Differences
This shows you the differences between two versions of the page.
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techtalk:ref:engmech07d [2020/10/02 15:41] hippysmack created |
techtalk:ref:engmech07d [2023/12/26 21:24] (current) hippysmack |
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| Blowby pertains to the condition of ring seal at the cylinders / pistons. \\ | Blowby pertains to the condition of ring seal at the cylinders / pistons. \\ | ||
| Combustion above the piston is pushed past the rings and into the crankcase. \\ | Combustion above the piston is pushed past the rings and into the crankcase. \\ | ||
| - | It is fundamentally just exhaust that went past the rings instead of out the exhaust port. ((aswracing oftheXLFORUM http://xlforum.net/forums/showthread.php?t=1946516&page=4)) \\ | + | It is fundamentally just exhaust that went past the rings instead of out the exhaust port. ((aswracing oftheXLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-intake-and-exhaust/sportster-motorcycle-air-intake-carburetor-efi-fuel-and-exhaust/180842-crankcase-vent-question/page4?t=1946516&page=4)) \\ |
| It's depleted of oxygen, it's hot, and it picks up moisture and oil in it's travels through the crankcase and into your intake tract. \\ | It's depleted of oxygen, it's hot, and it picks up moisture and oil in it's travels through the crankcase and into your intake tract. \\ | ||
| So it's displacing oxygen in the intake charge (through the air cleaner) that would otherwise contribute to combustion. \\ | So it's displacing oxygen in the intake charge (through the air cleaner) that would otherwise contribute to combustion. \\ | ||
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| It's well worth it to remove it from the intake tract and vent it to the atmosphere or exhaust instead. \\ | It's well worth it to remove it from the intake tract and vent it to the atmosphere or exhaust instead. \\ | ||
| - | What actually 'blows by' the rings and into the crankcase is a mix of unburnt fuel, water, soot, acids etc. ((bunny32 of the XLFORUM http://xlforum.net/forums/showthread.php?t=67658&page=2)) \\ | + | What actually 'blows by' the rings and into the crankcase is a mix of unburnt fuel, water, soot, acids etc. ((bunny32 of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-bottom-end/35356-install-new-crankcase-vent-04/page2?t=67658&page=2)) \\ |
| - | Regarding blowby at high revs, the key factor is ‘ring-flutter’ or ‘ring-seal’. ((bunny32 of the XLFORUM http://xlforum.net/forums/showthread.php?t=67658&page=6)) \\ | + | Regarding blowby at high revs, the key factor is ‘ring-flutter’ or ‘ring-seal’. ((bunny32 of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-bottom-end/35356-install-new-crankcase-vent-04/page6?t=67658&page=6)) \\ |
| Starting with a dead cold engine, there’s no blow-by measurable for a time after start-up. \\ | Starting with a dead cold engine, there’s no blow-by measurable for a time after start-up. \\ | ||
| Then at warm idle, it starts. Above idle it either drops off or holds constant, as revs go up. \\ | Then at warm idle, it starts. Above idle it either drops off or holds constant, as revs go up. \\ | ||
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| **Gapless rings**: \\ | **Gapless rings**: \\ | ||
| - | <blockquote>We've just historically had trouble with wet sumping when using gapless rings. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=75740&highlight=reed+valve&page=6)) \\ | + | <blockquote>We've just historically had trouble with wet sumping when using gapless rings. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-engine-conversions/38153-xr750-883-series-race-engine-venting-etc/page6?t=75740&highlight=reed+valve&page=6)) \\ |
| Basically, the better your ring seal, the more likely you are to have a wet sumping issue. \\ </blockquote> | Basically, the better your ring seal, the more likely you are to have a wet sumping issue. \\ </blockquote> | ||
| - | A lot of guys who work on a lot of gas/diesel/car/truck/bike/old/new performance stuff have moved away from the gapless second ring. ((thecarfarmer of the XLFORUM http://xlforum.net/forums/showthread.php?t=1204854&page=4)) \\ | + | A lot of guys who work on a lot of gas/diesel/car/truck/bike/old/new performance stuff have moved away from the gapless second ring. ((thecarfarmer of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-era-specific-and-model-specific/ironhead-sportster-motorcycle-talk-1957-1985/122424-breather-diagrams/page4?t=1204854&page=4)) \\ |
| It traps pressure under the top ring. \\ | It traps pressure under the top ring. \\ | ||
| In fact the trend has become to run the gaps looser on the second ring to allow what gets thru the top to not get stuck. \\ | In fact the trend has become to run the gaps looser on the second ring to allow what gets thru the top to not get stuck. \\ | ||
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| ==== New ring / cylinder install ==== | ==== New ring / cylinder install ==== | ||
| - | Neither new rings nor cylinder bores are perfectly round. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=15705)) \\ | + | Neither new rings nor cylinder bores are perfectly round. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/10013-blowby-article?t=15705)) \\ |
| As a result, when you put a new ring on a piston and into a new bore, there's actually very little surface area of contact between the two. \\ | As a result, when you put a new ring on a piston and into a new bore, there's actually very little surface area of contact between the two. \\ | ||
| The honing process puts a texture on the cylinder wall that allows the ring to machine the wall into the same shape as the ring during operation. \\ | The honing process puts a texture on the cylinder wall that allows the ring to machine the wall into the same shape as the ring during operation. \\ | ||
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| The ring is said to be "seated" when it has carved the cylinder into it's shape and there's contact all the way around. \\ | The ring is said to be "seated" when it has carved the cylinder into it's shape and there's contact all the way around. \\ | ||
| - | <blockquote>Many, many times I've pulled bikes apart and looked at the cylinder walls and spotted places where the ring was never touching it. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=15705)) \\ | + | <blockquote>Many, many times I've pulled bikes apart and looked at the cylinder walls and spotted places where the ring was never touching it. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/10013-blowby-article?t=15705)) \\ |
| It has a huge amount to do with the accuracy of the boring job as well as the accuracy of the rings used. \\ | It has a huge amount to do with the accuracy of the boring job as well as the accuracy of the rings used. \\ | ||
| If it was bored perfectly and the ring was perfectly round, there would be no seating even needed.</blockquote> | If it was bored perfectly and the ring was perfectly round, there would be no seating even needed.</blockquote> | ||
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| ==== Ring seating during break-in ==== | ==== Ring seating during break-in ==== | ||
| - | There is a risk of ring microwelding by getting too aggressive in the break-in. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=15705)) \\ | + | There is a risk of ring microwelding by getting too aggressive in the break-in. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/10013-blowby-article?t=15705)) \\ |
| HD's break-in procedure, and S&S's, and others are designed to minimize heat build-up. \\ | HD's break-in procedure, and S&S's, and others are designed to minimize heat build-up. \\ | ||
| Be gentle on the motor, don't put it in a situation that makes it hot. \\ | Be gentle on the motor, don't put it in a situation that makes it hot. \\ | ||
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| ==== Normal blowby ==== | ==== Normal blowby ==== | ||
| - | + | In the absence of any blow-by getting past the rings, the crankcase alternates from atmospheric (pistons down) to a vacuum (pistons up). ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/10013-blowby-article/page2?t=15705&page=2)) \\ | |
| - | In the absence of any blow-by getting past the rings, the crankcase alternates from atmospheric (pistons down) to a vacuum (pistons up). ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?t=15705&page=2)) \\ | + | |
| But in the real world, a little gets past the rings, so there's a net outflow equal to that. \\ | But in the real world, a little gets past the rings, so there's a net outflow equal to that. \\ | ||
| - | Conventional rings have a ring gap and the combustion pressure is very great. ((Deimus of the XLFORUM http://xlforum.net/forums/showthread.php?t=67658&page=3)) \\ | + | Conventional rings have a ring gap and the combustion pressure is very great. ((Deimus of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-bottom-end/35356-install-new-crankcase-vent-04/page3?t=67658&page=3)) \\ |
| So you can bet some of this tremendous pressure is entering into your crankcase instead of 100% of it exiting your exhaust pipes. | So you can bet some of this tremendous pressure is entering into your crankcase instead of 100% of it exiting your exhaust pipes. | ||
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| ==== Testing ring seal ==== | ==== Testing ring seal ==== | ||
| - | A leak down test is the best way to check ring seal. ((aswracing of the XLFORUM http://xlforum.net/forums/showthread.php?p=110375&highlight=variable+volume#post110375)) \\ | + | A leak down test is the best way to check ring seal. ((aswracing of the XLFORUM https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-motor-engine/sportster-motorcycle-motor-top-end/5818-oil-puking-from-breather?highlight=variable+volume#post281111)) \\ |
| The tester is not expensive and it's handy as hell. \\ | The tester is not expensive and it's handy as hell. \\ | ||
| Listen for where the air is coming out during the test: intake port, exhaust port, or breathers. \\ | Listen for where the air is coming out during the test: intake port, exhaust port, or breathers. \\ | ||
