Another oil pressure question, help needed
Seasoned HDF Member
Joined: Dec 2010
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From: Coromandel Peninsula New Zealand
I'll say it again...the breather does not affect oil pressure in any way at all......look in an Evo factory manual at the oil flow diagram....the breather allows air and oil mist into the cam chest and this means there is no effect on oil pressure.....by the time the oil reaches the breather it has exited the pressure side of the system and been splashed all over the pistons and flywheel.
Oil is pushed into the breather by crankcase pressure and exits the breather into the cam chest where it collects in a passage and is picked up by the oil pump.
If your breather was slack in the crankcases you would have increased oil consumption, smoking and a dripping or spewing breather....it would not cause the probs this bike is having which is all on the pressure side of the system which begins at the pump rotors and ends at the rocker boxes.
Oil is pushed into the breather by crankcase pressure and exits the breather into the cam chest where it collects in a passage and is picked up by the oil pump.
If your breather was slack in the crankcases you would have increased oil consumption, smoking and a dripping or spewing breather....it would not cause the probs this bike is having which is all on the pressure side of the system which begins at the pump rotors and ends at the rocker boxes.
Seasoned HDF Member
Joined: May 2008
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From: South Carolina
Originally Posted by Joso
I am quite sure my problem is coming from the poor seal of the breather gear....
I am quite sure my problem is coming from the poor seal of the breather gear....
Forget about the breather gear.
You need to troubleshoot the pressure side of the lube system (the breather gear is part of the scavenge side of the lube system).
Like Spanners says, look in the shop manual, read the description of the lube system and look at the diagram.
Last edited by Dan89FLSTC; Apr 23, 2012 at 08:26 PM.
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1st Gear
Joined: Apr 2012
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From: Kansas City
Ive read the manual and studied every diagram I can find and fully understand that the breather is the return side of the system. I very much think the crankcase vacuum is leaking by the breather gear and causing a vacuum in the camchest and pulling the oil down through the clearance between tappets and tappet blocks instead of pumping into tappets and up pushrods.
Seasoned HDF Member
Joined: May 2008
Posts: 21,032
Likes: 12,560
From: South Carolina
Ive read the manual and studied every diagram I can find and fully understand that the breather is the return side of the system. I very much think the crankcase vacuum is leaking by the breather gear and causing a vacuum in the camchest and pulling the oil down through the clearance between tappets and tappet blocks instead of pumping into tappets and up pushrods.
But it is your bike, and you should feel free to ignore people who have been working on these things for years.
Stage I
Joined: Apr 2012
Posts: 1
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From: USA
pqbaker04
2004 FXSTBI 40,000mi .cam bearing failed .HD rebuild is replacing OEM oil pump with a scream eagle oil pump,backing plate,updated chain adjuster.Anyone else with this problem?
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Seasoned HDF Member
Joined: Dec 2010
Posts: 7,736
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From: Coromandel Peninsula New Zealand
Cam bearing failure is very common on TC's.......always update ASAP if you have the spring tensioners rather than the hydraulic one.
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