jonsered 621

[razor]

hi all

im trying to get me dads jonsered 621 chainsaw running, last time we used it about 6 years ago, if i remember rightly it would start and cut fine for about 5 mins or so then it would start reving like buggery like it was running lean or running out of fuel, tried opening out the low and high speed needles didnt make any difference, fuel lines all clean, carb looked all clean the diaphams looked abit flat but no splits as far as i could see.
today ive been having a never go at it and decided to take the cylinder off, every thing looked fine but i noticed that the piston had a chip about half inch wide by half inch deep in the skirt facing the exhaust outlet side. so im thinking that a bit of fuel/air mix might be escaping out the exhaust but would this be why its not running right? or is it just down to a carb fueling problem ?

thanks for any help

 

[Landmark]

Ive not been working on saws long but one of these other members can prob help you. Imo it sounds like it sucking air somwhere. The piston def needs replacing and cylinder inspected for scouring due to cracked piston. Then pressure test the saw and rebuild the carb. Check intake and fuel lines for leaks. Spray alittle carb fluid and see if it revvs saw up. Maybe by doing these simple things you can eliminate the problem and freshen up your dads saw. Welcome to AS.

 

[razor]

thanks for the warm welcome and advice dave,
i will take a closer look at the fuel lines might be a split or pin hole that ive missed, ive also ordered a carb kit for it so hopefully that should eliminate any air getting in and any fueling problem, fingers crossed. the cylinder looks in pretty good shape no major scouring so should be alright. i just need to get my hands on a new piston for it then, ive had a look on ebay and can only find second hand ones but there in the u.s.a im in the u.k so postage will probably cost more than the piston itself. do you know if any other piston readily available will fit the jonsered 621

thanks rich

 

[Landmark]

thanks for the warm welcome and advice dave,
i will take a closer look at the fuel lines might be a split or pin hole that ive missed, ive also ordered a carb kit for it so hopefully that should eliminate any air getting in and any fueling problem, fingers crossed. the cylinder looks in pretty good shape no major scouring so should be alright. i just need to get my hands on a new piston for it then, ive had a look on ebay and can only find second hand ones but there in the u.s.a im in the u.k so postage will probably cost more than the piston itself. do you know if any other piston readily available will fit the jonsered 621

thanks rich

use the search forum feature on this site and read about jonsered 621 pistons. im sure there's info on that saw. good luck with your saw

 

[razor]

thanks for that i have looked but cant seem to find anything, the only posts i can find are in the same boat as me trying to find parts that aren't made any more. does anyone know if there is a aftermarket piston that will fit? would be a shame to scrape it

 

[Cantdog]

If you have as big piece missing from the lower skirt on the ex side it will do just as you thought...this is called "free porting" a bad situation...

No there no aftermarket pistons for the 621........watch on ebay....you may find an NOS or good used piston........or try the trading post on this site...

 

[razor]

ok thanks robin,

i will keep my eyes peeled for one on ebay, im sure one will turn up sooner or later. if not then welding the piston might be an option but thats a last resort jobbie.

thanks again rich

 

[SawTroll]

Robin is the prime AS expert on those saws, so go with what he said!

Hopefully the missing piece of the piston didn't mess up the bottom end in any way.

Those saws were far ahead of their time, and are well worth fixing!

 

[Cantdog]

Look here........a bit spendy but if the rest of the saw is in good shape either of these items will get you going...

http://www.sawagain.com/jonsered-621-piston-rings-new-oem-504421900/ This one doesn't come with the wrist pin



http://www.sawagain.com/jonsered-621-piston-rings-assembly-new-oem-504421900/ This one does come with the keepers and wrist pin.



http://www.sawagain.com/jonsered-621-oem-cylinder-cylinder-piston-rings-assembly-504421900/ Then there is this used entire top end with new gaskets etc.........cyl looks clean and in good shape.....


I've had good luck with this guy...like I said ...spendy....but options are few and getting fewer and further between all the time for NOS Jonsereds parts.........Just some suggestions.....

 

[SawTroll]

From here, those prices don't look bad at all - but my 1970 vintage 621 still is going strong as is!

The top cover is beat up, and held together by ductape, but otherwise it is fine. The color of the tape fits the silvertop perfectly!

 

[Cantdog]

No they really aren't that bad.......about the same as when you could buy them at the dealers....

 

[razor]

thats a great find robin, ive just worked out for the piston and rings its about 40 pounds sterling which we would be more than happy to pay as long as postage on top isnt too much. i am just going to ask local dealer over here first on odd chance of them having one sat on back of shelf .
sawtroll the bottom end seems fine, ive had a close look inside the crankcase and cant see any sign of the bit missing not even any tiny metal fragments it must of spat it all out, and the bearings seem fine no play or binding at all. will let you know how i get on.

thanks

 

[razor]

got some good news the saw is back in action!!!

its like a new saw now, runs really well. me and dad are well chuffed with it
i went with robins find after and purchased the new piston and rings from saw again and good service from them it was too, they shipped it next day so didnt take long to get here .
right you know i said the carb was lovely and clean yeah i was wrong there is a tiny filter under the little welsh plug that was complety blocked up with saw dust and
what have you.
another problem i found was on top of the fuel tank there is a white thing that all the fuel pipes and vent pipe runs into, well where the rubber fuel pipe inside the tank connects to the ridged pipe on this white thing there was a split in it just above the top of where the rubber pipe joins on so in less the fuel tank was filled to the brim it would of been sucking in air , luckily the split was not right at the top so i just pushed the rubber pipe up abit more over the split and fixed a good pipe clamp to it.
in the end probably cost around 70 pounds to fix thats for everything piston rings and cylinder gasket including postage and carb kit. it was worth every penny and very satisfying too

thanks for your help everyone

 

[Cantdog]

got some good news the saw is back in action!!!

its like a new saw now, runs really well. me and dad are well chuffed with it
i went with robins find after and purchased the new piston and rings from saw again and good service from them it was too, they shipped it next day so didnt take long to get here .
right you know i said the carb was lovely and clean yeah i was wrong there is a tiny filter under the little welsh plug that was complety blocked up with saw dust and
what have you.
another problem i found was on top of the fuel tank there is a white thing that all the fuel pipes and vent pipe runs into, well where the rubber fuel pipe inside the tank connects to the ridged pipe on this white thing there was a split in it just above the top of where the rubber pipe joins on so in less the fuel tank was filled to the brim it would of been sucking in air , luckily the split was not right at the top so i just pushed the rubber pipe up abit more over the split and fixed a good pipe clamp to it.
in the end probably cost around 70 pounds to fix thats for everything piston rings and cylinder gasket including postage and carb kit. it was worth every penny and very satisfying too

thanks for your help everyone

Sounds like you've done very well!!!! Congrats!!!!

On that fuel line......did yours still have what looked like a crushed clamp on the top end?????

If it did.....there is more to it than it would seem......this looks like a one time use clamp .....it isn't. Don't try to straighten it out. You pry it down until it is off the hose barb.....remove the fuel line and replace with new Tygon line or similar....then slide the clamp back up the hose and over the hose barb again...done.....it's kinda weird but works very well once understood.....fuel line never falls off.....

 

[razor]

thanks robin!!!

the clamp fitted was a ear clamp you know the one where its pinched each side to clamp it down, is that the clamp your on about ?
i put that clamp back on but i also put a spring clamp on too just for extra hold to stop the rubber fuel hose slipping down over that split in the ridged pipe on that white one way valve thing .

 

[Cantdog]

thanks robin!!!

the clamp fitted was a ear clamp you know the one where its pinched each side to clamp it down, is that the clamp your on about ?
i put that clamp back on but i also put a spring clamp on too just for extra hold to stop the rubber fuel hose slipping down over that split in the ridged pipe on that white one way valve thing .

Yes that's the kind of clamp I was talking about......a lot of people don't understand how they are meant to work and just toss them....they work really well with the correct size fuel line.

 

[razor]

well to be honest i always thought they were a one time use clamp, but i always reuse them or keep them for future use. glad to hear im not just the only one who reuses them then and that im not just a tight git

 

[Cantdog]

No....you did good!!......That's the way these ones are supposed to be used.......makes it so you don't have to remove the white plastic block to get a clamp on when replacing the in-tank line....just reach in with a screwdriver and pry it off/on....easy peasy.....slick rig....