Makita 6400 Mysterious Oil Leak

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rta01

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Hope someone can help me figure out where the bar oil is coming from.

Backstory: Bought a used HD Makita 6400 several years ago. Got it home, couldn't get it to start, replaced a bunch of parts and cleaned it up real good. Finally figured out I was flooding it on startup. Have to be extra careful on cold start not to flood. Half the time or more have to pull the plug and clear excess fuel before I can get it to start. Other than that, runs fine.

About 6 months ago, went to use it, filled with gas and with the first pull found gas leaking out the bottom. Ordered both seals and gasket for the cylinder. Started trying to track down where the leak was coming from. was dripping out the bottom, but could not see any leak around the cylinder housing. Took the starter side apart first and found that seal was leaking. Replaced that seal, reassembled and took the clutch side apart down to the oil pump. Cleaned up all the oil and debris and set it upright for a couple of days. No gas leaking, but oil was leaking. Gas problem appears to be solved.

Couldn't tell where the oil was leaking from, so took off the oil pump and cleaned and reassembled and sealed hose connection with Permatex Ultra Black. Let it sit for a couple of days and bar oil was still leaking out. Not bad, but enough to be irritating. Decided to get the oil pump rebuild kit to see if that would solve it. I cleaned up all the leaked oil so that I could hopefully better see where the leak was coming from and then set it with the clutch side up so that it would not leak until I could get it sealed back up.

That was about 3 months ago and the saw has been sitting with the clutch/oil pump side up the entire time. It has continued to leak bar oil. It look like it is coming out of the oil line at the oiling slot where it would go into the bar and running down around the oil pump. It has leaked enough oil that it has filled up all the little cavities in the case to the bottom of the oil pump. Still haven't installed the oil pump rebuild kit.

So, my question is, how is oil running uphill from the oil tank? Even if it's leaking from the pump, wouldn't oil still have to run uphill? And, before anyone asks, no, I did not loosen the oil cap to let off pressure, but I figured that over 6 months of not running, any pressure would have dissipated. My only thought is that the bar oil is thick and sticky enough that it is being drawn up by capillary action. Seems like a reach, though.

Any ideas?
 
On these saws when You have an oil leak You swap out the oil lines and the leak is no more.
It has been commented that the lines seem to shorten as they age/dry out thus no longer seal well.

I just let mine leak, it is good for the oak boards they are sitting on - no bug will ever dare take a bite out of them, I bet rot will also stay away.
 
My 6401 was leaking oil. It would soak the sides and the bottom of saw and my work bench with oil. I cleaned everything, ordered an oem hose and it has not leaked a drop since. The old pick up hose and all on mine were black, the new hose was makita blue.

Mine I could clean the area around where the pick up hose grommet fits into the case and then slowly watch it weep oil there. After a couple days it would have the saw and my bench soaked which is very aggravating. I love the saw so I was determined to get it fixed
 
You have fluid in a tank with a one way vent... When it gets warm it expands and pushes it out of the oiler or whatever it can. When it cools it draws air in the vent then starts all over the next day:)
 
You have fluid in a tank with a one way vent... When it gets warm it expands and pushes it out of the oiler or whatever it can. When it cools it draws air in the vent then starts all over the next day:)

Now that makes sense if the check valve in the oil pump was not completely sealing. The rebuild kit should take care of that - when I finally get around to putting it in.
 
There’s an updated oil line for that saw. I believe it’s green.

I had replaced the line from the pump to the oiling slot with the newer green. May look into the suction line replacement, too, if the current parts don't stop the drip. Just does not look like the oil is coming from any of the junction points. Looks like it's coming out where it is supposed to, but when the saw is not running.
 

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