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Discussion Starter · #1 ·
I bought a used 05 Road King custom and decided to change the oil. Originally it was designed for conventional oil but was talked into going with synthetic. Immediately got a leak. Went back to conventional and the leak persisted. Can't tell exactly where it's coming from. Any ideas about common leaks in this situation? I would appreciate any ideas....thanks
 

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How was it designed for conventional? I have an 05 Fatboy and have always ran synthetic.. Have you looked to find the leak? Is it even motor oil and not a primary or tranny leak?
 

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I don't think synthetic oil caused the leak, probably already had an issue and maybe it cleared away some crud....
are you sure it's motor oil? as said above...
primary or trans ? Did you check oil filter for leak ?
 

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The discussions not about the synthetic oil but more so to do with identifying the location of the leak(s). Wash the drive train really good, go for a short but not high speed ride, return home and inspect for leaks. After identifying the leak, you or someone skilled to do so, must determine why it leaked and how to prevent it from reoccurring. I have a large lapping plate just for this purpose. Good luck with your project.
 

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Clean it up and look for the leaks, it's not rocket science.

Unmolested twin cams are really not prone to leaking oil onto the floor, unless it came out of the air box. But the primary's often leak, as do the trans seals.
 

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Discussion Starter · #6 ·
I'm sure you're right, I assume conventional. It's really hard to tell where it's at. As it's sitting on the kickstand, it drips right below the clutch cover. From what I see, it may come from more toward the middle of the bike but gravity makes it drip there. I don't see how it could be anything else , cuz it started right after the oil change. Dry as a bone before that.
 

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I'm sure you're right, I assume conventional. It's really hard to tell where it's at. As it's sitting on the kickstand, it drips right below the clutch cover. From what I see, it may come from more toward the middle of the bike but gravity makes it drip there. I don't see how it could be anything else , cuz it started right after the oil change. Dry as a bone before that.
That's were the trans and primary seals will drop oil. Its also where the primary drain plug is and where the derby cover will drop oil is its leaking.

Did you just change the engine oil? Or all three holes?
 

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Discussion Starter · #9 ·
True enough, but I find it pretty difficult to get a good look at what's going on underneath. Guess I'll get a good mirror and see what I find.
 

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True enough, but I find it pretty difficult to get a good look at what's going on underneath. Guess I'll get a good mirror and see what I find.
The camera on your phone is excellent for out of the way viewing.

Sent from here.
 

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I had mirror torch and could not find the leak so i removed primary and found it to be the inner primary starter seal. Mine only leaked after a ride and left mark on floor the size off around 1 inch.
 

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Discussion Starter · #13 ·
It's looking more like it has to be something else. The timing was crazy though. I'm going to get to the bottom of it this weekend.
 

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What a coinkidink!

Nobody would ever suspect a 16+ year old motorcycle, service and maintenance history completely unknown to ever develop a new leak. It could have been sitting for a year or more and suddenly it was subjected to a burst of activity.

Go ahead and finish your fluids change. You know, trans and primary too. Use some RedLine Heavy Shockproof in the trans. It's good stuff, and also known as pink milkshake. Then, there would be no way to mistake the difference between those 2 fluids. Pink means trans.
 

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Discussion Starter · #15 ·
I will for sure check it out. It had set for a while. The gentleman I bought it from said he started it now and then and it did have a plate from 2020. It only had 6000 miles on the clock. Since the leak started the moment I changed the oil I assumed it had to do with that. They say on older cars not to use synthetic cuz the gaskets aren't designed for the thinner oil. I thought the same thing was happening in this case, evidently not.
 

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Did you get at least an Owner's Manual with the bike? Something with a maintenance schedule. Maybe even some records of what has been done. Sometimes there is a good chance you'll get at least that with a one owner bike. If it was serviced at a particular dealership, they might have a history file somewhere.

You will need to look close at the schedule. And don't think that just because it only has 6K miles, that it is a new bike. Lacking any kind of documentation, changing all the fluids on a bike you just got will give you a starting point going to the future.

If you plan on keeping it, putting a lot of saddle time in, making it your main ride, then you should seriously consider getting the Factory Service manual, Electrical Diagnostics manual, and Parts book for it. These bikes can get pretty expensive when you have somebody else do all the work on them.

And might want to start looking for a lift. Especially if you do some or all your own work. Getting it up in the air, even just a foot or 18" makes it a lot easier to see and work on.
 
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