MS391 not oiling a 25 in bar

[sb47]

If oil is slinging off the tip of the bar, then it is working normally. Both the gas tank and oil tank are made to both be empty at the same time. You should be using almost a full oil tank for every tank of gas you run. If the oiler puts out to much oil, it will make the oil tank empty to fast and you will run out of oil before the gas tank is empty. If the cahin is getting dull to quickly, then you have something else going on.

 

[Wood Doctor]

Here's a piston blocker that I have used often without breaking anything:

The knots work as cushions. Some guys just use a knotted rope without any metal fasteners.

 

[SteveSr]

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. Here is the pic of the tool.

You likely got your piston stop stuck in the exhaust port and possibly damaged the piston in the process. The stop is designed to fit between the top of the piston and the roof of the combustion chamber.

 

[Bob_w]

O my goodness! I'll pull the muffler and take a look.
The bit off piece could be in the muffler.

Thanks for the Piston Block tool suggestion.

 

[sb47]

O my goodness! I'll pull the muffler and take a look.
The bit off piece could be in the muffler.

Thanks for the Piston Block tool suggestion.

You don't have to put a knot in the rope. I just stuff enough rope in the spark plug hole to stop the piston from moving.

 

[buzz sawyer]

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.

Is the oiler run by the clutch drum on this saw? If so, no oil should be coming out if the drum is not turning and it should not be turning at idle. Run the saw faster so the drum turns.

 

[Bob_w]

You don't have to put a knot in the rope. I just stuff enough rope in the spark plug hole to stop the piston from moving.

Finally got the clutch off. I used a knotted rope, but it compressed and went by. I had to apply a lot of torque.I was inspired by one of the members showing his breaker bar and pipe. so I blocked the Flywheel, and worked up the pressure until it finally broke free. I'll upload pics a little later. Lotta force. Reminded mo of applying 24 ft lb to the flywheel. If I did slip the flywheel timing, that will be a easy fix, compared to a piston. Now I'm on to the oiler, and oiler line checking.

 

[Bob_w]

Is the oiler run by the clutch drum on this saw? If so, no oil should be coming out if the drum is not turning and it should not be turning at idle. Run the saw faster so the drum turns.

Thanks buzz sawyer, I did run it fast as well. It looked pathetic to me. So oilier disassembly is next.

 

[Bob_w]

Buzz, You are right. I'm pretty sure I revved it up too. Got the Clutch off finally. Removed and cleaned the oil tube, screen, and pump with carb cleaner. Tomorrow, I can test.

 

[Bob_w]

Here are the proper tools that got the clutch off. Position the punch on the flywheel where there is enough meat in the proper direction through the cover mounting hole, or use a 5mm x 2.5 in screw, that you use for pulling the fly wheel. The Flywheel came off hard, at least like the 24FT lbs that the flywheel needs. Later on today I'll find out if I slipped the flywheel timing.

 

[SteveSr]

Here are the proper tools that got the clutch off. Position the punch on the flywheel where there is enough meat in the proper direction through the cover mounting hole, or use a 5mm x 2.5 in screw, that you use for pulling the fly wheel. The Flywheel came off hard, at least like the 24FT lbs that the flywheel needs. Later on today I'll find out if I slipped the flywheel timing.

Looks like a great way to bust off a cooling fin or shear the key on the flywheel! There is a reason that the manufacturer uses a piston stop.

 

[Bob_w]

Yes you have to be careful about the cooling fin. That's why the punch is resting on the magnet part of the casting. On this saw, the shear key was already sheared when I bought it used.

The proper torque holds the flywheel on the crank shaft. Timing was the first problem that I had to fix.

No test today, had visitors.

 

[Jasonrkba]

Hopefully the crank didn't bend. I use a heat gun, penetrating oil and an impact. I avoid piston stops when I can but sometimes you gotta do what you gotta do.

 

[Bob_w]

Hopefully the crank didn't bend. I use a heat gun, penetrating oil and an impact. I avoid piston stops when I can but sometimes you gotta do what you gotta do.

That is why I pinned the Flywheel with the pinch. I would rather replace a flywheel than a piston.

I tried impact, 14.4 Volt, but not 100 psi automotive impact. No dice. I had the piston roll around with the rope too. The piece of the Stihl piston stop was in the muffler, So it got bit off by the exhaust port. I put it in too far.

Finally got to look at oiling. I removed the oil line, and blew it out with carb cleaner. Then I removed the oil pump. I blew that out with carb cleaner too. I did take out the pin, but decided against removing the brass end piece, feeling that I would cause more damage than repair.

I put it back together and ran it. Revved up with no bar, I was not impressed with the oiling, but there does not seem to be an issue now with the 25 in bar with the skip chain. The oil pump drive wire needs to go into the notch on the sprocket, I figured that out.

Since I bought this used, There could have been assembly problems here too. Notably, the flywheel timing. was off when I got it. Flywheel not on tight enough. The timing slipped.

The oil system might have been just plugged up.

So now its working. Needs bigger spikes, new chain.

Thanks for everyone's help here. I really enjoy this site. I will be posting some helpful stuff in the future.

 

[byronputman]

I have a set of dual Dawgs on my 391 they are sweet and cheap. My tank protector was way more expensive but worth it.

 

[Bob_w]

Now suddenly, I have low compression. I may have been taken. How was the compression made good enough to run for a short time? Now it's a project saw. I've bought 3 working saws since then. So I have 2, ms391's on the shelf for later.

 

[SteveSr]

The piece of the Stihl piston stop was in the muffler, So it got bit off by the exhaust port. I put it in too far.

You probably ruined the piston doing this by collapsing the ring groove. Pull the muffler and post some photos.