High Quality Chainsaw Bars Husqvarna Toys

Jonsered 920 w/GD - Interesting numbers

Deputyrpa

Super OPE Member
Local time
7:25 AM
User ID
3090
Joined
Apr 27, 2017
Messages
209
Reaction score
588
Location
Fort Ann, NY
Country flag
I'm interested in some comments. Really interested!

So I was able to obtain an OEM "open" transfer cylinder for the Jonsered 920 to replace the closed port cylinder. I put in a new VEC piston in it and slapped on the open port cylinder with Motoseal.
The numbers I got on the wheel are:
Exhaust: 118
Transfers: 128
Intake: 72

10 dungarees of blowdown is some interesting stuff. I will have it back together tomorrow and see how she runs. I'm guessing she'll have some grunt, but not rpm. What do you all think about those numbers?
 

Ketchup

Epoxy member
Local time
5:25 AM
User ID
5594
Joined
Mar 12, 2018
Messages
1,756
Reaction score
4,845
Location
Colorado
Country flag
I would think the same thing. Those are your numbers without a gasket?

That’s not many dungarees. Did you take any photos of the case, transfers, piston? What’s your squish?

920/930 have a good reputation. Interested to see what it tachs out at.
 

cus_deluxe

terms of service violator
Local time
7:25 AM
User ID
393
Joined
Jan 3, 2016
Messages
5,195
Reaction score
24,216
Location
Michigan
Country flag
are you positive on the exhaust height? 124 degrees of duration is not much.
 

Deputyrpa

Super OPE Member
Local time
7:25 AM
User ID
3090
Joined
Apr 27, 2017
Messages
209
Reaction score
588
Location
Fort Ann, NY
Country flag
I would think the same thing. Those are your numbers without a gasket?

That’s not many dungarees. Did you take any photos of the case, transfers, piston? What’s your squish?

920/930 have a good reputation. Interested to see what it tachs out at.
Yes, that's just with Motoseal. I took the cylinder off again to compare it to the original (they're both OEM) cylinder. I'm having some coffee, and I will compare them with a ring and caliper in a couple minutes. Pics too.
 

Deputyrpa

Super OPE Member
Local time
7:25 AM
User ID
3090
Joined
Apr 27, 2017
Messages
209
Reaction score
588
Location
Fort Ann, NY
Country flag
are you positive on the exhaust height? 124 degrees of duration is not much.
Yeah, I'm by no means an expert, and those number even raised my eyebrows. I recalibrated the wheel with a piston stop each time and re-measured it several times to be sure.
 

Deputyrpa

Super OPE Member
Local time
7:25 AM
User ID
3090
Joined
Apr 27, 2017
Messages
209
Reaction score
588
Location
Fort Ann, NY
Country flag
Here's a pic of both cylinders, and each one separately showing the relationship between the transfer port and exhaust port.
 

Attachments

  • IMG20230518101725.jpg
    IMG20230518101725.jpg
    158.2 KB · Views: 20
  • IMG20230518101751.jpg
    IMG20230518101751.jpg
    105.2 KB · Views: 18
  • IMG20230518101807.jpg
    IMG20230518101807.jpg
    133.7 KB · Views: 19

Deputyrpa

Super OPE Member
Local time
7:25 AM
User ID
3090
Joined
Apr 27, 2017
Messages
209
Reaction score
588
Location
Fort Ann, NY
Country flag
Here a pic of the cylinders with a ring pushed in with a piston, rotated 180 to keep perspective. the bottom edge of the rings are positioned at the opening edge of the transfers. The measurements between both cylinders are idenitcal. So the area from the top of the exhaust ports to the bottom side of the rings is all that is open when fuel begins to come in. It's less than halfway.
 

Attachments

  • IMG20230518102813.jpg
    IMG20230518102813.jpg
    178.8 KB · Views: 20

Ketchup

Epoxy member
Local time
5:25 AM
User ID
5594
Joined
Mar 12, 2018
Messages
1,756
Reaction score
4,845
Location
Colorado
Country flag
Just from photos the transfer upper to exhaust height looks pretty normal. I would run it before grinding anything.
 

Deputyrpa

Super OPE Member
Local time
7:25 AM
User ID
3090
Joined
Apr 27, 2017
Messages
209
Reaction score
588
Location
Fort Ann, NY
Country flag
Just from photos the transfer upper to exhaust height looks pretty normal. I would run it before grinding anything.
I didn't plan on grinding it. Those OEM cylinders are hard to come by, and my mistakes are easy to come by. lol! I'm interested to run it too. With the OEM cylinder with a gasket, it was a torque monster. The reason I obtained that open cylinder was because Jonsered found that port design for the 930 gave more power, and retrofitted the later 920s with that design. With a gasket delete, it should be even better. The squish with the gasket delete is .031
 
Last edited:

ErnieG

Super OPE Member
GoldMember
Local time
7:25 AM
User ID
15345
Joined
Jan 12, 2021
Messages
489
Reaction score
616
Location
Northeast PA
Country flag
I didn't plan on grinding it. Those OEM cylinders are hard to come by, and my mistakes are easy to come by. lol! I'm interested to run it too. With the OEM cylinder with a gasket, it was a torque monster. The reason I obtained that open cylinder was because Jonsered found that port design for the 930 gave more power, and retrofitted the later 920s with that design. With a gasket delete, it should be even better. The squish with the gasket delete is .031
One of my 930's has a gasket delete and it's a great running saw for sure ...they take a gasket delete very well !

Ernie
 

ErnieG

Super OPE Member
GoldMember
Local time
7:25 AM
User ID
15345
Joined
Jan 12, 2021
Messages
489
Reaction score
616
Location
Northeast PA
Country flag
I didn't plan on grinding it. Those OEM cylinders are hard to come by, and my mistakes are easy to come by. lol! I'm interested to run it too. With the OEM cylinder with a gasket, it was a torque monster. The reason I obtained that open cylinder was because Jonsered found that port design for the 930 gave more power, and retrofitted the later 920s with that design. With a gasket delete, it should be even better. The squish with the gasket delete is .031
If you have a local machine shop or your handy with a grinder you can turn that 920 cylinder into a 930 ...I've done that with two of mine .
Ernie
 

Redfin

Meh...
Local time
7:25 AM
User ID
159
Joined
Dec 24, 2015
Messages
7,645
Reaction score
39,980
Location
Central Pa
Country flag
Curious, are you referring to “open” and “closed” transfer by the lower tunnel opening to the case?
 

Deputyrpa

Super OPE Member
Local time
7:25 AM
User ID
3090
Joined
Apr 27, 2017
Messages
209
Reaction score
588
Location
Fort Ann, NY
Country flag
Curious, are you referring to “open” and “closed” transfer by the lower tunnel opening to the case?
Yes, for lack of a better term. But they're not "open" as in trenched.
 

drf256

Dr. Richard Cranium
GoldMember
Local time
7:25 AM
User ID
319
Joined
Dec 29, 2015
Messages
9,334
Reaction score
61,419
Location
Strong Island NY
Country flag
Were the stock pistons the same, or was one windowless? Are the cutouts in the case the same on both models?

What Jawney is trying to say is that “open” transfers refers to them having no bridge between the lower and upper. They are just open, with a full view of the outer tunnel and the piston itself acts as the inner tunnel.

What you have there is a partial/hybrid case fed and side fed lower transfer on a closed transfer jug.
 

Deputyrpa

Super OPE Member
Local time
7:25 AM
User ID
3090
Joined
Apr 27, 2017
Messages
209
Reaction score
588
Location
Fort Ann, NY
Country flag
Were the stock pistons the same, or was one windowless? Are the cutouts in the case the same on both models?

What Jawney is trying to say is that “open” transfers refers to them having no bridge between the lower and upper. They are just open, with a full view of the outer tunnel and the piston itself acts as the inner tunnel.

What you have there is a partial/hybrid case fed and side fed lower transfer on a closed transfer jug.
The pistons were the same and the case notches are as well. Yes, I know they are not open, so I put quotations around the word "open" for simple distinction's sake.

Spike60's Saw College on afleetcommand's YouTube channel provided an interesting history of Jonsered's 900 series progression to this notched cylinder design.

Irrespective of the difference in the jugs, the timing numbers are still quite different and interesting. 10 degrees of blowdown is just odd, but I'm no enginerd. If I could get the starter pawl springs to do their thing, I will run it today. Thanks.
 
Top