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blowing motor oil

This is a discussion on blowing motor oil within the Yamaha YFZ450/450R (2004-Present) forums, part of the Performance /Technical category; I have 2 yfz's. one 6 mo older than the other. I noticed on the newer on that an excessive amount of oil was on ...


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Old 11-02-2004, 08:47 AM   #1
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I have 2 yfz's. one 6 mo older than the other. I noticed on the newer on that an excessive amount of oil was on the air filter, and it seemed to be comming from the little hole in the left side of the air box. the tube leads to the "black box" mounted in front of the coolant resivoir. the vent hoses from the motor lead to this box. I thought at first, the oil comming out was because I put a little too much oil in the motor after chainging it. so I drained some out. the motor end of the vent hoses are dry, but yet oil still comes from the little black box. it seems to be glued together, so I couldn't take it apart to clean it. Does it work like a pcv in a car? do I just need a new one? my older yfz doesn't have this problem, but my kid rides the newer one alot harder than I ride the older one.
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Old 11-02-2004, 09:07 AM   #2
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Man you know i talked to yamaha about this because i have quite a few that do it around here, and they said it only happens when you get excessive crankcase pressure and its normally caused by worn rings but i dunno, i have not had it happen to me yet, but i have seen it alot, dunno if thats whats goin on but thats what they told me,
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Old 11-02-2004, 09:46 AM   #3
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That's caused from blow-by time for a top end rebuild.
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Old 11-02-2004, 10:38 AM   #4
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but this is in a bike with 1/2 the ride time as mine. and the hoses at the motor and starter are dry. would a leak down test tell me if the top end is any good? how long and how much pressure should it hold?
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Old 11-02-2004, 04:39 PM   #5
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mine does it too,and i've had it about 6 months
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Old 11-02-2004, 05:42 PM   #6
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you're getting blow by man, like xcracer said, time to take the piston out and hone that sucker and get some new rings. :(
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Old 11-02-2004, 07:09 PM   #7
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Before everyone is quick to jump on the blowby wagon, keep one thing in mind. There are 2 hoses that feed that box. And, one of them is directly off the crankcase. Excessive crankase pressure could cause this, and would have nothing to do with rings.
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Old 11-02-2004, 07:50 PM   #8
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GUYS GUYS GUYS before doing anything i mean anything. Almost every motor such as in any type of cars have tube which comes off the engine block and feeds into the intake tubing. For us it goes from the black box to the air box. Anyways its just blowback in cars its for emmisson purposes, it blows oily gas poluntants back into the airbox. Its the same thing for the 450. Now to make your 450 motor run better(so only clean air goes in the intake) this is what i did. Take the black box off. See the tube which runs on top of the block by the spark plug. Well just buy an air breather from any local automotive store ex. Autozone thier like 10bucks anyways attach that to the end of the tube and mount anywere so its out of the way. ( I ran mine all the way past the air box by the rear fender. It dosenot suck air in but only blows air out so no worrys about dirt from the rear fender. Now the other tube which leads from the lower part of the block simply feed the tube(if the tube is to short just buy a longer one from any automotive store they come rolled up on a spool and thier cheap) to where all the other overflow tubes are by the swing arm(with the carburators hoses etc.) Walla your done just check your oil level more frequently and that all. Sorry for my shitty writing but if you have questions just let me know. Hope this helps.
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Old 11-02-2004, 07:57 PM   #9
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Quote: Originally Posted by smartini
GUYS GUYS GUYS before doing anything i mean anything. Almost every motor such as in any type of cars have tube which comes off the engine block and feeds into the intake tubing. For us it goes from the black box to the air box. Anyways its just blowback in cars its for emmisson purposes, it blows oily gas poluntants back into the airbox. Its the same thing for the 450. Now to make your 450 motor run better(so only clean air goes in the intake) this is what i did. Take the black box off. See the tube which runs on top of the block by the spark plug. Well just buy an air breather from any local automotive store ex. Autozone thier like 10bucks anyways attach that to the end of the tube and mount anywere so its out of the way. ( I ran mine all the way past the air box by the rear fender. It dosenot suck air in but only blows air out so no worrys about dirt from the rear fender. Now the other tube which leads from the lower part of the block simply feed the tube(if the tube is to short just buy a longer one from any automotive store they come rolled up on a spool and thier cheap) to where all the other overflow tubes are by the swing arm(with the carburators hoses etc.) Walla your done just check your oil level more frequently and that all. Sorry for my shitty writing but if you have questions just let me know. Hope this helps.
Or, just "t" the both of them together, and run the line down by the swinger. No filter, unless you just feel like spending $ for no apparent reason. That is where mine is, a few others, as well as the yz450 dirtbike.
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Old 11-02-2004, 09:22 PM   #10
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Do what you want i just said what i did.
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Old 11-02-2004, 10:16 PM   #11
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Quote: Originally Posted by smartini
Do what you want i just said what i did.
As did I. never said your way was wrong. Just gave another options. Don't let your panties bunch.
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Old 11-03-2004, 06:25 AM   #12
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Quote:
Excessive crankase pressure could cause this, and would have nothing to do with rings.
What do you think causes excessive crankcase pressure? Bad Rings!!!!!

Oil could also get there from standing it on end.
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Old 11-03-2004, 07:29 AM   #13
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Quote: Originally Posted by xcracer999sdad
Quote:
Excessive crankase pressure could cause this, and would have nothing to do with rings.
What do you think causes excessive crankcase pressure? Bad Rings!!!!!

Oil could also get there from standing it on end.
How can it be bad rings if it is coming from the crankcase? I am not talking about the breather on the cam cover. Go look at your yfz. There is a breather that comes out of the starter gear cover. This has nothing to do with the rings.
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Old 11-03-2004, 09:13 AM   #14
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Quote: Originally Posted by xcracer999sdad
Oil could also get there from standing it on end.

I think you hit on something. My kid has been racing alot in the mud, and after every race, I tip the bike up on the grab bar to take the skid plate off and start the cleaning process from the bottom up. next time I'll pay more attn. to oil draining thru the breather tubes.
thankx...........
BTW I like smartini's suggestion on eliminating the "little black box". I was looking at the wr schematics (because it also has a starter), and the breather hoses don't really seem to go to anything. I'll have to look at the dirt bike in person to make sure.
I thank all of you for your imput.
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Old 11-03-2004, 01:48 PM   #15
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Quote: Originally Posted by xcracer999sdad
Quote:
Excessive crankase pressure could cause this, and would have nothing to do with rings.
What do you think causes excessive crankcase pressure? Bad Rings!!!!!

Oil could also get there from standing it on end.
overfill the oil in the crankcase??
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Old 11-03-2004, 03:32 PM   #16
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If the rings are bad it allows the pressure from the cylinder around the piston causing excessive pressure in the engine the top breather would never come into play because that is just a valve cover. I'm saying this from first hand experience my sons quad did the same thing and still ran good. Once we took the engine apart we couldn't believe it even ran there was .084 end gap on one ring with the limit being .022 and .089 on the other with the limit being .034. Also the three intake valves were cupped and had to be replaced expensive little buggers. We also never saw any oil in the hose. Take the hose off the engine and run it revving it a couple time let it get warm and see if there is oil coming out that crank case breather is so I believe your rings are shot if not then it's maybe just happening when you stand the quad up. Removing that black box does not solve your problem if your rings are bad it just keeps your air filter from getting oil on it. Hope it's not the rings this is just my past experience. Hope it helps.
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Old 11-03-2004, 04:00 PM   #17
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Quote: Originally Posted by xcracer999sdad
If the rings are bad it allows the pressure from the cylinder around the piston causing excessive pressure in the engine the top breather would never come into play because that is just a valve cover. I'm saying this from first hand experience my sons quad did the same thing and still ran good. Once we took the engine apart we couldn't believe it even ran there was .084 end gap on one ring with the limit being .022 and .089 on the other with the limit being .034. Also the three intake valves were cupped and had to be replaced expensive little buggers. We also never saw any oil in the hose. Take the hose off the engine and run it revving it a couple time let it get warm and see if there is oil coming out that crank case breather is so I believe your rings are shot if not then it's maybe just happening when you stand the quad up. Removing that black box does not solve your problem if your rings are bad it just keeps your air filter from getting oil on it. Hope it's not the rings this is just my past experience. Hope it helps.
thanks, I'll try that also, tonight.
would a "leak down test" tell me ig the rings are good or not? how much pressure for how long? I know you can't do a compression test (because of the decompression mechanism).
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Old 11-03-2004, 07:20 PM   #18
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Quote: Originally Posted by xcracer999sdad
If the rings are bad it allows the pressure from the cylinder around the piston causing excessive pressure in the engine the top breather would never come into play because that is just a valve cover. I'm saying this from first hand experience my sons quad did the same thing and still ran good. Once we took the engine apart we couldn't believe it even ran there was .084 end gap on one ring with the limit being .022 and .089 on the other with the limit being .034. Also the three intake valves were cupped and had to be replaced expensive little buggers. We also never saw any oil in the hose. Take the hose off the engine and run it revving it a couple time let it get warm and see if there is oil coming out that crank case breather is so I believe your rings are shot if not then it's maybe just happening when you stand the quad up. Removing that black box does not solve your problem if your rings are bad it just keeps your air filter from getting oil on it. Hope it's not the rings this is just my past experience. Hope it helps.
While I agree to you to some extent, please explain to me why all of the 470's that I have spoke with thus far, do the exact same thing? Mine included. Keep in mind, I have checked the ring gap, and compression, and all is well.
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Old 11-03-2004, 08:06 PM   #19
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i ride tons of wheelies and i am up on one tire occasionally and thats when i notice it mainly.
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Old 11-03-2004, 11:24 PM   #20
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Riding wheelies will do it also. I have been talking about a stock engine all along I can't answer any questions on a 470 yet.
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