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techtalk:ih:oil03j [2025/09/06 00:10] – [Wet Sumping vs Horsepower] hippysmacktechtalk:ih:oil03j [2025/09/06 18:04] (current) – [Installing 1972-1976 Oil Pump (Complete) on 1971-Earlier Motors] hippysmack
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 ====== Diagnosing Scavenge Ability ====== ====== Diagnosing Scavenge Ability ======
 From barefoot: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/184882-building-my-baby-86-big-bore-stroker/page5#post4008899)) \\ From barefoot: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/184882-building-my-baby-86-big-bore-stroker/page5#post4008899)) \\
-If you can get a dangerously low amount of lube in there, put an add up and all the XR guys will be pounding on your door asking how. Axtell used to run sump-chop dyno runs - like a plug chop. But instead of checking the plugs, you check the oil (by measuring amount of oil you can drain from the crankcase). The least they were able to get (as far as I know, anyhow) was two ounces. If they ever had one bone dry, they'd have been jumping up and down like cannibals at a missionary cookout. +If you can get a dangerously low amount of lube in the crankcase, put an add up and all the XR guys will be pounding on your door asking how. Axtell used to run sump-chop dyno runs - like a plug chop. But instead of checking the plugs, you check the oil (by measuring amount of oil you can drain from the crankcase). The least they were able to get (as far as I know, anyhow) was two ounces. If they ever had one bone dry, they'd have been jumping up and down like cannibals at a missionary cookout. 
  
 From mrmom9r: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/184882-building-my-baby-86-big-bore-stroker/page5#post4008899)) \\ From mrmom9r: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/184882-building-my-baby-86-big-bore-stroker/page5#post4008899)) \\
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 From thefrenchowl: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/203717-brought-a-dragbike-that-s-been-sitting-20-years/page6#post4564967)) \\ From thefrenchowl: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/203717-brought-a-dragbike-that-s-been-sitting-20-years/page6#post4564967)) \\
-I do not agree... I hear a lot of complaints from K, KH and early X owners about fouling plugs, excess oil in exhausts etc... I can really say I never encountered such issues on any of my K, KHK, XLH or XLCH over the 40 years I have rode them so far... And it made no real differences if I use pre-72 or post-72 breather towers... So I ask me why? And the only answer I can come up with is that I always ride them like there's no tomorrow and use all the revs available to me, and sometimes more... To me, it seems that this 750 WL/1000 FL antiquated oiling system only works well above a certain rpm, let's say 4000rpm. The racing oiling problem is another issue, let's face it, a Daytona KRTT revs at 7500rpm and a decent iron or alloy XR 7500 to 9500rpm. So the towers must have encountered other issues over say 6000rpm... Then the real problem boils down that this engine needed a sump from the day one... It only got one circa 1975 on the alloy XR and 1977 on the street Sportsters... So all the mods are really to evacuate as much oil as possible from the crank cavity, not really a problem with the scavenge side of the oil pump... \\+I hear a lot of complaints from K, KH and early X owners about fouling plugs, excess oil in exhausts etc... I can really say I never encountered such issues on any of my K, KHK, XLH or XLCH over the 40 years I have rode them so far... And it made no real differences if I use pre-72 or post-72 breather towers... So I ask me why? And the only answer I can come up with is that I always ride them like there's no tomorrow and use all the revs available to me, and sometimes more... To me, it seems that this 750 WL/1000 FL antiquated oiling system only works well above a certain rpm, let's say 4000rpm. The racing oiling problem is another issue, let's face it, a Daytona KRTT revs at 7500rpm and a decent iron or alloy XR 7500 to 9500rpm. So the towers must have encountered other issues over say 6000rpm... Then the real problem boils down that this engine needed a sump from the day one... It only got one circa 1975 on the alloy XR and 1977 on the street Sportsters... So all the mods are really to evacuate as much oil as possible from the crank cavity, not really a problem with the scavenge side of the oil pump... \\
    
 From mrmom9r: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/184882-building-my-baby-86-big-bore-stroker/page8#post4008899)) \\ From mrmom9r: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/184882-building-my-baby-86-big-bore-stroker/page8#post4008899)) \\
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 From needspeed: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/184882-building-my-baby-86-big-bore-stroker/page8#post4008899)) \\ From needspeed: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/184882-building-my-baby-86-big-bore-stroker/page8#post4008899)) \\
 When I was drag racing I knew the value of not having too much oil in the crankcase, so after every run I would decrease the oil feed. The bike ran great until I ruined a set of special pistons from lack of oil. It's hard to know when enough is enough and too little is too little. I guess you have to have some part failures to find out. \\ When I was drag racing I knew the value of not having too much oil in the crankcase, so after every run I would decrease the oil feed. The bike ran great until I ruined a set of special pistons from lack of oil. It's hard to know when enough is enough and too little is too little. I guess you have to have some part failures to find out. \\
 +
 +====== Most Pump Mods Are Used in Combination w/ Engine Mods ======
 +Most of these mods were dreamed up before the invention of the mini-sump addition to the crankcase. \\
 +Some of the oiling problems in the crankcase were later solved with the mini-sump engines (1975-up XR-750 and 1977-up production XLs). So to the fact of a magazine article from  Custom Bike Magazine from October 1976 "Mini Sump Your Sportster". In this article are instructions on adapting 1977-earlier Sportster engines with some of the oiling provisions of 1976-later Sportster motors. Case alterations include extending the bottom of the cases and alterations to delete the affects of the timed breather (while physically keeping it) as well as deleting the transfer valve. Oil pump alterations were basically to adapt the -72 production oil pump to the configuration of the 1975 XR-750 oil pump. \\ [[techtalk:miscres:miscres150|Click Here]] to read the full article in the Sportsterpedia.
 +
 +Then again, some were advised by HD Racing Department in an overall view of things. \\
 +This document, "Engine Oiling System Mods for Cooling and Increased Performance" (date not available), shows many mods for both the case and pump. And these suggestions made their way around the Sportster community and showed up in some of the mods on this page. \\
 +{{:techtalk:ih:oil:engine_oiling_sys_mods_for_cooling_and_increased_performance_pic1_from_dr_dick.jpg?direct&600|}} ((provided by Dr Dick of the XLFORUM)) \\
 +
 +{{:techtalk:ih:oil:engine_oiling_sys_mods_for_cooling_and_increased_performance_pic2_from_dr_dick.jpg?direct&600|}} ((provided by Dr Dick of the XLFORUM)) \\
  
 ====== 1/4 Speed vs 1/2 Speed Oil Pump ====== ====== 1/4 Speed vs 1/2 Speed Oil Pump ======
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 The 1975-1987 XR-750 pump does not have a feed bypass. But it does have a hose nipple in the rear of the pump just like the -72 production pump does. And that nipple is tied into the return gears instead of the feed gears. This pump has no external inlet for tank feed oil as required to mount on 1967-up XLH and 1970-up XLCH. \\ The 1975-1987 XR-750 pump does not have a feed bypass. But it does have a hose nipple in the rear of the pump just like the -72 production pump does. And that nipple is tied into the return gears instead of the feed gears. This pump has no external inlet for tank feed oil as required to mount on 1967-up XLH and 1970-up XLCH. \\
  
-====== What Era Factory Oil Pump Would Be the Most Benificial on a Street Performance Build ======+1954-1976 KH and Sportster pumps do not have afeed bypass built in although there were a few different versions of those as well. \\ 
 + 
 +====== What Era Factory Oil Pump Would Be the Most Beneficial on a Street Performance Build ======
 From Dr Dick: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/107411-76-later-oil-pump-on-earlier-cases/page2)) \\ From Dr Dick: ((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/107411-76-later-oil-pump-on-earlier-cases/page2)) \\
 I like using 72-76 pump. It has the best return to feed volume ratio. To take full advantage, you need to drill the additional hole in the mountin surface of the crankcase like the 72-76 case has. This pump feeds a lot of oil so it's not the setup for all out hp. But that volume means more cooling, best for longevity. Get a complete unit. It will have the breather gear with the big slots. Also gives you the option of not using the (thru the case) feed passage, goin direct to pump like xlh or 72-76. Some feel this is better cause the feed oil don't get preheated goin thru the hot case. I have also built many using the 62-71 and opening the breather slot up or using the -72 breather gear & snap ring. You must install the return gear upside down, so the counterbore for the original half moon retainers is not facing the snap ring when using -72 breather with -62 body & gear set. I think it's also important if using an oil filter that a low pressure return bypass be fitted to keep the restriction down at high rpms. Also note that there is an extra oil return hole from the case to the return side of the pump on a -72 pump that is not there in the '69 case unless you drill it. The benefit of the -72 pump is increased scavenging capacity which helps prevent wet sumping at sustained highway speeds. It doesn't do much if you don't allow more oil to get to it. Many people believe it also has the breather timing of the race pumps but that is not entirely correct. When timed on the mark, they have the opening point of the race pump (15 degree ATDC ) but not the closing point. The breather slot needs to be enlarged to achieve a closing of 85 degrees ABDC if you're wanting to match the race pump timing. It's a worthwhile modification when building the motor if you have a degree wheel to verify the results. Otherwise don't worry about it. They're still an improvement over the early pump. The benefits of the race timing are a few free HP, lower oil temps, better fuel mileage and all the things that come from an engine running with less drag. \\ I like using 72-76 pump. It has the best return to feed volume ratio. To take full advantage, you need to drill the additional hole in the mountin surface of the crankcase like the 72-76 case has. This pump feeds a lot of oil so it's not the setup for all out hp. But that volume means more cooling, best for longevity. Get a complete unit. It will have the breather gear with the big slots. Also gives you the option of not using the (thru the case) feed passage, goin direct to pump like xlh or 72-76. Some feel this is better cause the feed oil don't get preheated goin thru the hot case. I have also built many using the 62-71 and opening the breather slot up or using the -72 breather gear & snap ring. You must install the return gear upside down, so the counterbore for the original half moon retainers is not facing the snap ring when using -72 breather with -62 body & gear set. I think it's also important if using an oil filter that a low pressure return bypass be fitted to keep the restriction down at high rpms. Also note that there is an extra oil return hole from the case to the return side of the pump on a -72 pump that is not there in the '69 case unless you drill it. The benefit of the -72 pump is increased scavenging capacity which helps prevent wet sumping at sustained highway speeds. It doesn't do much if you don't allow more oil to get to it. Many people believe it also has the breather timing of the race pumps but that is not entirely correct. When timed on the mark, they have the opening point of the race pump (15 degree ATDC ) but not the closing point. The breather slot needs to be enlarged to achieve a closing of 85 degrees ABDC if you're wanting to match the race pump timing. It's a worthwhile modification when building the motor if you have a degree wheel to verify the results. Otherwise don't worry about it. They're still an improvement over the early pump. The benefits of the race timing are a few free HP, lower oil temps, better fuel mileage and all the things that come from an engine running with less drag. \\
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 ====== Installing 1972-1976 Oil Pump (Complete) on 1971-Earlier Motors ====== ====== Installing 1972-1976 Oil Pump (Complete) on 1971-Earlier Motors ======
-  * The bigger return gears in the -72 pump suck up more oil at a higher suction (vacuum) rate.+  * The bigger return gears in the -72 pump suck up more oil at a higher suction (vacuum) rate. The faster they rotate, the more vacuum is created.
   * As mentioned above, the return hole in the case mounting surface needs to be enlarged with a second hole to lower the added vacuum generated by the return gears. Gravity does little to flow oil through that return hole. The pump depends on suction (vacuum) from the gears AND positive crankcase pressure (piston downstroke) that makes it's way into the cam chest to push the oil in the cam chest sump (below the cam floor screen) to the oil pump's vacuum chamber.     * As mentioned above, the return hole in the case mounting surface needs to be enlarged with a second hole to lower the added vacuum generated by the return gears. Gravity does little to flow oil through that return hole. The pump depends on suction (vacuum) from the gears AND positive crankcase pressure (piston downstroke) that makes it's way into the cam chest to push the oil in the cam chest sump (below the cam floor screen) to the oil pump's vacuum chamber.  
   * Lowering the vacuum created from the bigger gears in the -72 pump also allows the pump to suck up more oil without added stress, which lowers the possibility of making froth in the oil due to higher vacuum sucking on the single inlet hole in 71< motors.   * Lowering the vacuum created from the bigger gears in the -72 pump also allows the pump to suck up more oil without added stress, which lowers the possibility of making froth in the oil due to higher vacuum sucking on the single inlet hole in 71< motors.
   * Using pre-72 pumps on pre-72 motors creates a factory designed amount of vacuum on the return inlet of the pump. \\ Using -72 pump on pre-72 motors increases the amount of vacuum on the return inlet of the pump (more than the factory designed). This may not be an issue on low to medierate RPM but will most likely be an issue for racing applications.   * Using pre-72 pumps on pre-72 motors creates a factory designed amount of vacuum on the return inlet of the pump. \\ Using -72 pump on pre-72 motors increases the amount of vacuum on the return inlet of the pump (more than the factory designed). This may not be an issue on low to medierate RPM but will most likely be an issue for racing applications.
-  * Plugging the feed inlet fitting on the top of the case and plumbing the hose to the feed fitting on the rear of the case takes oil from the tank directly into the pump, bypassing the hot engine case, without the added heat from the case.+  * Plugging the feed inlet fitting on the top of the case (if you have one) and plumbing the hose to the feed fitting on the rear of the pump takes oil from the tank directly into the pump, bypassing the hot engine case, without the added heat from the case. 
 +  * You can always plug the rear feed fitting on the pump and use the feed fitting on top of the case instead (if you have one). You get the same amount of oil from either connection. Gravity only pushes the oil to the return gears. The return gears are sucking on the oil as well. And you'll never pump more oil than can collect in the gears per rev.  
  
 {{:techtalk:ih:oil:1957-1971_xl_case_mod_for_1972-1976_oil_pump_compiled_by_hippysmack.jpg?direct&400|}} ((compilation by Hippysmack)) {{:techtalk:ih:oil:1971-earlier_case_mod_for_-72_oil_pump_by_thefrenchowl.jpg?direct&300|}} ((photo by thefrenchowl of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/203717-brought-a-dragbike-that-s-been-sitting-20-years/page6#post4564967)) \\ {{:techtalk:ih:oil:1957-1971_xl_case_mod_for_1972-1976_oil_pump_compiled_by_hippysmack.jpg?direct&400|}} ((compilation by Hippysmack)) {{:techtalk:ih:oil:1971-earlier_case_mod_for_-72_oil_pump_by_thefrenchowl.jpg?direct&300|}} ((photo by thefrenchowl of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/203717-brought-a-dragbike-that-s-been-sitting-20-years/page6#post4564967)) \\
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     - Feed side: \\ Making the long inlet wider/deeper reduces the vacuum pull on the hose from the tank. It may have little affect at idle but could lead to oil starvation at higher revs. If you port the short outlet area near the gears (without making the hole bigger) you lose that tiny "shelf" which acts as a backstop and helps usher oil into the feed hole. Making the outlet hole bigger slightly reduces outlet pressure inside the pump and consequently to the motor.     - Feed side: \\ Making the long inlet wider/deeper reduces the vacuum pull on the hose from the tank. It may have little affect at idle but could lead to oil starvation at higher revs. If you port the short outlet area near the gears (without making the hole bigger) you lose that tiny "shelf" which acts as a backstop and helps usher oil into the feed hole. Making the outlet hole bigger slightly reduces outlet pressure inside the pump and consequently to the motor.
     - Porting the return side: \\ Making the long outgoing oil path wider/deeper reduces the pressure put out by the return gears and slows down the oil traveling to the hose and then tank. With oil staying in the pump longer, it also allows the hot oil to stay in the pump longer which increases the heat on the pump body. What is the gain? If you port the area around the return inlet hole at the gears, that could lead to faster sucking on the oil there and slower on the actual inlet hole just as in the long feed path. Making the inlet hole bigger on pre 1972 pumps negates some of the vacuum that the return gears create. You think, but the -72 pump has 2 return inlet holes so what's the big deal? The -72 pump has bigger return gears and makes more vacuum than previous year pumps. So the bigger gears compensate for the double barrel holes. Why did the MoCo bore that second hole? If thinking seriously about it, the 1 single inlet hole is big enough to suck a whole lot of oil into the pump without falter. But with the bigger return gears in the -72 pump making more vacuum, they also stand the chance of choking down the incoming feed oil on high rpm. Not enough to choke it closed but surely enough to slow the flow at a percentage of rpm. So the double barrel holes relieve some of the added vacumm on the gears so flow is not impeded.     - Porting the return side: \\ Making the long outgoing oil path wider/deeper reduces the pressure put out by the return gears and slows down the oil traveling to the hose and then tank. With oil staying in the pump longer, it also allows the hot oil to stay in the pump longer which increases the heat on the pump body. What is the gain? If you port the area around the return inlet hole at the gears, that could lead to faster sucking on the oil there and slower on the actual inlet hole just as in the long feed path. Making the inlet hole bigger on pre 1972 pumps negates some of the vacuum that the return gears create. You think, but the -72 pump has 2 return inlet holes so what's the big deal? The -72 pump has bigger return gears and makes more vacuum than previous year pumps. So the bigger gears compensate for the double barrel holes. Why did the MoCo bore that second hole? If thinking seriously about it, the 1 single inlet hole is big enough to suck a whole lot of oil into the pump without falter. But with the bigger return gears in the -72 pump making more vacuum, they also stand the chance of choking down the incoming feed oil on high rpm. Not enough to choke it closed but surely enough to slow the flow at a percentage of rpm. So the double barrel holes relieve some of the added vacumm on the gears so flow is not impeded.
 +    * **If you clearance and polish the gears in the pump they leak a bit more**. ((Ferrous Head))
  
 {{:techtalk:ih:oil:1957-1962e_oil_pump_mod_-_poor_porting_labeled_by_hippysmack.jpg?direct&400|}} {{:techtalk:ih:oil:1967-1971_xl_oil_pump_w_return_fitting_mod.jpg?direct&400|}} \\ {{:techtalk:ih:oil:1957-1962e_oil_pump_mod_-_poor_porting_labeled_by_hippysmack.jpg?direct&400|}} {{:techtalk:ih:oil:1967-1971_xl_oil_pump_w_return_fitting_mod.jpg?direct&400|}} \\

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