Sorry for all the questions, But another PC50 question! OIL?

[SpannerMonkey]

I'm burning oil on the bike as we all know, but from what I can see, the oil that was in the bike seems to be really thin in viscosity.
IIRC a thinner oil works its way past the piston rings and valve seals/seats or something like that causing it to burn oil.

Also... I remember reading up that modern multi-grade oils are also full of detergents and additives (No shit...) that classic and vintage engines (Such as mine, being a 1972 four stroke) do not get along with.

So... for an engine I pretty much thrash MERCILESSLY with no oil filter... what would you recommend? Average riding time on it is 15 mins to 20 mins.

Is any of what I said correct?
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[hmmmnz]

chuck the cheapest oil in you can find, 30/40 may be,
i don't know if you can even buy that any more


basically you want an oil with a low second number, the lower the number the thicker the oil

eg 0w/50 is thick on start up (to build up oil pressure quickly) but gets really thin when warm
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[SpannerMonkey]

Well I have 20-50 to put in as temporary... I thought it was the other way around and 50 was thicker than 40. not sure what made me think this.
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[weasley]

The first number is for cold start; the lower it is, the colder it will work at (and thus the thinner it is at a given cold temperature).

The second number is for operating temperature; the higher the number, the thicker it is at 100 deg C.

You will not find a 0W-50.

20W-50 will probably suit your needs but TBH it'll probably be a case of trial and error to find a modern oil that matches your, ahem, classic machine.
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[SpannerMonkey]

Another quick thing, no point starting a new thread... I have a VERY slow leak in my crank-case gasket right at the top. Not too much to worry about, but I've seen things out there that apparently stop gasket leaks? like oil additives? any idea what this stuff is like?
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My bike? A YX140 powered one-off Monkey Bike, something a little different!

[Noxious89123]

[jimspeed]

snake oil dont bother basically mate, all they attempt to do is swell the gaskets up to seal the problem. also any additaves you put in the oil may not agree with the engine etc.
does the clutch run in the oil too like most bigger bikes?
(I had one of those when I was 14 to thrash round the fields by home so it brings back memories lol)
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[stinkwheel]

As I recall (and this is pretty dimly mind, it's been a long time since I guddled in one of those engines), there is an oil filter, and a very good one. It's just not what you'd think of as an oil filter in the traditional sense.

It's a centrefugal filter. The oil passes through the rotating part of the clutch assembly. As it does so, it gets flung to the outside of a metal plate which is aprt of said clutch assembly. There are a series of notches round the edge of this plate which trap any particulate matter in the form of sludge. Once in a blue moon, you take the engine cover off and scrape the sludge out with an old screwdriver.

I think there is also a basic gauze type filter on the oil pump pickup which is worth giving a clean if you're in there.

As such, detergents are actually a good thing because they help keep any muck suspended in the oil which the filter can then catch rather than sludging it in the sump. Other additives may or may not be a good thing depending on their effect on the clutch.

Pretty sure I used to use 20w-50 in mine but it's possible they were designed to run on either straight 30w or 50w oil initially, you'd meed to check a manual. This doesn't mean that is what's best, it's just what was available at the time. Multigrade oil is almost certainly better.

Ring blowpast shouldn't be an issue, the Japs build tight engines and always did. That motor should have two piston rings, a three piece oil control ring and I can confirm they have very tight valve guides with seals on. If you're getting blowpast, it needs new rings or a rebore.

Where exactly is this oil leak? I don't recall there being a gasket at the crankcase join, it's metal to metal.

EDIT: I wonder if your crankcase breather is blocked. You have many of the symptoms. ie down on power, burning oil, oil leaks from the crankcase. I honestly can't remember where the breather is on these, it's probably just a small hole in the top of the crankcase somewhere.
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[SpannerMonkey]

The oil leak is from top of crank case... it's VERY slight, I cant see where it originates from as the frame is in the way and I do NOT want to undo any bolts on this if I can help it!
And yes... The minute you mentioned crankcase breather I prettymuch facepalmed... It does feel like the engine inside has a LOT of pressure... Exessive engine braking... it burns oil (BUT... Only on startup, fades after a min or 2 to nothing)
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My bike? A YX140 powered one-off Monkey Bike, something a little different!