ms260 not pulling fuel through

[Andrew Cork]

Hello all,

 

I lent my trusty 260 to a mate to cut some logs and typically it mysteriously seized on him....

 

After inspection, a part of the piston casting had broken off (low down below the rings and pin). Being a cheap skate I've cleaned it out and reassembled it. Everything seems smooth and goes round, good compression but it will not start. The plug sparks well, diaphragm's good, checked filters and pipes etc but no joy.

 

It does fire with a little damp start in cylinder.

 

It seems that there is no fuel being pulled through, does the piston need to be complete to aid fuel flow in some way?

 

Any ideas anyone?

 

Thanks, Andrew.

[Tyz05]

It needs to be complete to to cover inlet and exaust ports at the correct point of the engine cycle. One of the clever members will explain shortly.

[Andrew Cork]

thanks for the quick reply, that's technical enough for me - been a busy day...

 

I had a feeling it was something like that, i'll get a new piston ordered, don't think they cost the earth.

 

thanks Andrew.

[Tyz05]

Need to find why it broke/seized in the first place.wait to hear what some of the other members have to say or check out the thread "what's on your bench today" in the chainsaw section. It ain't gonna be as simple as fit a new piston,it never is.

[Andrew Cork]

yep, got a bit enthusiastic there!!

 

Everything else looks pretty sound tho, I'm thinking it may have been down to dodgy fuel, it smelled pretty rough - no idea what mix he was using?

Guess I should have sent it along with my own fuel to make sure.

 

Anyway, I'll wait and see if there are any other opinons out there.

 

Cheers, Andrew.

[spudulike]

The timing parts of the piston are the top of the exhaust side and bottom on the inlet side - the inlet side determines inlet duration, the exhaust side determines high revs plus also has an effect on compression.

 

Which part is missing and have you tried holding the throttle wide open with the choke on?

 

Sounds more like the height of the metering needle arm needs to be raised slightly.

 

The piston could have sustained a crack and parts just breaking off are rare - have you inspected it fully - could it have contacted the flywheel, are your big,small and crank bearings all ok?

[Andrew Cork]

Thanks for the reply Spud.

 

The damage is in the at the bottom edge in the centre of the front of the piston. I couldn't say for sure if i've tried starting with choke and full throttle but I guess I probably did along with any other combination that I could think of.

 

You've got me with the metering needle arm tho - it's been a few years since college!! I'm guessing it's in the carb, is this something I should be able to adjust myself?

 

The saw is all locked away now but i'll check the bearings over tomorrow and try to track down the metering needle.

 

It's a pretty old saw so just trying to see if I can salvage it myself, rather than spend out on workshop labour. That money could go towards a nice shiny new one.

 

The help is much appreciated tho.

 

Thanks, Andrew.

[spudulike]

Thanks for the reply Spud.

 

The damage is in the at the bottom edge in the centre of the front of the piston. I couldn't say for sure if i've tried starting with choke and full throttle but I guess I probably did along with any other combination that I could think of.

 

You've got me with the metering needle arm tho - it's been a few years since college!! I'm guessing it's in the carb, is this something I should be able to adjust myself?

 

The saw is all locked away now but i'll check the bearings over tomorrow and try to track down the metering needle.

 

It's a pretty old saw so just trying to see if I can salvage it myself, rather than spend out on workshop labour. That money could go towards a nice shiny new one.

 

The help is much appreciated tho.

 

Thanks, Andrew.

 

The front edge of the piston skirt makes no difference to the port timing, sometimes the crankcase gasket can wear a groove in the piston otherwise I don't know why it should have broken, a loose bearing or busted big end may smack the sides of the skirt but not in the centre. Get us some photos if you can as it will tell a thousand tales.

 

I am hoping the exhaust side of the piston was silver grey and smooth - no vertical scoring?

 

The metering arm is sited under the diaphragm (under the four screw cover) in the carb - just tweak it away from the carb body by 0.2mm - (Very slightly) with a small screwdriver - it may help, had a couple of carbs have sticky needles after rebuild and this cured them.

 

Good luck

[GardenKit]

Hello all,

 

I lent my trusty 260 to a mate to cut some logs and typically it mysteriously seized on him....

 

 

 

Thanks, Andrew.

 

The clue may be in the wording 'siezed'. If it actually did sieze then that may explain why the skirt broke. As Spud says, check for scoring on the piston, and on the bit of skirt if you have found it. If there is scoring then that will also explain why the petrols not coming through.

Either way, as Tyz05 said, it needs a new piston at least, but find out the cause of siezure first, i.e was it due to lack of oil (insufficient quantity or quality, or seperated) or was it lean siezure (incorrect carb settings, ingress of air) Stale fuel also causes lean siezure even if not seperated, as the lower energy value of the fuel effectively lowers the fuel to air ratio.

Or just dont bother and stick it under the bench for spares.

[Andrew Cork]

... managed to take a look in better light today and the piston is pretty badly damaged upto the ring on the exhaust side and there are some vertical marks. The back is clean, smooth and shiny metal grey.

 

The inside of the cylinder looks undamaged to the untrained eye.

 

I'm trying to find the camera cable to stick some pics on but do the descriptions point to a possible cause?

 

The fuel that I took out smelled pretty stale and very red - i'm thnking he had his mix pretty wrong...