Jonsereds 80 rebuild

[Cease232]

Working on this 80 that sat with the muffler and spark plug off for 5 years in a woodshop. Piston and cylinder looked fine but I pulled it to clean up the layer of sawdust that had accumulated on top of the piston. Found this damage on the intake side. Found a small pebble inside the case. I also see what looks like a chunk of metal lodged in a hole. Not sure if it's supposed to be there (couldn't dislodge it easily). The opposite side is clear. Any advice. The cylinder has some damage as well but not terrible. Thanks everyone.

 

[Chainsaw Jim]

Well it's likely a bearing cage let a chunk loose and it tore things up. It looks like it's time for the case to be split for a bearing replacement.

 

[Cantdog]

Ouch.....you definitely had serious contamination!! Hard to say what though....may well be as Jim said.....but the size of the scoring puts me more in mind of roller bearing chunks......or something ingested through the carb.....I doubt the pebble was the culprit......more likely it entered through the open plug hole or the exhaust port while sitting in a wood shop all those years, Whatever happened, if you still intend to continue the project, the cases will need to be split and all con rod bearings inspected thoroughly and the main bearings simply replaced with new and new crank seal installed as well.....the bearings and seal can be sourced at your local bearing supply house as they are, of course NLA from the Jonsered dealers. Not to be a buzz kill but I probably would save this 80 for parts and seek out a less damaged project 80 as your jug looks rough, piston is toast and it is rather difficult to know exactly the lower con rod bearing condition at this point in time.......just MHO.....others may vary.

 

[Cease232]

Saw passed pressure and vac test. Bearings feel very smooth with no play and visual inspection (without splitting) of the case does not reveal any obvious damage. Is it possible the bearings failed and I just can't tell? If all's well I may just put a new piston in and see how she runs. Im actually fixing it for my brother and he's cheap haha. It'll most likely be my saw someday as he hasn't used it in years and will probably get very little use out of it anyways.

What about that piece of metal in pic #2? I'm not very familiar with these saws and do not have the IPL. Is that something foreign? Thanks for the reply's fellas.

 

[Chainsaw Jim]

It is very very possible for the bearing cage to be missing a chunk and still roll smooth and tight. The scars on the piston are exactly what you'll see when a flake of metal from the cage gets caught from the underside.
You have to hold the crank to the side while you use a pick to rotate the big end bearing until you find the bad spot. The crankcase bearings would be the next set to check if that one passes inspection.

 

[LegDeLimber]

2nd pic. Is that drill bit in the hole?

 

[Cease232]

2nd pic. Is that drill bit in the hole?

Dang, good eye! That's what I've been trying to figure out. Why in the hell would someone be drilling that out? No wonder there's shards of metal flying around inside the cylinder.

 

[Cantdog]

Another couple questions.....in the top pic of the piston. Is that the ring end index pin right where there is a rather large piece of the edge of the piston crown missing? If it is, is it still there or is it loose? Is the ring complete or broken? Odd that a chunk is missing from the crown edge but only from the ring up....and from the damage, it looks like it was pushed up....

That does look awfully like a drill bit broken off in the bearing vent hole......and it looks to have been there a while.....however the vent is located dead center of the bearing and the piston looks untouched by anything foreign directly under the wristpin.......so....it may well be that the piston damage and the foreign matter in the vent hole are totally unrelated. Or perhaps what is in the hole is not a drill bit but bearing retainer bits coming up from the damaged main bearing below.

Very hard to accurately define the forensics of a chainsaw homicide from a remote position using only a few pics to go by.....the possibilities of what could have happened and what actually did are quite a wide range. All things mentioned are certainly possible as well as many not yet mentioned. It may well be that your lower end could be in great shape and only need a thorough flushing to remove any metal particles....but from my experience it is way better to tear the crankcase down, thoroughly clean, inspect and replace any damage found with new readily available parts or a good used crankshaft with new bearings and seals in this case. Then you know what you have and that is a good foundation to build on.

 

[Cease232]

Another couple questions.....in the top pic of the piston. Is that the ring end index pin right where there is a rather large piece of the edge of the piston crown missing? If it is, is it still there or is it loose? Is the ring complete or broken? Odd that a chunk is missing from the crown edge but only from the ring up....and from the damage, it looks like it was pushed up....

Finally back to the saw,
The indexing pin is intact and the rings were not broken. I dont think a piece of the piston top edge detached its just pushed up.
That damage on the piston is very peculiar. This whole thing is perplexing. after closer examination I'm 99% sure thats a broken drill bit. With that information who knows what the previous owner did to the piston.
It seems very likely judging by the location of the damage that the contamination came from below the piston. I guess i'll be pulling bearings. Thanks fellas.

 

[Cantdog]

Finally back to the saw,
The indexing pin is intact and the rings were not broken. I dont think a piece of the piston top edge detached its just pushed up.
That damage on the piston is very peculiar. This whole thing is perplexing. after closer examination I'm 99% sure thats a broken drill bit. With that information who knows what the previous owner did to the piston.
It seems very likely judging by the location of the damage that the contamination came from below the piston. I guess i'll be pulling bearings. Thanks fellas.

A bunch of extra effort but that's the only way you'll know for sure what's what.

A Jim said earlier take your time an examine the lower conrod bearing carefully by sliding the rod all the way to one side and with a pick pull the bearing cage all the way in the other direction so you can see as much of the bearings as possible, then slowly rotate the bearing a full 360 degrees inspecting each roller as you go. If good reverse every thing and do the same inspection on the other end of the bearing. And of course you'll be looking for any cage damage as well. This is a very important step as the whole saw is literally built around this one non-replacable bearing. The main ball bearings are easily replaced from your local bearing supply.....can't remember off the top of my head but I think they are 6203 C-3 bearings......the numbers will be right on the bearings anyway. When you get crank seals be sure to specify double lip type.....they need to hold pressure and vac....I've had good success with these but there are others as well.

 

[Cantdog]

Oh one other thing I forgot to mention......I don't know if it's just the pic but that crank and rod look unnaturally dry......I know it has sat for a long time but oil doesn't evaporate.....lower ends are usually quite oily.....so if it is as dry as it looks be sure to look for any blueing or scoring on the lower conrod bearing rollers.....

 

[Cease232]

Thank you, all very good advice, greatly appreciated! I inspected the lower connecting rod bearing with a pick as suggested and it appeared to be in good order. If my memory serves it was quite dry inside the case. What would this suggest?

 

[Cantdog]

Thank you, all very good advice, greatly appreciated! I inspected the lower connecting rod bearing with a pick as suggested and it appeared to be in good order. If my memory serves it was quite dry inside the case. What would this suggest?

Lack of lubrication for what ever reason.....no idea why...any more than why there might be broken drill bits in vent holes...LOL!!

As long as the bearing hasn't suffered from it you're likely OK. If it had, it would be visible.

 

[Cease232]

Who knows. This saw was pulled from service most likely for a carburation issue. Supposedly it ran just fine before that. Although thats relative of course.

 

[Cease232]

Hey Cantdog, I've now realized that what I have is an 801. Is it possible to replace the P/C with one from a 90? They look identical on paper but not sure it would mount up. What do you think?

 

[Cantdog]

Hey Cantdog, I've now realized that what I have is an 801. Is it possible to replace the P/C with one from a 90? They look identical on paper but not sure it would mount up. What do you think?

Yes either an 80 or 90 top end will bolt right up....same upper rod bearing/muffler/carb/air filter etc, I have seen early 801s without the hole in the top cover for the decomp but the later ones had the 90 top cover with a plastic plug in that hole.