1982 Honda CM 450A tapping sound

I was browsing around the net looking for suggestions / info on my tapping issue.

My cm 450A is tapping and have been told it’s the lifters and they need adjusted, what tools and what do I need to do to resolve this issue? I have been to several bike shops around me locally and have been told they can’t work on anything that old due to this issue or that.

The bike runs like a champ, no over heating issues, cold starts without a hitch, hasn’t died on me while driving upwards of 2 hours straight knock on wood. It’s just loud, sounds like it’s chopping rice like a moped…

So it looks like I’m stucking doing this on my own. Any advice would be greatly appreciated.

P.S. I am somewhat mechanically proficient when it comes to vehicles, however all the work I’ve done on this bike (New handle bars, new headlight assembly, paint work, new seat cushioning and cover, new battery, oil change, new plugs and wires) I’ve done myself without a manual. But when it comes to opening up the engine, I’m clueless.

Hi Onnie,

Tapping from the top end is commonly due to valve clearances that are out of adjustment. If valves aren’t kept in spec for long periods of time, damage can be done to the valve train. A rattle sound is often caused by a stretching cam chain.

You’ll be surprised to learn how simple it is to adjust the valves on your bike. It should be done every few thousand miles. I generally check my valves whenever I change the oil – it’s easy enough.

For tools you won’t need much. You’ll need a basic set of metric sockets, a flat head screw driver, a 10mm (or is it 12mm) wrench,and a set of feeler gauges

Motorcycle Feeler Gauges tools

Feeler gauges can be bought at most auto parts stores, or Sears always has them as well. Just make sure to get a set that has the sizes you need. For your bike the intake clearances are 0.08-0.12mm and the exhaust clearances are 0.12-0.16mm . So just make sure your set has sizes in that range and a couple up and down in each direction.

You can download the repair manual for your bike from my site: Honda CM450 Service and Repair Manual. Valve adjustment procedure starts on page 68.

Let me know how it goes.


Ok so I adjusted the lifters to spec accoring to the manual exactly like the manual said. The bike now seems to have a more rumble to it, the lifters are still tapping but sounds like a lower pitch as if they may be now too loose…

Before they sounded like a air compresser tapping, now sounds like a box fan tapping if that makes sense. I watched a couple videos on youtube of others adjusting their valves and one guy said you cant hurt anything going a little loose but you can hurt the engine if going too tight.

So in this case should I leave it as is (seems to be running fine, just as a lower pitch with a little more rumble) or should I tighten them back up to where there is no play in the lifters just like when I started?

Great Onnie! Yes, you’re right, it’s better to have them too loose than too tight. You won’t physically damage anything by having the clearances set too loose, but the bike may not run properly. Sounds like you’re probably OK. Keep in mind that every tappet valve train is going to make noise. Even with the valves in perfect spec there will still be some tapping – it should sound like a sewing machine.

Just let them be, and next time you change your oil check them again.


i did exactly that but now i cant keep the bike running for crap

Well – having the valves set isn’t your issue then!

If the valves are now in spec than that’s one thing to check off your list. Getting an old bike to run sweetly takes some effort and can be frustrating at times. What’s the symptom? Carb related?


Evan Fell

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