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YZ_MAN

Would belray EXL 10w-40 be good in YZ 250F

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Yes. I used that oil in my 426 for quite a while before switching over to the EXS. The reason for the switch was to try to improve the somewhat notchy shifting...which it did. Change it often and you will be fine.

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can't see any probs using a 10w-40 in a 250F and bel-ray is usually pretty good quality oil. though i'm runnin aral 0w-40 in my '04 450F, motorex do a 0w-40 too but i havent tried that yet

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can't see any probs using a 10w-40 in a 250F and bel-ray is usually pretty good quality oil. though i'm runnin aral 0w-40 in my '04 450F, motorex do a 0w-40 too but i havent tried that yet
Why would you think it would not be good???

10w-40 is a recommended oil grade. I use it, and I think it's nearly ideal, although I don't use the Bel Ray. But use caution with any multigrade oil with greater than a 3:1 ratio between the low, "winter" viscosity grade and the higher. Stick with a good full synthetic, or an oil that you know will retain its viscosity if you use an oil with a 4:1 ratio. I am very suspicious of all 0w-? oils, and I have avoided using a 5w-? oil up to now for the reasons I lay out in my responses on page two of the following thread:

http://www.thumpertalk.com/forum/showthread.php?t=270883&page=2&pp=10&highlight=multigrade+viscosity

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aside from the technical reasoning, the aral oil has a genuine porsche part number on the barrel it comes in, if its good enough for a 1/4 million dollars worth of car its well and truly good enough for my $12000 (aussie dollars) dirtbike.

manufacturers recommendations are designed to keep a chimpanzee from stuffing his bike. while one of us are chimps it is worth being aware that there is more scope for performance than what the manufacturer dictates. 43.1hp at the treads on a dyno dynamics dyno (not a dynojet!!) isnt a bad effort considering it started life at 34 or so and has since copped a set of kibblewhite valves springs and retainers, a valve seat job to suit the new valves and correct the inconsistencies from the factory, a flow job on the head, hotcams, a new exhaust , a new air filter, and some largeish holes in the airbox to help it breathe and jetting to suit.

i want to be clear about one thing though, i mean no disrepect to grayracer513 in my comments. what it really comes down to is that there are many ways to approach the set-up of your bike. its your baby after all and if you are comfortable using bel-ray go for it, i like my aral zero weight it works for me, joe bloggs down the road may prefer custard for whatever reason. if youre happy with it and its not gonna destroy your pride and joy then use the oil and go forth and roost

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And I mean no disrespect to you, or Porsche. Nevertheless, let me point out that Porsche does not recommend that oil for use in a transmission, but that's where you are putting it, and it's what makes and issue of this particular aspect.

If you want to be certain, all you have to do is take sample with 10 hours on it in for analysis. When it gets back, look at the viscosity. You may be surprised.

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at 10hrs the oil is dumped and a fresh batch is put into the bike, along with a new paper element filter (as per the genuine yamaha part). as such the change in viscosity at the 10hr mark is not particularly important. the engine as you're no doubt aware is that of a race bike albeit with a milder cam in stock form, and being a race engine i treat it as such in the regard of trowing high quality oil at it regularly. however, i will look into getting the viscosity tested as that particular piece of information would be handy to know.

when i do get the info on the used oil viscosity i'll be sure to forward it to you if you like

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...as such the change in viscosity at the 10hr mark is not particularly important.
Then sample it at 5. I rather doubt the oil suddenly changes at the tenth hour. The moderator on the 250F forum had a sample of 10w-40 come back as 8w-19 after one 1 1/2 hour race.
when i do get the info on the used oil viscosity i'll be sure to forward it to you if you like
Please post it. That would be great.

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