EVO: Oiling & Lubrication

Oil Leaks

First and foremost, do not use silicone sealer on any engine, oil pump or related parts or gaskets to stop a leak.
The heat coupled with crankcase pressure pulses can break pieces of it loose and send them through the engine.
These pieces may stop up oil passages and starve the engine of oil.
The gaskets / seals made for Sportsters are more than efficient for stopping leaks.
If you have continual leaks after installing new gaskets, chances are it's not the gasket's fault.
There may be manufacturing, fitting, high internal pressure pulses, warped sealing surfaces or other issues to address.

Silicone can break up into small film sheets and float around the oil path stopping up the small restricted passages.
Both feed and return sides of the oil pump create suction on their inlet sides as they rotate.
The feed side of the pump is gravity fed from the tank and the feed gerotors send pressure into the engine.
It is mainly dependent on gravity oil from the tank.
The scavenge side of the pump is fed by crankcase pressure pushing the oil to the scavenge port in the crankcase.
It is more dependent on the flywheels to get the oil to the scavenge port.
If there is an obstruction in the return path from the crankcase to the oil tank, it will slow the flow of oil out of the engine. This can cause weak or no oil flow.
If the scavenge side of the oil pump is not flowing oil fast enough to the tank, oil will build up in the sump.
This can result in higher crankcase pressure, more oil film spinning around the flywheels, engine drag, blowing rocker box gaskets and general oil leaks.
In an instance where used silicone was used to seal the gaskets, pieces of silicone (or sheets) could be sucked in, stretched and broke off into the engine.
This silicone 'gummy bear' sheet was found in the oil pump.

An oil leak could also be a crankcase pressure problem. A situation where the engine is both blowing out and then pulling in air from the rocker box gaskets.
04-up engines seem to be more susceptible to crankcase pressure problems.
It's important to inspect and change out the breather valves periodically. Read more about the breather valves below.

Oil Consumption Service Bulletin - August 10, 2005

This Tech Tip reprinted by Krayven Sumhead of the XLFORUM 2)
See the original Tech Tip (#59, 8-10-05) PDF here in the Sportsterpedia.

Diagnosing Oil Consumption
There has been a rise in oil consumption complaints on 2005 – 06 model year vehicles. The intent of this Tech Tip is to 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 customer complaint and vehicle condition.
    • Many times fuel delivery related issues cause smoking complaints and may even gas wash cylinders leading customers to believe they have an “oil burner” on their 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?
    • Customers 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 discussion with the customer on the complaint and a brief inspection of the vehicle you should be able to determine if you a dealing with a rich condition, oil consumption complaint, or customer misperceptions.
  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 and tape the filler neck closed.
      Note on that tape the mileage and the date.
      • For those with a cam chest breather hose or an external breather hose mod; 3)
        Remove the breather hose from the carb backing plate and stick it into a catch bottle.
        The catch bottle should be non- breakable, such as a plastic baby bottle.
        Remember to cover the fitting in the carb backing plate.
        Secure both the bottle and the hose firmly to the vehicle.
        Don't seal the top of the catch bottle as this could pressurize the system.
        Instruct your customer to check the catch bottle every day.
        If the catch bottle begins to fill with oil, the vehicle should be returned to your dealership.
        Start looking for a restriction on the return side of the pump.
        Here is an article in the Sportster with pics on Building a test catch can
    • Have the customer 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 with the customer 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, Technical Service is sure to ask for them.
    • 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 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 - August 10, 2005

  • 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 will be moving to this design in the near future with middle-weight powertrain and service parts to follow shortly thereafter.
  • Please utilize this new design during any future top end services.
  • Warranty and Service Procedures
  • Any individual 18094-02 valve seals in your inventory may be used on Middle-Weight Powertrain repairs.
  • Current engine gasket kits may be used on 2004 - 2006 Sportster and 2003 - 2006 Buell engines.
  • Current gasket kits (top end p/n 17052-99B and engine p/n 17053-99A) may also be used on 2004 and earlier Twin Cam 88/88B engines without any special steps.
  • When using current gasket kits (top end p/n 17052-99B and engine p/n 17053-99A) on 2005 and 2006 Twin Cam 88/88B models discard the 18094-02 valve seals included and use part number 18094-02A in their place, and the included seal protector during installation.
  • For warranty repairs that involve the use of these engine gasket kits (p/n 17052-99B & 17053-99A), you may also claim 1 valve seal kit p/n 18094-02A as part of the repair.
  • These additional parts will only be allowed on MC warranty claims filed against your existing inventory of gasket kits used to repair 2005-2006 Big Twins.
  • Future kits will have the new valve seals included so additional parts should not be listed on warranty claims. 18094-02A Valve Seal Identification

Visual Inspection

Loose Bolts

  • DO NOT try to simply tighten the head or rocker bolts that may be loose. Cylinder head fasteners should never be re-torqued on any Evolution engine. 4)
    All multiple bolt fasteners are required to be torqued in a cross pattern.
    Likewise, simply tightening only the bolts that are loose will change the clamp load on the ones that are tight and not touched.
    If you feel it's simply a loose bolt, loosen all the bolts on the rocker box / head / etc.
    Then torque them back using the correct specs and tightening sequence.
  • The two center cylinder studs on the right side of the engine are prone for stripped threads.
    This ends up loosening the heads and causing leaks. If it persists, the oil may be originating from the crankcase cylinder stud threads.
    The fix is usually a helicoil or other thread repair insert into the case.
    Remove the suspect stud and discard, apply 242 Loctite to the threads of the new replacement studs.
    Reinstall as per your FSM. See also Cylinder / Head Bolt Issues and Repair in the Sportsterpedia.

Leaking with Engine Running (weeping gaskets)

See also Wet Sumping in the Sportsterpedia.

Weeping cylinder base gaskets:
Please do not jump the gun. Clean the area and ride the bike.

  • Checklist for weeping gaskets:
    • The first thing usually thought of with weeping gaskets is loose bolts.
      See Loose Bolts above.
    • Too much vacuum in the engine caused by failing breather valves can implode or work loose gaskets.
      See Crankcase Pressure Problems below.
    • Don't rule out a crankcase seam leak until you've cleaned and inspected it.
    • Testing breather valve(s) from the outside:
      • You should be able to blow in one breather bolt and get air from the other.
        But there should be some resistance if you blow hard and you'll still get air from the other.
        Light breath = less resistance.
        Heavy breath = should be resistance.
        So it's not conclusive to test the umbrella(s) like this.
    • If the umbrella(s) are hard and not flexing to allow air to and fro like they should, that'll cause crankcase pressure problems.
      And it could easily cause weeping gaskets.
    • The top rocker box cover fiber washers could allow air past them, increasing pressure problems.
    • If the oil tank vent line is plugged/kinked, that'll cause pressure problems.
    • If you have too much oil in the tank, that'll cause pressure problems.
    • If the transmission vent line is kinked, that could cause pressure problems.
    • If you have a non factory (modified) breathing setup with a filter on the end of your breather hose, it can stop up and cause pressure problems.
    • Or any combination of the above can cause pressure problems.
    • Running the bike hard shouldn't be an issue.
      However, running the bike hard compounds the problem if there are any issues listed above.
      High RPM makes these issues worse.
  • Using powder to detect a leak:
    • Degrease the bike until there's no oil remaining.
      Then take some Soft n Dri (women's antiperspirant spray), talcum powder etc. and spray it around the rocker gaskets (or other suspected leaking area). 5)
      It will go on clear but when it gets heated will turn to a white powder. Just a light film is all it takes.
      Whenever it starts leaking it'll show up exactly where the leak is.
    • Clean the engine, then start it and use a bright light to see where the leak is coming from. 6)
      The light should make the liquid oil shine. You may only have to run your scoot for a few seconds to start leak.
Rocker boxes sprayed with powder antiperspirant to detected oil leaks. 7)

Leaking with Engine Shut Off

Sit Sumping. See more about Sit Sumping in the Sportsterpedia.

  • Clean the area thoroughly (like with rake cleaner and air blow dry). 8)
    Let it sit long enough to begin leaking and blow some talcum powder over the area.
    The talc will stick to the oil and pinpoint the origin.
  • Take an old bike tube and cut a piece while retaining the valve stem. 9)
    Use a hose clamp to tighten it over the filler neck on the oil tank.
    Then put a lb are two of air pressure on it and see if that helps you locate where it's coming from.

Leaking Out the Breather Vent(s)

Oil leaking out the breather vents (or oil carry-over) can happen for many reasons.
First, the air leaving the engine can carry oil mist with it which is normal.
Breather bolts on the heads (91-up) must have pipe sealant of some sort applied to the threads during installation (very critical). 10)

The MoCo has done a lot of re-engineering over the years, but the problem of oily air filters and oil drips never went completely away.
There are however, different degrees of oil carry-over out the breather(s).

  • Oil only in breather bolts and no where else.
  • Oil in breather bolts, small amount in sponge, small trace on backplate.
  • Oil in breather bolts, large amount in sponge, oil visibly thick on backplate, element still clean.
  • Same as #3. Filter element now collecting oil.
  • Same as #3, Filter element completely saturated.
  • Oil exiting air cleaner from backplate.

Oil is supposed to be fed to the engine, lube the related parts and be sent back to the tank as quick as possible.
If the oil is allowed to stay in the engine too long before returning to the tank, the result is more oil 'carry-over' inside the engine than designed for.

Carry-over , where do you start? What are you looking for? First you've got to qualify the complaint.
Ask the right questions.

  1. When does it carry- over?
    1. Driving at steady highway speeds? See Wet Sumping here.
    2. After the bike's been sitting for a couple of days and you start it up? See Sit Sumping here.
  2. Clean the affected area and ride or run the bike and reproduce the problem with the breather hose in a baby bottle (or other) test catch can as described here.
    This will help you better understand the amount of carryover you're dealing with.
  3. Start the diagnostics and separate the systems qualifying each one as you go.
    1. Oil tank: see Inspecting the Oil Tank above.
    2. Return lines: see Inspecting the Oil Return System above.
    3. Venting system: see Crankcase Pressure Problems below.
    4. And finally the motor: see Internal Inspection below.

Diagnosing the Cause of Oil Leaks

See also in the Sportsterpedia:

Obviously you must find exactly what is leaking before you can determine what will be needed to fix it. 11)
Degrease the area in question and run the bike a little and watch the area for the beginning signs of seepage.
Check torque on the bolts on covers and parts with gasket/seals but do not tighten more than the specs in the FSM to stop a leak.
That may result in stripping the threads.
If you have a gasket / seal that has needed replacing several times, you must find the cause of the continued failure and then repair that.
In some cases, a considerable amount of the engine has to be disassembled just to get to the problem. Refer to your FSM for the proper procedures.
Always keep a close watch on oil levels if you know you have a leak.

Crankcase Pressure Problems

Excess oil coming from the breather vent(s) could be a symptom and the root cause can sometimes be related to an imbalance in crankcase pressure.
Fixing the imbalance can be mean from re-routing the vent lines to replacing the umbrella valve(s) to replacing the rings.
It depends on what the problem is.

  • Engine crankcase pressure is designed to have a slight vacuum with the engine running.
    Non functioning umbrella valves can create a situation where air is not able to leave the engine normally to the point where oil/air mist gets too thick.
    Then the oil doesn't separate fast enough from the air and comes out the vents.
  • In a perfect world, you would only have a slight oil mist coming out of the crankcase breather which could easily be routed into the air cleaner.
    (keeping the E.P.A. happy by depositing the oil back into the engine instead of dripping on the ground).
    This problem has been almost eliminated with the OEM breathers venting into the A/C.
    But the problem still appears on Sportsters with external vent lines added.
    To clarify, oil mist is always present to some degree. It's just not as visible when the vents are connected to the air cleaner.
  • If you have external breather vent hoses, make sure there are no kinks in the lines(s) that would stop or slow down the engine from breathing.
    This would bottle up crankcase pressure and cause the internal pressure to implode the gaskets and create a leak.
    Also make sure there are no obstructions (sludge) in any bends that may be in the lines.
    However, a few drips of oil out a vent hose while parked is normal.
    This does not qualify as oil 'puking' out of the vent (which is more of a sudden rush of oil).
    See also Breather Venting / Relocation in the Sportsterpedia.
  • The breather vents usually work fine on OEM engines. Problems have been noted however when bigger pistons / performance upgrades have been added.
    Engine upgrades sometimes comes with extra baggage.
    Bigger pistons brings with it more air displacement under the pistons (higher air volume in the lower case, more oil getting splash around).
  • Aftermarket accessories sometimes seem better than they are. Just because someone made it doesn't make it work as it should.
    Some aftermarket breathing systems and accessories can make normal oil carryover visible sooner than OEM systems.
  • A stopped up / restricted air filter can back up crankcase pressure and cause an imbalance inside.
    (especially with a filter on the end of a vent hose)
  • Heavy oil flow 'puking' from the breather vent(s) only on cold start up could be from a sit-sumping condition where oil is draining into the sump when parked.
    Your motor may be filling with oil while the bike is not running and it all gets pushed out the breather when you start the bike.

Inspecting the Oil Tank

Overfilled Oil Tank

Read more on Overfilling the Oil Tank here in the REF section of the Sportsterpedia.

How about that oil sucking gremlin that steals half a quart every evening? You feel compelled to bring that oil level up to spec the next morning. 12)

  • Before topping off the oil tank, run the engine if possible for about a 30 min. ride.
    • This heats up the oil to operating temperature and suspends the solids in the oil instead of it laying on the bottom of the case.
    • This also allows the oil pump to send most of the oil in the engine back to the tank before you add more so you get a more accurate account of the oil level.
  • Failure to warm the engine first can result in an overfull condition in the system and you can end up blowing the cap off the oil tank and a big mess.
  • Overfilling your oil tank can also result in engine drag (wetsumping) and puking oil out the air cleaner.
    When the tank is slightly over filled, oil that was standing in the sump is added to the tank via the oil pump, thus raising the level in the tank.
    The excess oil in the tank will either flow back into the gearcase via the tank vent or up and out of the oil cap.
    Excess oil that returns to the gearcase through the tank vent is picked up with crankcase air pressure and blown out the engine breather valve(s).
    So, depending on your venting setup, oil can be blown into the air cleaner or out the vent lines due to overfilling the oil tank.
  • The oil tank is vented to the gearcase / cam chest in the engine using a stand pipe in the oil tank.
    Too much oil in the tank overcomes the vent (which is only supposed to send air from the tank to the gearcase).
    The result will be oil being sent back to the gearcase and out the engine breather.

Damaged or Flooded Oil Tank Vent / Return Tube

Vehicles with oil tanks, that have all the fittings on the bottom of the tank, use a stand tube inside the tank for the vent line. 13)

  • Short, damaged or tilted stand tubes:
    • The top of the stand tubes should be above the oil level at all times. Check aftermarket oil tanks to be sure of this before using them.
  • If the stand tube is damaged below the oil level or the level of oil is above the top of the stand tube;
    Oil carry over will continue until the level of oil is below the damaged portion or the top of the stand tube.
  • Tilted stand tubes:
    • Oil may carry over thru a tilted stand tube as long as the oil supply exists.

Diagnostics #1:

  • With the oil level correct in the tank and the ignition off, pinch off the vent hose and remove it from the crankcase vent hose fitting.
  • Direct the hose into a catch pan and un-pinch the hose.
  • Bike should be upright.
  • If oil begins to trickle out of the vent hose, allow it to run until it stops.
  • Recheck oil level in the tank.
  • Down a quart? Must be a short or damaged stand tube.
    • Replace the oil tank.
  • No oil ran out the vent hose?
    • Don't give up.
  • Leave the vent hose unconnected and cap off the crankcase vent fitting.
    Note: If you do not cap off the vent fitting, you're going to have a real live mess.
  • Now start the engine and remember to keep that hose pointed into the catch pan.
    • If oil begins to trickle out you have a tilted stand pipe.
  • Try switching the return oil hose with the oil tank vent hose at the oil tank before you replace it.
    This simple act may save both time and money by not replacing the tank.
  • No trickle from the vent hose?
    • So the problem's not in the oil tank. Reconnect the crankcase vent hose and move on to the next step.

Diagnostics #2: Return system vs motor:

  • Remove the return hose at the oil pump return fitting and plug the hose so oil doesn't run everywhere.
  • Select a length of oil hose long enough to reach the oil tank filler neck when connected to the oil pumps return fitting.
    Note: Before connecting the test hose, note the number of threads exposed on the return fitting to return elbow connection.
  • Remove the fitting and elbow and inspect how far the fitting is screwed into the elbow.
  • The fitting may be restricting the return oil flow. If so, modify the fitting as required and reinstall.
  • Now connect the test hose to the return fitting and direct the open end of the hose in to the oil tank.
  • Run the engine and note if the carry- over is much improved or stops.
  • If it stops or improves, the problem is between the oil pump return fitting and the oil tank.
    Note: In rare instances you may have to ride the bike to reproduce the same set of circumstances to be sure you've corrected the problem.
  • Remember, put the breather hose in a non-breakable container, secure both the bottle and hose to the frame.
  • A plug must be fabricated to hold the test return hose in the oil tank filler neck and control spillage of oil from the oil tank.
  • A modified oil dipstick plug may fill the bill.
    Important: No restrictions in the test return hose.
  • The carry-over cleared up?
    • Start looking for that restriction i.e., a pinched return hose, after market oil filter, oil cooler, plugged fitting or hose.
  • Friends let's bow our heads and repeat after me.
    I will never willingly install any fittings, probes or adapters which reduce the oil pump's ability to return oil to the oil tank as this will lead to carry over big time.

Inspecting the Engine Oil Return System

Restricted Oil Return Hose

  • Oil carry over will occur while driving the vehicle at highway speeds. The amount of carry over is directly related to the amount of restriction. 14)
  • More restriction, more carryover. In most cases the restriction is minor and translates to a small amount of carry over, which if left alone creates a bothersome mess.
  • Start looking for pinched hoses or a restrictive oil filter.

Engine Oil Leaking Into Primary Case

Pull the clutch inspection (derby) cover off the primary, smell the oil and check the primary oil level.
It should not be over full and should smell like gear oil (rough smell compared to engine oil).
If the oil level is higher than it should be or smell like gas, the engine sprocket seal could have failed or have been compromised.
The seal is between the engine and primary oils. If it is bad or has been temporarily compromised, engine oil infiltrates the primary and out the trans vent.

Engine Sprocket Seal

Engines with Timken bearings:
According to the Timken website, both their single and double lip seals have a max pressure rating of 4.267 psi.
That should be more than enough protection against seal leaks between the primary and the crankcase.
Pressure can either pull or push depending on it's source.
Their should be a slight predominant vacuum in the crankcase unless the breathers aren't working right.
And even then, enough vacuum to make over 4 psi and blow the seal is very excessive.
A better bet is the seal is deteriorated or was damaged / nicked during installation.

Transmission Vent Hose

Check the tranny vent hose for kinks or a blockage.
Blow on the hose end to make sure you can push air thru it. Do not used compressed air as that can damage the sprocket shaft seal.
Reroute the hose if it is showing a kink in placement or replace it if you can't blow through it.
There should be no sags in the hose between the attachment to the engine and the open end of the hose.
There are a couple of Service Bulletins discussing proper vent hose routing with illustrations.
You can download the bulletin PDFs, M-1103 (rigid mounts) and M-1143 (rubbermounts) here in the Sportsterpedia.

1998 XL1200S Transmission Vent Hose Location 15)

Test for Excess Primary Compartment Vacuum

You can test for too much vacuum in the primary with the engine running / transmission in neutral. 16)
You can make your own slack tube pretty cheap out of some 2×4 pieces, a 2-3 ft ruler and a clear tube.
Or you can adapt a clear hose to the tranny vent line and drop it into a glass of water.
If one inch or more of vacuum is present, the sprocket shaft seal may be allowing engine crankcase pressure (air/oil mist) past it.

Primary Oil Smell Like Gas?

Where did the gas smell come from?
See Why Does the Oil Smell Like Gas in the Sportsterpedia.

A failed transmission sprocket seal will allow engine oil/mist mixed with fuel into the primary.
The rotation of the sprocket rotor, clutch and transmission gears, especially at high revs, has the capability of making a lot of positive (pushing) pressure.
This generated air pressure is usually vented from the tranny vent hose.
If the carb were to leak gas into the crankcase and mix with the engine oil;
Then the pressure builds in the primary due to a kinked hose;
The primary pressure could open the seal and vent into the crankcase.
The crankcase is always pulsating positive and negative pressure (push pull air motions are generated).
So while the primary opens the seal, the CC is pulsating oil/gas/mist into the primary.
There is an internal spring on the seal to hold it against the shaft.
If the spring fails, it's failed for good until it's replaced.
However, higher pressure than designed for can skeet oil past the seal.
And when that pressure subsides, the spring lays back down.
The seal still works as long as the nitrile rubber hasn't been compromised in the process.

Internal Inspection

Check the breather valves (umbrellas)

The umbrella valves are simple rubber flaps that will get hard over heat and time.
They should be inspected periodically for hardness and replaced if they are not soft.

  • 86-03 umbrellas are now obsolete parts. You may find some NOS ones at your local dealership or online.
    An alternative is to install an external reed valve inline when your OEM umbrella fails.
  • 91-03 models have the umbrellas visible with the top rocker box section removed.
  • 04-up umbrellas are not replaceable themselves as they are built inside the 'replaceable' plastic breather valve assembly.
86-90 cap, tube and umbrella 17) 86-90 breather baffle tube installed 18)
91-03 breather valves 19) 04-up breather valves 20)

Check the spark plugs for oil fouling

Worn rings or an imbalance in crankcase pressure can send oil up into the combustion chamber and foul the plugs.
Check the plugs for wet oil saturation.

21) 22)

Check intake and exhaust ports in the heads

You can pull your exhaust pipes and intake manifold and look at the valves to see if the oil is leaking past the valve stem seals. 23)

24) 25) 26)

Check oil smudge marks when removing the heads

When dismantling the top end (or to bring parts to your mechanic)and before cleaning the head gaskets / surfaces, check them for oil smears. 27)
Smudge marks can be a give away as to where any leaks might occur. Also take a few pics of them (no flash, direct light and a steady hand).
The gasket has been known to raise around the head oil drain and only on the inside edge of the gasket.
So no outward sign of the leak. With the head removed an experienced eye may be able to spot the problem.

photo by (-_-) of the XLFORUM, annotated by Hippysmack http://xlforum.net/forums/showthread.php?t=2074835&page=3
3) , 4) , 12) , 13) , 14)
HD Tech Tips dated November 8, 1985
10) , 16)
HD Tech Tip #36 dated October 1993
photos by Hippysmack
photo by Hippysmack
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