On 30/06/2018 12:39, Dave Plowman (News) wrote:



400 miles a litre is *not* a badly worn engine. Even more so if it runs
OK. Could be something as simple as valve stem seals failed. And using a
much thicker oil in an attempt to reduce costs may just result in the
engine really wearing out faster.


As you almost suggest, the devil is in the detail.

This is what tabby said earlier

"20/50 is thicker, changing to that *can* reduce consumption. It's a
common tweak on a worn engine, the cost is a fraction more friction, but
not enough to notice any difference at idle on an open loop controlled
engine.

A litre per 400 miles isn't good, you *may* want to consider the other
dodge of adding a tin or 2 of that treacley oil to the engine oil.
Really reduces oil burn"

and he's right, that was one of the traditional routes from the days
where bore and ring wear, or valve stem wear, resulted in significant "burn"

As you say, it *could* be failed valve stem seals. No such thing in the
old days, but I've never seen a comparison of how much of the historical
improvement in consumption comes from the introduction of seals, and how
much from improved materials and engineering of piston rings and bores,
plus better anti-wear oil additives.

My academic friends in places like Leicester and Warwick reckoned that
one of the big steps forward was the introduction of plateau honing for
bores. You arrange for the first machining to introduce deep scores (and
high peaks), then you remove the peaks by honing to provide the running
surface for the rings, while the scores provide an oil reservoir which
gets replenished from below. It's certainly remarkable how you no longer
have to "run in" a new engine, or pistons following a rebore like we all
did when I first started rebuilding engines in the 1960's.

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