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Blowby on a bike

Discussion in 'Technical and Troubleshooting Torque' started by pengo, Jan 16, 2011.

  1. G'day

    I've got a GPX250R that suffers blowby and so is throwing oil into the airbox.

    Short of an engine rebuild, would using a thicker or thinner oil help to alleviate this blowby somewhat, so not as much oil is transported thru the crankcase breather hose into the airbox? When would the blowby be throwing the oil into the airbox tho most, when the bike is cold or warmed up and running at optimal temp? I guess the catch22 is that if a thicker oil would not get thrown into the airbox as much, coz it doesn't get as thin, due to take longer to heat up its less efficient than a thinner oil. Since its not providing as good protection as engine oil works the best when its heated up fully and at its thinnest?

    So far I've tried 10W50 Motul 5100 and Shell Advance SX4 15W-50 and bother oils end up in the airbox. If I dont drain the airbox via the drain hose, it'll build up in there and end up leaking out the airbox water drain hole.

    So yeah just wondering - as a long shot if a thinner or thicker oil would help at all? Also I live in SE QLD so I think I could "get away with" a thicker oil?

    I found it difficult to source 20W-50 bike oil after looking into it previously, so from browsing the oil threads here I was just gonna try some 20W-50 Valvoline XLD. Is there any XLD versions I should not get (incase of friction modifiers etc)?

    Also I want to try Delo Multigrade but I got warned away from using it in a bike with blowby and it might cause damage? Would the same be the case with the Valvoline? Why would as I'm lead to believe a high quality oil like Delo cause a problem, where something of lesser quality (but made for a bike) like Shell Advance SX4 won't?

  2. Are you sure it's blow by? It could be a problem with the crank case pressure relief tube. This usually is a small tube going from the crank or gear case to the inlet chamber (no longer legal to vent to atmosphere). I've got an M109R which this is a common complaint as surge causes the oil to slurp up there and get sucked into the left airfilter. The fix for me was to put an PVC valve in the tube which restricts the flow when the airbox depressurizes.
  3. When you say throwing oil do you mean a quantity of liquid oil?

    Its normal for an engine to release blowby gases from the crank / cam breather, its only when its excessive that it can be an indication of a worn engine.

    Also an oil mist will come out of the breather pipe, especially when the airbox is lower pressure. Its completely normal, and also normal to build up an oil sludge after about 10 years of use.

    So the grade of oil will make no difference. Just stick to the proper grade and give the airbox a good clean out, maybe the carbs too if theres obvious oil sludge on them.
  4. Do you know who stocks that?

    I'm getting an ex racing mechanic, recommended to me off a local riders forum to do a compression test (and possible valve check/clearnace; tho trying to keep costs under $100) this week so I guess we will know for sure. Tho I've already had one mechanic look at it and he said blowby. I've also had a "bike enthususiast" with a decade or more of experience with bikes have a look over it and he rekons blowby as well. If the valve clearances are wrong, what would this lead to? Would it actually lead to compression issues? The bike does not lack power or blow smoke, I went on a long club ride and one guy road behind me purposely to watch to see if the bike was blowing smoke and it doesn't.

    I've spoken to a mechanic about doing something like you describe and others have suggested the same, but the mechanic I spoke to recommended against it as he was concerned about pressure being restricted and so possibly leading to a blown engine. Tho I'll raise it with this ex racing mechanic this week to see what he said, it looks like he might be better able to help as he has some contacts that might be able to supply an oil catchcan (at the very least) for my bike as a bandaid fix, as from riding to Brisvegas from the Goldy each day I need to drain anywhere from 25ml-75ml from the airbox drain hose (the one with the cap and metal clip). Also when I went to clean the air filter and check the airbox, it was full of oil and the filter absolutely drenched in oil.

    As far as modifying the crankcase breather, others have suggested the same but after speaking to a mechanic he recommended against it. As he was concerned it would lead to a blown engine due to it restricting release of pressure out the crankcase. Tho I'll see what this ex-racing mechanic has to say, as thru his racing experience he might know what could be used to allow pressure release but restrict oil from travelling into the airbox. Tho I'm aware oil vapour is meant to go into the airbox via the crankcase breather, but the problem I'm having is that its not vapour its actual oil (as I guess the pressure is so great oil is able to be forced thru the s shaped breather hose into the airbox).

    Basically the airbox has been cleaned out numerous times and the spark plugs replaced (when the plugs were replaced, the mechanic said the old ones were in acceptable condition) with the carby balanced. As far as lacking power I don't really know as my only experience with bikes is this one and the ones I rode during qride training and compared to the 250s I rode then my bike doesn't seem lacking at all. Also on the M1 I am able to get to speed (ie 100-110) without much effort, it takes as long as a 250 should short of a 2 stroke I believe. Tho the mechanic will know for sure I guess.

    I guess the compression test will be a big indicator on whats causing so much of the oil to get thrown into the airbox?
  5. Supercheap Auto carries Penrite motorcycle oils, pretty sure I've seen that particular oil in my local store before.
  6. Fit an oil catch can that vents to the atmosphere. It's against EPA regs but meh! Better than your bike choking on it's own vomit!
  7. Sounds like its overfilled, thats the first thing that comes to my mind anyway.

    On your valves, poorly adjusted valves will generally make your bike perform poorly and not be as easy to start. You may notice a loss of power, you may not, but either way its bad for your bike as valves can tighten up and eat into the valve seats in the head of your engine. This can need costly repairing if left too long.

    - boingk
  8. Its not overfilled as I did an oil change to switch to shell advance, and only topped it up to 1.7L, purposely stopping short of the required 1.9L and it sitll did it.

    Just drained it now and approx 1L came out. So yeah wasn't overfilled.

    Got the penrite from supercheap, piked up two 1L bottles.

    Anyway bought some poptops and gonna to empty one out (drink its contents!), and tape it to the airbox drain hose.

    I'll still leave the crankcase breather connected to the airbox.
  9. I'm with UDLOSE. Pipe it overboard and keep an eye on the level.
  10. Ideally you want something with a baffle before the breather because you don't want it overflowing out especially infront of the rear wheel!
  11. If I dump it onto the ground its liable to get onto my rear wheel... not a good idea!

    I've rain the airbox drain hose inot a (squished) poptop bottle. Going to go out testing it now.
  12. You run a length of flexi hose out to behind the numberplate and dump it behind the back wheel.
  13. Yeah good idea, bunnings would prolly sell something I take it? Just gotta make sure its rubber anything else that could melt.

    Just got back from testing, nothing has run off into the bike so far.

    Maybe the Penrite 20W-50 oil has fixed it? I noticed the bike ran pretty sweet on it. Not that the bike was running horribly on the previous all, but definately no problems or anything bad to report. Geer changes smooth as and acceleration is fine.

    Guess we will see how it goes over the course of this week.
  14. Yeah, tell us how the 50 weight goes in it.

    Another thing you may want to try if the 20W-50 Penrite still doesn't go well, is to try some 15W-40 in your bike. It'll be fine for your GPX and I've run a heap of bikes on 15W-40 without any problems at all. You may find the lwoer viscosity helps stop the problem.

    Lastly, you may have just had a partially blocked oil passage somewhere. The multiple oil changes might've flushed something out. Either way, let us know how you go.

    Cheers - boingk
  15. I just used Supercrap 1/2" heater hose on MrsB's Ural. Supposedly not oil proof but I had a roll at the time so it got pressed into service. It's not caused any problems so far, presumably because the actual quantities of oil are miniscule and the temperature and pressure are basically ambient for most of the pipe run.
  16. Got a compression test done today, mechanic said its compression is fine....

    As he comes from a racing background, he said on KTMs and other bikes they would either run a catchcan in the airbox or stuff the crankcase breather hose with gauss. So he stuffed my crankcase breather hose with some guass, gave it a test ride and then thing didn't blow up so all good... I guess we will see how she goes on the ride back home today, as its a good 1hr and a bit ride on the highway.
  17. I had an old '79 XS 650..she would wheeze oil and fumes from her crankcase breather hose. I just re routed it so it would drop any oil onto my chain.
  18. There's an idea.

    Self lubing chain LOL!

    One problem, engine oil isn't chain oil? Wouldn't the oil flick everywhere and possibly onto the rear wheel?
  19. Any oil is fine on a chain, it's only real purpose is to keep water away. The actual lubrication is taken care of by the grease that's packed inside the chain in the factory.