Jonsereds resurrection

[Peter Y]

I picked up a '70s Jonsereds MK70 cut off saw last fall. It is built off of the 70E powerhead

With all of the chaos going on, I finally found time to dig into it. Outside of being extremely neglectfully dirty, it is in pretty good shape. With that said, it was straight gassed for an unknown amount of time.

I need some guidance from you folks on a few points.

1. Does a cut off saw need bar oil? This one had a full bar oil tank but I cannot see how it is needed.
2. What are your thoughts on the P&C? It had 135psi of compression cold when I tore it down. I can get an aftermarket piston for not much coin.... worth the hassle or should I just run what came out of it? If it matters, I am splitting cases to change main bearings and seals.
3. What have yall used to seal the case in the absence of a gasket? I cannot find a gasket for this saw.

 

[Peter Y]

Bump.

 

[Cantdog]

I picked up a '70s Jonsereds MK70 cut off saw last fall. It is built off of the 70E powerhead

With all of the chaos going on, I finally found time to dig into it. Outside of being extremely neglectfully dirty, it is in pretty good shape. With that said, it was straight gassed for an unknown amount of time.

I need some guidance from you folks on a few points.

1. Does a cut off saw need bar oil? This one had a full bar oil tank but I cannot see how it is needed.
2. What are your thoughts on the P&C? It had 135psi of compression cold when I tore it down. I can get an aftermarket piston for not much coin.... worth the hassle or should I just run what came out of it? If it matters, I am splitting cases to change main bearings and seals.
3. What have yall used to seal the case in the absence of a gasket? I cannot find a gasket for this saw.

View attachment 812472View attachment 812473View attachment 812475View attachment 812476View attachment 812478

No cut off saw doesn't need bar oil.
You will need to clean that cyl and get ALL the alum transfer off it before you can tell if it's useable...likely it is but that is the first step.
That piston is not great but looks like it will clean up......I'd lightly clean it up with a little scotchbrite and rering it with a new Caber ring 50MM X 1.5MM. I've not seen any AM 70E pistons for sale with the reputable AM companies....perhaps Golf makes one but I would run the worn stock one rather than use a pitiful, cheap piston....needs to be made by Meteor, Episan or perhaps VEC are the good AM pistons. I see NOS Mahle 50MM 70E pistons for sale on ebay from time to time. You could run what you have with a new ring and keep an eye out for a NOS one .
You definitely need a case gasket if you break the cases.....are you sure the bearings are beat? If there is no up and down play they probably are fine. You don't need to split the cases to replace the seals. But if you do you will either need to find a NOS gasket or make one....quite a few threads on here about making gaskets.

 

[Peter Y]

The bearing on the flywheel side is definitely past it's service life. Very noticeable up and down wiggle.

Thank you on the idea of just re-ringing the original piston. I just picked up a bottle of Muriatic acid yesterday so I will get going on getting the aluminum transfer cleaned out. I assume I am looking for a nice clean wall under the transfer? What is there feels fairly faint.

I am seriously struggling trying to find a case gasket. I will keep looking.

 

[svk]

You may want to check out the youtube videos on how to remove transfer without acid. Maybe a bit safer method.

Good luck with your project. Those are nice powerheads.

 

[Peter Y]

You may want to check out the youtube videos on how to remove transfer without acid. Maybe a bit safer method.

Good luck with your project. Those are nice powerheads.

Good timing. I just watched those videos and will be going that route instead.