To fill or not to fill is the question...
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Cruiser
Joined: Nov 2025
Posts: 196
Likes: 82
From: Long Island, New York
To fill or not to fill is the question...
Ok, I'm bored today so I thought I'd ask a question that should get the flames started. I noticed that the Shovelhead oil filter is pretty much the last thing the oil goes through before it goes back to the tank. That's backwards of most engines and, in my opinion, one of the completely ridiculous things that Harley did with them. Since the filter is after all the oil comes from the engine, is it necessary to fill it before you put it on? Though I did fill mine and it's not going to hurt I don't think it really matters. It should have no effect on the pressure at start up. What do you guys say? Are the newer engines like that also? Evo or TC or do they clean the oil right before it goes through the engine?
Club Member
Joined: Mar 2009
Posts: 66,115
Likes: 51,404
From: Niles Canyon Ca.
Weird way of looking at the oil system bud, to get oil into the engine on shovels & evo's it's gravity fed with a suction assist the pump creates pushing the oil through internal porting throughout the engine. No way to filter it in that loop, filter always goes in the return loop as that's where the pressure is.to push oil through a filter. Far as twinkies and M8's with this topic, different animal in design and operation, oil tanks under the pump level not over it.
Stock shovel oil system is byzantine nightmare, started life as a total loss system due to the chain oilers. the crank vent line ported into the primary along with a dedicated feed off the pump to spray the primary chain. Primary was designed to run in a vacuum with all the metal shavings clutch plate fibers and other fun stuff flying around inside there getting sucked directly back into the cam chest through crack breather port , look in the breathe hole if you have a chance you'll see the port back in there, all the crap from the primary that didn't stay in the breather got sprayed all over the lifters , cam and sucked into the oil pump to be pushed to the in tank filter, half of which were bypassings or owners left them out.
This is why the bigger majority of owners went sealed primary like the later bikes, fewer lines & fittings, less leaks and cut of the crud going through th motors.
Want an education, if it hasn't been don't since you owned the bike, next time the oil tanks empty take a long screw driver and dig around the bottom of the the tank inside around the feed line port, see what comes out.
Stock shovel oil system is byzantine nightmare, started life as a total loss system due to the chain oilers. the crank vent line ported into the primary along with a dedicated feed off the pump to spray the primary chain. Primary was designed to run in a vacuum with all the metal shavings clutch plate fibers and other fun stuff flying around inside there getting sucked directly back into the cam chest through crack breather port , look in the breathe hole if you have a chance you'll see the port back in there, all the crap from the primary that didn't stay in the breather got sprayed all over the lifters , cam and sucked into the oil pump to be pushed to the in tank filter, half of which were bypassings or owners left them out.
This is why the bigger majority of owners went sealed primary like the later bikes, fewer lines & fittings, less leaks and cut of the crud going through th motors.
Want an education, if it hasn't been don't since you owned the bike, next time the oil tanks empty take a long screw driver and dig around the bottom of the the tank inside around the feed line port, see what comes out.
Seasoned HDF Member
Joined: Jan 2015
Posts: 15,997
Likes: 7,111
From: Sandy Eggo's North County
Doesn't it make sense to filter the oil immediately after it gets thru the engine, where contaminants and byproducts of combustion are fresh in the oil?
This way, the filtered oil would travel back to the sump to be pumped again.
This way, the filtered oil would travel back to the sump to be pumped again.
Thread Starter
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Cruiser
Joined: Nov 2025
Posts: 196
Likes: 82
From: Long Island, New York
This is why the bigger majority of owners went sealed primary like the later bikes, fewer lines & fittings, less leaks and cut of the crud going through th motors.
Want an education, if it hasn't been don't since you owned the bike, next time the oil tanks empty take a long screw driver and dig around the bottom of the the tank inside around the feed line port, see what comes out.
Thread Starter
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Cruiser
Joined: Nov 2025
Posts: 196
Likes: 82
From: Long Island, New York
Agreed. It's not needed. But if the filter is before the engine it will take time to fill and if I can mitigate some of that pressure loss I will. So I do it anyway if the filter is mounted vertically. After all these years it's just become habit really, until I came across the Shovelhead engine which made me rethink it because the oil is filtered before it goes back to the tank.
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Cruiser
Joined: Nov 2025
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From: Long Island, New York
Agreed. Not something I found in cars very often.
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Thread Starter
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Cruiser
Joined: Nov 2025
Posts: 196
Likes: 82
From: Long Island, New York
Not really, if you've ever scraped the bottom of your oil tank like Twizted describes above. Mine had about a 1/2" of solid crud at the bottom. Looked like what you'd find on a magnet in a transmission during a service. Most modern engines filter the oil before it goes through the system. But most modern engines have oil pans not gravity fed dry sump systems.
