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Old 03-10-2011, 03:10 AM   #1 (permalink)
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Unhappy Shovelhead Crankcase Pressure

Hi there wonder who may have some advise, I have a 1980 FLT Shovelhead, seems to be a lot of pressure coming out of the crankcase vent. blowing oil out ...why what and what to do about it

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Old 03-10-2011, 06:03 AM   #2 (permalink)
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If the bike has been sitting a while and first starting it's common for them to puke a little oil.It will stop very quickly,other than residual oil dripping out of the breather pipe.It's excess draindown oil in the crankcase and the engines way of clearing it's throat so to speak.
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Old 03-10-2011, 02:07 PM   #3 (permalink)
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run engine

when you say stop quickly.... please explain... I rode it a few miles and a lot of the oil was blown out... onto the rear tyre.... slippery as ice ...have maybe ran the engine for a total of 2 hours

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Old 03-10-2011, 08:39 PM   #4 (permalink)
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Quote:
Originally Posted by unclebill View Post
Hi there wonder who may have some advise, I have a 1980 FLT Shovelhead, seems to be a lot of pressure coming out of the crankcase vent. blowing oil out ...why what and what to do about it

Thanks Uncle Bill
There is a "fix" to the oil bleeding into the crankcase ( which causes the condition you are experiencing .. known as blowby ) after sitting for a long period of time. Stop by the HD shop and get a new check ball and spring ( some guys get two check balls ... they take one and use a hammer and drift and give the check ball a "love tap" to reshape the seat in the pump housing then remove the ball and place the new one along with the new spring ) . This is a quick and easy repair. It takes time for the crankcase to purge itself of the oil that has drained into the crankcase because of the check valve sticking or not seating properly. Start the engine and let it run at idle for a while with a drain pan under the crank case vent line. This may take a bit of time but it will eventually purge itself of excess oil. Hope this helps!
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Old 03-10-2011, 09:12 PM   #5 (permalink)
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I personally do not perscribe to the hammer and ball method for working on oil pumps. Here is an alternative method.... http://www.bigboyzheadporting.com/showthread.php?t=87
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Old 03-11-2011, 09:10 AM   #6 (permalink)
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Crankcase Blow By

Here is a link to an illustration of the oil pump. The ball, check valve and spring are numbers 18, 19 and 20. http://demonscy.ipower.com/manuals/s...mp_68-84_1.jpg
Springer has also provided you with a link that offers a good solution. The procedure that you follow will obviously be based on your mechanical abilities. As I stated earlier the oil leaking/spewing out of the breather should subside after a few minutes of idling. If this continues you are going to have to look further for a cause.

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Old 03-11-2011, 11:49 AM   #7 (permalink)
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All the above fixes are for a situation called "wet sumping". This is basically oil bleeding back by the check ball (in the oil pressure system) and filling up the crank case after moderate to long periods of sitting.

These are solutions to that problem... but I don't think they are answering your question.

Your question is in regards to the source of pressure... specifically crank case pressure... and what and when to do something about it. Yes? (Or maybe I don't understand)

Assuming I do, I will go with the following:
How much blow by is normal? Dividing an engines maximum horsepower output by 50 will give you a ballpark number for how much blow by you would normally expect to see. For example, a street performance engine that makes around 500 horsepower will typically have about 10 cfm of blow by with conventional pistons rings and ring end gap tolerances. Higher performance engines that are built to tighter tolerances will usually have less blow by, as might those with gapless piston rings. An 800 to 900 horsepower NASCAR motor, for example, might only have 5 cfm of blow by.
Less blow by means more usable horsepower. Being able to baseline the actual blow by in an engine means you can then go back and try different ring configurations, ring types (conventional or gapless), different ring end gap settings and cylinder wall finishes to see which combination gives the best seal and the least amount of blow by.
Measuring blow by has been one of the best kept secrets with performance engine builders because it allows them to see how well the rings are or are not sealing. It also allows them to detect any ring flutter that may be occurring within a particular rpm range, and to then change the mass or end gaps of the rings to minimize the problem.
Keep in mind that this is not PSI… it flow… and you will need a flow meter (or the like) to measure CFM.
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Old 03-12-2011, 07:35 AM   #8 (permalink)
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Make sure all oil return lines are clear and not kinked.

Check to be sure that oil is being returned to the tank.

Make sure you are using the correct oil filter.
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