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Discussion Starter · #1 ·
Hello all, this is my first time posting since joining. I own a 2018 street rod xg750a, and about a month ago while riding , once the engine was well warmed up I had a relatively major oil leak (approx 100ml from 20 mins of riding) coming from the breather line located on the air filter housing/throttle body. I separated the lines to isolate the leak only to realize that the source of the leak is in fact from both cylinder breather lines!

I've dropped it off at a Harley dealer for them to take a look at it, and so far over a few weeks of them disassembling the engine and inspecting, they have no answers yet.

My question is if anybody has ever experienced a similar issue or has had any similar problems to give me any tips or plans of action, any help would be much appreciated!
 

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That does sound a lot of oil. Mine, and most everyone else's I guess has a small residue in there - this is normal and is caused I believe by a vacuum it is easily cleaned away at service time and will do no harm.
I am surprised that the monkeys at HD have not been able to sort it as the problem is very likely caused by pressure forcing the oil out of the breather?
I am amazed that you say that they had had it for several weeks and would imagine that for 90% of the time the bike has simply been left standing in the corner as this is an issue that can be remedied quite quickly.
The simple issue and I don't wish to insult you is too much oil in the crank? No doubt you checked this so that can be ruled out.Also are you using the correct grade of oil 20w50?
The next thing could be worn rings / valves - again very unlikely. Only usually occurs after very high mileage or engine abuse.
There could also be an air leak in the system (damaged breather pipe / leaking gasket) causing too much air in the crank or finally do you lean your bike excessively into corners?
If I had the bike here I would clean it thoroughly as well as all vacuum hoses, breather pipes, air filter etc. then ride it for around 20 miles at varying speeds and see if it happens again and check what is contaminated with oil i.e. breather pipes etc. - it is more than likely a simple issue that will very likely be sorted by a simple means.
Would love to know what the monkeys say it was when they finally sort it.
 

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Discussion Starter · #3 ·
I've done all that you've said.. I'm an aircraft mechanic by trade so I do have some mechanical ability myself. The oil type and level is fine(if anything was a tad on the low side). The mechanics as well as myself have done compression tests which all pass. They now have the engine apart and say everything looks brand new on the inside in regards to the piston, rings, valves etc. The leak only occurs after riding for 10-20 mins, and as I said in the original post, the leak originates from the breather hose from both cylinders. Thanks for the help though, any ideas help!
 

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I am not a motorcycle mechanic. I am a ASE Certified Auto and Heavy diesel mechanic. Have you changed your airbox? I only ask because I read that the Arlen Ness Naked air breather can cause heavy vaccum pressure through the pcv. Although, 100ml is alot for that. If this was a Volvo D-13 I would bet on the oil pump. So I would check it to make sure its in specs. Do you ride it hard from a cold start? I am with Botty, too. Is the oil the right viscosity?
It could be something as simple as the lines have been shortened. Is there a way to know how long the lines are supposed to be? I have seen this cause issues in cars before. Again, I am not a motorcycle Tech by any means. But I am curious because 100ml is alot of oil to be coming our of the air filter crank pcv tubes.
 

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Discussion Starter · #5 ·
I appreciate the response. Airbox is stock, breather lines are stock length, I try to ride it easy until warmed up, but now that you mention it I never did check the oil pump and nor did the techs. Maybe it is pumping too high of pressure somehow? I'm not sure how it works exactly. Thanks again
 

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I appreciate the response. Airbox is stock, breather lines are stock length, I try to ride it easy until warmed up, but now that you mention it I never did check the oil pump and nor did the techs. Maybe it is pumping too high of pressure somehow? I'm not sure how it works exactly. Thanks again
my 2017 street rod was dumping endless oil after recently doing oil change realized it was my oil filter. Don’t use k&n oil filters stick with stock filter no leaks anymore
 
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