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Ironhead Sportster Motorcycle Talk (1957-1985) For all those that wanna talk about Ironhead Sportster Motorcycles

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  #21  
Old 29th November 2021
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^^ because they're not good at getting rid of the forementioned crankcase pressure?
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  #22  
Old 29th November 2021
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Mostly mods done by owners who think they are mechanics.
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  #23  
Old 4th December 2021
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So the sportster oil pump is 2 pumps in one. We all know the scavenge pump has a greater capacity then the feed pump. This means that more oil is trying to be pumped out of the motor then is actually pumped in.

So how do we get the oil out of the crankcase? We need to supply a medium that moves this oil out of the crankcase so the oversized scavenger pump can pick it up . That that medium is air.

It's just like the top side of the piston, we can't Scavenge the combustion chamber without air flow. Valve timing or port sizes don't mean **** if no air is flowing. Put your hand over to throat the carb or the exhaust pipe and sooner or later your engine will die. No airflow.

In order to scavenge the sump same thing has to happen. It's not gonna happen because of oil flow, that is a set quantity. It's gotta happen with air flow which is not a set quantity.

Now here's the question?
how does this extra scavenge air get into the sump, and what happens to this airflow as RPMS change.
These are same questions you ask yourself when selecting cams, valve sizes, carburetors, and exhaust systems.

So understanding air flow under your Pistons is just as important is understanding what happens over your Pistons.
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  #24  
Old 4th December 2021
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I've always thought the area of concern for us with this system was the gallery at the back of the cases. My understanding was that the "positive" flow of air as the pistons descend help to push the oil down this gallery and into the can chest area.
I've also always assumed the engine will wet sump if any of this first part of the process isn't sufficient.
ie if the gallery were to fill up no more oil could be scraped off the wheels into the gallery.

This may not be correct, just my assumptions.

My thoughts were it was always a race between the first part of this oil return system and the amount of oil being delivered to the crankcase.

And that the timed breather was timed to produce the highest differential in air pressure to induce the highest velocity of air at this point.
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  #25  
Old 4th December 2021
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the timed breather was my first thought,but it became obsolete in 1976 replaced by a one way valve in'77.
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  #26  
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Quote:
Originally Posted by Ferrous Head View Post
. My understanding was that the "positive" flow of air as the pistons descend help to push the oil down this gallery and into the can chest area.
your a racer and tuner so, please explain to me---where does the cyclical
replenishment of "positive flow of air flow" come from?
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  #27  
Old 4th December 2021
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I don't play much with the later stuff. But the oiling system was changed for 77 with the new pump as well. I don't know what other improvements may have been made.

I know that at slower speeds the scavenge pump works OK. You can see the oil being returned as "spurts", not a steady stream. To my mind this means the amount of oil going into the scavenge pump is not sufficient to flood the pump.

I think the "timed" breather system can be timed to get maximum benefit whereas the OCV id going to be more arbitrary.

And the garroter pump with PCV may work perfectly for stock or longer stroke engine but what would happen if you de-stroked it and ran it to much higher rpm's ?
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  #28  
Old 4th December 2021
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Quote:
Originally Posted by DR DICK View Post
your a racer and tuner so, please explain to me---where does the cyclical
replenishment of "positive flow of air flow" come from?
Sorry, not meaning that the air flow is only one way.

Just "positive" in terms of moving the air from the cases into the gear case.

Your always going to have some blow-by into the cases.

Between the maelstrom that must be going on inside the cases and effects like inertia (the bike isn't often just standing still) it amazes me the system works at all.
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  #29  
Old 4th December 2021
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I took my info from the FSM.
8. Oil accumulated in the crankcase base is scavenged by the flywheels to the breather oil trap.
9. The rotary breather valve is timed to open on the downward stroke of pistons allowing crankcase exhaust pressure to expel scavenge oil from crankcase oil breather trap into the timing gearcase.. Breather closes on upward stroke of the pistons creating vacuum in the crankcase.

Now we know this system works up to a point.

We also know that the HD racers running 750's way back when at Daytona had problems with oil buildup in the cases. This only became apparent at sustained high rpm.

Has this ever been a problem on stock engines or stroker engines ?

My best guess is probably not.

The HD race department got around it by reducing the output of the oil pump on the feed side.
Later on the went to a "mini sump" engine that allowed oil to collect in a small sump where it was scavenged from.

S&S have their pinion shafts Drilled and tapped to take a restrictor (several sizes were available). this prevented too much oil from going into the bearings and cases to begin with.
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  #30  
Old 4th December 2021
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I'll be honest and say I'm not that impressed with the IH oil system.

But is has worked reasonably well for many years in stock engines.

Had this been a tractor or stationary engine it would have been fine from the start.

I know they worked out timing points and widths of windows to get the maximum bang for the buck and used a 1/4 speed oil pump to help. But this just tells me the system was marginal to begin with.

And in fairness it was designed for a 30 hp 750 engine to start with. We stretched that envelope somewhat.
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