However, like Achilles, they do have one weakness: the engine uses an interference design on the pistons and valves, so if your timing belt breaks, it's an engine rebuild. That's why my first GL1000 project had the engine in several Rubbermaid tubs when I acquired it -- the timing belt had broken, and the p.o. overestimated his ability to repair the damage. I don't want to tear down the engine on this bike, so I decided to replace the timing belts before I ever even start the engine!
The procedure is pretty straight-forward:
- Loosen the radiator, and pull it as far forward as you can, to provide access to the four bolts that hold the timing belt cover in place;
- Remove the four bolts that hold the two timing belt covers in place;
- Remove the left-hand and right-hand timing belt covers (I had to use a rubber mallet to break the covers loose);
- Use a 17mm wrench to rotate the crankshaft (the two, stacked gears in the center of the engine) until the alignment marks on the left-hand and right-hand crankshaft pulleys line up EXACTLY with the markings on the engine case:
- Verify that the engine crankshaft is at TDC:
- Loosen the timing belt tensioner wheels, and remove the tensioner springs;
- Remove the belts;
- Install the new belts, making sure that you do not rotate the crankshaft or either cam gear (yeah, right...);
- Reattach the spring to the tensioner, then tighten the tensioner bolts as required;
- Verify the timing marks on the cam gears and crankshaft. If they aren't right, loosen the tensioner(s), remove the belt(s), and try it again. It took me three tries (per side!) to get everything lined up properly ;)
- Turn the engine through AT LEAST two full revolutions by hand (17mm wrench on the crankshaft gears again) to make sure everything is working properly;
- Reinstall the timing belt covers;
- Secure the radiator.
This, of course, is a highly simplified, ideal case. When I dug into my bike, I found that the radiator was almost immovable, that I had to remove the engine guards in order to remove the timing belt covers, that I had to remove the horns (there are two on my bike; not sure if that's typical) to remove the engine guards, and that I needed (okay, "wanted") to clean up the timing belt covers because they were kinda nasty ;)
Also, I didn't bother to check the crankshaft position after lining up the camshaft gears when removing the belts, which means that I don't know if the previous owner botched the belt alignment, or if the crankshaft and camshaft gears rotated a bit when I removed the belts. This is why it is IMPERATIVE that you check and recheck the alignment before buttoning everything up. If your cam timing isn't set properly, at best the engine won't perform as well as it should, and at worst, you could break pistons and valves. Here is how my timing looked when I double-checked alignments:
Cams are aligned, but the crankshaft...not so much.
And here is how the cams looked with the crankshaft at TDC. I had to pull the belts and rotate both camshaft gears until they were aligned properly. It would have saved a lot of time had I checked the crankshaft position before initially installing the belts. <shrug> I'll know better next time.
Edit: I hadn't reinstalled the timing belt covers yet when I wrote the post above. After finishing with the timing belts, I grabbed one of the covers, and decided it needed a good cleaning before I put it back on the bike:
After about three hours of quality time with a Scotchbrite pad, some Meguire's Metal Polish, and several paper towels (and maybe a little swearing), I was rewarded with this:
Not perfect (not really even close, to be honest), but a lot better than they were. I intend to ride this bike, not enter it in shows, so I'm not going to obsess on polishing a steel cover that is placed squarely in the middle of the spray coming off the front wheel ;) In this case, "good enough" is exactly that.