1. Make sure your spark plug socket is the correct size before attempting to remove the plugs - a suitable one is supplied in the motorcycle's tool kit which is stored under the seat. Note that each cylinder has two spark plugs.
2. Access to the front cylinder spark plugs is best achieved after removing the fairing side panels (XL600V and XRV750) or the fairing (XL650V) as described in Chapter 8 (see illustrations). While it is possible to access the plugs with the panels in situ, access is very restricted, making the task fiddly, and the panels can be easily damaged should a tool slip.
5.2a. Front cylinder - right-hand plug
5.2b. Front cylinder - left-hand plug
3. Access to the rear cylinder plug on the righthand side is best achieved by either raising the rear nf the fuel tank or preferably by removing the tank (see Chapter 4). although on XL600V models removing the right-hand side panel gives limited access (see illustration). Access to the rear cylinder spark plug on the left-hand side is easy and unrestricted.
5.3. Rear cylinder - right-hand plug
4. Work on one plug at a time. When working on the front cylinder left-hand plug and the rear cylinder right-hand plug, clean the area around the plug cap seal on the valve cover before removing the cap to prevent any dirt falling into the spark plug channel. When working on the front cylinder left-hand plug take great care not to damage the radiator fins (see illustration 5.2b).
5. Pull the cap off the spark plug (see illustration). Clean the area around the base of the plug to prevent any dirt falling Into the engine. Using either the plug removing tool supplied in the bike's toolkit or a deep socket type wrench, unscrew and remove the plug from the cylinder head (see illustration).
5.5a. Pull the cap off the spark plug
5.5b. If you are using the Honda tool, locate it onto the plug and use a ring spanner to turn it
6. Inspect the electrodes for wear. Both the centre and side electrodes should have square edges and the side electrode should be of uniform thickness - if not, they are worn. Look for excessive deposits and evidence of a cracked or chipped insulator around the centre electrode. Compare your spark plugs to the colour spark plug reading chan at the end of this manual. Check the threads, the washer and the ceramic Insulator body for cracks and other damage.
7. If the electrodes are not excessively worn, if no cracks or chips are visible in the insulator, and if the deposits can be easily removed with a wire brush, the plugs can be re-gapped and re-used. If in doubt concerning the condition of the plugs, replace them with new ones as the expense is minimal.
8. Before installing the plugs, make sure they are the correct type and heat range and check the gap between the electrodes (see illustrations). Compare the gap to that specified and adjust as necessary. If the gap must be adjusted, bend the side electrodes only and be very careful not to chip or crack the insulator nose (see illustration). Make sure the washer is in place before installing each plug.
5.8a. Using a wire type gauge to measure the spark plug electrode gap
5.8b. Using a feeler gauge to measure the spark plug electrode gap
5.8c. Adjust the electrode gap by bending the side electrode only
9. Fit the plug into the end of the tool, then use the tool to insert the plug (see illustration). Since the cylinder head is made of aluminium, which is soft and easily damaged, thread the plug as far as possible into the head turning the tool by hand. Once the plug is finger-tight, the job can be finished with a spanner on the tool supplied or a socket drive (see illustration 5.5b). If new plugs are being used, tighten them by 1/2 a turn after the washer has seated. If the old plugs are being reused, tighten them by 1/8 to 1/4 turn after they have seated, or if a torque wrench can be applied, tighten the spark plugs to the torque setting specified at the beginning of the Chapter. Otherwise tighten them according the instructions on the box. Do not over-tighten them.
5.9. Fit the plug into the tool (the rubber insert should grip around the plug top) and thread it in by hand
You can slip a short length of hose over the end of the plug to use as a tool to thread it into place. The hose will grip the plug well enough to turn it, but will start to slip if the plug begins to cross-thread In the hole - this will prevent damaged threads.
10. Fit the spark plug cap, making sure it locates correctly onto the plug (see Illustration 5.5a). Install all other components previously removed
Stripped plug threads in the cylinder head can be repaired with a Heli-Coil insert.