MS391 not oiling a 25 in bar

[Bob_w]

Recently, I got a new, 2017, MS391, my second one.

After I got through the loose flywheel, and got it timed and tightened correctly, It screams pretty well. When the chain is sharp, it cuts well for about a minute, then chain stretch cuts in. This is a STIHL chain, not sure what type maybe a RS3, or a RSC. Some oil is sprayed by the bar, maybe not enough. I have cleaned the chain grooves, and oil holes in the bar. The studs look to be not sticking out, making an oil leak, so maybe its a weak pump or a clogged line. I'm cutting dry, hard maple. Right now, I'm grinding the chain to 25 degrees, which seemed to be the angle that was there.

The oil filter will not pull all the way out of the filler hole, So I have blasted it with brake cleaner. I may try to running some ATF through it to see if there are places that need to be cleaned out in the pump system since ATF is 5 weight I believe. Maybe my bar oil is too heavy, I may dilute it with a little ATF and see what that does.

I'm trying to not learn how to rebuild an oil pump. I also don't want to change in the oil pump from my other MS391 which is half apart at the moment. I want to do simple things first.

Thanks for reading all that. This forum is very helpful. I am enjoying reading and helping here when I can.

Any suggestions?

 

[ballisticdoughnut]

Have you run the saw without bar and chain to verify the oil pump is pumping or not?

 

[Bob_w]

no not really. I did not expect this. it does spray some oil with the end of the bar, I'll try it

 

[Bob_w]

Nope, Oil is just dribbling out! I've seen videos of oil squirting out. That is not happening here.

 

[ballisticdoughnut]

Nope, Oil is just dribbling out! I've seen videos of oil squirting out. That is not happening here.

If you’ve got a steady run of oil out of the pump it’s most likely working as it should. You mentioned your getting oil sling off the tip of the bar, sounds like it’s oiling to me. Are you able to post a picture of the bar rails/groove and the chain? A closeup of both would be helpful so we can see any irregular wear due to lack of oil. The Stihl homeowner and farm/ranch saws don’t put out a ton of oil to begin with just for the record.

 

[Bob_w]

That's good that's hear that the oiler is probably working. I'll get some photos and put it back together.

Meanwhile using an older Husky 272xp, I felled a 10 inch maple tree. I didn't like that way it was cutting but I kept on. I used the rope, truck, shallow backcut technique to pull it over. Then I ground the chain, checked the rakers ... then I find out that the front bar stud on the 272 was missing. Apparently it went into the oil tank.

Now the MS391 is back in deck to cut up the downed tree.
Something new every day.

 

[Bob_w]

After cleaning out the grooves, and oil pathways I ran the saw with no bar. the oil drools out slowly at idle. No oil spray onto the wood with the bar today. I tried trimming a few limbs on the downed tree.

 

[ballisticdoughnut]

Not seeing any evidence of wear due to lack of lubrication on the bar or chain. Use a piece of dry cardboard to check oil sling off the chain next time you run the saw.

 

[stihltech]

Would likw to see a pic of the saw teeth from above looking into the gullet.

 

[ballisticdoughnut]

Just remembered, make sure the oil pump is turned up all the way. 291 and 311 have adjustable oil pumps.

 

[HarleyT]

While apart, take a pic of the drive sprocket, since you mentioned "stretch"..

 

[HarleyT]

Also, a side note. This model uses the same oil pump as the 029/ms290 series saw.

 

[Bob_w]

Guys, Thanks for responding. It looks like I will be rebuilding an oil pump or changing a filter, or both

I put an older 16 in bar on, which had a larger oil hole. But the performance was pathetic. The 25 in bar has a 3/32 oil hole while the 16 in bar has a 1/8 in one. Here are the requested pictures.

For the test, I was running 2 oz of ATF, and the rest bar oil to make it thinner. It should have worked a lot better.

Thanks

 

[SteveSr]

Guys, Thanks for responding. It looks like I will be rebuilding an oil pump or changing a filter, or both

There is no filter, only a screen to keep large chunks out of the pump. The pump is likely not rebuildable.

I put an older 16 in bar on, which had a larger oil hole. But the performance was pathetic. The 25 in bar has a 3/32 oil hole while the 16 in bar has a 1/8 in one. Here are the requested pictures.

That chain in the photo is duller than dirt! Dull chains and stingy oilers don't mix!

For the test, I was running 2 oz of ATF, and the rest bar oil to make it thinner. It should have worked a lot better.

Thinning is not likely to be effective unless you are in sub-freezing temperatures. The oil is the "seal" in your pump. Thinner oil may cause more bypass resulting to less to the chain.

 

[Wood Doctor]

Check this:

This might be partially blocked further in towards the exit that leads to the oil port, even if the screw is not missing as shown here.

 

[SteveSr]

Guys, Thanks for responding. It looks like I will be rebuilding an oil pump or changing a filter, or both

There is no filter, only a screen to keep large chunks out of the pump. The pump is likely not rebuildable.

I put an older 16 in bar on, which had a larger oil hole. But the performance was pathetic. The 25 in bar has a 3/32 oil hole while the 16 in bar has a 1/8 in one. Here are the requested pictures.

That chain in the photo is duller than dirt! Dull chains and stingy oilers don't mix!

For the test, I was running 2 oz of ATF, and the rest bar oil to make it thinner. It should have worked a lot better.

Thinning is not likely to be effective unless you are in sub-freezing temperatures. The oil is the "seal" in your pump. Thinner oil may cause more bypass resulting to less to the chain.

 

[Jasonrkba]

Drive out the pin holding the adjuster in. That pump comes apart. Clean it up and there are a couple o rings if I remember correctly that can be replaced. The pin only comes out one way and there is a small washer inside at the end of the plunger. There is only a couple parts but be careful not to lose any and remember how it came apart. Those pumps don't put out a lot but they are pretty durable.

 

[Bob_w]

I was trying to pull off the clutch. Trying to get to the oil pump. Turning CW on the clutch, with the STIHL piston holder in place. Nope, cracked the holder. Is the impact wrench next?

 

[Wood Doctor]

Can you take a Pic of that cracked holder and post it here? I must admit that one time I broke a crank shaft rod using a piston block and on another occasion I damaged the piston. Looks like your clutch is on so tight that damages are possible.

 

[Bob_w]

Can you take a Pic of that cracked holder and post it here? I must admit that one time I broke a crank shaft rod using a piston block and on another occasion I damaged the piston. Looks like your clutch is on so tight that damages are possible.

Yep, Don't want to break anything, But impact wrench seem to be next. Just a light CW squeeze. The oiler needs to be fixed. Could use mapp gas. That seems extreme. Here is the pic of the tool.

On the MS391, you can stop the crank from turning by removing the recoil start side, and taking a 5mm x long screw and jamming the flywheel. put the screw through the Left hand cover mounting hole. I did that once to get the 24 FT-lb torque on the Flywheel nut. Be careful to apply screw to a thicker part of the flywheel near the magnets in the desired torque direction