new piston and rings 2 stroke

[angellonewolf]

i know we have a few people on here that use 2 stroke tools for a living so im hoping i can ask a question

at work we had a husky big chain saw its been well used and lost it compression so a new piston rings and cylinder was installed (not by me) was used after the rebuild it run but starting to get hard to start with in a very short time and was dumped in the shed

i as some on here know i play with 2 stroke just for fun so took it home to have a play

cleaned the carb (was nothing wrong with it)throw fuel in the bore nothing bit of smoke now and again but not even tryed to run

so looked it over and thought just cheak the nuts torque on the bolts holding the bore on 1 was not tight 1 i could not even get my allen key in looked at it with a camera and found the head broken off shearded off (i dont think it would be like this when built) so i had to remove the head to get the snaped bolt out

on lifting the cylander there where large scrach marks all over the piston

any ideas what could have caused this ?

the parts where cheapy stuff so i was told

and the 2nd part im most way through a sthil piston and rings replacment and want to know what you do after install more oil in the fuel for the first couple tanks ?

its not as though you can take it steady for a while like breaking in a bike apart from not reving it with out load on it

only reason im asking is as im doing the piston swap want to know what i need to do to run it in or such as ive done a few pistion and ring changes but not meny as cost wise your better off buying a working 2nd hand one by the time you buy all the parts on most 2 stroke stuff (only sthil seam to beable to get cheap bits for)

 

[angellonewolf]

Pic of the husky piston

And this is the new one that has only done 30 mins or less cutting

 

[tom2207]

wrong mix ,,, or no mix at all looks like the culprit here . Unless the piston and rings were tight going in on the rebuild thats it really ,,, loose carb could cause lean mix too of course , air drawn in to cylinder without fuel and oil , burns hotter and no lube , then again poor seals could do the same , but then it wouldnt have started after the build ,,, the ring looks surprisingly good for the state of the piston skirt though ,,,
look at the fuel thats left in the tank for traces of oil ,, or not.
Whats the bore like for scoring too ??
Use fully synthetic two stroke , fresh mix every day , and I personally never trust the 50:1 thing at all ,, id rather see a bit of smoke than a lot of scoring ,,, and remember too that saw carbs are not set up like strimmer carbs .

 

[angellonewolf]

i dont think its fuel mix in the tank as we run a lot of 2 stroke stuff and use gallans of it and have 3 fuel containers on the go at one time if it was just the fuel we would have had a few items go down

now as i found 1 that was not tight could been that making the mix lean sounds it could be right and thats what caused the problem if thats a thing but would have thought a bore not niped up right would have caused loss of compression so would not start to even do the damage ?

 

[angellonewolf]

oh and not hyad a look at the bore yet just lifted it to remove the broken screw and sliped it back down

i dought unless im board one week end the bore in the cylinder well get looked at as its wasted time to look at some thing if it cant be fixed with resonable cost

 

[8ob]

Where to start ?
Too much oil in the mix will make it run lean, think fuel viscosity and jet size.
Other air admittance on the inlet side.
Crank seals, might be worth filling the crankcase while the barrel is off.
General crud build up in the cooling system.
Operator error, seen guys blocking off the cooling air vents when cutting very low to the ground.
Caning the granny out of it with a blunt chain.

Bob

 

[dobbslc]

My bet is the head / barrel being loose has let air in and its run lean. I did similar damage when I forgot to aneal the copper head gasket on my race bike once. Check the crank seals as they can let air in.

 

[roofman]

Looks like its been started after the piston kit and canned...I always like to let a 2 stroke idle for 5 mins at least, this loads the crankcase up with oil from the fuel and just when it gets loaded that much it starts fogging then let it rip with some full throttle runs to clear its throat and bed the rings in.

 

[tom2207]

Looks like its been started after the piston kit and canned...I always like to let a 2 stroke idle for 5 mins at least, this loads the crankcase up with oil from the fuel and just when it gets loaded that much it starts fogging then let it rip with some full throttle runs to clear its throat and bed the rings in.

Im always happy if I can get them to idle ,,, at all . lol

 

[Old Dog]

If the bore was loose to the crankcase it will draw in air and run lean, it doesn't take much of a air leak to pick up on the piston.

 

[Migmac]

When I rebuild saws, all the new bits are coated in 2 stroke oil. It’s started and left to tick over for a while. I use rockwood pistons and barrels, not the most expensive but they seem to work. Air getting in due to the loose barrel would be my guess as to why the piston is scored

 

[Kram]

I had the same with a chinese 2 stroke earth auger. It was getting harder and harder to start, and somone had showed me a trick of brake cleaner in the intake. That got it running. Some time later it wouldnt run at all so I stripped it. The head was loose and the piston was badly scored, but the rings looked ok.

I filed the rough piston smooth and refitted. Its ran fine after than tho I only did about 30 more holes

 

[Nomad]

Watching this as I'm always learning and 2 strokes are something I'm using more of these days.

I picked up a non running strimmer (no history), I fitted a cheap pattern barrel & piston as the originals were badly scored and it's working fine - so far / touch wood !

Christmas quiz - starting elderly 2 stroke gardening equipment

Hi everyone. As I have a couple of quiet days I'm doing "fun" stuff and looking at some "when-I-get-time projects :laughing: Does anyone have any info, advice, or links to get old 2 stroke motors running again? All have been in storage for a while. History in unknown so maybe they were working...

www.mig-welding.co.uk