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2T Oil Mix

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by C15CO, May 30, 2012.

  1. Hi,

    Since rebuilding my engine a month ago it has been suggested to me that it would be a good idea to add 100ml of oil to my 10.5L petrol tank (this is on top of the oil that sits in the 2T tank) as a bit of insurance against a future seizure.

    I've read some mix opinions online about too much oil causing the oil to thicken up restricting the flow and therefore running lean.

    What do you guys think?

    Is it a good idea?
  2. It's not that the oil thickens up the petrol that causes the leanness, it's that the oil takes up space that would otherwise be occupied by petrol so less petrol goes through the jets, resulting in a lean mixture.

    However, 100 ml in a (full) 10.5 litre tank works out at ~100:1 which I doubt would make a discernible difference.

    Nonetheless, If you're running a good quality oil in the oil injection system, the oil pump is correctly adjusted and the rebuild was done properly, followed by running in according to the book, additional oil in the tank shouldn't be necessary.
  3. I've heard of a few guys in the UK with worked motors running 100:1 in addition to the oil pump for peace of mind for bottom end lubrication, so depends where you are trying to protect the seizure from. If you said approx ~33:1 is the oil pump mix (I dont know the nsr's oil pump mix), you are talking about replacing 1% of the remaining 97% fuel with some oil. Which brings it up from 3.0% to 3.9%, or a mixture of 25:1 instead of 33:1. It doesnt sound like much but is nearly a 30% increase in oil to the mix. At the end of the day rich and lean refers to the amount of fuel in the mix for a given volume, not the oil, it's the fuel that keeps the cylinder temp in check, so at face value adding that oil will lean the fuel mixture by 30%. There's some guru 2 strokers here surely that can drive a hole through my napkin logic.
  4. I've personally doe this. It doesn't hurt at all and is good insurance to help protect your engine a little further.

    In my case my modified Aprilia RS125 wasn't supplying enough oil at cruising RPM/Throttle Position resulting in the crankshaft big end bearing running dry and destroying itself.

    Finally at a ratio of 100:1 so your 100ml to 10.5L tank the change in fueling from oil displacing petrol is so minimal that you may as well not worry at all. Just think of it this way, 100:1. That's 1%. There's more effect on your engine's fueling requirements from a ambient temperature change of about 4.C

    Oil added to the air fuel mix via the oil injection is irrelevant in regards to tuning as this has no effect on fuel metering. All you need to worry about is how much oil is displacing petrol as it passes through the jets in the carburettor :)
  5. Thanks for the advice so far. I'm a little confused which way to go. Does anyone else have any further advice?
  6. I was advised to add one or two capfuls of oil each time I fill up my RS 125 by someone who loved their RS 250. I was also advised to slosh it around and not just chuck it in. Dunno how it'll go but I intend to do it.
  7. 100:1? Jeez my old dirt bike took 35:1

    Doesn't your RS125 have a separate oil injection tank that you fill up? If not then premix it properly unless you want your motor to blow up...
  8. #8 Ljiljan, Jun 2, 2012
    Last edited by a moderator: Oct 24, 2015
    Guys, please read. He's adding an extra 1:100 to the oil already in the mixer. Essentially turning a 1:40 ratio to 1:30 or 1:35 to 1:25.

    • Like Like x 1
  9. Oh yeah no shit...
  10. Possibly recommended that extra 100:1 for break-in after the rebuild. It probably is "broken-in" by now.
    Here's one engine rebuilder who actually doses the tank for a break-in but they don't say how much. http://www.dehnerssports.com/Breakin.html
    They do say to carry a set of plugs during that period because of possible oil fouling.
    I've heard of some car owners adding 2T to Fuel but at about 2 ml per litre.

    Edit: above link would be using 1 pint for 6 gallons so 1:48 in tank for break-in.
  11. Good point (y), go for it then.