Technical Q and A for classic motorcycle maintenance and repair.
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Q: I have a 1972 Triumph T100. While riding, an exhaust rockerbox cap came off and the adjusting pin and lock nut came off also. I probably rode it a couple of miles home with it just running on one cylinder. I replaced all four adjusting pins and lock nuts, and set the valves correctly. The bike started on the first kick and sounded good in the garage, but when I tried to take off, it has no power. I will readjust the valves, but I suspect a burned valve. What do you think? — Doug/via email
A: Burned valves usually result from valve clearances being too tight, keeping the valve off its seat, where the heat gets transferred from the valve to the cylinder head. In your case, the clearances were too loose, so the valve didn’t lift at all. You didn’t say whether it was an intake or exhaust valve that the adjuster fell off of, but it shouldn’t really matter in this situation. Check your compression, and if possible do a leak-down test. That should give you more info about the condition of your engine. It’s possible that there is some carbon buildup on a valve stem or seat that is keeping it from closing fully. That would also affect power output.