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[stinkwheel]

Worth remembering the main point of "synthetic" oils which is they will take longer to break down and start to lose their lubricating properties and correct viscosity when under stress. So a fully synthetic oil will effectively last longer.

Taken to extremes, I have a friend who uses "royal purple" engine oil in his 1100cc air-cooled endurance race bike. This stuff is super expensive. The engine gets a full strip down and rebuild after each race but he catches the oil, runs it through a filter and puts it back in again for the next race.

So while you can question the point of using synthetics in a bullet, it's certainly not wrong.

I'm pretty sure the amount of sludging that happens is more down to the detergent content. As I implied above, on old engines with no oil filter, sludging was desirable so any particulate matter settled and accumulated in the bottom of the sump/oil tank and could be drained off. Hence the practice of flushing engines with thinner flushing oil during an oil change to remove the sludge. On an engine with a filter, it's desirable for any particulate to remain suspended in the oil so it can be caught and removed by the filter. Also why that infamous video of the Indian streeet mechanic flushing the hell out of a UCE motor with oil then petrol is so cringeworthy.

So in an ideal world, in an iron barrel bullet, you'd use a fully synthetic oil with a high detergent content and as many friction modifiers as they can cram in there. In the real world, it's probably an unecessary expense.

Another thing worth considering -which has given synthetics a bad rep over the years- is if you start putting high detergent oils in a motor which is a bit worn and hasn't been using them, it will start to flush deposits away from where they have built up. All of a sudden they start burning oil. The oil didn't cause it, it just unmasked it.

Used to be a common thing in the forces when someone pinched military spec oil for their old beater car. The military oil has a LOT of detergent in it. The car would start smoking like hell and running like a dropped toolbox falling down the stairs.

[Wheaters]

I fitted a used engine to the previously mentioned trials car, bought from a dismantler. It came with a three month warranty. I had no service history for it but it came from a relatively low mileage car and despite the oil being very dirty it ran really well. I changed the oil and filter twice in quick succession as a precaution. However, after a couple of thousand miles it suffered a major oil pressure surge when starting from cold. It went off the scale on my oil pressure gauge (100 psi), the canister type oil filter was forced off the block and all the oil blew out onto our block paving driveway in a few seconds. I soon worked out that the pressure relief valve in the pump had jammed closed. I took it off which is a big job on these engines; the oil pump assembly is a casting which forms the lower front half of the engine and its lower edge is where the sump pan bolts up. The cam belt etc also has to be removed, because it’s crank driven and sits behind the crank pulley.

The PRV was seized totally solid and the entire assembly had to be replaced. It could only have been caused by loose debris in the oil system. I suspect my oil changes had flushed it out from the sump. I had used part synth oil, as per the manual. This oil has detergents designed to carry the debris round the engine. I then discovered that a new pump would cost over £300 from a UK Suzuki agent. Thankfully I managed to import one from USA at far less cost.

[windmill john]

Interesting the references to the iron barrel models burning oil.
I ran a 350 for 20k miles and never had to add oil between changes. I did change at 2k miles though.

Lucky bugger, I’ve just added 300 ml-ish and only covered a few hundred miles from the last change.

I used to worry about oil types... still do! But I feel a bit better since someone posted “Some oil is better than no oil and new oil is better than old oil”.



John

[Cranky]

They wont tell you but oil is pretty much indestructable these days--just your normal stuff let alone fully synthetic 0 viscosity.

They love you to buy the best for your engine like the best ring for your girlfriend --don't make things better though does it.

Its getting so expensive these days that truckers use oil filter changes rather than oil changes . The oil is fine just keep it clean.