second compression ring, also called the

middle or scraper ring, installation. The "dot" should face up, but even more

important the outer bevel slants toward the piston and it has a slight chamfer on

the ID that goes to the bottom to allow it to function properly. It is rare but

sometimes the "dot" is up and ring's taper face is wrong.

While you are looking at the rings check their wear patterns. A ring that is over

spread or twisted during installation will not seal properly.

Leak down past the valves and into the ports requires you inspect them for bad

seats and bent stems, or you may find carbon built up to the point they just were not

able to seal the combustion chamber.

Heavily carbon'ed valves and oil in the intake or exhaust ports (you did

remember to take note of that right?) are indications of leaking valve seals.

It also pays to look for the unusual, like leakage between the valve guide and the

cylinder head. Are the guides loose? Was the head's guide bore scored or

damaged during guide installation? This can sometimes be indicated by

unusually clean or unusually golden patches in specific spots around the guide.

The same is true if there is actual porosity in the head.

 

Valve Seal Updates;

2005 models and early production 2006 vehicles use a one-piece valve seal and

lower spring seat design (p/n 18094-02) that can cause oil leakage between the

guide and the seal when side loaded or miss-installed. These can be identified by

the silver seal ring and black rubber material.

A new version one-piece valve seal and lower spring seat design (p/n 18094-02A) is

being implemented into service parts to improve sealing properties and minimize

installation issues.

The first batch of this new seal can be identified by a green seal ring as shown

below. Towards the end of the month 18094-02A seal kits will change to an orange

colored rubber material to improve visual identification of the new parts.

Twin Cam 88/88B production has moved to this design with middle-weight

powertrain and service parts.

Utilize this new design during any future top end services.

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