Cam chain tensioner removal

While there have been a few reports of failure, the cam chain tensioner is not a big issue for 250 owners. Leon, a long-time club member and multiple 250 owner, says not to worry about it: "I've never had an issue with a cam tensioner on the Ninja. In this case, fixing it before it breaks may be what causes it to break."

How it works

The purpose of the tensioner is to take up the slack on the cam chain as it stretches with normal use. So, it's designed to only move in one direction. The springs push on the push rod, which pushes on the cam chain guide. The ball and retainer assembly, in combination with the push rod and the tapered barrel of the chain tensioner housing, form a ratchet mechanism that allows the plunger to go out but not come back in under normal use.

The negative part of all this is that when the tensioner goes, the cam chain can slap around within the engine, tearing off bits of the plastic that are there to help guide it and protect the metal... which then float around in the engine until they get stuck somewhere or do damage. The chain can also jump teeth, in which case the timing is off and the bike runs terribly, or you have that unhappy valve-to-piston contact.

The usual noise for a tensioner getting worn is a loud (usually consistent) ticking on the upper right side of the motor, similar to noisy (loose) valves. If you have these symptoms, and you know the valves to be correct, you should replace the cam chain tensioner. A new one is about $35. Part number for the whole assembly is 12048-1106.

Tensioner removal

• Remove the right hand side panel.
• There are 2 bolts that hold the tensioner to the crankcase. The tensioner is under pressure from a rather strong spring, so be sure to back the mounting bolts out a little at a time on each side so the tensioner assembly does not become "cocked". Take special care toward the end of the mounting bolts' travel. Two 1/4-drive ratchets used simultaneously work well for this, or you can go back and forth with one ratchet. A 3/8-drive ratchet may be too big to work.
• Carefully extract the tensioner assembly while watching for any parts that may fall. Don't let any of the red Loctite fall into your engine.

Disassembly

• Remove the ball bearing and retainer spring.
• Loosen the pushrod locking screw about 2 mm.
• Carefully pull the pushrod and tensioner spring from the tensioner body.
• Remove the ball bearing and retainer assembly and tensioner spring.
• Clean all parts thoroughly with brake cleaner. Toothpicks and Q-Tips can assist with hard-to-reach locations.

Reassembly

• With one hand, squeeze the piston/pushrod and springs into the bore until they bottom out. With the other hand, tighten the set screw until it stops (don't torque it down!). This will hold the piston up during installation.
• Slip the ball bearing and retainer spring over the pushrod.

Installation

• Place the assembly over the crankcase mounting position and insert the tensioner pushrod into the hole.
• Assure the ball bearing and retainer spring and the O-ring remain in place as the mounting bolts are progressively tightened.
• After installation of the tensioner, loosen the lock screw enough to free the pushrod (about 2 mm). You should hear a click as the pushrod releases.
• Tighten the lock screw again. Put a drop of blue Loctite on both bolts.
• The stiff spring in the push rod should now be firmly against the rear cam chain guide.

Sometimes, even though you put it back together right, it may take more than one try to get it to "set" properly. If you install it and it still rattles, pull it back out and try installing it again. Sometimes they like to be loved "just so".