Well...here's what I'm working with. I bought an '87 883 that needed the right half of the crank replaced. Split it down and built it back with 1200 cylinders, KB pistons, freshened 883 heads, Andrews V2 cam set, and a new Dyna ignition. I installed the drag pipes that it came with and re-jetted the Super E. Unfortunately, I had most of the build finished when a hurricane destroyed my garage and there was about a year delay before finishing the build. I got it started and it runs good. However, it started leaking oil from the top of the pushrod tubes. So, I pulled the rocker boxes and installed new o-rings. Fired it up and it's not leaking from the tubes, but it started leaking oil from around the bolts that hold the chromed breather tube that connects between the heads. The breather hose from the cam cover connects to this chrome tube that is connecting to the heads, So, here's what I've done so far. I pulled the breather hose off the cam cover fitting, put a spare piece of hose on the fitting and found that it restricts air going in, but air can flow out. So, I assume the breather valve is working correctly. I then started the engine without the breather hose connected and found that I have a serious amount of oil blowing out that cam cover fitting. That means it's blowing oil out the fitting and up the hose connecting to the chrome tube between the heads and then leaking out around the bolts. Any suggestions? I'm thinking that the leaking pushrod tubes were the result of whatever is going on with this thing. Thanks in advance for the help, Steve

Here's some additional info. I just went out and checked the oil level in the tank and there's nothing showing on the stick. I know the return lines are okay. Is the pump failing to return the oil from the engine to the tank? Is there a check valve somewhere that might prevent the return flow? That would give me an engine full of oil and would probably be the reason for the pushrod tubes starting to leak around the o-rings. I should probably start it and see if there's any oil pressure.

 

Should the cam cover hose be connected to the tube between the heads? I don't think so.

 

Not sure about that one, but that's how it was connected when I got it. There's no place for connection to the S&S air cleaner. Either way, it shouldn't be spitting oil out the cam cover fitting. I could change where the hose connects but that's not going to solve the problem.

 

heads can puke on ground
on ironheads, that vent by gen used to too. ran out bottom, tho
not sure on alumheads where that should go

 

So, here's a question. If the cam cover fitting was blocked off would that prevent oil from returning to the tank? I just ran a hose from the cam cover fitting back to the oil tank fill and started it up. The engine returned the oil to the tank, it has stopped spitting oil from the cam cover fitting, and the leaks have stopped. So, blocking crank case pressure prevents the oil from returning to the tank?

 

crankcase needs to "breathe" and it is timed to scavenge oil
blockin any breather prolly not good idea, which i think havin it to heads did
hopefully someone knowin more than me will add to this

 

Do you have later than 1987 heads? There are no breathers in the 1987 heads, so perhaps someone fitted later (5 speed) heads to your 4 speed? I'm not sure if that might be why you are leaking oil from the pushrods, I believe the spacing may be different. That hose from the crankcase may be blocked the way you have it connected. Those pushrod tubes do not look parallel to me, and I think they are supposed to be, it looks narrower at the heads than at the case.

John

 

Check the breather line coming from the heads. With the engine running, hold a finger to close off the line. There should be excess crankcase pressure pulsing out of it. IF ya got air escaping, it's been converted. If not, remove that Head Breather stuff. Now check the camcover vent that same way. Got AIR pulsing out ? GOOD! That tells ya the breather check valve in the camcover is working. If not, ya need to replace the camcover breather umbrella valve.You hooked the AIR vent tube to the OIL tank and oil is returning to the tank. Time to check if the 3 oil lines are connected to the oil tank properly. 1, feed to pump - bottom, 2, oil return - top, 3, camchest vent - lower than return fitting. Hope this helps ya out.

Breather Parts - 26854-82 umbrella valve, 26916-84 cap baffle, 26917-84 tube baffle


1986-1990 engines continued the breather baffle tube system (implemented in L1984) incorporated into the cam cover in the area behind the oil filter.

• The baffle tube mounts into the cam cover and the rubber umbrella installs into the center of the baffle tube. 1)
• On each piston downstroke, crankcase pressure (air and oil mist) is routed to the breather baffle at the front of the cam case.
• Oil is separated from the air pressure by the one-way umbrella valve.
  • The oil then drains into the cam chest through a drain hole in the breather valve compartment.
• Exhaust air escapes past the one way umbrella valve in the baffle tube and into a vent fitting on the cam cover.
  • The air is then routed into the rear of the air cleaner via an oil hose to the cam cover.
  • In 1991, along with the 5-speed transmission, the MoCo moved the crankcase breathing from the cam box cover outlet to breather bolts in the heads.
    Previously, these bolts were just used to mount the carb and air cleaner to the heads
  • 
    

 

As has been pointed out, 4-speed heads don't have a breather facility on those two bolt holes. The bolt holes are 5/16-18 and blind.

5-speed heads on the other hand use 1/2-13 bolts (i.e. considerably larger) and the hole connects to a vertical hole that comes out on the rocker box deck surface. 5-speed rocker boxes facilitate a path for the blow-by to go through an umbrella valve and into that passage. 5-speeds do not have a vent off the cam box cover.

So it's possible someone has modified your 4-speed heads, or it's possible someone has put 5-speed heads on it. In either case, you'd also need 5-speed rocker boxes to make that work.

But regardless, if you're connecting the cam box vent to the head breathers, whether the heads really breathe there or not, you've closed the system. Blow by can then pressurize the crankcase, and oil leaks become inevitable. It's just a matter of when and where they pop up.

The crankcase needs to be vented. From the factory, it's vented into the air cleaner, which recycles the blow-by back through the motor. Many guys reroute the crank vent to the atmosphere instead. You need to do one of those things, you can't have a closed system, not unless you like oil leaks anyway.

One note about 5-speed heads on a 4-speed, just in case that's what happened here. 4-speeds use off-center tappets, 5-speeds use on-center tappets. Therefore 4-speeds have the tappets farther apart, and thus the pushrod angles are different, as compared to 5-speeds. Thus the holes in the undersides of the heads, where the pushrods pass through the head to the rocker boxes, those holes are in a slightly different place on a 4-speed as compared to a 5-speed. Because of this, 5-speed heads on a 4-speed often results in pushrod rub right there, which can cause both noise and leaks.