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I have never tried tooth paste (for this purpose, I might add...), but fine valve lapping compound from the auto parts store works. I believe its 600 grit, and it's especially made to lap metal parts.
 

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About 30 something years ago, when I was first being taught to work on engines by some Old Timers I learned a few things that stuck. Using tooth paste or making a paste with baking soda and water to lap valves. For the brave, I was taught to make a slurry with baking soda and gas to dump down the carburetor to lap valves on a running engine. A few years later, I learned that you could buy Valve Lapping Compound in a tube.
 

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About 30 something years ago, when I was first being taught to work on engines by some Old Timers I learned a few things that stuck. Using tooth paste or making a paste with baking soda and water to lap valves. For the brave, I was taught to make a slurry with baking soda and gas to dump down the carburetor to lap valves on a running engine. A few years later, I learned that you could buy Valve Lapping Compound in a tube.
Whoa... That would probably lap the rings and cylinder walls more than it laps the valves!
 

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Valves actually spin when an engine is running. If you pull a valve cover, put a mark on the valve stem and start it up, you will see it. You are right though, it will lap the rings as well. I guess some of the old school hacks would really make most either cringe or think about it.
 

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Valves actually spin when an engine is running. If you pull a valve cover, put a mark on the valve stem and start it up, you will see it. You are right though, it will lap the rings as well. I guess some of the old school hacks would really make most either cringe or think about it.
I'm a shade tree mechanic/hot rodder/drag racer and I grew up with a lot of old timer hacks, some work and some are questionable at best. I figure the most questionable ones came from my dad, and I just loved to prove him wrong. So yeah, the valves can turn a bit, but not by design. It's only an effect of slight misalignment in the valve stems and the rockers, and most importantly: The valves will actually have to turn while seated for any lapping to take place.

I'm thinking about the good, ol' days when I was lapping Chevy small block heads by hand, took a lot of work to get a good seat. Got the first one done, then thinking "only 15 more to go... where's the damn beer!". Anyway: I figure the "hot lapping" won't do much to the valve seats, it will pretty much only wear the rings and the bores unless you can really make the valves spin while seated under spring pressure.

A slight digression from the topic, although interesting. :)
 

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You can get sets of 3 different grits of lapping paste from Amazon pretty cheap watch Mel64d all bolt lapping video since you have to remove the barrel anyway it’s worth doing. Lap them til you have full contact …
 

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Discussion Starter · #27 ·
You can get sets of 3 different grits of lapping paste from Amazon pretty cheap watch Mel64d all bolt lapping video since you have to remove the barrel anyway it’s worth doing. Lap them til you have full contact …
Yeah that’s what I wound up doing. Ordered some wheeler lapping compound 3 grit type set. Supposed to get here sometime this weekend. Guess I should watch Mel’s videos on it in tye meantime.
 
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