Stihl 391 top end rebuild issues

[tek9tim]

First, a little background; I've been rebuilding Stihls for about 15 years. Can do a top end swap on a pro saw in less than 30 minutes. (using a drill with a t27 bit) I seriously have no idea how many saws I've done top ends on. I do my own port work. But, I have never touched one of the god awful homeowner saws with a plastic crankcase. Until last night.

A guy I work with somehow melted down his 391 just days outside warranty. I thought I'd help him out and put a new piston and cylinder on for him. I won't make that mistake with a homeowner saw again.

I need to know the tricks for this saw. In particular, the reassembly. The trouble I am having is the intake port on the saw is not close to lining up with the hole through the back of the carb box, making it impossible to bolt the intake boot on. I can't figure out how to get the carb box off all the way, or even loose enough to move around since it isn't attached to the gas tank like on a respectable saw.

I have this to say: the 391 is an absolute piece of crap. I had this opinion before, but that was just based on pro saw bias. I can now say that this saw has an absolutely horrible design that completely precludes service. If you are thinking about buying this saw, kick yourself in the crotch and buy a used pro saw instead. If you just have to buy something new, buy a real saw.

 

[motorman1]

I've not worked on that series of saws, but have done a few of the 1127 series "clam-shells" before. Not the quickest saws to work on, but not hard either. Hope this link to parts diagram helps. I don't have access to a service manual for it.

http://www.worldoftrainz.com/Downloads/Files/Stihl Manuals/MS391 - 1140.pdf

 

[blueberrymuzik]

First, a little background; I've been rebuilding Stihls for about 15 years. Can do a top end swap on a pro saw in less than 30 minutes. (using a drill with a t27 bit) I seriously have no idea how many saws I've done top ends on. I do my own port work. But, I have never touched one of the god awful homeowner saws with a plastic crankcase. Until last night.

A guy I work with somehow melted down his 391 just days outside warranty. I thought I'd help him out and put a new piston and cylinder on for him. I won't make that mistake with a homeowner saw again.

I need to know the tricks for this saw. In particular, the reassembly. The trouble I am having is the intake port on the saw is not close to lining up with the hole through the back of the carb box, making it impossible to bolt the intake boot on. I can't figure out how to get the carb box off all the way, or even loose enough to move around since it isn't attached to the gas tank like on a respectable saw.

I have this to say: the 391 is an absolute piece of crap. I had this opinion before, but that was just based on pro saw bias. I can now say that this saw has an absolutely horrible design that completely precludes service. If you are thinking about buying this saw, kick yourself in the crotch and buy a used pro saw instead. If you just have to buy something new, buy a real saw.

I have a copy of the service manual. Let me know if you need it and I will send it along.

Jim

 

[jughead500]

Yeap bought an ms311 a few weeks ago.serious meltdown.very few usable parts.carank bearing let gosending shrapnell thru the top end.cant stuff enough rope thru the spark plug hole to hold the piston enough to turn off the flywheel and clutch.just hops over and keeps turning.guess I'll surgically remove the crank from the case.thats absolutely the last one of those I buy.ill just stick with the ms270 and 280's if any ever turn up to rebuild.

 

[tek9tim]

Well, turns out that it wasn't entirely my ineptitude with a different saw than I was used to. Stihl changed the cylinder and intake from the early design. Here I thought that somehow the cylinder wasn't seating (you can't see the base of it to tell) and not allowing enough room to get the intake bolted up through the back of the carb box. It's a different intake port shape, which requires a different carb box and intake boot.

So there you go. If you melt down a 311 or 391, look at the number of bolts holding on your intake boot and order your parts accordingly. A shoutout to the guys at Madsen's for helping me sort it out. They didn't know about it either, but they do now.

 

[AKDoug]

Yeap bought an ms311 a few weeks ago.serious meltdown.very few usable parts.carank bearing let gosending shrapnell thru the top end.cant stuff enough rope thru the spark plug hole to hold the piston enough to turn off the flywheel and clutch.just hops over and keeps turning.guess I'll surgically remove the crank from the case.thats absolutely the last one of those I buy.ill just stick with the ms270 and 280's if any ever turn up to rebuild.

Use an impact... no rope needed.

 

[dom1971]

Does anyone have or know of a video on how to rebuild the 391 ?