Add a Crankcase Breather

Unless you have extremely high mileage on your Vulcan or you are mysteriously losing a lot of oil this may be the most unnecessary bit of bling ever added to these bikes. That said, it's really a nice looking piece and it 'might' (depending on the condition of your engine) actually serve a useful purpose.

The breather filter shown above is from J&P Cycles, about $14 at this writing but there are lots of other sources ranging from your local Harley Davidson store to Amazon. They all look pretty much the same, they all do the same thing. So, you ask, what is it these things do?

The best way to explain is to plagiarize an article printed in the February '05 issue of "Motorcycle Cruiser" magazine. Someone had written to the Q&A tech tip section about excessive blow-by that was causing oil to drip out the air cleaner and down the right side of his FLHR. His oil consumption kept going up and the bike was using a quart every 2500 miles (not considered excessive for a big V-twin by the way). His question was whether the oil consumption might have something to do with the blowby problem.

And now the answer and possibly a reason to install a crankcase breather separate from the air filter someday:

"When blowby occurs on an engine using a crankcase vent routed into the air filter (which is the case with Vulcan's), oil makes its way through the engine breather into the air cleaner [or airbox in our case] and is then pulled into the engine along with the fresh intake charge and burned. That oil tends to carbon up the rings and glaze the cylinder walls resulting in a less than perfect top end seal. Once this occurs the die is cast. The poor top end seal leads to more blowby which pushes even more oil into the intake air which is then forced into the engine creating more blowby and so it goes."

Still with me here? Ok, in a healthy engine this isn't a problem, you're not really getting an oil mist blowing into the carb or throttle body, just air created by some over pressure in the crankcase, nothing to worry about. If, someday, you find a film of oil inside that right side air box (assuming a stock intake) then it might be time to pull the hose and vent it outside. If you install an aftermarket air cleaner you might choose to add this breather instead of drilling a hole in the back of your new air cleaner.

Heads up. You may smell oil fumes (downside for some), especially sitting still in traffic even if you have a healthy engine but especially if your rings are about ready for replacement.

What You'll Need

  • 1- Crankcase vent from the vendor of your choice. There are different styles but I'd suggest paying a couple of dollars more for the higher quality types as some of the cheapo's tend to self destruct fairly quickly.
  • 1- Optional piece of clear hose (if you'd like to monitor oil collection in the vent system)

How To Do It

Breather mounted with fast idle
The photo at right shows the install on my '01 Nomad. Note the clear tubing. That's just so I could keep track of any oil that might be collecting in the low spot of the hose. (Note: with about 10,000 miles since the install the clear tubing hasn't collected any oil but it's looking pretty crusty).

The vent hose originates just in front of the #1 (front) cylinder. You'll notice a hose clamp and rubber hose attached to the crankcase. The stock hose runs from that location up over the top of the engine then back down to the bottom of the air box backplate on the right side of the engine.

At your option, you can remove that entire hose, measure off enough to reach wherever you choose to mount your filter and just run directly to the filter or, if you think someday you might want to go back to the stock setup, just insert a hose splice (any auto supply store) and run some additional hose from where the OEM piece attaches to the backplate to your filter.

If you choose to remove the original hose it will help to remove or at least lift the gas tank to extract the OEM hose.

If you are using the stock backplate or have an aftermarket intake with a hole already drilled for the vent be sure to plug the opening so unfiltered air can't reach the throttle body or carb.

To mount the filter in the location shown in the picture with the fast idle knob and ignition still in place you'll have to grind a little off the top of the bracket holding the fast idle knob. This is so you can swing it a little to the right and up out of the way. Use a good looking stainless steel bolt and you have a tidy installation.

If you've re-located your ignition and/or choke or fast idle knob then mounting the filter is much easier, just use the tab on the frame.

Done? Go ride.


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