Cam chain tensioner removal

Introduction

The cam chain tensioner is one of the known problem areas on the EX250. Doing a little routine maintenance every oil change, or every other one, should help this piece of your engine last longer. If you're having trouble seeing what it looks like, take a look at the diagram at the Ron Ayers parts fiche. Part # for the whole assembly is 12048-1106.

Camshaft chain tensioner removal

• Remove the right hand "knee grip pad" (side panel). You will most likely find the combination of a 1/4" socket drive, a 1/4" extension, a 1/4" drive universal joint, and an 8mm socket to be the most useful means of removing the mounting bolts.
• 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 bolt's travel.
• Carefully extract the tensioner assembly while watching for any parts that may fall.

Camshaft chain tensioner disassembly

• Remove the ball bearing and retainer spring.
• Loosen the push rod 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. Toothpicks and Q-Tips can assist with hard-to-reach locations.

Camshaft chain tensioner assembly

• Lubricate the pushrod and tensioner spring with a good quality grease before insertion in the tensioner body. Silkolene Pro RG2 Synthetic is a good choice. Any good molybdenum grease will also work. Assure that any grease you select is safe for use with aluminum.
• It would seem that Kawasaki (in the service manual) neglected to mention lubricating the tensioner before reassembly. So, make sure that you don't skip that part.
• Compress the pushrod and tensioner spring fully into the tensioner body.
• Turn in the lock screw so the pushrod remains in the tensioner body.
• Grease the ball bearing and retainer assembly before placing it over the pushrod and pressing it into the tensioner body.
• Slip the ball bearing and retainer spring over the pushrod

Camshaft chain tensioner installation

• Place the assembly over the crankcase mounting position and insert the tensioner pushrod in to 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.
• The stiff spring in the push rod should now be firmly against the rear cam chain guide.

Cam chain tensioner theory

How the tensioner works: The springs push on the plunger, which pushes on the cam chain. The springs are a specific strength so as to put the correct tension on the chain. There's also a ratchet mechanism in there that allows the plunger to go out, but not come back in under normal use (you can override that for installation).

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. It's not quite as bad as losing the timing belt on a car (with an interference engine), but it's not good.

It could be worse: Kawi does a better job than Suzuki on their tensioners.