spudulike

All non strato/autotune saws are on borrowed time so if you are looking for a 395, 390 and any other saw or this generation, grab it now as these saws if looked after, will be banging away for 15-20 years!

Something nagged at me on this one. Couple of things - when I look at pistons, I see casting flash, slight unevenness in inner surfaces or casting witness marks and then machining to the critical surfaces and parts. The piston body shows obvious signs of casting - the machining will be common to all pistons. I then remember my days on bikes and being able to fit Wiseco "Forged" pistons and then thought, if all pistons are forged, why make such a thing out of being forged. So...basically, cast is molten metal in to a moulding cast and forged is battering solid metal using heat to soften and "forge" shape - like a blacksmith making horseshoes! I then Googled it and most pistons are cast but the top end ones for racing or high revving engines are forged.....ah, reconciliation in my head once more Sorry but your statement is wrong, perhaps you have come from only using race pistons - come across them in bike and car track racing and drag racing then assumed....... No offence meant and don't intend any ridicule but this one just "niggled" at what I understood to be fact!

Not sure what year but there was definitely a shift from say the 064 to the 066. The older saws typically had dumb one setting coils but the later ones would roll the ignition timing advance to almost zero at start and then start advancing the timing dramatically from a few thousand rpm. Get a strobe timer on the saw and shine it at the flywheel, that will tell you what's what!

Interesting - Rolls Royce used harmonic resonance in their turbines, hit them and measured the resonance in the metal to see if the castings were good.

I did have a vague feeling it was yours, it was running like a bag O S and not revving, the coil sorted it whilst you were supping Prosek in Croatia I believe!

The term is "Woodruff" and yours looks 100% fine. It is quite usual to get a couple of degrees movement in the flywheel and is of no concern. If the woodruff key is sheared or missing, then you have a real issue. The facts are the ignition seems to have gained advance - how........my bet is either the flywheel to coil gap is too large or the coil has gone bad. I did have a 361 in once where the thing would only rev to around 7Krpm and a new coil sorted it out. If you want to try to manually retard the ignition a few degrees then opening up the spark plug gap to 2 -3 times the original gap and opening up the coil the flywheel gap will do this but reckon your fault is probably the automatic retard circuit in the coil has failed giving full advance from low revs.

On the MS461, there is a strange alloy bracket that bolts across the crankcase mouth and goes right up in to the piston. There has been a lot of speculation on what it does but the clever money is on dome sort of diverter creating a strato effect on a relatively standard engine design. See pic below. I believe that the piston probably had a very fine crack in it after I tried to remove the central boss from the clutch after an employee of the saws owner didn't fix the e clip on correctly. The clutch grenaded and did the boss up super tight. I used pretty much all the force I could muster to shift it and ground it off in the end with a diamond burr after I couldn't shift it - it lasted a few months before letting loose. The stop I used was the Stihl one followed by rope when the damn thing didn't shift. Got it back together again and hope it lasts now, all the parts looked good and measured OK but it is damn difficult to tell if components have micro cracks or a bit of stress damage. I know a few tricks in checking engine components and agreed with the owner that the repair bill was worth paying to see if it lasted - the other option was a complete rebuild with new components which didn't make sense.

Imagine a lump of flapjack, dipped in araldite and left to bond to your chainsaw - that is bio oil that is! I have had to grind the stuff off the fins of cylinders with a 4mm drill before now - a right bar steward of a job! If you don't mind wrecking a good saw over a period of time, carry on with the oil!

When you use an oil that can dry and go hard, please don't knock on my door and expect me to service and clean it!

Nice Mac, the sap sounds like bio oil....spawn of Beelzebub.

And that's the way it goes sometimes, hopefully the next five on the bench will go smoothly and make up for one saw that just saps time. Been there and sympathise!

At this rate, the saw will be completely OEM Had a 372 set to over 14200 once, pulled like a train but wasn't very standard

As ADW said, the autotune likes a perfect engine and doesn't take wear and tear as a friend. Expect any wear in the engine to cause idling issues like this. It is a shame you cant raise the idle speed but guess it will breach the emissions the machine is certified to produce....give me a standard carb any day! If the machine marks on the piston have smoothed then it is usually best just to fit a new piston as the saw is a bit of a bitch to strip down in my humble opinion!

The saw had been serviced by me about a year ago and had tached it, found it to be over revving, pulled the limiter, backed it down and then re-tached it at around 12500. It than came back as the owners employee had not put the clutch e clip back on correctly and the clutch had grenaded. It was tached again and OK and after repair, even with the bar off, it didn't over rev so know it wasn't down to that. This work was months ago, one of the lower window supports has a crack in it and the crown has a fine crack running up the shattered skirt and across the crown that looks slightly older but with no signs of impact or poor piston stop use The piston was in good shape and the machine is also. I reckon the skirt shattered and it took out the strato flange - I had always wondered what damage would occur if this let loose - I know now! It may be a casting flaw, one of the lower skirt supports has a very slight honeycomb look about it and it is possible the piston just cracked - not a nice one but hope there are no little hidden surprises - worth a punt on a relatively cheap repair on a very decent ground saw.

Had a MS461 in from a long standing local customer, it felt like the crank had failed or there was a big piston issue. Took a look down the plug hole with the customer there and the crown of the piston looked cracked to me Had the machine apart and either the strato flange had busted shattering the piston or the piston skirt had shattered taking out the flange but it was a BIG mess. The screws were still in there and tight so the flange hadn't come loose. All the debris was cleared, the bore looked OK, no indentations in the squish band or ports and the crank ends were straight, the big end looked OK and the rod was incredibly straight. Fitted a new piston and flange and the saw now runs, am hoping there are no hidden nasty surprises that time will unleash but a risk worth taking.

Never seen one of these fuel tank screws break, more common on the recoil cover. Sounds like all is good now, simple fix.

Unless the OP is dragging his Einhell up Ben nevis, I think altitude in the UK doesn't come in to this issue! Thought you had become a Trappist Monk!

Ya bloody big member

There is a small window of time when both the ring and cylinder are relatively rough. Run it hard for shorter periods of time to get the two friction surfaces bedded in quickly.

Now he is calling us members - isn't a member another name for a blokes appendage.....i.e. cock

You would need to remove the top handle and fuel tank. The biggest issue with removing them is keeping the drill central to the broken screw and not drifting off in to the softer alloy. It won't be great leaving it like it is but the saw will still function OK and be safe. The lack or screws may put stress on the remaining ones and these could break! You may be able to cut a slot in the screw with a Dremel cut off bit causing little damage to the alloy and use a screwdriver on them. Just depends on how flush with the flats the broken screw is.

Masterity New one on me....I wouldn't expect this damage to create any running issues!

er... it is in the name...a pump...pumps and a meter.....well it meters out fuel in the correct amount! In a saw, the fuel is typically held below the carb. Liquid doesn't run well upwards so the saw uses the positive and negative pressure of the crankcase to pump the fuel upwards in to the carb by use of a pumping diaphragm in the carb.

The impulse line carries the positive and negative pressure in the crankcase in to the carb that moves a pump diaphragm (not the metering one) up and down to pump fuel in to the pump section of the carb and is then allowed in to the metering section once fuel is depleted in the metering section allowing the nipple on the metering diaphragm to push on the metering arm thus opening the needle valve allowing fresh fuel in to the metering section of the carb. How does that description grab ya? The OP still has a dodgy Chinese saw though!

I know a trainer in this area - don't know if he could be of help?