Oil Stop Leak Additives?

[Admiral Beez]

My 1982 GS650G with 45,000 km on the clock burns about a litre of oil every 800 to 1,000 kms. There's no leaks and no visible smoke behind (so my riding mates say), and the plugs looks good, a little black, but grey on top, but the oil continues to burn. I've last week switched from 10w40 regular motorcycle oil to Motul's 15w50 synthetic to see if the thicker oil makes a difference. I've recently had the valve clearances checked and shimmed, and the compression is good, over 120 PSI on three cylinders, one above 100 PSI, but only just.

Presumably the motor needs a tear down, with new guides or rings. But that would be an mechanic expense beyond the value of the bike, I don't plan on keeping the bike for years, it's my only machine and I want to ride. Thoughts on oil additives like https://www.canadiantire.ca/en/pdp/l...-0380260p.html

[Grimly]

That's just a seal sweller, which is of value as a stop-gap measure until you can get to the seals and replace them. It won't do much, if anything, to cut down oil burned in the bores. You might find the switch to a thicker oil will work well enough, as the 10w40 you've been using might be prone to high evaporative losses. Even another 10w40 with different characteristics might do the trick.

[salty_monk]

You could do the teaspoon of oil compression test to work out if it's in the bores or if the stem seals need doing. Often it's just the stem seals have dried out. It's possible to do the stem seals whilst the engine is still together & in the bike..... It's quite a low mileage for one of these bikes, I'd be surprised if the bores are worn.

[Admiral Beez]

That's just a seal sweller, which is of value as a stop-gap measure until you can get to the seals and replace them. It won't do much, if anything, to cut down oil burned in the bores. You might find the switch to a thicker oil will work well enough, as the 10w40 you've been using might be prone to high evaporative losses. Even another 10w40 with different characteristics might do the trick.

One of my mates rides a high milage older bike and said his oil burn vanished once he switched to synthetic and a heavier weight. It is a funny thing, no smoke, plugs are okay, no drips underneath, lots of power. Where's the oil going?

[Grimly]

Before the top-end rebuild I was using oil at about 300 miles per pint. Not a trace of oil smoke or haze from the exhaust, either. It was just tired rings and old rock-hard valve stem seals causing it. That was with all oils I had in it, but mostly 10w40 and 5w40.
Evaporative losses in lighter oils can be a significant cause of mysterious oil consumption even in an engine that's otherwise good.