Blow by into top breathers
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5th Gear
Joined: Oct 2011
Posts: 9
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From: canada
Blow by into top breathers
I have a 97 heritage softail. Mikuni 42 carb, with a wimmer super squat air filter and hanging top breathers. I had new rings installed and valves lapped last spring. After about 200 miles of riding on the new engine parts, i got excessive blowby coming thru the breathers and splashing all over my oil tank.
I checked oil level, changed breather filters, and have the same recurring problem. should the rings have been slightly bigger? dont know what else to adjust at this point.
Help
I checked oil level, changed breather filters, and have the same recurring problem. should the rings have been slightly bigger? dont know what else to adjust at this point.
Help
Road Master
Joined: Oct 2006
Posts: 1,165
Likes: 33
From: Acworth
Blow by is what causes excessive crankcase pressures. Blow by is caused by weak compression,-compression leaking by the rings when the compression stroke occurs. I would have the compression checked with a guage to see what psi the engine makes. If engine has low compression, the topend needs to be removed and propery re assembled. You stated you had the rings replaced, For starters, I would ask whoever who did your work about this.
Road Warrior
Joined: Jun 2010
Posts: 1,337
Likes: 4
From: Sunny South Florida
with only 200 miles I would say your rings have yet to seat or the cylinders are scared causing blow by. I agree with Mikey, compression test to tell the story. If there are no issues with compression I would second guess the oil levels. Or perhaps the baffle material in the breather port is missing or installed wrong allowing raw oil to just drip into the carb or breather filters
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5th Gear
Joined: Oct 2011
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From: canada
Thanks for the info. compression should tell whats happening with the rings, I know that the shop did score and cross hatch the cylinder walls.
I have about 2000 miles on the new rings and same amount of blowby now as i did at 200 miles'
I have about 2000 miles on the new rings and same amount of blowby now as i did at 200 miles'
Seasoned HDF Member
Joined: Nov 2009
Posts: 15,706
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From: Farmington ,MS
What does your mechanic that did the work say? Is the problem the same as before he did the work? Could be a problem with the breather valve in the cam chest...either worn out or out of time.
Tourer
Joined: Nov 2011
Posts: 324
Likes: 1
From: USA
If there is any question that you have excessive blow by, a compression test and/or leak down test is definitely in order.
Could also be a sumping issue. Someone already mentioned the possibility of the oil pump not scavenging properly, there's also a check valve that keeps oil from back flowing through the return line. If it's not working right, a lot more oil will seep into the sump than normal while the bike sits.
Actually, blow by occurs during combustion. The small amount that leaks by on the compression stroke (compression loss) is nothing compared to the rapidly expanding hot gases that 'blow by' during combustion.
Could also be a sumping issue. Someone already mentioned the possibility of the oil pump not scavenging properly, there's also a check valve that keeps oil from back flowing through the return line. If it's not working right, a lot more oil will seep into the sump than normal while the bike sits.
Actually, blow by occurs during combustion. The small amount that leaks by on the compression stroke (compression loss) is nothing compared to the rapidly expanding hot gases that 'blow by' during combustion.
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