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My 81 GW has had what sounds like valve tappet noise for years. I've checked and set the rocker arm clearance twice over the last two years, probably within a 1000 miles since the last time. Still the noise persisted. No exhaust leaks, couldn't nail down any spark leakage (even changed to automobile coils, which works nicely by the way). The tapping was slowly getting worse, and I found some tiny shiny stuff in the oil yesterday. I figured it was soon done for given the price of parts to overhaul.
I wanted one last check so I removed the right valve cover and timing belt cover. Cut off the top 1/3 of an old valve cover and put that on so I could see it run without dumping oil everywhere - I was thinking maybe a worn rocker shaft moving around or something. The cam belts ran smoothly, the valves all seemed normal enough. Pushed one of the tappets against the valve - the noise changed. Turns out the end of the valve stem was seriously dished. Using a flat feeler gauge gave a false reading. It has actually chewed down the end of the valve over 1/16." I screwed in the tappet, the tap tap tap went away and just left a nice purrrr.
Gotta admit I felt a little dumb. It sounded just like a collapsed lifter on a car I used to have, but I had checked the clearance! I've worked on engines for 35 years and this was a new one to me.
Wayne
I wanted one last check so I removed the right valve cover and timing belt cover. Cut off the top 1/3 of an old valve cover and put that on so I could see it run without dumping oil everywhere - I was thinking maybe a worn rocker shaft moving around or something. The cam belts ran smoothly, the valves all seemed normal enough. Pushed one of the tappets against the valve - the noise changed. Turns out the end of the valve stem was seriously dished. Using a flat feeler gauge gave a false reading. It has actually chewed down the end of the valve over 1/16." I screwed in the tappet, the tap tap tap went away and just left a nice purrrr.
Wayne