High Quality Chainsaw Bars Husqvarna Toys

Combustion chamber in the wrong spot??

Red97

Mastermind Approved!
GoldMember
Local time
8:03 AM
User ID
385
Joined
Jan 2, 2016
Messages
7,451
Reaction score
53,837
Location
MI
Country flag
So, back at these silly echo projects.
After boring welding boring welding grinding welding boring and finally sleeving a cylinder.
Just to bore it and hone it to size.

I end up with this...
20220908_153212.jpg

Now it is hard to tell, but the flat band is about .300" wide then a 5* taper into what is left of the combustion chamber.

So I did this. Made this pop up, head the other direction.
20220908_080449.jpg

Figured I need less comp and more volume.

Thoughts? Comments? Concerns?

Thanks.
 

Eagle1899

Well-Known OPE Member
Local time
8:03 AM
User ID
4484
Joined
Oct 31, 2017
Messages
53
Reaction score
206
Location
Central Minnesota
Country flag
Like a diesel piston. If I'm thinking correctly, it should respond well to a timing advance. Combustion taking place in a smaller area.
 

Red97

Mastermind Approved!
GoldMember
Local time
8:03 AM
User ID
385
Joined
Jan 2, 2016
Messages
7,451
Reaction score
53,837
Location
MI
Country flag
Good idea. Also more surface area for the expanding gases to press upon.

I knew the pop up was a no go right off, but curious to see the wash pattern? Can see the gasses staying in the dish, but not sure if that is a good or bad thing..

Sachs Dolmar did this years ago with a few models where the piston had a dish.
They claimed it put more pressure on the piston on the combustion stroke and
making more power.

Interesting, I was just hoping to get the compression down to a manageable number on this build. Back when it was still 54mm with a flat top, it had mega compression. May need an extra degree or 2 off the exhaust roof.

Smaller area is not the right word. Lower combustion chamber would be more accurate. Smaller dome with a dished piston effectively moves the chamber lower.

Curious as to how it will affect heat any, having most all of the "chamber" closer to the exhaust roof. Seems if the psi is manageable, it could almost run cooler. Doubt it is enough to notice though.
 

Mastermind

Chief Cat Herder
Staff member
GoldMember
Local time
7:03 AM
User ID
4
Joined
Dec 3, 2015
Messages
47,013
Reaction score
304,250
Location
Banner Springs Tennessee
Country flag
I knew the pop up was a no go right off, but curious to see the wash pattern? Can see the gasses staying in the dish, but not sure if that is a good or bad thing..

I don't pay much attention to wash patterns. The bottom line....how does it run?

We'll see.
 

Nutball

Here For The Long Haul!
Local time
7:03 AM
User ID
7732
Joined
Oct 31, 2018
Messages
4,038
Reaction score
11,007
Location
Mt. Juliet, TN
Country flag
Would the increase in piston surface area put too much heat into it?
 

Bigmac

Mastermind Approved!
Local time
5:03 AM
User ID
5937
Joined
Apr 19, 2018
Messages
5,407
Reaction score
37,255
Location
Oregon
Country flag
I don’t have the calculator for it, but a maximum squish velocity would be interesting on that. A increase in squish could still yield more the correct velocity, at the correct compression. A dish will help compression, ideally I would like to see it match the squish band, otherwise it possible for detonation to occur.
 

drf256

Dr. Richard Cranium
GoldMember
Local time
8:03 AM
User ID
319
Joined
Dec 29, 2015
Messages
9,280
Reaction score
61,095
Location
Strong Island NY
Country flag
Always wanted to do a dish, especially in 1122 Stihl and other models where dropping the jug to the wanted ex roof caused too much compression.

I was told the negative was that loop scavenging would not being able to clear the piston off. I can’t see that being true because the piston is in constant movement. The increased surface area will add heat to the slug, but no more than a pop up would.

I don’t buy the whole more surface area to push on. Pressure is pressure. No more force is added or obtained from a different in surface area.

Does the squish area on the piston match the squishband?
 

Nutball

Here For The Long Haul!
Local time
7:03 AM
User ID
7732
Joined
Oct 31, 2018
Messages
4,038
Reaction score
11,007
Location
Mt. Juliet, TN
Country flag
Always wanted to do a dish, especially in 1122 Stihl and other models where dropping the jug to the wanted ex roof caused too much compression.

I was told the negative was that loop scavenging would not being able to clear the piston off. I can’t see that being true because the piston is in constant movement. The increased surface area will add heat to the slug, but no more than a pop up would.

I don’t buy the whole more surface area to push on. Pressure is pressure. No more force is added or obtained from a different in surface area.

Does the squish area on the piston match the squishband?
Pressure is pressure, it's the straight down force vector we care about. But could the side vector of the gas on a sloped surface of the piston have a ramp effect at least helping increase the piston speed possible from the same rate of gas expansion if not also add to the downward force?
 

Loony661

Stock chainsaws suck.
GoldMember
Local time
7:03 AM
User ID
2584
Joined
Feb 4, 2017
Messages
3,951
Reaction score
23,780
Location
Winona County, MN
Country flag
I would just break the edge in the combustion chamber - sharp edges create a detonation point because they get/stay hotter, acting as an ignition source.
 

Red97

Mastermind Approved!
GoldMember
Local time
8:03 AM
User ID
385
Joined
Jan 2, 2016
Messages
7,451
Reaction score
53,837
Location
MI
Country flag
Always wanted to do a dish, especially in 1122 Stihl and other models where dropping the jug to the wanted ex roof caused too much compression.

I was told the negative was that loop scavenging would not being able to clear the piston off. I can’t see that being true because the piston is in constant movement. The increased surface area will add heat to the slug, but no more than a pop up would.

I don’t buy the whole more surface area to push on. Pressure is pressure. No more force is added or obtained from a different in surface area.

Does the squish area on the piston match the squishband?

The flat part of the squishband is just a bit smaller than the flat of thr piston crown. Ended up thst way so I could blend the taper in.
 
Top