# pop up piston 101



## Teddy.Scout (Jan 10, 2010)

What is the basic idea in a nut shell!
Lets say for a 090, 066, or a 044-046?

Or just get me to a good thread, searches here for pop up piston gives me an enormous range.

Thanks guys!


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## blsnelling (Jan 10, 2010)

The basic idea is to create higher compression. With the squish set back to where it was, there's now piston sticking up into the combustion chamber, thereby reducing volume. Higher compression generally equates into greater torque.


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## parrisw (Jan 11, 2010)

Ya, more compression=more power.


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## Teddy.Scout (Jan 11, 2010)

I am assuming the piston is machined.
If so, how are pistons chosen?


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## wigglesworth (Jan 11, 2010)

Didnt Nik do a video here recently of doing a pop up?


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## parrisw (Jan 11, 2010)

Teddy.Scout said:


> I am assuming the piston is machined.
> If so, how are pistons chosen?



Usually you use your stock piston. You machine the crown down as far as you can go to the ring land. .100" is a safe didtance, I've done less. Then you machine down the base of your cylinder to achieve the correct squish. You can get into piston swapping if you find a suitable replacement. Like my 395 is running a Husky 2101 piston. 

Here it is.

Its the one on the right. Its about a .035" popup. Now doing this I didn't have to machine down the cylinder since the 2101 piston had a taller crown height to begin with.


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## parrisw (Jan 11, 2010)

wigglesworth said:


> Didnt Nik do a video here recently of doing a pop up?



No, he did a cylinder.


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## blsnelling (Jan 11, 2010)

Are you ceramic coating your piston crowns now?


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## Arrowhead (Jan 11, 2010)

Please correct me if Im wrong, I honestly don't know for sure. Could'nt you weld onto the top of the piston and dress it with a lathe? Then you can leave the jug/squish the same.


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## AUSSIE1 (Jan 11, 2010)

Dropping the jug isn't a problem if you are going to increase durations.


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## Jacob J. (Jan 11, 2010)

Arrowhead said:


> Please correct me if Im wrong, I honestly don't know for sure. Could'nt you weld onto the top of the piston and dress it with a lathe? Then you can leave the jug/squish the same.



It can be done, but very carefully as to not warp the piston.


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## parrisw (Jan 11, 2010)

blsnelling said:


> Are you ceramic coating your piston crowns now?



I didn't do it. Yes they are ceramic coated. 



Arrowhead said:


> Please correct me if Im wrong, I honestly don't know for sure. Could'nt you weld onto the top of the piston and dress it with a lathe? Then you can leave the jug/squish the same.



Yes you can, but not everybody had that amount of welding skill or the welder necessary to do so.


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## AUSSIE1 (Jan 11, 2010)

Will, is that left piston a turned down 395 for a jug drop?


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## parrisw (Jan 11, 2010)

AUSSIE1 said:


> Dropping the jug isn't a problem if you are going to increase durations.



ya for sure. Usually if your machining the piston and the cylinder, there isn't that much difference in change of timing.


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## stihlboy (Jan 11, 2010)

i know a few guys who could weld me one up


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## Teddy.Scout (Jan 11, 2010)

ALRIGHT!

My brain is turning!!!
So what you want is to decrease the combustion space!
What are some of the tolerances? Is there a rule for piston size, or is it based on clearance only?


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## parrisw (Jan 11, 2010)

AUSSIE1 said:


> Will, is that left piston a turned down 395 for a jug drop?



sorta. Its a 2101 piston as well. Its a Espian brand, but not a full circle like the one on the right. It is destined for a 395/394 though, one day.


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## Arrowhead (Jan 11, 2010)

parrisw said:


> Yes you can, but not everybody had that amount of welding skill or the welder necessary to do so.



I wish I could learn how to weld aluminum properly, I'm great with steel but my aluminum looks like a beer can that was tossed into a bonfire.


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## parrisw (Jan 11, 2010)

Teddy.Scout said:


> ALRIGHT!
> 
> My brain is turning!!!
> So what you want is to decrease the combustion space!
> What are some of the tolerances? Is there a rule for piston size, or is it based on clearance only?



All your usually worried about is squish band clearance, that the clearance at the outside of the piston crown. Big saw, I wouldn't go less then .020" for a work saw, that's just me, other do different, usually with a popup the compression is already high enough, you don't need squish that tight. My 395 has squish of .023" and had 195psi before even breakin.


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## parrisw (Jan 11, 2010)

Arrowhead said:


> I wish I could learn how to weld aluminum properly, I'm great with steel but my aluminum looks like a beer can that was tossed into a bonfire.



ha ha ha. I've never even tried.


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## Hddnis (Jan 11, 2010)

Arrowhead said:


> Please correct me if Im wrong, I honestly don't know for sure. Could'nt you weld onto the top of the piston and dress it with a lathe? Then you can leave the jug/squish the same.





As others have said, it can and has been done. 

It's tricky though, I trashed a bunch of pistons when I first tried it. 

Finally I realized I know better welders than myself and they have done it for me.

I'll try again soon, I hate being beat by anything.



Mr. HE


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## parrisw (Jan 11, 2010)

Hddnis said:


> As others have said, it can and has been done.
> 
> It's tricky though, I trashed a bunch of pistons when I first tried it.
> 
> ...



You must keep your cards close. Never knew you did that kind of work. When are you going to showcase something?


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## Teddy.Scout (Jan 11, 2010)

Some one send me a piston! and measurements!

I have learned the trick for me!! With aluminum welding is like what I found with my bandsaw blades, I just try to keep the gas around the weld to keep a good burn, avoids the carbon deposits!


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## parrisw (Jan 11, 2010)

Teddy.Scout said:


> Some one send me a piston! and measurements!
> 
> I have learned the trick for me!! With aluminum welding is like what I found with my bandsaw blades, I just try to keep the gas around the weld to keep a good burn, avoids the carbon deposits!



You need a couple scrap pistons to practice on.


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## Teddy.Scout (Jan 11, 2010)

For fun, I have a 026 that is a decent runner(plastic is shot).
What could be the possibilities with the piston mod?
I have a spare jug, besides what's on it(in case I screw it up) and 4 good used pistons!


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## parrisw (Jan 11, 2010)

Teddy.Scout said:


> For fun, I have a 026 that is a decent runner(plastic is shot).
> What could be the possibilities with the piston mod?
> I have a spare jug, besides what's on it(in case I screw it up) and 4 good used pistons!



Well nothing to lose if your willing to try, measure your squish now, then maybe add enough material to make it 0 squish, then turn it down on a lathe to get the correct squish. There was a thread not too long ago about it, I'll see if I can dig it up.


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## Hddnis (Jan 11, 2010)

parrisw said:


> You must keep your cards close. Never knew you did that kind of work. When are you going to showcase something?




Maybe when I have something worth showing off. 

I tinker mostly. Used to build RC planes. That was just too expensive. If I had put all that money in the stock market back then I would not have to work today. Live and learn. lol



Mr. HE


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## parrisw (Jan 11, 2010)

Hddnis said:


> Maybe when I have something worth showing off.
> 
> I tinker mostly. Used to build RC planes. That was just too expensive. If I had put all that money in the stock market back then I would not have to work today. Live and learn. lol
> 
> ...



LOL, ya, I've done rc for years, nothing the last few years though. I got a shelf full of RC heli's right now.


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## parrisw (Jan 11, 2010)

Here is a welded pop up piston thread.

http://www.arboristsite.com/showthread.php?t=109461


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## Teddy.Scout (Jan 11, 2010)

It's on! Or at least a college try!
I will get back to you on the measurements, to make sure I am in the ballpark!
Some of the nomenclature used in this thread WAS(past tense) new to me!! LOL


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## parrisw (Jan 11, 2010)

Teddy.Scout said:


> It's on! Or at least a college try!



What welder setup do you have?


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## Teddy.Scout (Jan 11, 2010)

Tig. but will try to really get a strong bond by using, or trying to keep a good argon shield around it!?!?!?!
But can take it to my gear head buddies shop, he does alot! of fabs.
I will use his lathe as well.


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## parrisw (Jan 11, 2010)

Teddy.Scout said:


> Tig. but will try to really get a strong bond by using, or trying to keep a good argon shield around it!?!?!?!
> But can take it to my gear head buddies shop, he does alot! of fabs.
> I will use his lathe as well.



Ya, the gas is key for a good weld, you using pure argon? No mix.


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## Teddy.Scout (Jan 11, 2010)

I used argon for the blades
I will try it on the aluminum! But don't want to scorch it!(Been there with my trailer!)
Third time is a charm! glad I have 4 pistons!!! LOL


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## parrisw (Jan 11, 2010)

Teddy.Scout said:


> I used argon for the blades
> I will try it on the aluminum! But don't want to scorch it!(Been there with my trailer!)
> Third time is a charm! glad I have 4 pistons!!! LOL



Search around for some messed up pistons. I have a few but shipping isn't really worth it.


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## Teddy.Scout (Jan 11, 2010)

This welding gig is a forced upon issue with me!
There are so many ways, and techniques!
But I have been lucky to have some neighbors who will give me the time to TRY to teach me the different methods for different applications!!
And I always get that look on there face when I ask how to weld this???


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## parrisw (Jan 11, 2010)

Teddy.Scout said:


> This welding gig is a forced upon issue with me!
> There are so many ways, and techniques!
> But I have been lucky to have some neighbors who will give me the time to TRY to teach me the different methods for different applications!!
> And I always get that look on there face when I ask how to weld this???



ha ha. I wish I had a Tig to play around with.


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## Teddy.Scout (Jan 11, 2010)

We got lucky! C-list!
Divorced mad lady!
Nuff said!


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## injun joe (Jan 11, 2010)

Teddy.Scout said:


> Tig. but will try to really get a strong bond by using, or trying to keep a good argon shield around it!?!?!?!
> But can take it to my gear head buddies shop, he does alot! of fabs.
> I will use his lathe as well.



you could get a bigger cup for better gas coverage. all i kno is welding ANY nonferrous meteal the base metal has to be clean so with a piston you could use acetone. you probly know all that welding mumbo jumbo already though. just thought i would reiterate it.


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## Teddy.Scout (Jan 11, 2010)

injun joe said:


> you could get a bigger cup for better gas coverage. all i kno is welding ANY nonferrous meteal the base metal has to be clean so with a piston you could use acetone. you probly know all that welding mumbo jumbo already though. just thought i would reiterate it.




Never assume I know! any help I can get, or constructive criticism I appreciate it! Assuming I know(which in this case I DIDN'T) leaves room for error I my part! And if there is room for error I will find it!!!!!!!

The acetone makes sense! I was told buy a body repair men that it really cleans the super tiny stuff up, and it is a good start in any prepping!!! I can see with a dirty piston, that is just going to be a popping mess!!! Good call!


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## timberwolf (Jan 11, 2010)

Argon is the ticket, argon helium blends are hotter and more prone to melting through.

I find a gas lens helps give good coverage. Many say gas lens is not for AC welding, but works for me on pistons.

Filler is importaint too, 5356 for example is a bad choice as the intersection between the filler and high silicon base metal with degrade at elevated temperatures.

Rather than try to clean the piston crown for welding I just put it on the lathe and cut .001 giving perfectly clean base metal to work from. Actone alone does not remove the aluminium oxide and though it desolves grease it also spreads it around. Balancing the AC for more cleaning helps prevent melting through the center of the crown. Start in the center and work outward, add a ring of filler then let the piston drop back to ~500f then add another ring. last pass angle the torch towards the center to prevent overheating the edge of the crown and upper ring land.


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## little possum (Jan 11, 2010)

So is a pop-up a little easier mod? For a beginner anyways? Because when you mill down the jug, you have to mess with the timing right? But with just a pop up, nothing changes but compression
 I hope one day, all this just clicks, and makes since.


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## blsnelling (Jan 11, 2010)

Welding a popup on the piston crown would not affect any port timings at all. Turning a popup into the existing piston crown requires machining the base of the cylinder to bring if down over the popup, thus keeping the squish measurement the same. When both the P&C are brought down the same, the only port timing that changes is the intake. Exhaust and transfer timing stays the same. However, it's not enough of a change to really matter. For your purposes, you can disregaurd port timing if all you're doing is turning a .020"-.040" popup into the piston crown, and then bringing the cylinder down over it as required to set the squish you want. There are other things to consider, but that's the just of it.


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## little possum (Jan 11, 2010)

Thanks Brad


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## blsnelling (Jan 11, 2010)

IMHO, it's more desirable to turn the popup into the existing crown, in order to keep down the reciprocating mass. However, that's not always possible due to limitations in design. For example, there's not always enough crown thickness above the top ring groove. Avoid lowering the cylinder such that the piston skirt free ports at the bottom of the exhaust port when at TDC. You also want to make sure the NiSi or chrome plating goes high enough into the cylinder bore.


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## rupedoggy (Jan 11, 2010)

Brad did I read your meaning correctly that "timing on exhaust and transfers stays the same when you turn down the base"? I do not agree with this. Timber Wolf could you chime in? Mike


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## blsnelling (Jan 11, 2010)

rupedoggy said:


> Brad did I read your meaning correctly that "timing on exhaust and transfers stays the same when you turn down the base"? I do not agree with this. Timber Wolf could you chime in? Mike



When you bring the cylinder down the same amount as the height of the popup turned into the crown, exhaust and transfer port timing will not change. The both came down the same amount.


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## rupedoggy (Jan 11, 2010)

OK makes sense to me now. If you turn down the base .020 and the piston top .020, and leave in the original gasket, then original timing is maintained. I also agree that a lighter piston is better for the performance application. Welding on additional mass has several pitfalls. Removeable head, now that gives great possibilities. Mike


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## parrisw (Jan 11, 2010)

blsnelling said:


> When you bring the cylinder down the same amount as the height of the popup turned into the crown, exhaust and transfer port timing will not change. The both came down the same amount.



Yes, I agree with Brad, but usually you're not doing it the same, ex.. you'll want to machine the cylinder more usually to bring the squish tighter, even then there isn't much of a change in timing.


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## Teddy.Scout (Jan 11, 2010)

WOW!
Pop up piston 101 just jumped into POP-UP PISTON 1100.
AWESOME! This will make a great reference thread!
I will admit, it is a little tough to keep up on! But I will get there!
As for the 026 piston, there is a little room to work, you guys got me worried with the skirt room.


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## Rennsman (Mar 15, 2017)

Apart from the slightly different effects on port timing, when do you choose to make a pop up piston over machining the squish band of the cylinder? 
To get your target squish and compression numbers.


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