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Jonsered621 suddenly died

frankconley

frankconley

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Hi this is my first post. From what I've read you guys are nice upstanding people. So glad I found you. My saw was working fantastic. Cutting 17 inch logs with 16 inch blade. It was quite hot and when I pulled it out of the log it died and would not and still won't start. Smoke was coming out of the start rope cover. Please respond with any help.
 
Jasonrkba

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Pull the starter cover and look for anything obvious. Could just be a plug or coil. Also check the chain tension. After getting good and hot sometimes they can get tight and make it hard to start. Did you have to yank it out of the log?
 
frankconley

frankconley

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Pull the starter cover and look for anything obvious. Could just be a plug or coil. Also check the chain tension. After getting good and hot sometimes they can get tight and make it hard to start. Did you have to yank it out of the log?
Hi. Thanks. I pulled cover just saw flywheel. Everything looked fine. I didn't yank it out. It stopped right after it was out. Chain still like it was when I started.
 
Cantdog

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Id replace the plug and check for spark. Coils overheat and cause problems.
Welcome to the site Frank.... I too, would check for spark first thing. I you find it has spark then inspect your fuel lines.....there are two on the 621. One goes from the carb to fuel supply/vent block the other is in the tank....it's not unheard of for the fuel line to pop off the hose barb in the top of the tank, especially if it has been replaced and the original ferrule was not reinstalled properly. As was already said so many things to check so it's my policy to start with the easiest/cheapest items and work toward the more expensive/complicated ones. Also if when you removed the plug it is wet and oily you might blow the cyl out with a bit of compressed air......you may have just flooded it......doesn't take much when a saw is real hot.
 
frankconley

frankconley

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Id replace the plug and check for spark. Coils overheat and cause problems.
Welcome to the site Frank.... I too, would check for spark first thing. I you find it has spark then inspect your fuel lines.....there are two on the 621. One goes from the carb to fuel supply/vent block the other is in the tank....it's not unheard of for the fuel line to pop off the hose barb in the top of the tank, especially if it has been replaced and the original ferrule was not reinstalled properly. As was already said so many things to check so it's my policy to start with the easiest/cheapest items and work toward the more expensive/complicated ones. Also if when you removed the plug it is wet and oily you might blow the cyl out with a bit of compressed air......you may have just flooded it......doesn't take much when a saw is real hot.
Seems like there are so many obvious things to try first. How about you tell us what you have tried so far.
Hi. Thanks for responding. I found I have low compression. About 100 lbs. I thought it seemed different but I thought I was getting stronger. No such luck. If the compression suddenly drops what should I do?
 
frankconley

frankconley

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Welcome to the site Frank.... I too, would check for spark first thing. I you find it has spark then inspect your fuel lines.....there are two on the 621. One goes from the carb to fuel supply/vent block the other is in the tank....it's not unheard of for the fuel line to pop off the hose barb in the top of the tank, especially if it has been replaced and the original ferrule was not reinstalled properly. As was already said so many things to check so it's my policy to start with the easiest/cheapest items and work toward the more expensive/complicated ones. Also if when you removed the plug it is wet and oily you might blow the cyl out with a bit of compressed air......you may have just flooded it......doesn't take much when a saw is real hot.
Hi. Thanks for responding. Everything seems ok except compression. Should I take the piston out to start?
 
MontanaResident

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Hi. Thanks for responding. Everything seems ok except compression. Should I take the piston out to start?
No. Make sure the cylinder is tight to the base. If there is a decompression plug make sure it is tight. If the pull start is smooth pour a 1/4 ounce of 30w oil into the cylinder and see if that helps the compression.
 
Cantdog

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You cooked it
Yep....certainly sounds like it...….pull the muffler and see what the piston looks like. I've got a beauty 621 here that a guy I work with toasted....to bad too, it was a real low hour saw. I pulled the muffler, saw the scoring, pulled the jug and noticed the crank was dry as a bone...no oil to be seen. I drained the fuel into a glass jar......funny thing there was no oil in there either but the tank was 3/4 full of straight gas so that is how long a 621 will run without oil!!! It wasn't scored badly but enough to stick the rings and lose compression. Picked up a nice used piston from Bryan Plust on ebay…...we trade parts back and forth some so the owner is happy!!

IMG_0896.jpg IMG_0898.jpg IMG_0899.jpg
 
Cantdog

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Hi. Thanks for responding. I found I have low compression. About 100 lbs. I thought it seemed different but I thought I was getting stronger. No such luck. If the compression suddenly drops what should I do?
Compression on a good healthy, strong 621 should be around 225.....even with considerable wear they usually make 170 easily.
 
frankconley

frankconley

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Yep....certainly sounds like it...….pull the muffler and see what the piston looks like. I've got a beauty 621 here that a guy I work with toasted....to bad too, it was a real low hour saw. I pulled the muffler, saw the scoring, pulled the jug and noticed the crank was dry as a bone...no oil to be seen. I drained the fuel into a glass jar......funny thing there was no oil in there either but the tank was 3/4 full of straight gas so that is how long a 621 will run without oil!!! It wasn't scored badly but enough to stick the rings and lose compression. Picked up a nice used piston from Bryan Plust on ebay…...we trade parts back and forth some so the owner is happy!!

View attachment 828473 View attachment 828475 View attachment 828476
Hi. Thanks for responding. I looked in and it was bad. Do you think I can find the parts. Can I use the same rod? The one in there now. I ran it on 40 to 1 and I think it is supposed to use 25 to 1.
 
Cantdog

Cantdog

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I expect your rod and bearings are OK. Can you post some pics of your piston and/or cyl bore? Parts are not easy to find new old stock (NOS) however they do show up on ebay once in a while. Used in good condition is easier to locate. Here is a P&C set for "Best Offer" on ebay.

Not a bad price.....and with a new ring would likely work perfectly. However fixing the P&C is necessary, locating the reason the original failed is crucial......otherwise the same ending will happen to the new P&C. You likely have a bad crank seal which I would replace both of out of hand when rebuilding most any saw. Oil ratios are kind out the window. The ratio stated of, say 24:1 was intended for the oils currently available a the time of the saws manufacture. Oil technology has improved leaps and bounds since the '70's....provided you buy good quality synthetic oil. I use Stihl Ultra exclusively at 50:1 in all my old Jonsereds from the 49SP to the 111S and have never scored a piston. But any good quality synthetic oil other than Stihl is likely as good or better. My point is there is probably an underlying issue with the saw whether crank seals, leaking intake gaskets, leaking cyl base gasket or the carb simply adjusted to lean.....it's always better/safer to be adjust a bit to rich rather than any to lean.
 
frankconley

frankconley

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I expect your rod and bearings are OK. Can you post some pics of your piston and/or cyl bore? Parts are not easy to find new old stock (NOS) however they do show up on ebay once in a while. Used in good condition is easier to locate. Here is a P&C set for "Best Offer" on ebay.

Not a bad price.....and with a new ring would likely work perfectly. However fixing the P&C is necessary, locating the reason the original failed is crucial......otherwise the same ending will happen to the new P&C. You likely have a bad crank seal which I would replace both of out of hand when rebuilding most any saw. Oil ratios are kind out the window. The ratio stated of, say 24:1 was intended for the oils currently available a the time of the saws manufacture. Oil technology has improved leaps and bounds since the '70's....provided you buy good quality synthetic oil. I use Stihl Ultra exclusively at 50:1 in all my old Jonsereds from the 49SP to the 111S and have never scored a piston. But any good quality synthetic oil other than Stihl is likely as good or better. My point is there is probably an underlying issue with the saw whether crank seals, leaking intake gaskets, leaking cyl base gasket or the carb simply adjusted to lean.....it's always better/safer to be adjust a bit to rich rather than any to lean.
Hi. Great info. Thanks. I used 40 to 1 mixture. I was running in hard and it suddenly stopped. The piston looks bad. I will get pictures in one hour or less. The ebay ad states 45 mm piston included. Should I take mine out before ordering any parts? Hope you don't mind questions.
 
Cantdog

Cantdog

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Hi. Great info. Thanks. I used 40 to 1 mixture. I was running in hard and it suddenly stopped. The piston looks bad. I will get pictures in one hour or less. The ebay ad states 45 mm piston included. Should I take mine out before ordering any parts? Hope you don't mind questions.
Well.....ebay is fickle...sometimes if you wait stuff will grow legs and be gone. You know you need a piston so if you get a piston and cyl together so much the better. I'd offer him $50 and see where that goes. You might be able to save your cyl but that is also a lot of work/time with no way to know if you will be successful until you get it cleaned up.....after spending all that time on it you might find it to be ruined. You just never know when buying from ebay......after you order a used one a NOS one may appear. What I do is just buy what I need to get the saw running again then if I find a rare bargain on a NOS piston and/or cyl I'll buy those and swap them out when time allows. That's one of the nice thing about working on saws......top end swap shouldn't take more than an hour or so if you have everything ready.........usually takes longer to clean a saw up enough to work on than to actually do the work!!
 
frankconley

frankconley

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Well.....ebay is fickle...sometimes if you wait stuff will grow legs and be gone. You know you need a piston so if you get a piston and cyl together so much the better. I'd offer him $50 and see where that goes. You might be able to save your cyl but that is also a lot of work/time with no way to know if you will be successful until you get it cleaned up.....after spending all that time on it you might find it to be ruined. You just never know when buying from ebay......after you order a used one a NOS one may appear. What I do is just buy what I need to get the saw running again then if I find a rare bargain on a NOS piston and/or cyl I'll buy those and swap them out when time allows. That's one of the nice thing about working on saws......top end swap shouldn't take more than an hour or so if you have everything ready.........usually takes longer to clean a saw up enough to work on than to actually do the work!!
Wow. You are a godsend. You are probably sick of compliments. I just read your jonsered rebuild post. That's why I haven't sent pics yet. I was wondering if I could just pull cylinder and change piston and cylinder? Should I get rings and cylinder gasket kit I saw on ebay or use rings on replacement piston? Thanks.
 
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