If it was my machine, I'd have the breather hole on the front head drilled and tapped to 1/2-13 to match the rear one.

That would make it easier for you to install any air cleaner that you wish..

 

Lowbrow customs has a breather which isn't too expensive. Get a drag specialities breather kit to hook those heads up so they will vent.

 

How does the front head breathe with a solid bolt in it???

 

But there's more to consider here. All indications are what John Harper said: this is a 4-speed head on a 5-speed bike.

That bolt hole on a 4-speed is just a 5/16-18 thread into a blind hole. It's sole purpose is to support the air cleaner and carb.

On a 5-speed, it's a 1/2-13 hole, and it connects to a vertical hole into the rocker box, to provide a crankcase ventilation function in addition to supporting the air cleaner and carb.

So assuming this is 4-speed head on a 5-speed, which seems like a reasonable assumption, the crankcase isn't venting through that hole, and just drilling it out won't correct that. You also need to machine the vertical hole from the rocker box deck down. That's problem #1.

Problem number two with a 4-speed head on a 5-speed is the pushrod angles are different. This can cause pushrod rub where the pushrods pass through the head into the rocker box. This generally results in noise and possibly leaks. It's generally a bad idea to put 4-speed heads onto a 5-speed, and vice-versa, and this is one of the big reasons.

Now, all that said, there's a big caveat to this. I buy a lot of Sportster heads on Ebay, on behalf of my business (I'll decline to name it). Awhile back, there was a head offered on Ebay, a pristine new silver 883 front head, that by all appearances was a 5-speed head, even had the vertical passage to the rocker box machined. But that carb mount/breather hole was only 5/16-18, i.e. the factory had machined that particular hole like it was a 4-speed head. Many thousands of heads have passed through our shop over the years and I have never, ever, seen that. Every 5-speed head I've ever seen has had a 1/2-13 hole that connected to the vertical hole to the rocker deck, and every 4-speed head I've ever seen has had a 5/16-18 blind hole.

So that head always confused me. I saw it listed off and on for more than a year before it finally disappeared off of Ebay for good.

My guess is that some HD shop got that head from HD to repair someone's bike, discovered the factory mistake, and got another one. Eventually the incorrectly machined one made it to Ebay. So it's at least possible that particular head ended up on this particular bike.

This is why I suggested measuring the distance between the pushrod covers, and comparing the front to the rear. That will give a positive identification. If that's a 4-speed head, then the pushrod covers, at the top where they pass into the head, will be farther apart than the rear head. I don't remember the exact amount, but it's around a quarter inch difference between a 4-speed and a 5-speed head.

 

What a mess!

 

Replace the cylinder head with the correct part.

 

Here, I took a few pics of some heads laying around the shop that better illustrate what I'm talking about ...

First, the crankcase vent and the bole hole in question:


Above is a 5-speed head. Notice the vent hole on the rocker box deck, and the 1/2-13 bolt hole.


Here's that same area on a 4-speed head. No hole on the rocker box deck, and the hole is a much smaller 5/16-18 and it doesn't go anywhere, it's a blind hole.

Now on the pushrod spacing, this is a little harder to make out, but look closely and you'll see the difference:


On a 5-speed head, the two holes measure 1-3/4" center to center


On a 4-speed head, the two holes measure 1-7/8" center to center