Stihl ms290/390 pop-up piston kit - To be sold soon??

[Black Dog Chainsaw]

@Gentleman

Ok so I have the prototype piston for the 49mm 039/390 Farmboss.

Unfortunatly, I need a couple farmboss chassis's. Normally I have 3-5 of them sitting here but right now I have ziltch since my neighbor just picked his up to cut some firewood.

I will get more information down soon from what I learned but from memory... It's a 0.040 pop up that will fit the OEM cylinder and the Cross Performance cylinder. The cheaper 49mm Chinese cylinder from HLS won't fit due to its "D" shaped chamber and the taller piston (again from memory). Piston height and skirts were almost identical between the Cross and OEM. The pop-up prototype was made from a 49mm Cross piston. To keep everything as even as I can, compression readings will be from...

1.) Stihl OEM top end
2.) Cross kits with Caber rings
3.) Cross pop-up piston with cabers and cross cylinder
4.) Cross pop-up piston with cabers and Stihl OEM cylinder

My initial guess will be a 20-40 psi bump in compression, but we will see after testing. I would do video test cuts, but there is too much variation between saw carburetors, timing, clutch wear, variation in wood size/density, chain, etc... etc... The compression checks will be done with OEM crank, OEM bearings, and OEM clam shell bottom. I'm just out to see the bump in compression knowing that it will ultimately lead to more torque.

 

[Warped5]

 

[Onan18]

@Gentleman

Ok so I have the prototype piston for the 49mm 039/390 Farmboss.

Unfortunatly, I need a couple farmboss chassis's. Normally I have 3-5 of them sitting here but right now I have ziltch since my neighbor just picked his up to cut some firewood.

I will get more information down soon from what I learned but from memory... It's a 0.040 pop up that will fit the OEM cylinder and the Cross Performance cylinder. The cheaper 49mm Chinese cylinder from HLS won't fit due to its "D" shaped chamber and the taller piston (again from memory). Piston height and skirts were almost identical between the Cross and OEM. The pop-up prototype was made from a 49mm Cross piston. To keep everything as even as I can, compression readings will be from...

1.) Stihl OEM top end
2.) Cross kits with Caber rings
3.) Cross pop-up piston with cabers and cross cylinder
4.) Cross pop-up piston with cabers and Stihl OEM cylinder

My initial guess will be a 20-40 psi bump in compression, but we will see after testing. I would do video test cuts, but there is too much variation between saw carburetors, timing, clutch wear, variation in wood size/density, chain, etc... etc... The compression checks will be done with OEM crank, OEM bearings, and OEM clam shell bottom. I'm just out to see the bump in compression knowing that it will ultimately lead to more torque.

I have a MS 290 that needs a new jug and slug.

 

[TJ the Chainsaw Mechanic]

 

[Czed]

Cool.
Can't wait.

 

[srcarr52]

@Gentleman

Ok so I have the prototype piston for the 49mm 039/390 Farmboss.

Unfortunatly, I need a couple farmboss chassis's. Normally I have 3-5 of them sitting here but right now I have ziltch since my neighbor just picked his up to cut some firewood.

I will get more information down soon from what I learned but from memory... It's a 0.040 pop up that will fit the OEM cylinder and the Cross Performance cylinder. The cheaper 49mm Chinese cylinder from HLS won't fit due to its "D" shaped chamber and the taller piston (again from memory). Piston height and skirts were almost identical between the Cross and OEM. The pop-up prototype was made from a 49mm Cross piston. To keep everything as even as I can, compression readings will be from...

1.) Stihl OEM top end
2.) Cross kits with Caber rings
3.) Cross pop-up piston with cabers and cross cylinder
4.) Cross pop-up piston with cabers and Stihl OEM cylinder

My initial guess will be a 20-40 psi bump in compression, but we will see after testing. I would do video test cuts, but there is too much variation between saw carburetors, timing, clutch wear, variation in wood size/density, chain, etc... etc... The compression checks will be done with OEM crank, OEM bearings, and OEM clam shell bottom. I'm just out to see the bump in compression knowing that it will ultimately lead to more torque.

To clear things up since Nathan can't seem to remember what we discussed when I made the prototype pop-up at my shop.

The pop up piston will not fit the Chinese cylinder from HLS because the cylinder is shorter (about 0.015"), and the supplied piston has a shorter crown height to make up the difference. Using any normal crown height piston in the Chinese cylinder will result in squish that is 0.015" or less. The shortened height of the Chinese cylinder it really due to a small step (around 0.025" wide) at the corner of the cylinder and squish band.

 

[Chainsaw Jim]

That Chinese one sounds like some fun can be had with it.

 

[srcarr52]

That Chinese one sounds like some fun can be had with it.

I think you missed the last part. The squish is tight to to a 0.025" wide step at the corner in the squish band that is probably 0.010" tall. No buneo!

 

[Chainsaw Jim]

I think you missed the last part. The squish is tight to to a 0.025" wide step at the corner in the squish band that is probably 0.010" tall. No buneo!

I didn't miss one bit of it.
How many clam shell cylinders do you get to cut the squish band on without having to machine the bearing tracks and base? If the pop up doesn't work with it then it can still be done with another tall piston.

 

[srcarr52]

I didn't miss one bit of it.
How many clam shell cylinders do you get to cut the squish band on without having to machine the bearing tracks and base? If the pop up doesn't work with it then it can still be done with another tall piston.

Once you cut the step out you'll end up at 0.025"-0.030" which is right on par with an OEM jug.

 

[Black Dog Chainsaw]

To clear things up since Nathan can't seem to remember what we discussed when I made the prototype pop-up at my shop.

The pop up piston will not fit the Chinese cylinder from HLS because the cylinder is shorter (about 0.015"), and the supplied piston has a shorter crown height to make up the difference. Using any normal crown height piston in the Chinese cylinder will result in squish that is 0.015" or less. The shortened height of the Chinese cylinder it really due to a small step (around 0.025" wide) at the corner of the cylinder and squish band.

Sorry I didn't know if you wanted to be named in this project or not. All credit for the pop-up piston goes to Shaun. I am merely aseembling and doing the wrench work to figure out the gains.

I was right though that the HLS Chinese cylinder is "D" shaped and you expressed concern that the flat side of the chamber would contact a full circle pop up. [emoji16]

 

[Black Dog Chainsaw]

I have a MS 290 that needs a new jug and slug.

@Gentleman

It would be easier to assemble 2 of them at a time to take the measurements. It would be up to him on if you get to keep the top end for the loan of the saw. I would like to stipulate that it should be disassembled and cleaned first, PLEASE! Also you won't get to keep the pop-up piston as that will need to be copied even if he agrees.

Maybe a he could send a hyway 49mm and I can confirm whether one of those cylinders will work???? Or maybe Gentleman wants to keep it down to 1-2 options of cylinder for the pop-up pistons... idk...

 

[stihl_head1982]

readin and learnin

 

[Gentleman]

@Gentleman

It would be easier to assemble 2 of them at a time to take the measurements. It would be up to him on if you get to keep the top end for the loan of the saw. I would like to stipulate that it should be disassembled and cleaned first, PLEASE! Also you won't get to keep the pop-up piston as that will need to be copied even if he agrees.

Maybe a he could send a hyway 49mm and I can confirm whether one of those cylinders will work???? Or maybe Gentleman wants to keep it down to 1-2 options of cylinder for the pop-up pistons... idk...

I don't need the cylinders back. Just the pop up.
I have a clean 390 if you want to test on that as well.

 

[Dub11]

Man I have a 390 oem and a cross 390 kit going to a 029 If you need test beds I got em clean and waiting assembly. Just my job.wants me to work and crap.

 

[Dub11]

And this is just a little cool tidbit I was getting ready to open the exhaust port on the oem head and made a template thing stuck it in the Cross head and there identical! NICE!

 

[WooHoo223]

I have a 390 that torn down that's available to use also. Cylinder looks like it was straight gassed. It's still mounted to the case. I've also have a cross performance kit (NIB) to go along with it and a hyway 49mm piston kit NIB. All available to use. Can take pics if interested. Everything is boxed away for now. Not looking for anything, don't care about the burned up top end. Dub11 is closer, ahead in line.

 

[Gentleman]

Just let me know what you need and I can send it tomorrow.

 

[Terry Syd]

Watching and waiting for this piston....

 

[Black Dog Chainsaw]

Just let me know what you need and I can send it tomorrow.

If you want a hyway 49mm checked send one of them! If you have a chassis you need rebuilt send one of them to and I'll be sure to return it rebuilt. [emoji16]

Other wise I'll take one of these guys up on their saws.