I'm thinking about installing some external breather bolts that vent straight to the air (w/o a collector or filter hose assembly) on my 2017 Street Bob (103ci TC). The problem I'm running into is that I'm currently running an AN big sucker, which I want to keep, and am having a tough time finding breather bolts that are long enough to run thru the big sucker back plate and into the engine. I'm trying to avoid replacing the whole air cleaner assembly or doing any cutting to the existing back plate.

I found some Twin Cam compatible bolts from Seven Sins Choppers (pic attached) that I can get in either a 2" or 2.5" length which look like they could work, but does anyone know how far into the engine the bolt needs to thread in order to be "happy"...? I'm worried that the 2" length is only going to give me about a half inch of threads into the engine, while the 2.5" bolts will be about 1/4" longer than what I'm currently running with the AN big sucker hardware (most hardware seems like about 3/4" of threading screws into the engine).

Has anyone tried a similar set up with any success? Also, will just running a straight breather bolt through the big sucker back plate (I know it has its internal passages) cause any issues?

Thanks for the help!

 

The engineering rule of thumb is you want at least 1 diameter of thread engagement. So, 1/2" depth for 1/2" bolts. That is generally enough to develop the strength of the fastener (meaning the bolt will fail before the threads do).

Also, there are a few threads about adding external breathers. Most recommend blocking off the internal passages.

 

If your bike is a puker really consider catching the mist. I ran external breathers on my old sporty and ruined a lot of pants haha.

I'm running a horseshoe type arrangement now on my Dyna with a small breathable element, give it a wash out every oil change and life is good. It tucks up behind the AC itself.

 

 

Yep like I said above plug the holes with some good ultra black rtv and drill and tap em to a external breathing system....dk customs has kits

 

I had the Ness and did the external breather. I would definitely be concerned about oil on your clothes if you go with those bolts. Here's a short vid of what I did.

 

1 diameter is for steel bolts in steel not aluminum.....1 1/2 to 2 times diameter for aluminum