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Thread: Dorsoduro Crankcase Breather

  1. #1
    apriliaforum expert rule62's Avatar
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    Dorsoduro Crankcase Breather

    I was exploring how the crankcase breather worked on the DD 750 and noticed that there is no 1-way valve or oil catch-box between the crankcase and the airbox. There is simply a hose connected from the case to the airbox.
    Here are some pictures of the hose connected to the bottom of the airbox.
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    Here is the hose connected to the crankcase.
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    There are to schools of thought (at least) when it comes to crankcase ventilation. One says that any vacuum created by the airbox is better for the crankcase because it lowers the crankcase pressure thereby allowing the crank to spin more freely and eliminating oil blow-by past the cylinder rings into the cylinder. Another school says by venting the crankcase to the airbox (typically due to emissions standards) the engine air intake temperature is thereby increased and performance suffers. Both schools have some validity, but unless a mechanical crankcase vacuum is being used, or there is some specific race application, the effects are negligible.

    I removed the hose from the bottom of the airbox, started the engine and noticed (even at moderate rpm) there was little or no vacuum created by the airbox. This was done simply by placing my finger over the hole and checking for suction. In contrast, the hose from the crankcase was blowing quite strongly. This allowed me to side slightly with the second school of thought. Also, with no 1-way valve or oil catch-box, any oil mist the crankcase may be blowing out will definitely find its way into the airbox, and I don't like that.
    Click image for larger version. 

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    So I bought a 5/8" hole plug a the local hardware store and stuck it in the hole at the bottom of the airbox.
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    Then I fitted an inexpensive breather filter to the top of the hose.
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    I think there is a slight "bling-factor" and it makes my DD slightly less "vanilla" and slightly more "mine".
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  2. #2
    apriliaforum expert Frodo's Avatar
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    Yes, but doesn't it enter the bottom of the airbox before the filter? So wouldn't any oil mist be caught by the filter? In the case of my DNA filter, this shouldn't be an issue at all. Potentially could clog a paper filter. My 2015 has clear drain pipes presumably to release excess oil. Both are clear at the moment, but then the bike hasn't had a thrashing.
    When you put your finger over the hole into the airbox, I'm not surprised that there is no vacuum as even with the snorkel, the intake would have 100 x the area of the hole. There is probably only a noticeable vacuum at close to wide-open throttle.
    I think that this breather is primarily for emissions control and would not affect the running of the motor.

    That said, I think what you have done is elegant. But does it make any difference in performance?

    As an aside, the crankcase breather in my first bike, a silver XL250K2, vented outside with no valve. I once stalled it in the middle of a wide river. The crankcase cooled, it sucked water into the crankcase. When I got home the level of the milkshake, I mean oil, was way above normal. Thank goodness for roller bearings!
    And to continue the story, I changed the oil in the living room of the house I was renting (don't ask why!). A friend came home and stumbled over the full oil drain tray, spilling the oil over the carpet. Luckily there was a rug that fitted perfectly over the oil stain!
    Sorry for the hijack!
    Frodo
    2015 Shiver
    New Zealand

  3. #3
    apriliaforum expert rule62's Avatar
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    What you've stated is correct. No real chance for any oil to get past the filter. Just some possible accumulation in the bottom of the airbox (which may find its way to the clear tubes, or may seep otherwise and cause one to hunt a phantom oil leak.)

    No noticeable performance gain (slight decrease in intake air temp perhaps). Edit - Actually, judging by the amount of air being blowing out of the tube during my test, I wouldn't be surprised if the intake air temp was reduced quite a bit. However, I do not have the equipment to test that.

    I just figured if I was going to remove all that emissions stuff anyway (evap can, de-cat), why not get it all?

    My thought is that as long as all I'm putting in is filtered fresh air and gasoline, everything that comes out of the bike is waste (gas fumes or crankcase pressure), and I don't want to run it back through the intake tract.
    Last edited by rule62; 10-05-2015 at 02:00 AM.
    2014 DD 750 ABS - Spark exhaust, Arrow decat, headers (all ceramic coated), BMC filter, BikeMaster DLFP16-BS LiFePO battery, NGK iridium plugs, GPR steering damper, DD 1200 fully adjustable rear shock w/spring swap, 2016 Tuono Factory wheels, 15/44 520 conversion (PBR/Superlite/DID), Strada-7 fork preload adjusters, Samco 2-piece hose kit w/clamps, Engine Ice, Renazco Racing seat, EvoTech tidy tail, Aprilia grab handles, shorty levers, crank-case breather mod, evap-can delete... and a Rapid Bike EVO.

  4. #4
    apriliaforum expert rule62's Avatar
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    There was some tricked out white, pink, and purple DD I saw while doing my newb scroll through the DD photo gallery, which gave me the idea. $12.00 and 15 minutes got the job done.

    Oh... one more thing. If you happen to have a spare K&N style breather filter laying around and want to do this mod, you do not have to oil the filter element. Doing so may actually restrict the crankcase breathing a bit and will mist out (perhaps making a mess) as the crankcase pressure vents. Any oil mist that is brought up through the tube will take care of the filter element, in the rare event the crankcase should draw in instead of blow out. The cheapo little filter I bought already had a red filter element, which gives it the look of being oiled.
    Last edited by rule62; 10-05-2015 at 02:10 AM.

  5. #5
    apriliaforum expert rule62's Avatar
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    So... upon further inspection, it appears there is a catch-box incorporated into the right side of the airbox, then the blow-by tube runs to the top of the airbox, after the air filter and just in front of the intake air temperature sensor, above the velocity stacks. All the more reason I am very satisfied with this simple, inexpensive modification.

  6. #6
    apriliaforum expert High Country's Avatar
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    I vent my V-8 engine in my Camaro the same way.

    In the auto world, there is a third train of thought about the purpose of the airbox connection. The steam created from crankcase oil may have some impurities in it, which may eventually form a crust on the walls inside the crankcase. The intake vacuum on one side of the engine creates a cross flow, and pulls this air out and disposes of it.

    In reality, high end synthetic oils probably have very little impurities, so probably a non-issue. I run synthetics in the Camaro as well, so I'm not very concerned about it.

    I do notice that a mess of oil will form near that filter because of the steam exiting there, which requires cleaning up with a rag now and then. Personally, I would rather clean the area around the filter, than have to clean the inside of the airbox.

    In conclusion...nice mod.
    2009 Aprilia Dosoduro 750 (Adventurized: http://www.apriliaforum.com/forums/a...893274&thumb=1)

  7. #7
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    I did a similar mod on my old Gixxer, it was actually the valve cover breather I had to reroute.

    There is a large amount of steam generated from it, which surprised me, and I tend to agree with HC in that the airbox tends to "suck" the steam out of the crankcases/valve area.

    Who knows how important it really is.....? I suspect the main purpose is emissions related, rather than keeping the engine cleaner inside.

  8. #8
    apriliaforum expert rule62's Avatar
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    Judging by the high amount of air being blown out of the crankcase, and the low suction created by the airbox on these bikes, I do not think it evacuates any steam much better than simply venting to the atmosphere. Plus, I don't want any steam or anything else entering my intake after the air filter, or right near the intake air temp sensor. A larger displacement engine (Camaro V8) or higher revving engine (inline 4) might create more intake vacuum, but for this application, I think I'm benefiting pretty well.
    Last edited by rule62; 06-30-2016 at 04:35 PM.
    2014 DD 750 ABS - Spark exhaust, Arrow decat, headers (all ceramic coated), BMC filter, BikeMaster DLFP16-BS LiFePO battery, NGK iridium plugs, GPR steering damper, DD 1200 fully adjustable rear shock w/spring swap, 2016 Tuono Factory wheels, 15/44 520 conversion (PBR/Superlite/DID), Strada-7 fork preload adjusters, Samco 2-piece hose kit w/clamps, Engine Ice, Renazco Racing seat, EvoTech tidy tail, Aprilia grab handles, shorty levers, crank-case breather mod, evap-can delete... and a Rapid Bike EVO.

  9. #9
    apriliaforum prov-nov LuckyShiver13's Avatar
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    What type of plastic plug are you using Rule62? The closest thing i can find at my local stores are rubber stoppers or plugs for irrigation which only come in 1/2" and 3/4" standard

  10. #10
    apriliaforum expert rule62's Avatar
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    I went to ACE Hardware. They had a selection of plastic hole plugs in the aisles with the rest of the screws and nuts.
    2014 DD 750 ABS - Spark exhaust, Arrow decat, headers (all ceramic coated), BMC filter, BikeMaster DLFP16-BS LiFePO battery, NGK iridium plugs, GPR steering damper, DD 1200 fully adjustable rear shock w/spring swap, 2016 Tuono Factory wheels, 15/44 520 conversion (PBR/Superlite/DID), Strada-7 fork preload adjusters, Samco 2-piece hose kit w/clamps, Engine Ice, Renazco Racing seat, EvoTech tidy tail, Aprilia grab handles, shorty levers, crank-case breather mod, evap-can delete... and a Rapid Bike EVO.

  11. #11
    apriliaforum prov-nov LuckyShiver13's Avatar
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    Ok apparently they are superior to lowes or Home Depot lol. They have one in the city I will go to. Thanks again!

  12. #12
    apriliaforum expert rule62's Avatar
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    Yes. Home Depot and Lowes do NOT have the screw/nut/fastener/plug selection which can be found at ACE. "ACE is the Place"!

  13. #13
    apriliaforum expert 6M$MAN's Avatar
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    rule62 nice one! I think I may proceed with one. thanks for posting.

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  14. #14
    apriliaforum expert
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    ace is the bomb

  15. #15
    apriliaforum expert rule62's Avatar
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    Okay... so... I recently changed my oil. Went for nice ride to and from my AA homegroup meeting. Not terribly spirited. Mostly highway (75-80 mph). No wheelies. Got back to my garage and noticed a small amount of oil had gotten by the breather filter and was dripping down the frame. Checked my oil level and saw that I over filled everso slightly (about 1/8 inch above the top mark on the sight glass). Let out the extra bit of oil from the drain plug (just below the top mark) and now all is well.

    My point: If you've ever gotten oil in your air-box, just a slight overfill of oil may be the culprit. Whatever amount got past my crankcase breather mod would have otherwise ended up in my airbox, dripped out somewhere else, and had me hunting for a phantom problem. Just another reason I suggest this modification.

    ... pulled a fairly decent wheelie on my way home from another meeting just now, and no oil got past the breather.

    I picked up another little filter, just in case the original one got saturated and doesn't breather as well. Will be putting it on, and re-routing the gas tank breather hoses (combining both with a t-fitting) whenever the RapidBike EVO arrives.
    Last edited by rule62; 10-22-2017 at 01:24 AM.
    2014 DD 750 ABS - Spark exhaust, Arrow decat, headers (all ceramic coated), BMC filter, BikeMaster DLFP16-BS LiFePO battery, NGK iridium plugs, GPR steering damper, DD 1200 fully adjustable rear shock w/spring swap, 2016 Tuono Factory wheels, 15/44 520 conversion (PBR/Superlite/DID), Strada-7 fork preload adjusters, Samco 2-piece hose kit w/clamps, Engine Ice, Renazco Racing seat, EvoTech tidy tail, Aprilia grab handles, shorty levers, crank-case breather mod, evap-can delete... and a Rapid Bike EVO.

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