Engine Won't Turn Over - Hydrolocked
Posted: Thu Apr 02, 2015 11:53 am
I've seen an increase, lately, in the number of posts from folks with engines that won't turn over or that will turn for a small amount and then stop. These folks tend to keep trying, once they see this happen, using the electric starter. This is a bad idea and as this happens, these folks are potentially doing hundreds of dollars’ worth of damage to their XJ, without even knowing it.
If you encounter a situation where the engine won't turn over (and the battery is in good shape), don't try starting the bike again. Remove the spark plugs and then try to turn over the engine. If fuel spurts from the engine when cranked with the spark plugs out, you've hydrolocked the engine.
What causes the engine to hydrolock:
As the bike sits on its sidestand, fuel in the tank exerts pressure on the petcock. If the petcock is in good shape and does not leak, nothing happens. But if the petcock is old and does leak, fuel pressure will build up in the fuel line. If the float needle valve seals are weak, fuel will leak past the floats, into the intake, past the open intake valve and will fill the cylinder up with fuel.
When you try to turn over the engine, the piston in the cylinder will press on the fuel. But since fuel is imcompressible, the piston will stop dead and the engine won't turn over.
If you keep trying to start the bike, once its hydrolocked, one of two things will happen:
How do you fix a hydrolocked bike?:
This is simple. If you suspect a bike is hydrolocked, remove all four spark plugs and then crank it over with the starter. With the spark plugs out, fuel will be ejected out through the spark plug hole, alleviating the hydrolock.
Once the bike turns over and you've confirmed that fuel was indeed within the cylinder, replace the following parts to prevent the problem from occurring again:
If you encounter a situation where the engine won't turn over (and the battery is in good shape), don't try starting the bike again. Remove the spark plugs and then try to turn over the engine. If fuel spurts from the engine when cranked with the spark plugs out, you've hydrolocked the engine.
What causes the engine to hydrolock:
As the bike sits on its sidestand, fuel in the tank exerts pressure on the petcock. If the petcock is in good shape and does not leak, nothing happens. But if the petcock is old and does leak, fuel pressure will build up in the fuel line. If the float needle valve seals are weak, fuel will leak past the floats, into the intake, past the open intake valve and will fill the cylinder up with fuel.
When you try to turn over the engine, the piston in the cylinder will press on the fuel. But since fuel is imcompressible, the piston will stop dead and the engine won't turn over.
If you keep trying to start the bike, once its hydrolocked, one of two things will happen:
- If you use the starter, you will eventually strip the starter gears, resulting in an expensive, engine out, case-split repair procedure: Here's the potential damage that can result from trying to start a hydrolocked will be alleviated.
If you try to bump-start the bike, the crankshaft will be forced to turn while the piston remains stationary. This will likely bend a connecting rod. This repair requires splitting the cases and replacing the damaged rod.
How do you fix a hydrolocked bike?:
This is simple. If you suspect a bike is hydrolocked, remove all four spark plugs and then crank it over with the starter. With the spark plugs out, fuel will be ejected out through the spark plug hole, alleviating the hydrolock.
Once the bike turns over and you've confirmed that fuel was indeed within the cylinder, replace the following parts to prevent the problem from occurring again:
- Replace the vacuum petcock with a new one.
Replace the float needle valves with new ones.
Fit new o-rings on the float valve seats