IH: Engine Mechanicals

Crankcase Ventilation

See also in the REF section of the Sportsterpedia:

Here's a breakdown of XL & K model breathers, set-up, service and upgrades. 1)

52-76 models:

  • Timed Rotary Breather
  • Design & Function
    • Integral with the oil pump, timed to engine rotation.
    • 72 & up timing
      • Opens 25 degrees ATDC closes 85 degrees ABDC
    • 52-71
      • Breather timing was less duration.
      • Rotary breather connects flywheel area to gearcase.
      • Slinger separates oil from air.
    • 52-62
      • Special slinger on generator.
      • Spring loaded bushing in case rubbed end of slinger.
      • Breather pipe in gearcase cover open to atmosphere.
    • 63-76
      • Washer - 1 5/8“ dia. on end of generator.
      • 1/16-3/16” Clearance
      • Service
        • Pump had to be timed, line up these marks;
          • Ignition timing mark - center of window.
          • Dot on rotary breather should be centered in pump housing notch.
          • Changed by repositioning of pump gear to drive gear on pinion shaft.
    • 63-76 Slinger washer distance
      • 1/16-3/16“
      • Increase by grinding generator gear or add generator gaskets.
      • Decrease by shimming washer.
    • Updates
      • 52-71 Breathers
        • Install 72-76 pump.
        • Changes breather timing - benefit.
        • Modify feed supply.
        • Plug old fitting in case.
        • Run feed to back of new pump.
        • One Way Breathers 77-85.
    • Design
      • 77-78 - PCV type valve.
        • Inline with breather pipe.
        • 1-5/8” Slinger washer.
      • 79-E81
        • Stainless reed valve
        • Mounted in gearcase cover.
        • 1-5/8“ Slinger washer.
        • Breather hose to air cleaner '79 & up
      • L81-85
        • Rubber umbrella valve.
        • Very efficient.
        • Mounts in gear case cover.
        • 1-3/4” Slinger washer.
      • All 79-85 breather systems connect to air cleaner.
    • Service and troubleshooting
    • Inspection:
    • All valves should flow one direction only.
    • Slinger distance must be 1/16-3/16“.
    • Too little - increased crankcase pressures = oil leaks.
    • Too much - slinger won't separate oil = oil carry over
    • If bike smokes check breather valve operation.
    • If it sticks open there will be no crankcase vacuum to help evacuate top end oil
  • Updates
    • 79-early 81
    • Rubber umbrella breather is a retrofit, with 1-3/4” slinger washer.
      • Better breathing, less stiff than the metal reed and better sealing - doesn't stay open due to metal fatigue

Breather Valve


The later style system is just like your car. 2)
A deep sump was added to 77> casings and the scavenge side of the oil pump simply pulls the oil from there.
Holes were added between the crankcase and the gearcase / cam chest and crankcase pressure is vented to atmosphere from there.
(much the way your car's crankcase is vented out the top thru the valve covers)

The shallow sump, timed breather system, comes from the aviation world of old.
Piston driven aircraft had to be able to evacuate the oil from the crankcase regardless of engine altitude and that system does that.
At the time Harley adapted that system they were copying the highest engine technology of the day.
They just took too long to abandon it as technology advanced.

The sump system was brought into production to eliminate the need to time a breather to save time on the assembly line.
Documents from HD Racing from the period show no HP gain between the 2 systems when the breather is properly timed ( which didn't happen a lot).

57-76 Timed Breather Valve

Sub Documents

The rotary breather valve functions to relieve pressure in the crankcase caused by the downstroke of the pistons and it controls the flow of oil in the lubrication system.
It is timed to open on the downstroke of the pistons. 3)
This allows crankcase exhaust air pressure to expel the scavenge oil from the crankcase breather oil trap into the gearcase.
The breather valve then closes on piston upstroke, creating vacuum in the crankcase.
Crankcase exhaust air from the gearcase is sent out the breather tube.
Any oil still in suspension with the air on the way to the breather tube is separated by an oil slinger on the generator drive gear.

A street oil pump has 2 slots and is driven at 1/2 engine speed. 4)
A racing oil pump has 4 slots and is driven at 1/4 engine speed.
All 4 stroke engines takes two revolutions before you come back to the timing marks being all aligned.

How the volume compares when the breather opens as to when it closes: 5)
If we knew that, we'd have a much clearer picture of what actually happens.
This diagram shows the volume swept by piston action in a 1000cc motor.
It shows how much displacement is changed from min volume (0 cubic inches) to max volume(56.2 ci more than min).
6)

There's only 1.2 cubic inches of net outward flow per revolution.
(ignoring the dynamics of the inertia that the moving column imparts to the actual net movement)
So the actual movement is great but the net change is small.
How much actual movement?
About 45 ci on down stroke and about another 45 on the up for a total of app. 90 ci per rev trying to squeeze thru the open breather.
(which is fully open for exactly 1/2 the time of the 'just open' to 'just close' total time.

90 ci per revolution is about 1-1/2 quarts per revolution.
Multiply that by 5000 rpm and you get 7500 quarts per min.
That's almost 2000 gallons per min trying to get thru the breather.
Obviously that ain't happening and the highly revered 1/4 speed (R) pump has a way smaller opening yet than the street pump.

The pics below show the flow from the flywheel cavity to the return pump (applies to 76< only).
In stock configuration, most all used oil ends up in the flywheel cavity.
The small amount that gets supplied to the upper pushrod ball/socket goes into the gearcase.
While the splash oil to the exhaust valves enters the crankcase through the head drains.

There are only 2 areas that get supply (feed) oil pumped to them, the crankpin and the rocker shafts. 7)

Left is the unmodified 1/4 speed R
valve. Right is the 1000 stock.
R model is the left one.


There are only 3 rotor and tower slot widths for all 1937-76 4-cam engines (45, K, KH, XL, UL), which determine the complete breather timing interval. 8)

  1. Rotor .375“ (88°) + tower .34375” (81°) = 169°:
    all non-R 1937-71 engines; the exact opening-closing points vary between engines; 1952-71 K &c. slots are taller than 45 & UL.
  2. Rotor .594“ (146°) + tower .34375” (81°) = 227°: 1972-76 XL; these slots are also taller than 45 & UL.
  3. Rotor .214“ (99°) + tower .269 (125°) = 224°: all 1954-? KR, KHR, XLR (many mods to this)

77-78 Breather Valve

WHAT IS IT?

  • The complete assembly is part# (24633-77).
  • Thread size at cam cover is 5/8”-11. 9)
  • The slang term “FooFoo” comes from the annoying sound that it makes when it gets clogged up with oil residue. 10)
  • The engine breather (or crankcase vent) is to allow air out of the lower crankcase, but not in, as the pistons rise and fall. 11)
    Without some kind of controlled breather, the lower end would become a 1,000cc air compressor, robbing the engine of several horsepower.
    Old time tuners like Jerry Branch, Tom Sifton and Dick O’Brien paid much attention to the engine breather.
    They knew it could give them extra horsepower if set up right.
  • One thing not to do with an engine breather is to simply plumb a hose to the crankcase without some kind of one-way valve or timed breather valve.
    It is commonly done, but it wastes power and is not good for your engine.

WHERE IS IT? 12)

  • Pre-1977
    • There is a timed breather valve built into the oil pump drive, which vents crankcase pressure into the cam timing chest.
      A six-inch metal tube hanging down from the timing cover near the generator drive, at the 6 o’clock position vents that controlled pressure to atmosphere.
      A metal disc on the end of the generator drive gear centrifugally separates oil from the air as it is discharged overboard.
  • 1977-78 only 13) 14)
    • The timed breather on the oil pump drive was dropped.
      A new design breather valve (24633-77) was used in late 1977 model XL/XLCH/XLT engines produced around October 15, 1976.
      All 1000cc engine numbers (3A, 4A or 2G) 27940H7 and above had the new breather valve.
      It serves the same function as the gear driven breather valve used on 1976 and earlier engines to maintain a partial vacuum in the engine and prevent oil leakage.
      Due to it's improvements in doing so, it was suggested to be retrofitted to all 1977 XL & XLCH engines.
    • The one-way valve is contained in a fitting which screws into the gear-case cover below the generator mounting boss.
      The existing breather outlet pipe screws into the bottom of the new fitting.
      The outlet pipe, because of its lower position, must be directed outside (instead of inside) the frame tube.
      The rubber hose at the pipe outlet must no longer be used.
    • Because of the higher vacuum existing in the engines equipped with this new breather valve, a higher pressure oil pump check valve (26435-76A) was installed in L1977 oil pumps at the same time to provide higher oil pressure at the oil pressure light switch.
    • The new valve opens at 4-6 PSI whereas the old valve opens at 2-4 PSI.
      Pumps having the new valve are identified with a green dot.
      The existing 0-ring (26433- 77) was used for both new and old valves.
    • An external non-return valve was plumbed into the vent tube sticking down from the timing cover at the generator drive.
      This allows air out, but not in. It is sometimes referred to as the foo-foo valve.
      Searching the XLFORUM for foo foo valve or foo-foo will lead to extensive discussions of this mystical device.
  • Replacement options:
    • It's a possible option for the 77-78 foofoo valve to be replaced with an external breather valve.
      If you want to go this route, remove the internal valve as it will also change crankcase pressure with 2 valves in line.
      Then, you might want to consider installing something like the external Krankvent or others.
      Click here to see the Converting Head Breathers to Cam Chest Breather page in the Sportsterpedia.
      That page is for an Evo conversion to cam chest breathing but the Krankvent and plumbing is shown.
      You can also review this page in the Sportsterpedia Breather Venting / Relocation (especially the sub documents at the top of the page)
77-78 Crankcase Breather Valve 15)
  • This vent line mod was done due to problems fitting the stock tube as it hit the exhaust pipes.
    • Thread size for the breather fitting is 5/8“-11.
    • A piece of aluminum threaded rod, cut a small length to thread into the breather and drill / tap the hole for an 1/8” pipe thread.
    • A 45 ° hose barb fitting was installed to connect a length of hose that leads back along the frame.
      This way the oil mist gets directed out back and doesn't collect along the frame and engine.
Stock tube removed, fitted with 1/8“ 45 deg barb fitting. 16)

1979-E1982 Reed Valve

  • Reed Valve Assembly (26909-79).
    • Breather vent fitting thread size at the cam cover is 1/8” NPT. 17)
    • The external foo-foo valve and the six-inch metal vent tube at the front of the timing cover were done away with.
      Instead, a one-way foo-foo valve was built inside the timing cover.
      A rubber breather hose then ran from the generator drive area of the timing cover, at the 10 o’clock position.
      It connected to the stock air filter so that any oil mist was fed back through the engine, making the EPA pollutocrats more happier.
      (than they were with the idea of engine oil spraying out into the atmosphere)
      The generator had a (1-5/8“ O.D.) oil separator washer on the end of the armature shaft. 18)
    • The breather valve is a simple reed valve with a flap made of spring steel over a hole.
      Unless it's visibly damaged, there's no reason to mess with it. 19)
      If it stops up, you can try and spray some WD-40 in the hole to clear it.
  • Removal:
    • The reed cam be removed with a standard bushing / bearing puller with a 5/8”.
  • Replacement options / mods:
    • In L1982, a new style crankcase breather valve was used in production.
      The breather valve kit (26909-79A), which is functionally more durable and quieter than the early style reed valve, will fit 1979-E82 models.
      The late style breather valve incorporates a rubber umbrella valve attached to the base plate along with a larger diameter oil slinger washer.
      The oil slinger washer is bigger (1-3/4“ OD).
      These parts, used together, will replace the early style reed valve assembly and smaller diameter oil separator washer.
    • It's a possible option for the 79-85 breather valve to be replaced with an external breather valve.
      If you want to go this route, remove the internal valve as it will also change crankcase pressure with 2 valves in line.
      Then, you might want to consider installing something like the external Krankvent or others.
      Click here to see the Converting Head Breathers to Cam Chest Breather page in the Sportsterpedia.
      That page is for an Evo conversion to cam chest breathing but the Krankvent and plumbing is shown.
      You can also review this page in the Sportsterpedia Breather Venting / Relocation (especially the sub documents at the top of the page)
    • Click here to see the page on Adding a Secondary Vent Hose at the 6:00 Position.
      This mod has been done with agreeable results to improve breathing.

Here's the reed valve and the back side.
20) 21)

L1982-1985 Rubber Umbrella Valve

  • Breather check valve (26909-82).
    • The internal crankcase breather valve was redesigned to incorporate a rubber umbrella valve attached to the base plate.
      (along with a larger diameter 1-3/4” O.D. slinger washer)
  • Replacement options / mods:
    • It's a possible option for the 79-85 breather valve to be replaced with an external breather valve.
      If you want to go this route, remove the internal valve as it will also change crankcase pressure with 2 valves in line.
      Then, you might want to consider installing something like the external Krankvent or others.
      Click here to see the Converting Head Breathers to Cam Chest Breather page in the Sportsterpedia.
      That page is for an Evo conversion to cam chest breathing but the Krankvent and plumbing is shown.
      You can also review this page in the Sportsterpedia Breather Venting / Relocation (especially the sub documents at the top of the page)
    • Click here to see the page on Adding a Secondary Vent Hose at the 6:00 Position.
      This mod has been done with agreeable results to improve breathing.

The pic on the left shows the breather line coming out at the 10 o'clock position going up to the air cleaner.
The pic on the right is of an 85 cam cover with the foofoo valve (baffle tube) off to the left of it.

22) 23)

Oil Slinger

Sub Documents

Crankcase exhaust air escapes from the gearcase through the external breather tube. 24)
Any oil carried still carried by exhaust air is separated from the air by an oil slinger on the generator drive gear.
The oil slinger is powered by the generator and deflects oil away from air leaving the breather outlet to atmosphere.
It spins oil away from the breather hole by centrifugal force and separates the oil mist in suspension with the exhausting air.

Factory Oil Slingers: 25) 26) 27)

  • 1957 used the model 52 generator, no nut or washer, and a daisy wheel gear (31071-52A) pinned to the generator shaft.
  • 1958-1962 used the daisy wheel gear (31071-58), an integral slinger / genny gear bolted to the shaft.
    It looks like a gear with a tinker toy connector glued on the end.
    It's a lathe machined affair combined with a spring loaded sleeve in the cover.
    These are great gears but no one repops them and they are expensive and hard to find.
    • Just get rid of the timing cover sliding bush/spring if you want to upgrade to the big washer instead. 28)
      The sliding bushing assembly makes the early slinger works as a “labyrinth” since the air has to travel through its center to get out.
      That's why it's a better set up than the simpler washer setup. It doesn't allow for any oil to escape except if your engine is totally wetsumped.
      But the early slinger will work without the sliding bushing, just not as good.
      And you can't use the sliding bushing with the washer setup.
  • L1962-1978 used a more standard looking gear (31073-63) used with a 1-5/8“ washer style slinger (31067-63).
    Not as good but a lot cheaper to make. The washer itself looks to be just a normal fender washer.
    You may find an in use washer with grooves stamped in it. Grooves are an old mod done by owners/wrenches (not the factory).
    It is large enough in diameter to make installing the generator tricky at times.
    5/16” fender washers come in 3 sizes. 1.375“ (common), 1.500” (hard to find), 1.625“ (real hard to find).
    OEM is 1.625” although the 1.500“ washer usually works fine. The 1.375” washer may pass more oil out the vent than the bigger ones.
  • 1979-1981 used gear (31073-63A) with the 1-5/8“ slinger washer (31067-63).
  • 1982-E1984 used the same gear (31073-63A) with a 1-3/4” slinger washer (31066-82) to accommodate the larger crankcase breather valve.

To inspect or replace the slinger washer, remove the two bolts from the cam cover that hold the generator. 29)
Remove the wires from the generator and with a little fiddeling around, the generator will come out. The washer is on the end of the armature.
Make sure to put a new grade 8 nylock nut on if you remove the old one. They should only be used once or they lose their grip in that hot, oily environment. 30)

Check the oil separator bushing to bore fit in the cover. It should be a light press fit.
If it is loose, you can probably remove it, clean up the boss with brake cleaner and reinstall the bushing with Loctite or epoxy. 31)

58-62 generator gear / oil slinger (31071-58) 32) 63-later oil slinger washer (31067-63) 33)



3)
1960 HD FSM pg 3a-15
13)
Hopper
14)
HD Service Bulletin #M-708 dated December 1, 1976
16)
photos by ericfreeman of the XLFORUM http://xlforum.net/forums/showthread.php?t=1928882
18)
HD Service Bulletin #M-848 dated April 9, 1982
22)
photo by spammer80 of the XLFORUM
24)
1959-1969 HD Sportster FSM pg 3A-15
33)
photo by papphammar of the XLFORUM http://xlforum.net/forums/showthread.php?t=495298
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