Gasket Delete AND Pop-Up?

[ChillyB]

Project saw needs a piston. Figured to delete base gasket, Should I then avoid pop-up pistons? Is there a problem with doing both?

Thanks,
Chilly

 

[oldguy]

you won't know till you try it with your stuff.

 

[Kenskip1]

Sir in order to fully answer this we would like to know the make and model of the saw in question!

 

[Bob Hedgecutter]

Project saw needs a piston. Figured to delete base gasket, Should I then avoid pop-up pistons? Is there a problem with doing both?

Thanks,
Chilly

Thing is, if you have to ask and do not know how to measure/calculate safe parameters and final outcomes- you might just be a step out of your league in your proposals.
What you may (or may not) achieve are psychological gains, perceived gains, but in reality not much at all.
Worst case scenario, you pull cylinder bolts from threads and crack cylinder flanges.

 

[NSEric]

Depends on the saw.
Not all saws need the compression raised that much.
Too much compression makes them hard to start.

 

[sawmill sam]

Project saw needs a piston. Figured to delete base gasket, Should I then avoid pop-up pistons? Is there a problem with doing both?

Thanks,
Chilly

Do one or the other, not both, unless you know what you're doing! Ever heard of measuring squish?

 

[Mad Professor]

There is a good thread on "the other site" currently detailing a 034S build. Some good pictures of machining the cylinder's base and squish area, and mild port work.

If you can't do the above I'd stick with a base gasket delete and setting squish to ~0.020" with a fresh OEM piston.

 

[Gord404]

well be nice to know what saw it is- some of the older stihls are pretty good to start with- but then I have a lathe- porting is another way to wreak peformance if you don't know your exact numbers you are trying to acheve - knocks the port timing out of wack

 

[ChillyB]

It's a 365 Special. I know how to measure squish and have worked on just a few saws. I don't port because a faster saw that isn't used frequently can't save any appreciable time. I want to pull a 28" bar max and don't need to be in a hurry.

Goal is a basic reliable saw for occasional work where my 50-55cc saws aren't enough. I'm not interested to ride the edge of reliability for power gains, but I'll take free powers when it's available without risk. Tightening squish seems like free performance without risk, if one measures correctly. Maybe tightening squish with a pop-up gets outside of my goal and risk factor.

 

[oldguy]

A 372 cyl. & piston will bolt rite on that saw also.

 

[ChillyB]

A 372 cyl. & piston will bolt rite on that saw also.

That option is on my mind. Cylinder is soaking in carb cleaner, then I have to remove metal transfer to inspect. And I don't have a ball home to deglaze.

if one decides to do one or the other I'm inclined to think a base gasket delete with flat-top would be preferred to installing gasket with a pop up.

 

[oldguy]

It's a 365 Special. I know how to measure squish and have worked on just a few saws. I don't port because a faster saw that isn't used frequently can't save any appreciable time. I want to pull a 28" bar max and don't need to be in a hurry.

Goal is a basic reliable saw for occasional work where my 50-55cc saws aren't enough. I'm not interested to ride the edge of reliability for power gains, but I'll take free powers when it's available without risk. Tightening squish seems like free performance without risk, if one measures correctly. Maybe tightening squish with a pop-up gets outside of my goal and risk factor.

You can probably do one or the other, you won't know if both will work until you put the parts together to see if the squish is too thin or the popup hits top or the sparkplug.

 

[oldguy]

I use coarse emery cloth to remove transfer.

 

[James Sawyer]

Project saw needs a piston. Figured to delete base gasket, Should I then avoid pop-up pistons? Is there a problem with doing both?

Thanks,
Chilly

You're going to want to measure the squish to determine what piston clearance your saw going to have if you delete the base gasket. My opinion not worth going to popup piston but others have and do. The popup piston is to heavy, with the base delete you'll gain more intake timing and lower the exhaust and you'll gain bit more torque. The base gasket will drop the cylinder about .020 ~ 2 degree on your timing numbers. I had the same thoughts as you and bought a Hyway popup and did a comparison... my opinion it's just to heavy. So, here my results so you can decide.

 

[sawmill sam]

You're going to want to measure the squish to determine what piston clearance your saw going to have if you delete the base gasket. My opinion not worth going to popup piston but others have and do. The popup piston is to heavy, with the base delete you'll gain more intake timing and lower the exhaust and you'll gain bit more torque. The base gasket will drop the cylinder about .020 ~ 2 degree on your timing numbers. I had the same thoughts as you and bought a Hyway popup and did a comparison... my opinion it's just to heavy. So, here my results so you can decide.

I have both 460's and 661's stock and stock with popup. I will pay closer attention to the differences in torque between the two. A bit more hp but the torque difference not so noticable I think. Interesting!

 

[ChillyB]

Appreciate the informative replies. I think I'll delete gasket and stick with flattop (verifying squish, of course).

The more I look at it I'm considering cleaning up the piston, replace ring and wrist pin bearing, seeing how she runs. It's not deeply scuffed and the ring is not at all sticking. When a top end is absolutely needed I know where to get them. I think this top end, while not perfect, has life left in it. This is NOT a pretty saw.