Ninja 250: Overtorquing the rocker arm locknuts
There have been too
many Ninja 250 owners do their own valve adjustments and then end up
having to buy a new engine as a result. The problem is that they are
overtorquing their rocker arm locknuts.
Here is a photo of a new rocker arm and a worn out rocker arm:
Here is a photo of a new rocker arm and a worn out rocker arm:
The larger nut on the end is the locknut. To adjust the valves, you
have to loosen that and then use a screwdriver to turn the smaller screw
inside the nut in and out. Then, to keep the adjustment screw from
moving, the locknut is tightened back down.
It is when this locknut is tightened is where some people overtorque it and end up destroying the entire engine.
It is when this locknut is tightened is where some people overtorque it and end up destroying the entire engine.
At first glance, someone might conclude that the worst thing that could
happen is that you'd need to buy a new nut or perhaps, at worst, a new
rocker arm. But in reality, its more like lighting the fuse to a
nuclear bomb.
Overtorquing the rocker arm locknuts starts a chain reaction that ends with the total destruction of your engine.
The first thing that happens is that one of the the little dog ears on the rocker arm is snapped off due to the excessive torque on the locknut. There isn't much too them, and its easy to see how they can break.
Overtorquing the rocker arm locknuts starts a chain reaction that ends with the total destruction of your engine.
The first thing that happens is that one of the the little dog ears on the rocker arm is snapped off due to the excessive torque on the locknut. There isn't much too them, and its easy to see how they can break.
There should be two dog ears on the rocker - one on both sides. The dog
ears are what keep the rocker from coming loose inside the engine. The
rockers do not have hinges or retainer pins like they do in some cars
so once one of the dog ears breaks off, they are free to come loose.
The next thing that happens is that the loose rocker arm bounces around until it finds its way down the cam chain tunnel. There is really only one place to go at this point - straight into the crank's cam sprocket. What happens is that the loose rocker gets jammed between the chain and the sprocket.
Now when the crank rotates around with the rocker under the chain, it does several things. First, it breaks off a cam chain retainer that is molded into the engine block. Second, it causes the chain to skip several teeth on the sprocket resulting in a major valve timing error.
The Ninja 250 engine is known as an "interference" engine. This means that the valves and pistons take up the same space, but at different times. So as long as the engine valve timing is correct, the piston and valves never hit.
But when the valve timing is off, the pistons will hit the valves with enormous force. This causes several bad things to happen. The most common is that the remaining 7 rocker arms are broken in half.
The next thing that happens is that the loose rocker arm bounces around until it finds its way down the cam chain tunnel. There is really only one place to go at this point - straight into the crank's cam sprocket. What happens is that the loose rocker gets jammed between the chain and the sprocket.
Now when the crank rotates around with the rocker under the chain, it does several things. First, it breaks off a cam chain retainer that is molded into the engine block. Second, it causes the chain to skip several teeth on the sprocket resulting in a major valve timing error.
The Ninja 250 engine is known as an "interference" engine. This means that the valves and pistons take up the same space, but at different times. So as long as the engine valve timing is correct, the piston and valves never hit.
But when the valve timing is off, the pistons will hit the valves with enormous force. This causes several bad things to happen. The most common is that the remaining 7 rocker arms are broken in half.
If you are lucky, then that is the end of the damage. But if not, other things that happen are bent rods, bent valves, broken cam bearing blocks, cracked pistons and cracked engine blocks.
But now, instead of just one rocker wreaking havok in your engine, now you have 14 half rockers doing the same thing. At this time, the engine is not running, but is still spinning - so the little half rockers are going to make their presence known. If any of them get stuck between any gears in the engine, and there are a lot of them, then those gears are toast.
So anyway, I hope this explains why overtorquing the rocker arm locknuts is so bad.
