Opposite operations. Compression test you measure how much pressure is created as the piston comes up to TDC. Leakdown you fill the (piston at TDC) cylinder to a certain pressure, and see how it decreases over time past the rings. IIRC.

Compression test is generally easier to get a baseline compression, roughly 120-150 psi (8-10:1 compression@15 psi or 1 atm)

Not sure what psi you would fill the cylinder to for a leakdown test, at least the above numbers I would think.

John

 

I don't claim to know a great deal about Sportsters but if the vent system is anything like a Twin Cam you need a hose going to the ground or a catch can. The breather bolt holes on a Twin Cam are below a one way umbrella valve; if you don't have them routed to the intake; a hose that goes to the ground or a catch can all you're going to do is impede venting by filling up the hole with oil. You can't push it back up past the umbrella to return it to the engine; especially since there is pressure venting out while the engine is running and oil doesn't run uphill when the engine is off.

 

There can be a problem with Sportster, Twin Cams & M8's IF you do mostly short runs, especially in cold weather (less than 30 minutes).

Not that it will significantly impede the air flow...they will vent fine, since the air will push thru the oil...BUT, with lots of short runs the oil will build up, filling the cavities between the umbrella valves and the end of the breather bolts.

With longer runs (30 minutes and more) the oil will not build up, the heat of the engine will vaporize it, pushing it out with the vented oxygen depleted air.

 

I wouldn't run a rig like that. The Twin Cam breather bolt hole is essentially a blind hole with an entrance at the top for the pressure and oil mist to exit out of. There is no provision for oil left in there to drain back into the engine. I wouldn't bet on engine heat to eliminate the oil trapped in there to the point that some residual form didn't still reside. Heck, I wouldn't even think that's possible if you piped it to the cat converter. There's gonna be something left.

Mind you this is only an opinion and it surely isn't gospel. But if you go all that way to correct a poor design, why not do it right? It's kinda like putting your hand over your mouth when you feel yourself throwing up; it don't do much good

 

I think I've seen breathers that are already connected with metal pipe (horseshoe breather?) installed above the carb. I'm not sure how if it is above the carb and you had a hose from the outpipe down to the ground, the oil would migrate upward any more than the PO's system.

John

 

Like this one?

 

There are a lot of people running Drag Specialties horse shoe breathers on Sportsters. Me for one. I'm sure they were tested before being put on the market. Hammer Performance sells them. and those boys know a thing or 2 about Sportsters.

 

The difference between what you have and what's pictured above is that there's a place for the oil to go.

 

You're right, there is a way down for the oil, wasn't sure how they outpiped.

John

 

Thank you for all the replies. Really appreciate learning from you guys.

Yes, right off the bat I did have concerns about clogging... which is why I used a clear tube, so I can monitor what's coming out of the breather bolts.

Instead of just a hole at the top of the clear tube, I could put a filter. I ordered and received a tank lift kit from DK Custom yesterday. By raising the tank 2" I should be able to fit a filter in between the tank and the velocity stack. But then that kinda ruins the clean streamlined look I was hoping to accomplish.

Or, I could just route everything downwards and be done with it. That way, my gasoline smell issue goes away for sure. And I get to keep saying screw the epa

I know that none of the above addresses the possibility of bad rings; which was the reason for this thread in the first place. But I realize that even if I found out that the rings were letting gas through, I am not prepared to do anything about it right now. The bike runs really well and I am reluctant to change that for now. Later this year, I hope to save enough for a 1275, at which point the "bad ring" issue will then fix itself.