Bringing back a 621 Jonsereds

[Cantdog]

So....haven't done one of these in a while but I have a friend that really likes the old Silver Tops so I picked one to give him next time showed up. It had been sitting quite a while and had some visible issues (and some invisible ones too)......good start to a project though. Been working on client's saw the last week or so and getting them ready to go home. Got to looking at the 621 and got to thinking that this guy is super generous...and a wicked good guy to boot......I shouldn't give him an old broke down Silver Top 621....just ain't right. So I started the process of breaking the saw down, cleaning all the parts and seeing what it needed....this took a while....the fuel tank was in rough shape.....had four wallered out bolt holes (5 actually, I found out tonight) and the piston wasn't bad but had some carbon steaks......as I worked along it struck me that I might kill two birds with one stone........fix this legendary saw for a good guy AND do a build thread for those who have an interest in these old war horses and might need/like some reference as to what goes where and why. This is not going to be as thorough as some of my other (extinct since the hack) build threads nor is this a museum piece (though I like things as pretty as possible with the parts I have on hand). This is just a description, with some pics of a tear down and rebuild......hopefully resulting in a fine running example of the 621 Jonsereds....the father of all modern chainsaws. These were a cut above nearly or all others at the time of their coming into being.....one of the most pleasant saws to run with good cut rates and super torque for a 56 cc saw. Get your popcorn popped, beverages at the ready and we'll head into the past.

 

[Cantdog]

The saw has been torn down to the cases, the crank seals pulled, the bearing swabbed from the outside with mix and an acid brush and inside of the crankcase brushed and rinsed with mix and flushed repeatedly until the mix was as clean coming out as it was going in.
First thing to do is fix the bolt holes. I use steel inserts for this.....there are other ways but this is easy, available and not terribly expensive. The bolts are 4MM...so the inserts are 4MM ID and 8MM OD....so you bore the 4MM holes to 17/64 and tap to 8MM. The inserts have a screw driver slot in one end. They come with their own thread lock but I install these with red locktite.....they work good and seem very durable. I had to do both spike mounting holes, the front top cover hole and the upper right hand recoil cover bolt hole....and just found out I have to do the upper left hand bolt hole too.

 

[Cantdog]

So all the holes are repaired (except 1 that I just found and am out of inserts).....now on to crank seals.....on this saw I am using two NOS seals.....pretty straight forward...things have be lubed, for this I use Stihl Ultra on a Q-tip but most any oil will do....I lube the ID of the case bore, the OD of the crankshaft, the ID and OD of the seal itself....just lightly, just needs a thin coating. I push the seal into the case bore squarely with my thumbs, then tapping it with a 3/4 X 3/4 X 3" piece of Doug Fir.....I used to use a socket to drive them in but I find I have much better control and less chance of denting the metal part of the seal with the end grain of wood.....however you prefer to do it, the seals go in just flush with the case bore. These cranks do not have the step that some cranks have so that make the installation much easier. Both seals are the same on either end of the crank.

Now.....there is another crank seal to deal with.......this goes unnoticed and unspoken of generally.....fact is most who work on these saws don't even know it's there. It is located in the back of the timing plate....it is a small seal which is designed to keep moisture, oil and dirt out of the points box. Couple more pics of replacing this seal....

 

[Cantdog]

Sorry this may seem a little out of order but I did a bunch of this stuff before I decided to take pics and make this into a thread.
I have already removed the points from the points plate and found them to be in great shape...no pitting or burning, though they were oxidized and not allowing spark, so I very gently dressed them with a fine file and was rewarded with a perfect match first time. You must be very careful filing points as the contacts have a relatively thin, hard contact surface which you must not file through.....if you do the points are ruined.....and they are NLA. So I stress great care in dealing with these. After the filing I reinstalled the points in the points plate and now the points plate can be reinstalled on the case. Before removing the points plate I marked both the plate and the case so as not to lose the original ignition timing setting.....again I stress this point as important because if your timing is lost it requires special tooling that most folks don't have to get it back.
After the points plate is replaced in the correct position you must set the points gap and supply 2-3 drops of engine oil to the felt that rubs on the crank to lubricate the wear bar that follows the cam profile on the crank. The spec gap is 0.014-0.016"...I set them to 0.015 with a very light fit on the feeler gauge on the high side of the cam. Points always close up in use so it's best to set them on the wide side of spec.

 

[Cantdog]

Now the next thing to check and clean is the chain oiler filter located behind the chain catcher. This saw has had an owner who is good about maintaining chain tension.....the chain catcher show absolutely no evidence that the chain has ever contacted it...this is very rare.....good but rare. So you remove the three screws and there is a slot provided for a narrow screw driver to pry the catcher out of the case......behind that is a plastic screen and a baffle. Remove both of these and clean them. I used a NOS gasket and replaced the assembly.

 

[tbone75]

Looking real good Robin !!!

 

[svk]

Well done and looking forward to the rest of the build!

 

[heimannm]

The 621 is like a 65 Stingray, absolute classic that had features and performance ahead of its time.

Mark

 

[Stihl 041S]

Like a mini 111S..........nice work Lad.

 

[Cantdog]

Like a mini 111S..........nice work Lad.

Somewhat similar but actually closer to the 80 or perhaps I should say the 80 is more like the 621. But of the Jonsereds that are like different models the 621 stands rather alone. It has a totally different trigger handle/AV assembly than all the others, which is a holdover from it's ancestors the 60/601. Then it became the 62 which is indistinguishable from the 621. The 111S is that way too, being a very different way of doing things/design than all the others. As Mark said, the 621 was way ahead of the curve in the chainsaw world when it came on the market.

 

[Cantdog]

The next thing to fix is a bare spot in the kill switch wire.....if I had the correct wiring connector for the points end I would have replaced the entire wire. This is a special lug, very small in size so as to not contact the points plate.....using most any thing else I found rather unsatisfactory, I opted to spice the wire out. I cut the wire back so as to position the splice directly under the carb. This will keep the splice from being twisted or bent. Being in a marine environment I use only marine grade wire which is very fine copper wire that has been tinned with lead. By fine I mean the individual strands are of much smaller dia. than regular automotive type wire. However the original Jonsereds wire is finer still and tinned as well. It is so fine it's like twisting human hair. The reason for using this type of wire is, 1, the tinned wire is very resistant to corrosion and two, the fine dia strands make a very flexible wire that is much more resistant to failure at the ends due to vibration. Jonsereds used top quality materials in all their saws and the 621 was no exception. A few pics or this repair. I soldered the joint and then used heat shrink tubing to insulate the splice.

 

[Cantdog]

Now that the needed repairs/inspections have been done on the cases it time to reassemble the engine. The cyl bore was perfect but as I said earlier, the piston showed some small carbon streaks. Initially I intended to simply replace the rings with a pair of 45MM Cabers....but as most of my projects will attest, I tend toward doing the best with what I have at hand. What I had at hand was a complete NOS P&C and NOS piston minus the wristpin and of course several 1.5mm X 45mm Caber rings. The complete P&C was not necessary as the original cyl was spotless inside........hmmmm......I could use the NOS piston with the original wristpin but that wasn't quite right either as the wristpin had some wear. As I was pondering what to do I went looking for a new recoil screen.....I knew I had several of these and the original was quite dented (though it doesn't look that bad in the pic), but they were not where I thought they were so as I was pawing through boxes of NOS stuffs I came across a bag with 10 shiny tubes in it.....turns out they were 601/621 NOS wristpins!! Didn't even know I had them!! So that solidified my course....a NOS piston with NOS rings and an NOS wristpin it gets!!! However the screens were still at large......I went back to where I originally thought them to be and of course they were right there.....damn old eyes....

I used a NOS cyl base gasket......these are made of very thin paper. Over 30-40 years they dry out and wrinkle and become smaller. Any attempt to use them in this condition WILL result in failure. What must first be done it to lay the gasket on a paper towel, fold the towel over and saturate with water...let sit. When I am starting to get ready to install the piston is when I start soaking the gasket.....by the time I'm ready to install the cly it's good to go too. I use wooden blocks to support the piston while putting the wristpin in....always position the arrow on the piston crown towards the exhaust port and always position the ends of the wristpin keepers at 12:00 or 6:00 this will aid in them not coming loose at high speeds. I carefully lube the wristpin bearing and thrust washers and just the piston skirts and the cyl bore with Ultra again on a q-tip....no need to go nuts with the oil...just a thin layer is all that's needed for assembly......by the time there is enough fuel charge present in the cases for the engine to start there will be plenty of lube on everything. Next I position the now limp cyl base gasket in place and slide the cyl on over the rings and piston. There are many types of ring compressors that one may use but I find a pair of zip ties work perfect for me. The space where the tie connector comes together allows me to look and make sure the ring ends are positioned properly on the pins and this method leaves my with both hands free to manipulate the cyl into postion....once the piston is in the cyl the zip ties fall down around the con rod and and I snip them off with a pair of dykes that I have purposely placed within reach...(hopefully)LOL!!

 

[Lux]

Keep it up! This is better than tv!

 

[Cantdog]

Keep it up! This is better than tv!

And no commercials!!!!!!!

 

[heimannm]

Explain that rubber looking block with the fitting on top at the 12:00 position in the photo of the PTO side above...

I found the photos of my other 621, still has the original spark plug cover and Total bar.









Mark

 

[Cantdog]

Explain that rubber looking block with the fitting on top at the 12:00 position in the photo of the PTO side above...

I found the photos of my other 621, still has the original spark plug cover and Total bar.

View attachment 516215

View attachment 516216

View attachment 516217

View attachment 516218

Mark

Nice saw Mark!! The block you asked about is the carrier for the optional dealer installed chain brake.....the brake "shoe" slides up into this. If you go back and look the top pic in post 11, within the loop of brown wire you see a lock nut on top where the shaft from the "shoe" comes up through to attach to the cam over linkage of the brake arm/flag....this saw doesn't have the brake system. While on this topic, in the same pic below and aft of the locknut you see a black plastic do-dad with a round hole in the end and another at 90 degrees to it.....this is where the wire goes that grounds the kill switch when the brake is activated.....this is why all the old Jonsereds kill switches had two spade terminals when only one was used...generally speaking.

 

[SawTroll]

Nice saw Mark!! The block you asked about is the carrier for the optional dealer installed chain brake.....the brake "shoe" slides up into this. If you go back and look the top pic in post 11, within the loop of brown wire you see a lock nut on top where the shaft from the "shoe" comes up through to attach to the cam over linkage of the brake arm/flag....this saw doesn't have the brake system. While on this topic, in the same pic below and aft of the locknut you see a black plastic do-dad with a round hole in the end and another at 90 degrees to it.....this is where the wire goes that grounds the kill switch when the brake is activated.....this is why all the old Jonsereds kill switches had two spade terminals when only one was used...generally speaking.

 

[heimannm]

Hello Nikko, good to know you are still with us.

Of course I was aware of the brake option, since you pointed that out to me a few years ago when I stated emphatically that the 621 had no such device...I thought others would be interested in seeing how the technology has progressed.

Mark

 

[SawTroll]

Hello Nikko, good to know you are still with us.

Of course I was aware of the brake option, since you pointed that out to me a few years ago when I stated emphatically that the 621 had no such device...I thought others would be interested in seeing how the technology has progressed.

Mark

Yes - and this was an early chain brake design that wasn't as effective/fast/safe as many later ones, but likely better than none at all.

My 621 is a 1970 one, that doesn't have it. As far as I know, 1972 was the first year it was an option (and it always was an option).

 

[Cantdog]

Hello Nikko, good to know you are still with us.

Of course I was aware of the brake option, since you pointed that out to me a few years ago when I stated emphatically that the 621 had no such device...I thought others would be interested in seeing how the technology has progressed.

Mark

Yes the brakes of today far surpass that system which consisted of a metal "shoe" as wide as the clutch drum rim and perhaps 7/8" long which when activated pushed down on the drum....these didn't work very well even when new...compared to modern band brakes. However when coupled with the ign kill feature they were far better than no brake at all. Most of the kill switch features were disabled by saw hands that were not used to brakes at all and were mightily irritated with having to restart the saw every time they were activated......generally in a brush pile or some other inconvenient position....