Ways of quietening a rattly engine/making it last a bit longer?

Any tips for quietening a rattly/slightly smoky engine and making it last a bit longer? I gave my mate my '95 Cavalier (16v 2l engine, 108k
miles) with the warning that it needed an oil change and it was leaking oil from the rocker cover, and it needed regular oil checks.
Of course, he did nothing and let the oil fall below the bottom of the dipstick. The engine is now rattling - it sounds tappety - and burns oil (exhaust has blue-white smoke.) Engine was pretty good before this.
I've replaced the rocker cover gasket - it's a flexible rubber seal and had gone brittle and had cracked in several places - and have topped up the oil.
Any tips for making the engine last 11 months to the next MOT (I don't expect it'll pass on emissions, at which point he'll scrap the car) - will a heavier oil, any of the snake oil stuff (Wynn's, STP, Slick 50 etc.) help? It has 10/50 in at the mo, and I was thinking a cheap 20/50 might help.
Thanks.
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I have heard of sawdust in the gear box, perhaps it might help in the engine?
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Malc

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Malc wrote:

Well, it should stop the smoke.....
Chris
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The damage has already been done. Also, if it smokes, don't drive it (I f%^&ing hate following smokey old motors). The damage is probably top end, cams/followers but it sounds like the rings/pistons/bores are fubarred too. Just get a cheap s/h engine from the scrappy: Your one is terminal.
JB
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Out of the oil additives mentioned, Wynns is by far the best for quietening and preserving a clapped engine, and yes use it with Duckhams 20/50 or similar.
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