bmp01

...engine too small to drive the chain, buy a bigger, pro model saw....

So thats the whole point. .... Going to 8 tooth will increase chain speed by a multiple of 8/7 but it will reduce the torque by the same ratio. As is the way, you can't have something for nothing.

On an 8 tooth sprocket ?

Whether it cuts faster or not with 8 tooth will be dependant on a multitude of factors. Most important will be if you've got enough torque from the engine for the bar length you are using. A 260 with 8 tooth 3/8 maybe ok on 12 - 14 inch bar in soft wood, don't expect it to cope well with longer bar or hard wood. Also I'll state the blinkin obvious, you will need to change chain, sprocket and bar with a pitch change (nose sprocket in bar is pitch dependant). Have fun with it.

As above. Sawbits - M Jones - goes by the name of tesgol on e bay. His listing there is consistently VEC, origin India and no mention of Hyway. He must have hundreds of products listed - easy to make a gaff when cut 'n paste and editing. .... or maybe he changed source for that part. Worth an ask. Genuine piston price? ... about what I paid for the 'spares or repair' concrete saw in the first place?. Barrel has cleaned up ok 2 scores but not deep. It's getting an after market piston and liking it (for personal building project use) or its going for bits.

Yet another seized 2 stoke. ... ? Out of these two piston brands, which would you go for, Hyway (China) or VEC (India)? Price is more or less the same, I can't find a Meteor... L and S also do one but it's a no name piston. I'm leaning towards VEC but for no good reason. I'm hoping the answer of which brand might be useful to people here but I should state the piston is for a Makita concete saw DPC6410. And yeah, split impulse line probably... Thanks for any input. BMP01

Was that Bumstead or Bumsteer ..... ?

Yep. Wires in the air have no insulation on them. Have a look at where the wires are held, you'll see a isolator between wire and support. Proper scary stuff. ....

Don't think so, he said "No" to the top handle....

Google (or t'other search engine or your choice), type in " Arbtalk battery saw " You'll get plenty of hits and answers straight away. In particular Battery chainsaw recomendation was done quite recently..... HTH.

Or you could do your home work. Search here and elsewhere, find out what's possible and recommended in general with carb and muffler mods... just as everyone else does.

Blimey Wonky, I bet the performance of the saw was a bit up and down. .. How long did it run for - do you think - to create that amount of damage? And errr, was the nut a bit loose by any chance ??? BMP01

Outdoor Power Equipment forum.... American forum, mad keen on tuning amongst other stuff. I believe the forum is moderated by / run by / owned by (delete as appropriate) a well respected tuning guy....

Why does saw go better with a bit more advance ? Here's my go at a simple explanation. ... 1) There's an optimum igntion advance for performance. 2) What's optimum for one engine might be too much for another dependant on engine tolerances, engine maintenance, bad fuels, bad tuning., etc, etc 3) Manufacturers don't like their saws exploding, gives them a bad reputation, sales don't do too well, so they design in a bit of safety and retard the ignition a bit. 4) Advancing the ignition a small amount is just getting back to optimum.

I asked Matt the same question via the old messaging system. I think he was happy with it. He did some YouTube videos of it, I don't have the link he sent me any more but going by the dates on this thread and a quick search on YouTube I think this was it. ... h t t p s://youtu.be/l_1Jkg7AWWI (remove the obvious gaps in https, if I put it in correctly it auto plays!) Very difficult to judge the saws cutting performance, wood type, chain condition blar, blar, but it seems pretty responsive. Saw was obviously far from new at the outset. Matt told me he was visiting other chainsaw sites, American, for most of his saw tuning games, don't know if he's still on here. ... HTH.

If I'm understanding you correctly that sounds pretty good to me. The idea of squish band is to squish the gas mixture towards the centre of the cylinder, to promote good turbulence and rapid combustion. What you don't want is "end gas" stuck down the end of a narrow passageway where the combustion struggles to get to, that would be a waste of energy and won't do much for performance. You will get this if the squish band is too deep (radially). Edit: whether 3mm is the right number is one for the experienced tuners, I think I would punt for a slightly bigger number, say 5 or 6mm, depends somewhat on bore size and the combustion chamber shape.

Agreed, a big flywheel can't increase the torque of the engine. But a fast spinning flywheel has more energy than the same flywheel spinning slower. So for a short period of time the output from an engine and flywheel assembly can be more than the constant speed output of the engine. ... its just that during that time the engine and flywheel will be slowing down. That might be perceived as 'more torque' by the user. A good example of this on a chainsaw is if you're unsympathatic with the saw at the start of a cut, or maybe if you hit a bit of hard wood. A saw with a big flywheel will drop its speed but if the time is short it might clear the obstacle, while a saw with a small flywheel has less stored energy to devote to the cause and bogs down. (Same as the trials car). It's the store energy that counts. Can't remember the formulae, but maybe that's just as well

Interesting point that. Purpose of a flywheel - to give a more constant crank speed, primarily useful at low engine speed and crucial for starting. Not much use above idle speed, unwanted baggage. A key benefit of the fuel injection and engine management system (which control the sparks too I'd hope) would be much better fuel/air mixture. So starting will be more consistent and generally easier, Idle will be smoother too, both especially true from cold. The knock on - Stihl engineers can afford to reduce flywheel inertia (and weight). Nice fringe benefit to fuel injection. ....

Simple answer probably about the same, no reason why the manufacturer would derate one or the other intentionally. In a bit more detail, they are both 'home owner' saws, both "clam shell" type of engines, so with out a big amount of effort there is little you can do to improve the compression ratio. There is therefore little interest in measuring their compression unless diagnosing a sick engine. If i were to hazard a guess id say the MS025/250 would have a slightly higher ratio - they both have the same spark plug so each has to accommodate that feature which is of a certain volume. That will 'hurt' the ratio of the smaller engine more but it's probably insignificant. .... HTH, BMP01

Not a recommendation as such but Lidl have a small 20 quid one on their shelves at the moment.... I know nothing about it's performance, suspect its a little small for a cylinder though. Probably pants compared to a commercial cleaners with special cleaning fluids.

Flippin' excellent ! Obviously you have a good workshop skill set to have made that. What happens when the band breaks? You're in pretty close proximity to the action, from my school woodworking days I remember there was usually quite a bang when the band broke. ....

+1 I've had mine for a couple of years, used occasionally not every day. Does what its supposed to do with a quick response and update. Please note they are secondhand from this seller though and he doesn't have them on offer all the time. Also they are sealed units so once the battery expires it's expected to be a throw away item. Don't know if it's possible to dig out the electronics/battery...

It's a stuffer then ? To move air-fuel gas around under the piston.... Piston cooling ? Fuel preparation ? Pin bore lubrication ? Or can it change the air-fuel movement in the crankcase, for better scavenging or fuel preparation? Is it solid, this bit that goes up under the piston...? Are they reducing the volume in the crankcase (if its solid) or only displacing the air-fuel volume under the piston (hollow underneath)? Got to be the result of some computer modelling I think.

Come off it mate, nobody could be that stupid. They'd get sued left, right and centre for all the injuries and deaths...... At the very least you'd have to have some sort of licencing for who'd be allowed to buy and use one, based on training and qualifications.....

Spud, No offence taken. My statement was bollox (I now realise). It needed correcting and any confusion clearing up. Not good to have doubt thrown into ones understanding of things, sorry about that. And thanks for taking the time to point out my error. Yes I'm from a racing back ground but that's not an excuse, I believed (incorrectly) all modern pistons were forged, i was wrong, simple as. I'll go and adjust the grey matter now. Forged pistons - yes the're hit with a punch but the process is a bit slower than you might imagine, there's the initial contact followed by the second stage where the punch is pressed into the material. Even though the material is heated sufficiently to make it ductile the forge is a big bit of kit, close to 100 tonnes the one I experienced, maximum of 5 inch dameter forgings. The advantage of forging over cast (generally) is to get the material grain structure aligned to the shape of the piston, for strength and durability. Getting clear part numbers on a forged piston is relatively easy. Forgings were better than machined from solid but only marginally so in the game i was involved with. With a forging there's no way to get windows in the piston side panels nor the undercut below the g'pin boss, unless they're machined afterwards. So there you go chainsaw pistons often have both those features... must be cast. Fancy split tooling as well, to achieve that, split lines are the cause of the flash lines you see.