Tech Tips

How To Prevent Hydraulic Lock

Written by  March 31, 2007

Everyone tells me they have been almost stir-crazy these last few months; the weather patterns have been so unpredictable. Last month’s article was getting your bike ready for the riding season, and it covered the basics on common maintenance items that will get you ready for that first ride after winter storage. This month, I am targeting riders who may have improperly winterized their motorcycle or those who did not have time to address any winterizing issues.

The issue we are going to discuss will be a subject that not many people have even heard of. Hydraulic lock is a scenario that occurs when fuel has overflowed through the float and the float needle in the carburetor. This can result from something as simple as leaving your fuel valve either in the “ON or “PRI” position, and this is not specific to just when the bike is in storage. In the past I have seen this happen from having a rusty fuel tank and the rust from the tank making its way to the floats in the carburetor and letting gasoline fill up the crankcase. This is not only a dangerous problem to you as the rider, but also from an engine’s point of view-- oil and gas do not mix!

So what does that mean? Normally from H-D to metric models (and, yes, that means BMW as well) motorcycle engines are designed to hold no more than 4 or 5 quarts of engine oil. When you mix 4 to 6 quarts of raw gasoline in the oil, this will fill the cylinder with gasoline and immerse the crankshaft with a solvent that will clean ALL of the moving parts in the bottom of the engine and especially the metric bikes that have a transmission lubricated by the engine oil.

Hydraulic lock is what happens when this mixture of gas and oil is forced up past the piston rings and makes it to the top of the piston where when the engine is cranked it will basically slam the piston into the combustion chamber. That’s where it is basically stopped without coming to a complete revolution. This is extremely hard on the crankshaft and connecting rod bearings. I have seen this scenario in many sport bikes and cruiser models that have been improperly stored or when a rusty gas tank is present.

One of the simplest ways to find out if you have gasoline in your oil is to simply look at your oil level in the glass window (see the lead photo). H-D owners will have to pull the dipstick out of the oil tank, but this will surely flag you because the level of most Harley-Davidson applications is pretty high on the dipstick.

Most engine damage will occur when you continue to crank the engine and you hear a loud “clunk.” This is the point were you need to stop cranking the engine! The bike in the lead photo is actually my old Kawasaki ZX10 Ninja, and this bike was stored with a full tank of gas. The fuel valve was left in the 'on’ position, not turned off for storage, and the bike was on the side stand. The #1 carburetor leaked fuel into the engine filling the cylinder head and engine with 4+ gallons of gas, and the bike would not start. So after further diagnosis, we noticed that the oil window was overfilled. I suggested changing the engine oil and filter before we diagnosed the cause of the main problem. To make a long story short—if this bike would have started, the gas/oil mixture would have entered the entire engine and oil cooler with potential crankshaft damage.

Anytime that you see the oil level higher than the normal specified level you should investigate. Engine oil does not grow. If it’s a cost factor, ask yourself this question—which is cheaper? Changing the oil, or repairing the crankshaft? Changing the oil is the best way to prevent this destructive and unsafe condition that happens to so many motorcycles when gas enters the crankcase.

Now when it comes to the fuel injection, this condition is virtually eliminated because of the electronic fuel injectors; however, the bike in question that prompted me to write this tip also had an electric fuel pump, so I will leave that alone and just stick to my guns on the main issue—if your oil level is higher than normal, that means you have a problem with your fuel system or coolant has entered the engine from a blown cylinder head gasket.

I have factored this to be a 2 on our tough-o-meter scale because of the extreme fire danger and engine damage that can occur with this condition.

B-safe out there!

Dave Miller