Can anybody give me a quick rundown on the venting for 6400/7900 oil system. I have 2 saws down due to not feeding enough oil to bar . they are pumping just not enough are set wide open so I am thinking it is a vent problem ( one is a home depo makita 6401 this one has been hammer teched a bit-noT by me) and yes I looked at the parts diagram but do not see anything as a vent tube as such or is it through the cap? I know the pump system is behind the clutch I will have to get tools to remove that for any serious parts replacement. Thanks in advance.
Before you start taking things apart, have you tried running it with the oil cap loose? If your problem is the vent then opening the cap will make an immediate difference.
Have not tried with cap loose. Noticed problem at end of a cut. refilled. check against back drop nothing slinging off, chain dry also bar is clean in guide slot and ports are not blocked on bar as well as being opened up a bit from stock first thing I checked was blockage on bar. must be pumping some as I get some underneath. funny that it is two saws. two different bars. Tanaka bar oil. the one 7900 is about 10 years old, had since new. no idea age on the 6401Makita other than the abuse it has taken as a rental.
Well, I'd try cracking the cap open and running it, because that will either confirm or eliminate the vent theory with very little effort. Problems that could affect 2 saws simultaneously, hmm... thick oil? Dirt in the oil clogging the pickup strainers?
How much flow do you get with the clutch cover, bar and chain removed? Before tearing it apart maybe try flushing the oil tank with gas a few times
Have not run with bar & chain off yet, re-cleaned everything on 7900 unit. looked very closely at oil port on bar ( forrester) vs supply slot on saw. Oil port on bar pretty high vs saw, ground a chamfered lead into bar oil port long enough to fully cross saw oil slot. hose end on saw not plugged, just did same on 6401 ( home depot bar? private branded) as it looked some what high also. Will run a bit later sans bar and such and then with bar. Note after the modification I did get a spray off nose of 7900 bar as noticed on a block of wood in close proximity to bar nose. Not heavy considering it is wide open but wasn't running any real length of time yet. Will have to get something to flush oil tanks, do not want introduce that xyz ethanol in there- no idea what it may attack. Coleman fuel should be minus that xyz.( in the olden times we called it White gas-no lead) seeing how it is about 9am here I best be getting some customer stuff done.
Hi all, just pulled it all apart, Had to make a stop tool for the piston. A piece of Deralin rod turned down to just a bit over the od of the spark plug threads so it would screw in place worked very well as a piston stop. Used a punch to knock clutch loose but I will make a a 3 point/ finger tool for future use that fits on a socket wrench. Plastic parts of the oil pump assembly are melted and the two winged part of the large gear is shaved off on one side. so a complete new oil pump assembly will be needed. I am going to blame this on ethanol fuel as far as heat high enough to cause this is concerned. I run a little on the heavy side of a 50 to 1 mix but not as much as a 40 to 1. again this was a HD rental item. In another post a way back in time it was suggested to add a spacer behind the oil hose to raise it a bit for more positive pulse so I will do that also. I will post a couple pics in a bit. It is a bit of a hassle for me to get them reduced in size. Issues with this box.
