Motorcycling: Valve Adjustments

Valve adjustments are one of the still unresolved problems of motorcycle maintenance, although with incredibly careful design and modern metallurgy, engine now hold their adjustments for a long time. This is the result of careful design balancing the natural tendencies of some parts of the valve train that tighten up, and others of eventually loosening up. Back in the sixties, I needed to adjust the valves on my Honda 175 about every 3000 miles.

Then I had a ten year span of riding a Yamaha 250 two-stroke with no valves. It was so simple mechanically, yet conceptually it was hard to understand how the thing worked at all, with almost no moving parts. Well the pollution Nazis and clean air Gestapo put an end to that little idyll, and the next bike was back to adjusting valves, but not as often as before, and now we had 4 valves per cylinder. But two cylinders and screw type adjusters meant the job was easy enough to perform every 10,000 or so kilometers.

My next bike was the one with the legendary valve adjustment, as in "You ain't never seen nothing until you adjust the valves on a CBX!" The CBX not only had 4 valves per cylinder, but also shim adjusters. Six cylinders equals 24 valves. No simple screw adjustment, you had to measure shim thicknesses and buy new shims to get everything back in spec. I actually did an adjustment of those valves, one three day weekend. I needed to buy a caliper micrometer, and a special Honda shim removal tool. I did not lower the engine, as I was instructed by the shop manual, which saved some time. Then I had to devise a Lotus 1-2-3 spreadsheet to keep track of what shims I would need to switch, and which I needed to purchase. Also, I had to drive across town three times to finally end up with all the correct shims. That was the only valve adjustment I performed on the CBX.

My next bike was better and worse. The BMW had only four cylinders, so 8 fewer valves. But to remove the shims, both the camshafts had to come off, which also required a new special tool, which I ordered, then drove an hour to London to pick up when it came in. Then I drove to Newmarket to buy the shims (only one trip this time, one and a half hours each way). I got the job done, and again it was the last time I ever looked at the valves, and the bike lasted another 80,000 km before I got rid of it, and not because of the valves.

I have a new bike, the Vulcan 900, at 30,000 km, and no human being has ever seen the adjustment since new. I believe shims are involved.

But then there is Mary Ann's Suzuki Burgman 400. We bought it used at 2,000 km, and I hope somebody else performed the initial valve adjustment. Now it has 20,000 with no further inspections. I was only slightly concerned about this single cylinder engine running at ungodly rpm's on the 401, with the old fashioned screw adjusters that were not famous for keeping a steady clearance. Then two days ago her bike would not start, and one of the possibilities was the valve adjustment. I did eventually start it, but then decided it needed the adjustment anyway. My only choice was take it to a dealer or do it myself. This would have been the very first time in my life that I trusted a dealer to do a valve adjustment, so I seriously thought about doing it myself.

When I looked at the instructions for the Suzuki, I noticed that I needed to remove the passenger back rest pad. I should not need to explain how stupid that was to anyone with enough interest to read this far. Upon further reading of the instructions, I realized that the seat, the underseat storage, all the back body work, most of the front bodywork, the seat, the air filter box, the throttle body, and many other nameless items, electrical connectors, and hoses all needed to be disassembled just to get at the cylinder head. Every single one of these items was a puzzle to solve with only the guidance of the perversely obscure (I might even say obfuscating) shop manual. However, there was a Burgman 400 forum online, which had instructions plus photos in colour. In case you're interested, it's here:

With almost 200 parts to keep track of, I asked Mary Ann to act as kind of a parts storehouse manager, cataloging and labelling parts as they came off the bike and washing the parts that needed it.

I finally got the bike apart in about 4 hours, and checked the valve clearances. They were all OK. Mary Ann found this funny and broke out laughing, but you had to be there to understand the joke. Another three hours putting it back together, and it is NOT as easy as "assemble in reverse order of disassembly". I only lost one nut that fell into the engine compartment never to be seen again, and one plastic bodywork fastener that was left in an aluminum pie plate on the patio, but a squirrel ran off with it.