bmp01

Nope - just inspect the piston that comes out and then swap out the o ring or piston and ring depending on wear. If it doesn't last, I then do the mod but generally a new pump kit sorts the issue.

 

I just like to try to get the carb working as was intended rather than work around the proper fix as you can get a hesitant pick up from the mod but do see it as a viable fix if the new pump fails quickly.

 

Ream and custom pump.....you having a laugh:sneaky2:

Nope hand reamer, just to remove scoring, so oversize by 0.2mm say, reamer cost insignificant over 10 carbs or more. Batch of pistons, in plastic not plated brass, fiver each.... even if they were 10 quid each, your still saving heaps over a new carb. No use to me though, every saw i look at is different !

Working accelerator pump might be as manufacturer intended but the whole arrangement is a bodge to allow lean idle for emissions purposes, isnt it? Fold in the amount of PITA engine behaviour you get when the thing inevitably misbehaves and I'm all for deleting it and run idle mixture to give good engine response.

My experience is over approx 10 carbs (various engines) so no way is it conclusive. Totally accept your point re MS200T engine response too.

bmp01

I personally don't block the pumps now as it does cause lag in the pickup - just my preference.

Ok - you know better than me.

What's the alternative though if the accelerator piston and its drilling are scored?

-New piston and o ring is a temporary fix at best.

-I guess you could ream the drilling and make a bepoke oversize piston, actually that's quite realistic if you do loads of them.

-Or punt for replacement carb.... minefield - cost vs quality ...

bmp01

I don't think they are they look different on the images on tinternet.. looks like you can buy a new carb 200t on ebay for about 20 quid don't know what they would be like though.

Ah-ha, 201 is a strato saw, no way the carbs are going to be the same then.

I'd go with blanking the accelerator piston circuit on the original carb then. Nothing to loose, you can always get a new carb later. ...

bmp01

Don't suppose the carbs are inter-changeable between the 201 and 200 are they? Would be good to swap a known good carb on to the 200 ....

bmp01

Don't want to pi55 on anyone's bonfire...but....the lever being 2mm too high - that would have flooded the engine (direct opposite to what you experienced). I bet there are more gremins in there somewhere and someone tried to cure the symptoms of no fuel by wrongly adjusting that lever.

Personally I'd go through the rest of the fuel system and make sure it's right.

bmp01

This is well worth a look, Zama Technical Guide. You'll find the setting info for the metering lever in there.

http://www.zamacarb.com/pdfs/TechguideSO.pdf&ved=0ahUKEwiUlZudk7XTAhXIJlAKHb3RD18QFggeMAI&usg=AFQjCNGLlvPYMb6LZUNDqoT_UovEWcER1A

Just one question, that silver cross head screw inside the metering chamber, does that look messed with - has someone been in that carb before?

bmp01

Edit - metering lever looks like it is very high in your picture, is that just the cameras perspective or has that been messed with too?

That side of the carb is called the metering chamber, coz that's the side that controls the amount of fuel going thro the carb. .. Was it bone dry when you took the cover off? If so that tells you there was no fuel getting through. Now you need to figure out why.

Don't touch that brass coloured screw - that's a jet which will limit the fuel flow to the high speed side of carb.

The little Lever with the spring under it operates a valve - push down gently on the lever and you'll see the valve bring lifted. Does that work? The end of the lever should be flush with the face of the carb, when the spring has returned it to its rest position, is it?

Also, as you can take decent pictures, take the cover right off, turn it over and post a picture of that too.

bmp01

Must of been a Barsted to diagnose as it Probaly still had a good spark

 

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A bit awkward. The saw ran fine most of the time but harder and harder to start from cold, eventually it wouldn't. Decent spark with an old fashioned 'jump the gap' tester so I was convinced the problem was fuelling, but that theory started to be less likely when i swapped in a good carb and still no joy. Swapped the plug at some point because it was clear I'd flooded the engine. It started instantly then - just like restarting a hot saw, half way through pulling the cord. Didn't half make me jump

I must have swapped that plug in and out 5 times after that, before I accepted the fact the plug was knackered - and thats why I cut it up to see how it had failed. The arcing pattern explained everything. I concluded a damp plug - such as you get when starting on choke - just made it easier for the plug to short out and not arc across the gap.

Lesson learnt, just carry a known good plug and put it high up on the priority list of things to swap in when dealing with a PITA engine.

bmp01

Looks the plug was damaged either when. Someone removed it or been dropped on it. Cheap plugs are awful I have come across them dropping the elctrode.

 

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It's a NGK plug = good quality.

I took my ime to dissect it, the swaged section removed in the lathe, then the filler picked out gently. It was visually intact before i started the process. It had racked up tens of running hours, failing in service with the cracked ceramic.

It's possible it was subject to handling damage prior to fitting but only to the same level as any other plug.

bmp01

Only plug failure I've experienced was recently, with one of those small M10 plugs in an MS211. Ok, so the saw runs reasonably high compression of 195 psi but that's not extortionate and it shouldn't cause a failure anyway. I dissected the plug, ceramic was cracked, nice arc pattern confirmed it was shorting.... see attached pictures.

bmp01

I agree saw looks like it is running rich, probably rich at idle too.

I bet it is leaning out - that's to say getting closer to optimum - when hanging on the strop, so the idle speed goes up.

I wonder if in that orientation - the fuel line is pulling a mixture of fuel and air ie fuel pick up isn't fully dipped in the fuel. ..maybe the fuel level in tank is on the low side?

bmp01

As above but if it's sat for a while or had old fuel, it could be a part seized engine and you've got no crankcase pressure to operate the fuel pump in the carb. Whats the compression like on the pull cord?

What's the saws history? Has it gradually got worse or completely fine one minute, broken the next? Has it been stored for months on end?

Start with the easy stuff, fuel filter, fuel line, impulse line for the fuel pump. Beg, borrow or buy a known good carb to rule that out.

You can inspect piston with the exhaust off, that's quick and easy, good one to tick off the list etc.

Or take it in for repair / send it to someone to fix.

bmp01

You would only be talking 20 thou depth, you would just tension as normal, the pitch would be the same, this was standard practice when jack was a lad, appreciate there is little argument to support not replacing the bar, but if it's done properly i really don't see any great shakes, unless the new bars are laser welded in the root, in which case i can see it may not be the best way forward

But, but....

So 20 thou, 0.5 mm - how much extra life is that going to get you?

Compare it with a new bar, how much metal have you got before you run out of clearance, got to be 2-3 mm minimum??

In economic terms you've got;

Cost for bar rework to get you 0.5 mm life verse Cost of new bar with 2mm life...so in component costs alone the rework has to cost 1/4 of a new bar.

Cant see that happening.

bmp01

I would have thought replacing the nose sprocket ought to be economic, it's just driving out a few rivets, swapping out components, riveting - 5 minute job. Rest of the world doesn't see it that way though

If the drive links are bottoming out, you've had your money's worth

bmp01

Ah-huh, I did manage to break the throttle switch cover on my 211

Ok, so i could have just bought a new cover but this fix allows me to take it all apart without fear of breaking the next cover

Although I connected it up correctly when operating it didn't seem to open the carb much and therethere was a lot of extra play. However on starting this was fine.

You had to take the throttle switch cover off, to get that throttle rod engaged right? I haven't found a way to avoid that step. ...and it always feels like I'm going to break the cover when reinstalling.

It's worth checking you've got full travel of both the throttle spindles. Top one (air intake only no fuel) opens later in the application of squeezing the throttle trigger and if it doesn't open fully the stratified charge thingee.... won't be. Plastic contact points wear with usage, on mine i couldn't see any reason not to permanently twist the throttle rod to take up some of the slack, so thats what i did.

HTH.

bmp01

Hi, just to say that although silicon sealer is great stuff unless there's been a new type developed that I'm unaware of it's dissolved by petrol.

 

For many years while working on motorcycles I removed silicone sealers from engine parts the easy way by leaving it to perish by placing the components in a bath of petrol, it doesn't take long.

 

I also often encountered endless fuel system problems where silicone sealants had been used on carbs and manifold joints etc...... of course most of these machines were 4 stroke, I wouldn't use silicone on any part of a 2 stroke that comes into contact with petrol.

 

Personally I use Hylomar when assembling engines, for which the solvent is cellulose thinners, I haven't used Dirko so I can't comment but I did notice that it's silicone based and recommended for motorcycles ..... nearly all of which are now 4 stroke..... , perhaps you should try seeing what a soaking in petrol does to it.

 

Just my take on the subject of silicone sealers, there are many different options out there... cheers.

 

https://www.cromwell.co.uk/shop/adhesives-and-sealants/gaskets/hylomar-universal-blue-medium-40gm/p/HYL7032500K?utm_campaign=pla-Adhesives+%26+Sealants+-+&utm_source=google&utm_medium=shopping-pla&utm_keyword=HYL7032500K&istCompanyId=6aa6787b-063e-4414-802d-129f235df603&istItemId=aq

Nicely put, point taken, i was in two minds about using it, seems ok so far ... 3-4 years.

I used a bit of silcone hose as fuel line once. It increased its size 2 fold and lost most of its mechanical strength ie tore very easily. So yes, not very clever to use silicone sealant on the engine despite the tube of goo saying it is fuel resistant.

Dirko is spec'd in the Stihl parts lists. If it is also silicone based that's a worry....

Do you know, i think i still have a tube of Hylomar - I'll go see if i can find it and if its stil usable, must be 25 years old Good tip about the cellulose thinners, didn't know that.

Thanks for info.

bmp01

Red stuff is Dirko, highly rated by all accounts but expensive. I use high temp silicone sealant from Aldi I guess i need to test it for 10 years before i can say its any good.

Yeah thanks, been lurking a while, ditto with the US site - thats where I picked up on the different approach to cylinder cleaning. The normal abrasive approach used is emery cloth wrapped around a spindle run in an air tool, sort of flapper wheel. The abrasive cleaning is gaining acceptance there, advantages are speed and no acid to attack of the parent material. I think its ok but possibly needs more care. Oh and you need a lathe if you want to make sanding drums to a specific diameter

bmp01

Thanks and I had already found everything you say is right, the clutch and flywheel have to come off along with the ignition module. The choke link once removed allows the carb to slide up with the barrel but I'd already unbolted it.

 

Lord knows how I'm going the get the AV and handles back as it was a chinese puzzle getting it off.

 

Now here's the crunch: it's a 150 quid saw, to get to the same stage with a ms261 takes 30 minutes and the same back together again, because you leave most of the saw complete. This saw involves double or treble the work so even a minor repair becomes not worthwhile.

 

Also as it's a stratified charge engine in a narrow bore, cleaning aluminium pick up off the bore is fiddly and difficult to see.

 

I've ordered an after market piston but wish I hadn't bothered.

It's all true. T'is the way of the world. Cheap means when it breaks you DONT mend you bin it and buy another.

Being a sucker for this kind of thing, I've repaired a few, and tuned them too. My 211 runs a cylinder pressure of 190 psi, achieved by moving the crank centreline ! A muffler mod gives a big gain in percentage terms too.

To remove the seized aluminium from the cylinder i use a sanding drum and 120 grit emery cloth. I make the diameter of the drum approx 1 mm smaller than the bore to avoid a too focused abrasion. I try to move the drum around the area of deposited aluminum and at the end of the process put a cross hatch finish in the bore. Pictures of drum and a finished bore attached.

bmp01

Could someone give me a brief sequence for getting a MS171 barrel off, I've not done one with clamshell design and am a bit wary of disturbing bearings?

The clamshell engine only has one split line and that is horizontally through the crank centreline. ... the crank has to come out in order to get to the piston.

The basic strip down procedure - remove the front handle, then remove EVERYTHING attached to the engine, apart from the intake manifold and plastic divider thingee. Finally undo the 4 bolts holding engine into chainsaw body, remove engine incl intake manifold etc.

Just a note of warning, the engine pan (lower crankcase) is only held on to the cylinder with the sealant at this stage. (Its a s**t design imho, dunno how they are assemble them in the factory with out the worry of the engine falling apart while fiddling it in to the the chainsaw body).

bmp01

Actually the Meteor web site is pretty useful, have a look here

Meteor Piston Gardening - Forestry Products Catalog

I've copied a couple sections from the catalogue, first one is only useful to see the column headings.

Second one you can compare the piston dimensions for the MS230 and MS250 pistons. The top of the piston to the gudgeon pin centreline (18) is the same in both cases. The gudgeon pin is the same. Only the diameter and length are different.

I'd ask the question to confirm but it looks to me like the MS250 would fit you cylinder spot on.

bmp01.

I bet the Meteor piston for the MS250 would be the right one. Stihl spec for the European MS230 says it has the same bore and stroke as the MS250.

If it were my money I'd see if the barrel would clean up - it looks genuine Stihl. And ask Meteor directly (Meteor web site has contact info) if their MS250 piston can be used in the Euro MS230. Also ask what the pin to crown dimension is and compare with your chinky piston (but remember your chinky piston isn't guarenteed to be right). That approach costs you under 30 quid.

bmp01

Just a thought, what do you know about the saw history, is that the right genuine piston?

Rings look pretty free for a seized piston, seized on skirt so lubriction issue - old fuel or straight gassed.

bmp01

It measures 42mm top, middle and bottom. Plus it's stamped up 42mm in the photo I posted earlier.

 

I think it was straight fuel that caused the problem.

Yeah, i saw the cast '42'

With regard to measurements and from your picture, the piston looks pretty well trashed, do you think you are managing to measure a true diameter using undamaged surfaces? A measurement inline with and below the gudgeon pin looks about the only plausible place.... Apologies if I'm labouring the point !

I have a new piston for a husky here in front of me, made by Golf, (horrible thing but that's another story). Measuring diameters it's 37.78 at the crown, 37.95 on the skirt. It fits a 38.0mm barrel.

I also have a seized ms260 piston, heavily damaged on the exhaust side. It measures 44.5 just below the second ring inline with pin (only place without damage), and 43.5 across the skirt ie. 1.2 'ish mm of wear as barrel is 44.7 mm.

The way i see it, your piston measures a worn 42.0, you need allowance for thermal expansion, so barrel is probably 42.5 as that matches a MS230 spec. You either need to cross reference part numbers to confirm you have a genuine barrel, measure the barrel. Or just try a 42.5 piston on a suck it and see basis....

I can't help with part numbers, sorry. Look/ask for a parts list.

bmp01

Which end of the piston did you measure? Top of the piston is reduced diameter to take account of the expansion as it heats up. Measure the skirt end, in several places and away from the area that seized.

And if you can, measure the barrel or find something the right diameter and see if it fits. I expect it is a 42.5 bore, that was what was in the spec. But, I've been wrong before!

No idea what Meteor sell for this model. ...

If you are lucky you can some times pick up a second hand piston over on that auction site. A used, good condition, genuine piston is a good option in my opinion.

Got any ideas why your saw seized in the first place?

Good luck,

bmp01