Mikee Minute #8 - Crankcase Recirculation Systems

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mikenixon
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Mikee Minute #8 - Crankcase Recirculation Systems

#1

Post by mikenixon »

Not everyone realizes that motorcycles and other powersports vehicles did not come under emissions regulations until over 20 years after cars did. For motorcycles this was during the 1978 model year. Motorcycles did however get some emissions-anticipating specifications a little bit prior to this, in fact as early as the mid 1970s, one of which was crankcase recirculation. Crankcase recirculation has no formal name in powersports but is known in the car world as positive crankcase ventilation or PCV. An ancient and abiding specification on cars, powersports vehicle crankcase fume reingestion from the crankcase to the air intake in most cases has even today pretty benign effects on performance and maintenance while it of course improves hydrocarbon emissions. Again, just as on cars. No worries. Generally speaking.

But there are a few problems with this system on certain motorcycles. For one, on all powersports machines having this crankcase rebreathing, it means that over-filling of the crankcase (whether unintentionally through incorrect oil change technique, or due to either fuel or water dilution of the engine oil artificially raising its level) can affect the engine's intake system in some not-so-good ways, there being a more or less straight path from crankcase to intake. Even properly maintained crankcases on certain vehicles whose crankcase breathers are perhaps mounted a bit to close to their throttle bodies, can exhibit symptoms of crankcase pollution of their fuel systems. The result is fouled air cleaners, the accumulation of grime inside throttle bodies and carburetors, and accelerated carbon formation on intake valves. Not so good.

CV-carbureted bikes such as the venerable and highly valued late 70s/early 80s Honda multis -- of which I am an ardent, active supporter -- are especially vulnerable. Distilled crankcase hydrocarbons form a greasy slime on these carbs' moving parts, inhibiting proper function and when built up around the throttle butterflies, can affect proper engine idle. Hondas and Kawasakis using metal piston CVs form this black grease most notably on their slides, a sign that the crankcase is having undue influence on these machines' intake systems, and ultimately requiring cleaning of these parts to recover lost performance.

At the very least it is imperative on metal piston CV models that the airbox "dump" hose be inspected periodically (squeezed) to eliminate the buildup of distilled crankcase vapors. Consequently, knowing that most folks like me are lazy, I routinely encourage altogether defeating the crankcase recirculation plumbing on bikes having metal piston CVs. It's easy to do, reaps maintenance dividends and, well, I simply hate like hell seeing grunge being fed into carburetors!

Alright. One more thing. Now, knowing this, that these bikes are already predisposed to foul their intakes with the accumulation of hydrocarbon's black goo, you may want to think twice about introducing additives to either the fuel or oil systems.

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Last edited by mikenixon on Fri Mar 22, 2013 10:51 am, edited 1 time in total.
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

#2

Post by Track T 2411 »

Just out of curiosity, when you say "additives" might this include products like Seafoam, and Marvel's Mystery Oil? With the system defeated, are products like these less likely to introduce the "goo" you mention, or is part of the issue that additives may contain these hydrocarbons/pollutants to begin with?

Todd
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

#3

Post by mikenixon »

Track T 2411 wrote:Just out of curiosity, when you say "additives" might this include products like Seafoam, and Marvel's Mystery Oil? With the system defeated, are products like these less likely to introduce the "goo" you mention, or is part of the issue that additives may contain these hydrocarbons/pollutants to begin with?

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Approaching 60 years of age I find myself at an interesting point. On the one hand, more than any time in my life I increasingly recognize the value of relationships; their importance to life, how carefully they must be preserved, how tenuous and at the same time how precious, they are, thus how decreasingly important my *own* views are, no matter how hard-won and honestly acquired. Every one of use maintains relationships, from spouse to coworkers to neighbors, to even our children, by understanding and working within this realm of understanding. On the other hand however, I find myself increasingly less willing to budge on my convictions, which sociologists tell us is a sure sign of aging. :-). How both of these work together, and why they should both be intensifying in my old age, is a mystery to me still, and probably always will be. Sorry about being so philisophical, but all that said, yes, I am (sigh) saying I do not believe in the use of any additives, to either fuel or oil, for a number of reasons, and I don't want to go into them here. I believe I have come to these reasons in as objective and honest and informed and reasonable a manner as possible, while I also respect that others have other views. I'm good with that. We can all be winners, no problem. (There I go again.). The one hill I might choose to "die on" however in regard to this subject is this -- many of the additives folks use today do indeed distill onto the mechanical parts of your carburetors. I will post some pix later of what that looks like when it happens.

Yes, I am a firm believer in defeating the crankcase rebreather systems on Wings and CBXs and CB750s et al. Basically it means reverting them back to pre-1970s configuration. It removes the path from crankcase to intake, almost completely eliminating the effect the crankcase can have on the intake.
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

#4

Post by Hal »

Mike, sorry, I think I'm being a little hard of thinking tonight, probably not unconnected with having idiotically breathed a bit of iso-cyanate paint fog yesterday evening (don't ask...) but what exactly are you suggesting?

Simply pulling the airbox dump hose off the airbox?
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

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Post by mikenixon »

You can go as simple as disconnecting the hose from the right/rear of the airbox (and let it rest where it is under the side shelter cover), or as thorough as removing the hose and all it is attached to and substituting a crankcase breather filter.
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

#6

Post by sunnbobb »

Good advice Mike. I have opened up too many airboxes on wings to find the black hydrocarbon goo in the airbox. I started bypassing the system a while back. Thanks for the insights, and philosophy too!
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

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Post by evilratwing »

I do believe I've found my next mod.
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

#9

Post by AussieGold »

i will never use a fuel additive. i firmly believe they do more harm than good.if you suspect your carbs are dirty, pull them off and clean them... same for oil. the only way to ensure the oil is clean is to change it regularly. i change mine every saturday. usually....... and i have never run my bike with the crankcase breather attached, dont seem to hurt it.
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

#10

Post by Old Fogey »

Image

May I suggest that if you live in the kind of rainy climate that I live in, with the filter in this position there is the likelihood of water being dumped directly into the crankcase. Definitely not the best oil additive!
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

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Post by Old Fogey »

the pic Sunnbob posted of the filter. can't get the picture to come up!

*EDIT* fixed. roncar


May I suggest that if you live in the kind of rainy climate that I live in, with the filter in this position there is the likelihood of water being dumped directly into the crankcase. Definitely not the best oil additive![/quote]
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

#12

Post by Whiskerfish »

When I worked on helicopters for a living we had a oil monitoring program. Every so many hours (most were 50 hour intervals) we were required to take samples from every engine and gearbox and submit them for analysis. Samples were drawn immediately upon landing while systems were still hot and possible contaminates were still in suspension. If it was raining when the samples were drawn often times water would get into the gear box and the samples would spike. The "book" process was to drain and flush the box and resubmit the samples. That was time consuming and very often did not have a favorable result as it was a cold sample verses a hot sample and a simple drain and flush would not get all the water out. So then the aircraft would be sitting down for the next day or 2 while you did the process again and waited on the all clear from the Lab. A huge waste of time and money.

So anyway we learned that a Ground run of the Helicopter for 1 hours would 99% of the time result in a clean sample. The reason is that at operating temp the oil would basically cook out any water in the system and it would leave via the gearbox vents.

I believe the same to be true of this system. Obviously other contaminates like antifreeze or gas are different stories but I would not be concerned regarding plain water contamination unless it was known to be excessive.
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

#13

Post by CYBORG »

i agree with both mike and old fogey. i run remote breather on the crankcase, but always make sure the filter is lower then the outlet from the engine
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

#14

Post by ericheath »

The evaporation of water is a big reason all mechanics in the far north recommend bringing your car to full operating temperature often. If valve covers are removed from a cold motor which has been started briefly off and on, they find chunks of ice in the valve train. That can't be good for the rockers and springs. It will melt and end up in the oil. It probably contributes to gunk in the breathers and pcv's. I think it would be wise to stick an elbow on the breather so it is lower than the tube returning to the engine.
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Re: Mikee Minute #8 - Crankcase Recirculation Systems

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Post by mikenixon »

Whiskerfish wrote:When I worked on helicopters for a living we had a oil monitoring program. Every so many hours (most were 50 hour intervals) we were required to take samples from every engine and gearbox and submit them for analysis. Samples were drawn immediately upon landing while systems were still hot and possible contaminates were still in suspension. If it was raining when the samples were drawn often times water would get into the gear box and the samples would spike. The "book" process was to drain and flush the box and resubmit the samples. That was time consuming and very often did not have a favorable result as it was a cold sample verses a hot sample and a simple drain and flush would not get all the water out. So then the aircraft would be sitting down for the next day or 2 while you did the process again and waited on the all clear from the Lab. A huge waste of time and money.

So anyway we learned that a Ground run of the Helicopter for 1 hours would 99% of the time result in a clean sample. The reason is that at operating temp the oil would basically cook out any water in the system and it would leave via the gearbox vents.

I believe the same to be true of this system. Obviously other contaminates like antifreeze or gas are different stories but I would not be concerned regarding plain water contamination unless it was known to be excessive.
Cool stuff, very interesting. Real world maintenance meets politics. Though I mentioned water along with fuel contamination of crankcase oil, the latter is much more common, especially in carbureted bikes and particularly those whose carbs do not have bowl overflow systems, which ironically none of the Gold Wings do (unlike the majority of Hondas made at the time).
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