Jonsereds 70E build

[Chainsaw Jim]

I'm going to do a build/port job on the Jonsered 70e. Due to the extremely narrow transfers with little room to grind I'm considering an 044/440 piston. I'll cut the squish to fit the crown and then massage the ports into place. If my imagination is on track it should come close to doubling the flow.

I have a question...
What are the coils like on these models are they all unlimited?

 

[Chris Zautner]

@awol

 

[awol]

I've done a few using the 044 piston, and it works ok. To taylor the combustion chamber, requires the top ring to leave the plating a bit. My latest 70's use a 268 widowed single ring piston.
There are two different ignition system used, one with points under the flywheel, and one with a simple unit bolted to jug; neither one is limited. I prefer the points unit, as it allows a custom taylored advance curve. Some of the hs101c carbs had a governor that needs to be blocked.

 

[Fifelaker]

The coils were prone to failure, and are made of unobtainum. I don't think that they were limited.

 

[Chainsaw Jim]

I've done a few using the 044 piston, and it works ok. To taylor the combustion chamber, requires the top ring to leave the plating a bit. My latest 70's use a 268 widowed single ring piston.
There are two different ignition system used, one with points under the flywheel, and one with a simple unit bolted to jug; neither one is limited. I prefer the points unit, as it allows a custom taylored advance curve. Some of the hs101c carbs had a governor that needs to be blocked.

I'm comparing an oem and aftermarket 440 piston and the aftermarket has enough meat on the crown to keep the ring from leaving the plated area.

 

[awol]

I'm comparing an oem and aftermarket 440 piston and the aftermarket has enough meat on the crown to keep the ring from leaving the plated area.

Not if you want decent compression and retain the hemispherical combustion chamber. Remember the stock 70 piston is hyper domed.

 

[lwhaples]

Sounds like a good thread to watch.And learn.

 

[Chainsaw Jim]

Not if you want decent compression and retain the hemispherical combustion chamber. Remember the stock 70 piston is hyper domed.

I don't think it's gonna be a problem. There is barely anything left of the dome to cause any more than 5 or so pounds difference.

 

[5000+]

I never saw a 70E with points. Only the early plastic flywheel fan with the electronic module under the flywheel and the later one piece flywheel with the coil mounted on the cylinder and small module in the air box. Thought the E was for electronic.

 

[Heffalump]

....rubbing hands together with an evil grin.....

 

[drf256]

Interesting.

I wonder if a second ring only would work

 

[awol]

I never saw a 70E with points. Only the early plastic flywheel fan with the electronic module under the flywheel and the later one piece flywheel with the coil mounted on the cylinder and small module in the air box. Thought the E was for electronic.

I used to think the same thing, but have many 70E saws with both ignition systems; the early 70E is what was used on the Nordstrom Feller, and labeled as a 70E also.

Interesting.

I wonder if a second ring only would work

It would, but isn't necessary. Mike has been running his 70 in the woods a bit, and its ring is leaving the plating almost all the way around. It has about 175psi.

 

[Homelite410]

 

[drf256]

I used to think the same thing, but have many 70E saws with both ignition systems; the early 70E is what was used on the Nordstrom Feller, and labeled as a 70E also.



It would, but isn't necessary. Mike has been running his 70 in the woods a bit, and its ring is leaving the plating almost all the way around. It has about 175psi.

What percent of the ring leaves it Allen?

 

[Chainsaw Jim]

I have the squish cut and after careful measuring it appears no part of the ring will leave the plating. I took it as far as it will go before it freeports under the piston.
The factory squish with the stock piston was .040; after cutting the squish it will be around .020 so the compression should be good.

 

[Heffalump]

Jim,

If'n you'd rather use the aftermarket piston due to the height of the crown over the top ring, I'm fine with that.

 

[Chainsaw Jim]

I measured that last spec with the oem piston and that's the one I'll use.
I just pulled a comp test and it hit 170 on new rings without ever running. I used a very light smear of oil with a q-tip on the rings so the oil isn't helping the comp.

 

[Heffalump]

 

[Frank bierce]

Now if someone would come up with some
Plastic fans!!!! Lol

 

[Heffalump]

There is at least one successful 3D printed fan out there....