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| techtalk:ih:oil03j [2025/09/06 02:05] – [Most Pump Mods Are Used in Combination w/ Engine Mods] hippysmack | techtalk:ih:oil03j [2025/09/06 18:04] (current) – [Installing 1972-1976 Oil Pump (Complete) on 1971-Earlier Motors] hippysmack | ||
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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 | + | 1954-1976 KH and Sportster pumps do not have afeed bypass built in although there were a few different versions of those as well. \\ |
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| + | ====== What Era Factory Oil Pump Would Be the Most Beneficial | ||
| From Dr Dick: ((https:// | From Dr Dick: ((https:// | ||
| 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' | 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' | ||
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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 pump 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. | ||
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