MS291 idle and compression

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M

Müller

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Long story short. Scored piston and cylinder, due to straight gas, usual stuff. Changed the piston, cleaned cylinder, according to dealer also bearings and seals were shot, so changed these too. Now, she has 90PSI compression and starts after 10th pull. Low compression can be felt pulling the starter cord also. Then she idles forever but if I push the throttle it revs and then dies. What's confusing is that it idles normally with that compression. Usually low compression means no idle, they start but then die immediately. Can it be that there is just enough power for idling not for cutting or maybe I have to check the fuel line before tearing everything apart again. Tearing apart is not hard but takes time again which we all know is a rare commodity. Parts are all chinese, piston/rings RedBarn. Meteor sadly doesn't have newer version piston for MS291.
I have my suspicions about the cylinder also, maybe I went overboard with sanding and the piston/rings are not tight anymore. Sorry for my weird English, I'm not a native speaker.
So the main question, have you seen well idling low comp saw.
 
Müller said:
Long story short. Scored piston and cylinder, due to straight gas, usual stuff. Changed the piston, cleaned cylinder, according to dealer also bearings and seals were shot, so changed these too. Now, she has 90PSI compression and starts after 10th pull. Low compression can be felt pulling the starter cord also. Then she idles forever but if I push the throttle it revs and then dies. What's confusing is that it idles normally with that compression. Usually low compression means no idle, they start but then die immediately. Can it be that there is just enough power for idling not for cutting or maybe I have to check the fuel line before tearing everything apart again. Tearing apart is not hard but takes time again which we all know is a rare commodity. Parts are all chinese, piston/rings RedBarn. Meteor sadly doesn't have newer version piston for MS291.
I have my suspicions about the cylinder also, maybe I went overboard with sanding and the piston/rings are not tight anymore. Sorry for my weird English, I'm not a native speaker.
So the main question, have you seen well idling low comp saw.
Click to expand...
Did you measure the two pistons? Should be a 47mm
Meteor makes them for the 291

Possible that you got the 271 kit y mistake?
 
I havent rebuild the carb yet but opened it and it seemed clean, diaphragm seemed soft and no debris inside. I havent checked the fuel lines but to me it seems it's running rich anyway.
Yep, the piston is for MS291 (actually either the new or old version piston work in newer MS291) and it is 47mm. Only thing I didn't check was the gap of rings and between piston and cylinder. The piston might rattle a little bit if I over"bored" the cylinder with my sanding. I still have the meteor piston and rings, will try these too.
I wanted to put it back together fast:)
The saw has been used mostly during winters and moderately, I have Husqvarna 120 and a noname 54cc chinese saw and they together get more work done than 291. 291 is actually a heavy saw with not much power compared to either these two low budget saws. It was a gift from my mom, so I still want to put it together.
 
Müller said:
I havent rebuild the carb yet but opened it and it seemed clean, diaphragm seemed soft and no debris inside. I havent checked the fuel lines but to me it seems it's running rich anyway.
Yep, the piston is for MS291 (actually either the new or old version piston work in newer MS291) and it is 47mm. Only thing I didn't check was the gap of rings and between piston and cylinder. The piston might rattle a little bit if I over"bored" the cylinder with my sanding. I still have the meteor piston and rings, will try these too.
I wanted to put it back together fast:)
The saw has been used mostly during winters and moderately, I have Husqvarna 120 and a noname 54cc chinese saw and they together get more work done than 291. 291 is actually a heavy saw with not much power compared to either these two low budget saws. It was a gift from my mom, so I still want to put it together.
Click to expand...
Back when I lake raced snow machines, I (we) always replaced a stuck jug (metal transfer) if the transfer was excessive or the score marks were pronounced and we always used 'Easy Off' oven cleaner to remove the transferred aluminum, not other methods and we rarely did much more than a quick ball hone of the jug.
 
You did not over bore the cylinder with sandpaper unless you went through the nikasil bore.
90 psi on a brand new piston and rings is not too far off as the rings have not seated yet.

Did a little tech bulletin search. The new style piston only works with the new style cylinder (TI55.2013).
They DO NOT switch. May be an issue.
 
stihltech said:
You did not over bore the cylinder with sandpaper unless you went through the nikasil bore.
90 psi on a brand new piston and rings is not too far off as the rings have not seated yet.

Did a little tech bulletin search. The new style piston only works with the new style cylinder (TI55.2013).
They DO NOT switch. May be an issue.
Click to expand...
Being the genius I am I put a 44 mm piston in a 44.7 mm jug.
 
stihltech said:
You did not over bore the cylinder with sandpaper unless you went through the nikasil bore.
90 psi on a brand new piston and rings is not too far off as the rings have not seated yet.

Did a little tech bulletin search. The new style piston only works with the new style cylinder (TI55.2013).
They DO NOT switch. May be an issue.
Click to expand...

Thanks for the ideas guys and nope, I still have the never version in there, the right one but this guy got it working, that's why I assume it might work.
Here's the link:

If you look closely, he has a clamp style intake but put's a non clamp style piston into the cylinder. After that he starts the saw and it idles but yeah...not sure how long:) Also the idle seemed too fast...some say that the upper windows is just to reduce the weight of piston. I'm not an engineer, so if the lower window is reduced then maybe the transfers don't work...
If red barn really did send me 47 then it is 47, I didn't measure. 44 would just fall through the cylinder, isn't it?
The thing is, I have to other saws but now I'm almost obsessed with this idea of fixing this MS291, maybe I should just leave it.
 
I, too, have a new-style MS291 needing a piston. I have read mixed reviews about LRB stuff, and I plan to wait until Hyway or Meteor makes one. Maybe, they never will...who knows how that stuff works.

Perhaps the only reason they make a piston for the early MS291 is that it fits one of the pro saws, too.

I feel the 291 is something of a turd of a saw. For some reason, I am willing to wait forever but am unwilling to part it out.

Roy
 
I am in a very similar position. Saw wouldn't start at the beginning of this year - finally had time to take it in, my piston is scored up to the first ring. I'm breaking it down now - my girlfriend's ex ran it for half a season then it wouldn't start. Brand new saw, was told to sell it for parts.

Her dad is positive he didn't use stale gas, but he was an automotive mechanic so I'm almost thinking he may have done some tinkering. I can't see any signs of overheat on the clutch drum, and the piston is scored on the exhaust side only from what I can tell.

I'm thinking it was a combo of duller blade, a big man pushing hard on the hardwood logs, and an improperly adjusted carb (although, I hear from factory they're lean?)

Has anyone had success with the aftermarket piston? I'm probably going to do a hone. Anything else I should look for as far as air leaks, or just do all the gaskets to be safe?
 
Don't hone it. Use 220 wet/dry paper and fingers along with a dab of Muratic acid on a cuetip every now and then depending on how thick the transfer is. This is not a quick procedure. Acid on too long can degrade the plating.
Make sure to thoroughly rinse the cyl with water to get all the acid residue.
Polish the inside with 320g wet/dry and then green Scotch pad.
Just did this with a ms310...came out great.
 
asavageoak said:
Has anyone had success with the aftermarket piston? I'm probably going to do a hone. Anything else I should look for as far as air leaks, or just do all the gaskets to be safe?
Click to expand...

IMO, nearly every saw which gets a new piston needs a case P&V test. This is especially true of clamshells. And, double-especially true for saws which use the case as the bottom of the "motor."

The MS291 piston deal is, early-style saws use a piston which is easy to find good AM options for. The newer style...not so much. Only super-cheap-Ebay junk or LRB. My take is, LRB is all over the map as far as the quality of their pistons.

New style saws have a clamp-on intake; the older saws have bolt-on.

I have a late-model 291 and won't pony-up for OEM or buy LRB. I kind-of hope one of the better AM companies eventually makes the piston I need.

Not the World's Best Saw to start with.

Roy
 
asavageoak said:
I am in a very similar position. Saw wouldn't start at the beginning of this year - finally had time to take it in, my piston is scored up to the first ring. I'm breaking it down now - my girlfriend's ex ran it for half a season then it wouldn't start. Brand new saw, was told to sell it for parts.

Her dad is positive he didn't use stale gas, but he was an automotive mechanic so I'm almost thinking he may have done some tinkering. I can't see any signs of overheat on the clutch drum, and the piston is scored on the exhaust side only from what I can tell.

I'm thinking it was a combo of duller blade, a big man pushing hard on the hardwood logs, and an improperly adjusted carb (although, I hear from factory they're lean?)

Has anyone had success with the aftermarket piston? I'm probably going to do a hone. Anything else I should look for as far as air leaks, or just do all the gaskets to be safe?
Click to expand...

If you buy a piston and rebuild your saw, please start a new thread...it will be easier for people to find. I think there are a number of people with bad-piston 291s sitting in boxes under their work benches.

I, for one, would like to see how the LRB piston works out.

Roy
 

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