bmp01

The shaking of the bar nose thing (side to side), seen mid way through the video, i get that on pole saws which use the same narrow kerf chain and bar (1.1 drive links). Haven't got to the bottom of it, but does become more pronounced as the chain becomes slightly dull. I had assumed with the pole saw there was insufficient weight in the saw head along with a very flexible pole to hold the guide bar steady. Then again the guide bar is also quite flexible being so thin. Another thing with that bar length, you get an uneven number of left and right cutting teeth. Where the chain loop is joined you get 2 consecutive left hand cutter (or 2 right hand which ever it is). The little bit of OCD in me doesnt like the non symmetry. Ultimately I expect there is a solution in sharpening, depth gauges, chain tension - for the pole saw at Ieast.

Exactly, reving its nuts off. Ignition cutting is my punt based on the sound. Richen it up a tad and it will be 4 stoking just below the ignition cut speed. Must have leaned out a bit over time or increased its revs as engine friction (and / or chain friction) has reduced.

Nothing to see there, looks peachy. Marks in the bore are not causing any wear. I have nothing useful to add, certainly interested to hear the outcome though....

If the piston is at bottom of its travel are those marks above the piston crown ? Have you got a picture of the inlet side of piston please ? I can only imagine someone has had something like a scriber poking in through exhaust port while moving the piston up and down. Any damage to the top of the exhaust port ?

One way valve in the main jet - true story, and they do fail. Especially if compressed air has been blown through the carb without some sympathy. Some carbs have one way valves in other places that can get displaced by compressed air too. You can test the main jet one way valve - remove the hi screw, use a bit of soft hose to seal over the hole.... blow / suck on hose, if the valves working you'll know. Or try the same on the new carb for comparison. Drifting the main jet out is not too hard if you want to test it out of the carb, refitting is easy too.

Genuine got to be a good bet. Looks like DLA do a Caber ring if reqd. Says it fits 350.... delivery time ? https://www.dlastore.com/e_store/piston-ring-fit-husqvarna-50-special-51-55-epa-154-254-350-353-355-epa.html

Ring end gaps, yes ? I was attempting to put a number against the subjective piston to bore clearance.....obviously not very clearly. Cor blimey, just imagine 12000rpm, a piston clanking around with 20 thou clearance....

Isn't it something like 4 thou clearance piston to cylinder anything over and 'things' is worn ? Thing is, the piston and cylinder might be fine, not worn. The 'problem' is that you were expecting 346xp performance and engine speeds and you're not going to get it with the lower spec 350 top end. If the saw performs as well as a 350 that would be a surprise with the mismatch of parts. The only other issue was you couldn't tune the carb in - but you might want to review that in light of what you've found since then ?? (Edit - no load speed of 12000 still on low side ?) Sounds to me like you need a 346 cylinder to match that Meteor 346 piston you have ?? And your mate owes you some beers for sorting out his PITA saw.

Have you got a vernier to hand, I gotta know...... The other thing - if you've still got the 346 carb on there it might not be a good match for a 350 top end, that could explain why you couldn't tune it in. But again my knowledge of carb sizes / part numbers isnt worth much.

The plot thickens ! I have nothing to add regarding your question. So it's definitely been apart before then, what is the running spec of a 350, ie max speed, speed of max torque Also, what is that piston? Ring looks very thick, or is it just the picture? 1.5 mm rings found in old pistons and aftermarket lower grade pistons are not good for speeds over 12 k. I would have expected a 346 piston, genuine or Meteor, to be using a 1.2mm ring. Wheres someone with Husky knowledge....

Could be wrong, MS391 = clam shell engine? Doesn't have cylinder to crankcase gasket. But on the plus side, a pain in the backside to strip down Which makes it a priority to diagnose the problem with certainty before launching into it.

Damn, frustrating day, dissapointing experience to say the least. Nothing to add to the above, i expect by now you already know what's happened. Worth seeking more advice on here regarding how to fix it.

I can understand where you're coming from with the above comments if its freehand filing. With Witterings proposed Pferd 2 in 1 filing tool he'll be referencing off the top of the tooth, I think ?

Thought DCS6800i was after it ? Last post in previous thread... If not you know which spares I'm after - as per pm. PS - Predictive text or something on your mind ?

I can't see a problem. Important thing is getting the cutting angles on the top plate correct. Using your Pferd sharpner with the Pferd specified file diameter is more important in that respect. Ultimately the cut in the wood will give you your answer.

Damn, thats a bit of a bugger then.....

Think you've done enough engines by to know what to look for, residue on piston ie combustion gases passing the rings never a good sign. If the piston is unworn ie. still showing turning marks on the skirt and rings are unworn maybe the ring grooves are choked up with crud ? Piston ring does some sealing on its own but it also needs the combustion gas to get on top AND behind the ring to force it onto the cylinder wall. Obviously if the ring groove is too tight (piston made wrong or clagged up) - then that doesn't happen.... result is blowby past the ring. Swaping in new piston is obvious solution. Is the cylinder bore shiny ? Might be worth a gentle deglaze ? As an aside, ever heard of ring groove porting? Several small drillings to get combustion gas to the back of ring. Drillings in top edge of ring groove only.

Left your cleaning rag in the inlet port again did we ? It is 4 stroking at 12 k rpm is it ? Spark plug gone bad ? Genuine top end ? Aftermarket piston with thicker rings will not seal at high revs. Decent compression?

Inappropriate only in the sense that I don't know the part so I can't judge if the suggestion is appropriate or not. And sounds rude - only because the general discussion is about restoring the thread and i suggested hacking it away, well sort of. Just dont mention rude, reaming and entrance in the same breathe if you go to any engineering works though - gawd knows what might happen....

This might be totally inappropriate but I'll say it anyway .... could you live without the first few threads entirely? Machine a counter bore or Dremmel damaged threads away and survive on remaining good thread. Sounds a bit rude, but consider that the damaged threads might not be taking any useful load anyway depending on the thread restore technique.

Is it just me - why do people leave a saw running on concrete, stone, gravel etc ? They call it gravel rash for a reason. TBH that tells me all I need to know about the saw "from his private collection".

I wonder if they did any meaningful testing ? Cut times in wood all seem a bit inaccurate to me when you're looking for a few %. 10 % and maybe you'd see changes if you're careful with keeping everything else the same. Most likely if the saw feels zippier (out of the wood) the builder claims success.... A lighter piston or crank could feel a bit like that.... maybe.... Re balance - it's not a precise science. The counter weights should balance out all of the rotating mass plus a percentage of the reciprocating mass. Rotating mass is the crank pin, brg and the big end of connecting rod. Reciprocating mass is piston, gudgeon pin, brg and small end of connecting rod. Percentage ? Less than 50% for a 2 stroke. There's no exact number. 8mm change on piston diameter - you'd think that would weigh more, assuming piston design is same in both, they might have put big one on a diet ?

No. Not by itself. If there's a change in compression, change to combustion chamber shape, swap to single ring or some other thing then maybe but weight change by itself will not give more power. Plus it might screw up the balance of the engine and you'll feel it as extra vibration - those counter weights on the crank didn't get to be the size they are by accident. Edit: Meteor pistons seem to work well, often tighter squish by a few thou over oe piston. Piston skirt length isnt always same as oe piston. Small changes but sometimes these little bits add up in the right direction.

Nearly Stubby, been here before havent we.... Inertia is what something heavy has - its the resistance of the heavy thing to change speed. You have to put energy into or take out energy from the heavy thing to change its speed. A flywheel is a special case because it's a rotating thing, the flywheel effect that we understand is called "moment of inertia". The same rules apply though, to make it spin faster you put energy into the flywheel, and take energy out to make it go slower. Through a single engine cycle, energy is put into the flywheel (combustion) and taken out (over coming compression, powering the power take off etc). Importantly, a flywheel can not produce power on its own. It can give up some of its energy over several engine cycles but the result is that the engine slows down. "Big" flywheel with high moment of inertia has lots of energy so slows down less if you take out same energy per cycle. Moment of inertia is calculated as mass multiplied by radius squared, easy to work out for the pendulum, not so easy for flywheel, crank, rod and piston. But there are bits of kit to meaure moment of inertia and a CAD systm will have at calculating it. As mentioned above you can have a big diameter, light flywheel having same moment of inertia as a small diameter, heavy flywheel.

L & S Engineers says this part is used on the following saws: Description Tensioner Slide for Stihl HT73, MS230 Chainsaw Genuine Stihl Part OEM No. 1123 640 1900 Suitable for the Following Applications: MS180 / MS180C, MS210 / MS210C, MS230 / MS230C, MS250 / MS250C, MS171 / MS171C, MS181 / MS181C, MS211 / MS211C, 019T, 021 / 023 / 025, MS231 / MS231C / MS251 / MS251C, MS241C, E140, E160, E180, MSE140 / MSE160 / MSE180 / MSE200, MSE141 C, MSE170, MSE190, MSE210, MSE230, MSA160T, HT56 C, HT70 / HT70K / HT75, HT73, HT101, HT130, HT131, HTE60, HTA65, MS190T, MS191T, HT-KMTo Widely used, ---> design is ok. Either a one off bad part or user error. Single bar nut on 231 by the looks of it, wonder if it was left nipped up but not tight. If you had the broken parts to hand it might be obvious if not we'll never know.