I'm not a mechanic, maybe one here can answer this question, I also looked this question up but could not find anything to answer it specifically.

Case in point, I am looking at possibly buying a used 2009 Road King with the 103 CI motor (fuel injected), the thing I find strange is the owner says it has an oil catch can:


I was under the assumption modern Harley motors no longer needed an oil catch can for 'blow-by', I was under the premise that technology had fixed that issue on modern motorcycle motors and these were no longer needed compared to older bikes that did.
Or... is it this pointing out something that shouldn't be happening?

 

It's just an external breather. The Twin Cam motors are still "head breathers" and they're designed to reintroduce the crankcase blow by back into the carburetor or throttle body. Some have excess oil mist and lots believe it doesn't help the motor run to reintroduce it back in. What's in the photo is just that, a bypass, or external breather. Not necessarily a "catch can." However if it's dripping, the breathers in the rocker boxes may be clogged. There is an update for the older style breathers too.

 

Thanks for the heads up.

I thought I read someplace that the 'cans' were needed on mostly older carbureted bikes due to a defect in the engines design, that it was corrected with technology on the newer model engines Harley makes so they were no longer needed, that's why they are aftermarket products and not provided by the manufacturer...

 

As I attempted to elude to, a properly running motor will produce very little of anything other than a fine mist. If someone has a lot of oil puking out, something's wrong and they've just attempted a bandaid solution.

 

While the amount of oil blow by/mist/etc. is quite small with the newer motors, it is still enough to clog up the IAC needle/sensor within a few thousand miles.
I added a can similar to the one shown, simply to avoid having to disassemble the intake system to clean the gunk off the sensor every couple thousand miles.

 

I wouldn’t buy it.

 

you don't want to have the blow by bypassed, you want to recombust it......it lubricates the valves, spark plugs, etc, adds horsepower and makes your engine last longer

 

It's winter.

 

 

Catch cans are frequently found as add on to performance vehicles. You would be surprised how much "blow by" oil will be trapped in a high performance engine. There's lots of pictures of carboned up Harley heads and pistons attributed to the oil vapor blow by.