New cam chain at 53,000 miles

After cleaning out the carbs and re-oiling the filter, per my last post, I took advantage of the fact that the tank and fairing lowers were off to change Ruby's cam chain. I'd previously fitted a new tensioner spring, which had helped to quiet the cam chain quite a bit, but I'd decided that 53,000 miles was probably enough to warrant the cost of replacing the chain itself.

Cam chain replacement is not a difficult job to do on the T300s because the cam chain runs off of one end of the crank. Until the Kawasaki GPZ900R came along, it was typical practice is to drive the cams from the centre of the crank so changing the cam drive chain was a fiddle to say the least and typically was done with a split link. Having a cam chain that runs in a tunnel on the end of the crank means it is possible to use a stronger, endless chain - and avoid the risk of dropping bits of split link into the engine. Much better.

View of the cam cover (aka cylinder head cover)
protruding either side of the main spine frame tube.
The cam cover is retained by 10 mushroom-headed
Allen bolts, four are out of sight in this photo and
need care with a good Allen key to remove them 

I've previously written about removing T300 cams so won't repeat myself here. In short, the tank has to be off (watch out for the fuel lines and be careful in case the fuel tap is stuck open when you disconnect them), ignition leads removed (preferably coils as well - it will give you welcome extra room).

Wonderful T300 Green profile cams exposed,
cam chain emerging from its tunnel on the
right-hand side of the engine.

Remove the cam cover (use a good quality Allen key - access to two of the bolts is restricted by the main spine tube of the frame so you want to get really good purchase on these bolts), put the bike on its  side stand and remove the right-hand crank cover to expose the ignition pickups and cam chain drive sprocket.

Doing the last bit of the job on the side stand will stop engine oil running out. I was doing this along with an oil change anyway so losing oil was neither here nor there in my case. It also makes the job easier because this way the cam timing marks are tilted up for you to see.

Arrow mark on cam sprocket shown parallel
with gasket surface for cam cover. 

Make sure the bike is not in gear (it's on the side stand now, remember) and then use a big spanner or socket on a handle to turn the engine over. Do this with the large hex nut in the centre of the ignition rotor until the timing mark next to a letter 'T' aligns with the ignition pickup and the arrow marks on the cam sprockets are horizontal, parallel with the machined gasket surface of the cylinder head. The 'T' stands for Top Dead Centre - it means the point at which two of the four pistons are at their highest point in their never ending journey up and down inside the cylinders. The pistons work in pairs, cylinders 1 and 4 make one pair and cylinders 2 and 3 make the other.  It doesn't matter if the arrow points to the rear or towards the front of the engine. It is in a position either way which minimizes the load put onto the camshaft by the valve springs. This way, only the valves of one cylinder will be acting against the inlet cam and the valves of one other cylinder acting against the exhaust cam.

Next, remove the cam chain tensioner from the rear of the cam chain tunnel, and the steel arch that serves as a top guide for the chain. This sits between the two cam sprockets (not in these photos I'm afraid). Then gradually release the bearing caps on each camshaft. Do two turns on each bolt, working in rotation around all ten bolts as you go.

I use a good single hex 10mm socket on a 1/4" drive ratchet handle. Do this for the inlet camshaft first, lift off all the bearing caps and keeping them in a clean, safe place, then pull the camshaft up with one hand and unloop the cam chain from its sprocket with the other. Repeat for the exhaust cam, putting a bar through the chain to make it easier to remove later on.

The ignition rotor must be removed
by releasing an Allen bolt that retains
 a large nut, and refitted with thread
lock and to the correct torque
after the new chain has been fitted. 

Cam chain drive sprocket exposed. The ignition pickup is
the black lump to the bottom left with a round silver stud in
the centre. That stud is the reference point for valve and
ignition timing, when it aligns with the various
marks on the ignition rotor. 

The cam chain tensioner blade and ignition rotor must now be removed. The tensioner is held on by a single bolt left and just above the cam drive sprocket. Push as rag under the rotor now, before undoing that bolt, to make sure you don't lose the washers when you undo it. Pull the tensioner blade up and out of the cam chain tunnel.  The ignition rotor is a metal disk that is bolted onto the end of the crank shaft with an Allen bolt that passes through the large engine-turning nut. The Allen bolt will be tight because it is fitted with thread lock. Again, good-quality tools really pay off here. When the ignition rotor is pulled free, you'll see the cam drive sprocket. It is half the size of the sprockets on the cam shafts because the cams turn at exactly half engine speed.

Feeding the cam chain down the cam tunnel and
guiding it out, away from its drive sprocket. 

You can now remove the bar you put through the cam chain at the top of the engine and feed the chain down its tunnel and past the drive sprocket, before replaceing it with a new one. It is easiest to put your bar through the new chain and dangle it down the tunnel, using your other hand to loop it over the drive sprocket. Replace the cam chain tensioner blade (not the tensioner unit yet), feed  the cams through the new chain and lay them loosely in their bearings. Refit the ignition rotor and check that the T mark is still aligned with the ignition rotor.

Reassembly is, as they say, the reverse of the dismantling process. There is a trick with the tension though, and in settling the green cams in a way that keeps the timing correct. I'm out of time myself now, so more about these tricks next time.

Comparing wear in the old (top) and replacement (bottom)
cam chains by showing how much more lateral movement
is possible with the worn chain than with the new. 

 I find it very hard to measure wear in chains accurately. The photo above shows how much extra lateral movement the old chain has compared to the new one. This can only be accountable to additional play in the side plates. I think, for something like this, it's as much about peace of mind as being confident the engine is about to explode unless preventative maintenance is done immediately.

The new chain, coupled with new engine oil, has made the top end noticeably quieter and the engine feels taught too (not forgetting the carb and air filter clean). I used Shell Ultra 4T fully synthetic 10w40 oil this time. Any fresh oil is impressive, I've found, by smoothing out gear changes. I've ridden about 200 miles on it so far and it feels great. But then, it is Summer and I love my bike.