Oil Leaking From Air Filter Box Of My Bike(TBR7), Why?

I have drawn a line in the sand, no more oil leaking from the air filter box of my dirt bike. My TaoTao TBR7 motorcycle has a nasty habit of leaking oil from its airbox. I figured the source of the oil leak and took steps to minimize it, covered in this post: Oil In My Motorcycle AirBox, but the air filter box oil leak continues.

FYI: The source of the oil coming out of motorcycle’s air filter box is….. Drum-roll please:

Why Is There Oil In My Motorcycle Air Filter Box?

The most likely oil source is via the motorcycle’s crankcase ventilation system. This system vents the crankcase, removing pressure, and vents it to the airbox via a breathing hose. Pressure is normal, but the breathing hose can carry oil up into the airbox when excessive oil is in the crankcase.

I cover this information also in my earlier post: Why Is There Oil In My Motorcycle Air Filter Box?. FYI: I am looking at solutions for this problem and found many of my TaoTao TBR7’s Chonda-Cousins (RPS Hawk 250, Brozz 250, etc.) have the same problem ( Hawk 250 vs. TBR7 ). Oil in the motorcycle’s filter airbox is a common complaint.

OK, so I found crankcase pressure is expected with the movement of the piston. This internal pressure build-up can be made worse with bad piston rings that could leak excessive exhaust gases into the crankcase. So normal crankcase positive pressure shouldn’t be the source of a dirt bike leaking oil from its airbox.  

What Have I Done To Minimize Oil Leaking From Air Filter Box?

I can control piston ring leakage or minimize it with a proper motorcycle break-in period and regularly scheduled motorcycle maintenance like oil changes. I did the break-in and did frequent oil changes with good oil (See previous post: What Kind Of Oil Does The TaoTao TBR7 Take? – FAQ).

I can control overfilling my crankcase oil. The TBR7(Like the Hawk 250) has a small oil sump. About a litter, with a total capacity(See Previous Post: What Is The TaoTao TBR7’s Oil Capacity? – FAQ) of 1.1 liters. The 1.1 litters seem to fill the total oil system when dry. Since when I put in a liter jug of oil after an oil change, I could have a high level in the oil sump.

So now, after an oil change(See Previous Post: Steps I Take To Do My TBR7 Oil Changes.), I add about a quart of oil to refill the oil sump.

Where Is The Airbox Oil Leaking Coming From?

Where I used to see the oil was the outlet of the airbox, the inlet of the carburetor. Now that I have an air pod air filter(see previous post: TBR7 Air Filter Pod Replacement, DONE!), the oil seems to just splash out the front of the airbox now.

Why Have You Not Blocked The Airbox Outlet?

I planned to just seal the hole created from removing the air tube but couldn’t figure how. I saw people patching their Hawk 250’s with rubber and RTV, but with my oil problem, I figured I would just stuff a rag in the airbox till I addressed the oil source first.  

Once the oil in the airbox is fixed, I might just duct-tape the hole up.

My TBR7 sees very little off-road time, so some might not consider it a dirt bike, but I collect a lot of dirt on my bike with the oil leaking. And seems my right calf of my pants. 🙁

My Goal?

To address this issue immediately. I shouldn’t have any oil leaking from the motorcycle, especially the airbox that is not being used anymore for my carburetor’s intake.  

Airbox Oil Leak Solution Timeline?

Fast. That’s relative since I’ve lived with smokey engine and oil leaks down the carburetor air intake tube for months, and I just finally got fed up with it after the air pod upgrade.   Previous Post: TBR7 Air Filter Pod Replacement, DONE!

Well more fed up seeing oil and dirt-caked up on the right side of my dirt bike. Poor TBR7. 🙁

Oh, oil and dirt on my pants sucks too. :/

Stay tuned; I will come up with a solution soon. Thanks for following along with my adventures with my first motorcycle, my TBR7! Oil In Airbox Motorcycle Solutions, I Found.

Stop; if Your Dirt Bike Has One Oil Leak, It Might Be Leaking Oil.

Quickly check your dirt bike and find out how bad the oil leak(s) might be. Even though I am focusing on my TaoTao TBR7’s oil leak in the airbox, it’s creating a mess, and I might be missing other oil leaks. So check for additional oil leaks on your bike!

Prepare Your Dirt Bike For Oil Leak Checks

Keeping A Clean Workspace.

I put my TBR7 motorcycle over sheets of clean newspaper. Like an untrained puppy, sometimes I can catch a mess by looking for wet spots in the newspaper.

Having sheets of newspaper can help keep your garage clean and make it easier to clean up any leaking oil onto the floor.

My Motorcycle Garage Safety Rules – FAQ

Check The Motorcycle Engine Oil Level.

Let’s face it; an oil leak creates a mess on your dirt bike, the ground, your garage floor, etc. However, we don’t see the internal damage a low oil level can do to a running engine.

With a shutoff motorbike engine, be sure you are working with sufficient motor oil before proceeding.

FYI: FAQ – What Happens When You Have Too Much Oil In An Air-cooled Engine?

My Approach To Check For Leaking Oil.

Follow a systematic approach to looking over your dirt bike’s components and finding the oil leak. I do have an oil leak in my airbox, but from the photos you see, I could have additional spots of leaking oil. I don’t want to keep chasing after all the leaks, so a good inspection should help me plan for doing all my TBR7.’

Engine Oil Drain Plug

Now I know it’s common sense that I tighten the engine oil drain plug enough each time I change the engine oil, but my TBR7 is a street-legal dirt bike, so I do try to go ‘off-road’ occasionally.  

Off-road, for me, is more like fire trails and muddy puddles.

Nonetheless, the engine oil drain plug could have come loose with bouncy roads and rocks being thrown up. 

Also, what if, in a rush, I did the dreaded ‘cross-thread’ of death. I still finger-tighten all bolts before putting a wrench on it. Check the underside where the oil drain plug is for leaks and drain plug tightness, and move on.

Check Your Engine Gaskets.

Many times engine gaskets are exposed to motor oil with the engine stopped. My TaoTao TBR7 is a basic dual sport that has the same design.   

Check the clutch side engine gasket of your dirt bike. Also, check the shifter-side engine gasket, usually, oil isn’t in this space, but you might have an internal oil leak filling it.

Check bolts for tightness as well.

Check The Engine Shaft Seals.

My TBR7 motorcycle has shaft seals in various engine locations.

Left side engine shifter seal. Check this for any oil, and it might be a good time to check the seal overall. Does the seal look gouged or torn?

Check the engine output seals, This might require removal of the engine front sprocket guard and front sprocket, but gross leaks will be easy to identify without too much work.  

How does this engine output seal look if you remove the front sprocket and its guard?  

Check the Exhaust System.

This oil leak check should be first done with the engine off and exhaust cool to the touch.

I take a clean rag and wipe the inside of the tailpipe. Do you find heavy oil residue? Often just accumulated exhaust products can look like heavy residue, but does it look oily?

Note, following steps check for active leaking engine oil while the engine is running. Before doing this, I check all bolts for tightness while the engine is still cool to the touch.  

Now time to move on to doing oil leak checks with a running engine. Funny thing, I manage to burn myself too often and try to have safe work practices. 😀

Check the Engine Jug / Cylinder Connection.

With the engine on, wipe down areas with a clean rag and look for accumulated or actively leaking oil. Clean oil leaking can almost be invisible in the grooves and meeting surfaces of the engine. Using a good flashlight can help.

Often the tiny oil leak isn’t directly visible, but the dirt and grim it connects are. So create clean spots, monitor over time, and find what areas, especially metal seams, seem to get dirty the fastest.

Check the Valve Cover Gasket.

On my TaoTao TBR7, the valve cover is held down with three bolts, and the sealing surface is an o-ring. Due to valve clearance checks( Checking & Adjusting Valve Clearances On My TBR7 ), this o-ring can wear out frequently or get a cut. So be prepared for oil leaks in this area.

Again, check for leaking oil by wiping down areas and looking for any accumulated oil or active leaking.

Check the Intake Manifold Gasket.

Now this area can be more of an engine idle problem, with an air leak getting into the engine, but there is a little possibility of oil accumulating and leaking in this area, I am told.

Rare, but a chance. So I do a quick wipe down since if there were any oil leaking, it would be sucked right back into the engine intake—an excellent time to check the condition of your engine intake boot.

Check Your Motorcycle Crankcase For Leaking Oil.

Faulty crankcase gaskets(torn or worn) or improperly installed crankcase gaskets(pinched) can lead to oil leaks in your motorcycle.  

Check all the crankcase bolts, using an x-pattern, for tightness. Then wipe down the seating areas about the crankcase. 

Did you find leaking oil? It might not be an actual crankcase oil leak, but oil that has dripped down from a higher area. Monitor these areas for fresh oil or abnormal dirt collection to find your oil leak. 

If the motorcycle crankcase leaks oil, then consider looking into a new crankcase gasket. If this is the case, you should use this repair as a chance to do a regular maintenance item like replace the motorcycle clutch plates: two-birds, one-stone.

When All Else Fails Finding That Leaking Oil:

I wipe down the engine and whole dirt bike of any residual oil and leave the bike to sit overnight with a clean newspaper under it.

Hopefully, any dripping oil will leave a significant mark on the newspaper, and you can follow the oil back to the source. Starting low on the engine and moving up to the point where leaking oil stops.

Finding an oil leak on a motorcycle can be problematic, and finding a leak on a dirty dirt bike can be even more challenging. It might take time to find the leaking oil, but ensure you never let it leak so much that the oil levels drop too low.

No need to turn a simple not found fix into a found destroyed engine. Good luck, and if you have any tips for finding leaking oil on a dirt bike, please comment below.

Thank you, Ride Safe, Ride Fun.

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