| Author | Message | ||
     Eicas |
Dealer confirmed that the rear valve cover seal on my '08 XB12Ss is leaking and needs to be replaced. They will cover it under warranty this time, but said that the seal blew out because of my "breather mod". I modified by rerouting breather hoses to a "T" fitting that then combines the two hoses into one hose of the same size and running it to a "catch can" with a breather filter. Dealers mechanic said too much back pressure is what blew the seal out. Is the mechanic right? Mod was done about 4,000 miles ago, and bike runs better after the mod. What to do? Opinions? | ||
| Kdogshirow |
Is your hose crimped somewhere ? I have done this mod on two Buells and never had such a problem . The only way I would think is if you went to a smaller hose or had an obstruction of some sort . The comment the Shop made is typical of Harley dealers to blame any modification done to have caused whatever problem .(unless its a Screaming Eagle mod you payed them to do) | ||
| Froggy |
Tell your dealer to shove it. They are just trying to get out of warranty work, which doesn't pay as well as non-warranty repairs. If they prove that your mod caused the problem, then yes, you are stuck paying for it, but that is highly unlikely. | ||
| Bikertrash05 |
Sounds like my dealership. If they didn't do the work, your work is at fault. Like when I had a VRod and got the fuel flange problem. I had open exhaust, K&N, and a PCIII, and they said "we don't know what you did to the bike". Turned it back to stock so they would fix it, and it wouldn't run at all (PCIII was adding enough fuel to keep it running). | ||
| Xbgeorge |
My 08 had a bad valve cover gasket and I haven't done the breather mod yet. They are full of it. | ||
| Gentleman_jon |
The mechanic is lying. There is a never fail way to check on whether or not a Harley mechanic is lying about a mod you made. His lips are moving. Hope that helps.  | ||
| Ochoa0042 |
BS  | ||
| Mnbueller |
Well now you know to take your breather mod off, before returning for more service! Froggy - They don't have to prove that your mod did the damage, You need to prove to them that it didn't do the damage. Edit: I know from experiance when the line does get a kink, it just starts pushing oil up the clutch cable, and then out all over your left hand, and the left side of the bike! (Message edited by Mnbueller on September 10, 2009) | ||
| Canucklovingbrit |
Have to say, I believe my breather mod might have been the cause of blowing both valve cover gaskets. I'm thinking of re-doing the mod, using separate hoses, rather than linking them with a T. I'm concerned that there was too much back pressure caused by combining them. I know many owners have experienced no problems with the standard mod design using a T, but since I have had issues, I'm a little wary. | ||
| Eicas |
I agree with all of the above. The breather hoses were not kinked or twisted and I believe of sufficient diameter to more than pass enough air. I base the above on what my BMW R1000Rs has and some Continental 520 cubic inch engines have as breather hoses. Just the same, I am planning on redoing the mod using two hoses to save any future hassles. I am not going back to the original set up, bike just runs better this way. | ||
| 1_mike |
Well...lets think about this for just a minute.......... You have crank case pressure blowing from two locations...each cylinder. X-psi from each location...right? You have two tubes running into your air box base...right? Each one is free to breath on its own with very little restriction...right? Now...connect those two tubes to the same dia. tube (hose)...and guess what you've done...caused a restriction..!! Exactly how much is open for testing...BUT...that's exactly what you've done...restricted to breathing..! Gotta go..more later. Back...false alarm. Want easy proof...find two straws of the same diameter...stick'em both in your mouth and breath thru your mouth for about 45 seconds..now remove a straw and breath thru your mouth for about 45 seconds...feel a difference? Or...plug on nostral (hole in your nose) and do the same thing. IF..you have an engine that has a very good ring seal, you can maybe get away with two into the same size single. BUT...that all goes to hell if you have an engine with...not so good a ring seal...! I'd say up to about 4% leakage, no problem. Much over 5% or more, I'd say you are passing more blowby than a single small hose can keep up with. Mike (Message edited by 1_mike on September 10, 2009) | ||
| Boltrider |
Mike, your logic makes sense but this is a common problem on these bikes. My rear rocker seals were leaking and my breather hoses are in the stock location. | ||
| Bromanowski |
Mike, your argument is flawed. The amount of pressure being built up in the crankcase is a lot less than you are speculating. The hoses used in the breather re-route are of adequate size for large displacement V8 engines. They would have no problem relieving crankcase pressure from our engines. A better example would be in turbo charged applications. One bad weld in the charge piping that results in a pin hose size leak and the system will not build any pressure where it would normally build 20+ psi. Pretty much as long as there is a path for the pressure to vent to the atmosphere there shouldn't be any pressure. Now any kinks are obstructions would interfere and then you would see some. I think it would still take more pressure than the system would realistically build up to blow any of these seals. | ||
| 09ltrain |
Wouldn't the inverse up and down movement of the pistons offset excessive crankcase pressure buildup? One piston goes down and the other one goes up. I would think that the modified breather system would be able to handle the small amount of blow by. | ||
| Bromanowski |
All of the crankcase pressure is created by blow-by past the piston rings. Most engine manufacturers are required for emissions to route this back into the intake so any fumes or gases in the crankcase are burnt off and not just released into the atmosphere. Also you see a small performance gain as the intake creates a slight vacuum and creates a little negative crankcase pressure which will actually suck the piston rings to the cylinder wall. On some of the race engines I've built we will run vacuum pumps to create a lot of vacuum if allow by the racing class. Also dry sump systems also do this but it's more inadvertently as they are really sucking up the oil instead of just scavenging it from the pan thus creating the vacuum. | ||
| Brumbear |
man I thought there was porn here however if the breather mod is kinked or blocked maybe but...... | ||
| Eicas |
The way I read it is that the only time the pressure is being built up is when both valves are closed, either on the compression stroke or the power stroke. If one valve is open on a cylinder, there will be no meaningfully breather pressure being developed in that cylinder. I do not have the specs, but is there a time on the Buell when all the valves on both cylinders are closed? Also, how much breather pressure are we talking about. Would there be other symptoms? | ||
| 1324 |
There is 'pressure' built up in the crankcase with each engine revolution. This is a design characteristic due to the common crank pin (i.e. both pistons rise/fall at nearly the same time due to the 45 degree V). There is a slight time lapse between cylinders, but it is pretty darn close. Something like a 90 degree twin has much less pressure build up/collapse because of the cylinder arrangement and the crankshaft design. The arrangement of an L-twin has the pistons rising and falling at opposite times, so the crankcase volume is essentially constant. Same goes for I4's. If the t'd line from the breathers is undersized, you'll definitely have some pressure build up. The breathers might be oversized for the engine, but I haven't run through the calcs. Our engines have rather large pistons and a long stroke. In fact, the bore/stroke on the XB12 compares closely to many American V8s. The V8's crank volume will surely remain more constant as a result of its design. So, the breathers look huge on our engines, but when you consider what's going on...well, it might not be unreasonable. I don't know the breather diameters off the top of my head, so I'm not sure if this is reasonable...but if you're concerned - either size the tee so that the out branch's area is the same as the area of both breather line combined OR run two separate breathers. Two separate breathers would be optimal if you can package the filters nicely. You could use the same catch can for both... Now all the being said, the rocker covers on my XB9 leaked from day 1 and tee'ing my breathers didn't make it any worse. But, I also didn't get any gunk in the airbox. My XB12, however, has perfect rocker cover seal but my airbox is fairly oily. YMMV. | ||
| Beachbuell |
1_mike I agree 110%! | ||
| Pogue_mahone |
my knowledge of crankcase pressure is mostly vw derived. some of it is blown by from rings,any near worn out engine can show u by removing oil cap while it runs. now the other half of this equation is the air volume in the case --from the bottom of the pistons down--it pushes the volume near equal to the piston's stroke and it pressurizes the case and has to vent.low rpms low pressure,high rpm's higher pressure.as the oil is slung and hit by the crank and rods it goes to a fine mist and takes up volume and adds a bit to the pressure as well,and then as the pressure comes and goes it takes oil mist with it.many car crankcase vents have one way valves to stop any dirty oil or other contaminates being drawn back in. and of course ring leakage makes it worse.and that is better or worse depending on piston tightness to the cylinder and ring seal.i bet most decent running engines have less effect in the case from blowby than we all imagine.most of it is from air volume being compressed by moving machinery and needs to be vented. and that hd mechanic--he is full of $hite all the way and as i see it,the ONLY advantage of the vent mod is to be sure the intake is working with clean air.that air quality is the ONLY thing to make any difference to how it runs.it breathes the tiny bit of exhaust and oil,and the same air we breathe. with the mod,it is burning clean air and gasoline | ||
| Mmcn49 |
I did the breather re-route at about 2000 miles. I tried several variations but ended up using a catch can from American Sport Bike and a 30 micron pleated metal screen inside a modified housing instead of a filter. Around 9000 miles or so I developed a rocker cover leak on the rear cylinder. Even though the bike is still under warranty I decided to change the seals myself and avoid all the dealer hassles. After pulling the cover off, you could clearly see where the orange silicone seals had overheated. At several points the seals had turned black, became stiff and had shrunk in diameter. My seal failure was clearly caused by heat and not crankcase pressure. IMHO the seal design, (not the materials they’re made of) is very good. The seals are well captured and unless damaged by heat should be able to hold back most if not all of the crankcase pressure. I replaced the seals, coated the cover and head mating surfaces with Hylomar Flange Sealant, (Hylomar has a higher temperature rating than silicone) and installed a RSS from American Sport Bike. No leaks at 11,500 miles. |
