piston fit

[Jim Allen]

My thinking is the brass keeps the chamber temp more stable.

Can you explain exactly how "keeping the chamber temperature more stable" would have any effect on detonation, especially since the poor thermal conductivity of the brass would put more heat into the piston crown????

 

[Jeff Lutz]

My thinking is the brass keeps the chamber temp more stable.

As Jim stated, brass does not conduct heat like aluminum. Coefficient of thermal conduction (btu/hr-ft-*F) of aluminum is 104, when brass is 67. Nearly 1/2 like Jim said. But, aluminum dissipates heat quicker which makes up for some. All in all, brass -might- help achieve less temperature 'around the combustion chamber'. Hey Marty, How about a bimetal head, brass on the squish band , bowl still aluminum, send me a sample head and $300 and I'll make you one. Seriously though, I'm surprised of Marty having expansion problems, 2024 aluminum is 12.9, and yellow brass is 11.3. I still say mod your engine and stay with aluminum.

 

[Tom Foley]

Now I can buy that the brass does not show the peppering. The melting temp of brass is twice that of aluminum plus it is generally harder, so it will not show the evidence of detonation so easily. That does not mean the detontion is not there.

Andy, I always wondered about this myself. How JUST changing the material of the button, and making no other changes would magically rid the detonation that was taking place. I was always a bit skeptical about it. I think its still detonating, just not showing on the brass, there for not eating up the head like the aluminum ones do.

A lot like built up stresses in the products we build that eventualy lead to failure under abusive conditions from flexing then work hardening, even though very little visible flexing is occuring ,

Seems like some of the very best engines I have ever had are detonating slightly but not getting past the ability of the components cooling capacity to prevent burndown .

If it is detonating the shock impacts will be transferred somewhere , maybe the rod , crank, bearings , wristpin or piston . I kind of think of the aluminum head button as a replaceable sacrificial part .When it degrades from detonation in a really good running engine , replace it . I realize i'm not doing some of the extreme engine building some of you guys are , but right now we have some really strong engines out there that with a little tweaking are really amazing . Lots of great info here on this thread , Thanks !

 

[Jim Allen]

My thinking is the brass keeps the chamber temp more stable.

As Jim stated, brass does not conduct heat like aluminum. Coefficient of thermal conduction (btu/hr-ft-*F) of aluminum is 104, when brass is 67. Nearly 1/2 like Jim said. But, aluminum dissipates heat quicker which makes up for some. All in all, brass -might- help achieve less temperature 'around the combustion chamber'. Hey Marty, How about a bimetal head, brass on the squish band , bowl still aluminum, send me a sample head and $300 and I'll make you one. Seriously though, I'm surprised of Marty having expansion problems, 2024 aluminum is 12.9, and yellow brass is 11.3. I still say mod your engine and stay with aluminum.

Maybe that is because the yellow brass (#360) with the chrome plating actually expands at a slightly higher rate than the silicon aluminum piston & not at the 11.3 number. I would think if you put that #360 brass head (11.3) into that #360 brass cylinder that is chrome plated (8.3), the problem that Marty encountered will surely happen. Maybe that's why he stated he had to make the head button .001" smaller.

 

[Jeff Lutz]

My thinking is the brass keeps the chamber temp more stable.

As Jim stated, brass does not conduct heat like aluminum. Coefficient of thermal conduction (btu/hr-ft-*F) of aluminum is 104, when brass is 67. Nearly 1/2 like Jim said. But, aluminum dissipates heat quicker which makes up for some. All in all, brass -might- help achieve less temperature 'around the combustion chamber'. Hey Marty, How about a bimetal head, brass on the squish band , bowl still aluminum, send me a sample head and $300 and I'll make you one. Seriously though, I'm surprised of Marty having expansion problems, 2024 aluminum is 12.9, and yellow brass is 11.3. I still say mod your engine and stay with aluminum.

Maybe that is because the yellow brass (#360) with the chrome plating actually expands at a slightly higher rate than the silicon aluminum piston & not at the 11.3 number. I would think if you put that #360 brass head (11.3) into that #360 brass cylinder that is chrome plated (8.3), the problem that Marty encountered will surely happen. Maybe that's why he stated he had to make the head button .001" smaller.

For sure, the chrome on the liner makes it expand completely different. The first time I spoke to someone about this topic, they actually said , "With the brass head, it will expand better with the liner", I said "not with that chrome in the liner". But, 2024 aluminum with 12.9 does work. You even mentioned earlier you thought it would work, I would have like to have seen Marty operating his transmitter to see how he is operating that 3rd channel!! (Just kidding Marty).

 

[Jim Allen]

My thinking is the brass keeps the chamber temp more stable.

As Jim stated, brass does not conduct heat like aluminum. Coefficient of thermal conduction (btu/hr-ft-*F) of aluminum is 104, when brass is 67. Nearly 1/2 like Jim said. But, aluminum dissipates heat quicker which makes up for some. All in all, brass -might- help achieve less temperature 'around the combustion chamber'. Hey Marty, How about a bimetal head, brass on the squish band , bowl still aluminum, send me a sample head and $300 and I'll make you one. Seriously though, I'm surprised of Marty having expansion problems, 2024 aluminum is 12.9, and yellow brass is 11.3. I still say mod your engine and stay with aluminum.

Maybe that is because the yellow brass (#360) with the chrome plating actually expands at a slightly higher rate than the silicon aluminum piston & not at the 11.3 number. I would think if you put that #360 brass head (11.3) into that #360 brass cylinder that is chrome plated (8.3), the problem that Marty encountered will surely happen. Maybe that's why he stated he had to make the head button .001" smaller.

For sure, the chrome on the liner makes it expand completely different. The first time I spoke to someone about this topic, they actually said , "With the brass head, it will expand better with the liner", I said "not with that chrome in the liner". But, 2024 aluminum with 12.9 does work. You even mentioned earlier you thought it would work, I would have like to have seen Marty operating his transmitter to see how he is operating that 3rd channel!! (Just kidding Marty).

The reason that almost any aluminum will work is because the aluminum button with its water cooling can dissippate the heat much faster than either a brass liner that is chrome plated or an aluminum liner that is chrome plated. Actually, 2017-T4 not 2024-T4 is preferred in high performance two cycle engines because of its higher thermal conductivity. This would be true for cast & fully machined heads.

Jim Allen

 

[Jack ODonnell]

My thinking is the brass keeps the chamber temp more stable.

As Jim stated, brass does not conduct heat like aluminum. Coefficient of thermal conduction (btu/hr-ft-*F) of aluminum is 104, when brass is 67. Nearly 1/2 like Jim said. But, aluminum dissipates heat quicker which makes up for some. All in all, brass -might- help achieve less temperature 'around the combustion chamber'. Hey Marty, How about a bimetal head, brass on the squish band , bowl still aluminum, send me a sample head and $300 and I'll make you one. Seriously though, I'm surprised of Marty having expansion problems, 2024 aluminum is 12.9, and yellow brass is 11.3. I still say mod your engine and stay with aluminum.

Maybe that is because the yellow brass (#360) with the chrome plating actually expands at a slightly higher rate than the silicon aluminum piston & not at the 11.3 number. I would think if you put that #360 brass head (11.3) into that #360 brass cylinder that is chrome plated (8.3), the problem that Marty encountered will surely happen. Maybe that's why he stated he had to make the head button .001" smaller.

For sure, the chrome on the liner makes it expand completely different. The first time I spoke to someone about this topic, they actually said , "With the brass head, it will expand better with the liner", I said "not with that chrome in the liner". But, 2024 aluminum with 12.9 does work. You even mentioned earlier you thought it would work, I would have like to have seen Marty operating his transmitter to see how he is operating that 3rd channel!! (Just kidding Marty).

Were would one find the expansion rate of brass with chrome plating on it

 

[Jeff Lutz]

My thinking is the brass keeps the chamber temp more stable.

As Jim stated, brass does not conduct heat like aluminum. Coefficient of thermal conduction (btu/hr-ft-*F) of aluminum is 104, when brass is 67. Nearly 1/2 like Jim said. But, aluminum dissipates heat quicker which makes up for some. All in all, brass -might- help achieve less temperature 'around the combustion chamber'. Hey Marty, How about a bimetal head, brass on the squish band , bowl still aluminum, send me a sample head and $300 and I'll make you one. Seriously though, I'm surprised of Marty having expansion problems, 2024 aluminum is 12.9, and yellow brass is 11.3. I still say mod your engine and stay with aluminum.

Maybe that is because the yellow brass (#360) with the chrome plating actually expands at a slightly higher rate than the silicon aluminum piston & not at the 11.3 number. I would think if you put that #360 brass head (11.3) into that #360 brass cylinder that is chrome plated (8.3), the problem that Marty encountered will surely happen. Maybe that's why he stated he had to make the head button .001" smaller.

For sure, the chrome on the liner makes it expand completely different. The first time I spoke to someone about this topic, they actually said , "With the brass head, it will expand better with the liner", I said "not with that chrome in the liner". But, 2024 aluminum with 12.9 does work. You even mentioned earlier you thought it would work, I would have like to have seen Marty operating his transmitter to see how he is operating that 3rd channel!! (Just kidding Marty).

The reason that almost any aluminum will work is because the aluminum button with its water cooling can dissippate the heat much faster than either a brass liner that is chrome plated or an aluminum liner that is chrome plated. Actually, 2017-T4 not 2024-T4 is preferred in high performance two cycle engines because of its higher thermal conductivity. This would be true for cast & fully machined heads.

Jim Allen

For sure, I feel aluminum is the best choice in confused temperature condition. I mentioned a couple of posts back that aluminum dissipates better. The brass is also water cooled, and does not conduct heat as much. Brass and aluminum expansion is close.

 

[Jim Allen]

Jack,

There are no specifications for expansion rates on plated alloys such as those used in our engines. Even the thickness of the plate will change the expansion amount. I am sure that aluminum & brass liners that are plated with .003" of chrome/wall, will expand in a larger amount than their silicon aluminum pistons. If this was not the case, the engine would seize as it continued to heat up. In our engines, just the opposite happens, doesn't it?

Jim

 

[Jeff Lutz]

Jack,

There are no specifications for expansion rates on plated alloys such as those used in our engines. Even the thickness of the plate will change the expansion amount. I am sure that aluminum & brass liners that are plated with .003" of chrome/wall, will expand in a larger amount than their silicon aluminum pistons. If this was not the case, the engine would seize as it continued to heat up. In our engines, just the opposite happens, doesn't it?

Jim

Jim, I'm sure Jack was wondering how you come up with an expansion of 8.3 on a 360 liner chrome plated just a couple of posts back? And, how thick was the chrome?

 

[Jim Allen]

Jack,

There are no specifications for expansion rates on plated alloys such as those used in our engines. Even the thickness of the plate will change the expansion amount. I am sure that aluminum & brass liners that are plated with .003" of chrome/wall, will expand in a larger amount than their silicon aluminum pistons. If this was not the case, the engine would seize as it continued to heat up. In our engines, just the opposite happens, doesn't it?

Jim

Jim, I'm sure Jack was wondering how you come up with an expansion of 8.3 on a 360 liner chrome plated just a couple of posts back? And, how thick was the chrome?

The number comes from the RSA-444 T6 alloy that is use for pistons. The information is listed in the RSP Technology Catalogue under RSP Piston Alloys. I have already explained that the brass or aluminum chrome plated liner must expand at a slightly greater rate as the engine heats up, otherwise the piston would sieze in the bore. The plating thickness on my liners is .003"/ side, before grinding.

 

[Jim Allen]

As additional information, the following metals are listed in order according to their thermal conductivity amounts. It can be easily seen that brass & steel would not be the most desireable metals to use for a head. All numbers are BTU/in/hr/ft squared/deg F. All the numbers can be found on any available metal's specification sheet from Google.

1018 cold rolled steel - 360 BTU....

#360 brass - 804 BTU....

2024 aluminum - 840 BTU....

2017 aluminum - 930 BTU....

It doesn't take a rocket scientist to figure this out.

 

[Jeff Lutz]

Jack,

There are no specifications for expansion rates on plated alloys such as those used in our engines. Even the thickness of the plate will change the expansion amount. I am sure that aluminum & brass liners that are plated with .003" of chrome/wall, will expand in a larger amount than their silicon aluminum pistons. If this was not the case, the engine would seize as it continued to heat up. In our engines, just the opposite happens, doesn't it?

Jim

Jim, I'm sure Jack was wondering how you come up with an expansion of 8.3 on a 360 liner chrome plated just a couple of posts back? And, how thick was the chrome?

The number comes from the RSA-444 T6 alloy that is use for pistons. The information is listed in the RSP Technology Catalogue under RSP Piston Alloys. I have already explained that the brass or aluminum chrome plated liner must expand at a slightly greater rate as the engine heats up, otherwise the piston would sieze in the bore. The plating thickness on my liners is .003"/ side.

I did not see anyone ask why a piston does not seize in a liner, but you are so right! Earlier you said a 360 liner chrome plated had an expansion of 8.3. Now you are saying that expansion number of 8.3 is for the above piston alloy.

 

[Jim Allen]

Jack,

There are no specifications for expansion rates on plated alloys such as those used in our engines. Even the thickness of the plate will change the expansion amount. I am sure that aluminum & brass liners that are plated with .003" of chrome/wall, will expand in a larger amount than their silicon aluminum pistons. If this was not the case, the engine would seize as it continued to heat up. In our engines, just the opposite happens, doesn't it?

Jim

Jim, I'm sure Jack was wondering how you come up with an expansion of 8.3 on a 360 liner chrome plated just a couple of posts back? And, how thick was the chrome?

The number comes from the RSA-444 T6 alloy that is use for pistons. The information is listed in the RSP Technology Catalogue under RSP Piston Alloys. I have already explained that the brass or aluminum chrome plated liner must expand at a slightly greater rate as the engine heats up, otherwise the piston would sieze in the bore. The plating thickness on my liners is .003"/ side.

I did not see anyone ask why a piston does not seize in a liner, but you are so right! Earlier you said a 360 liner chrome plated had an expansion of 8.3. Now you are saying that expansion number of 8.3 is for the above piston alloy.

Even you should be able to understand if they have the same expansion rates the engine would never sieze. I have already said that the expansion rate of the liner with the chrome plate would expand a little faster. I guess the next thing that you will tell me is, you have engines that are seizing. LOL

 

[Ian Inverarity]

How do the temperatures of the piston, head button and liner compare? Surely they are not all the same temp? Thus the actual expansion would be a product of the material expansion rate and actual temp?

 

[Tim_Duggan]

Plus is the temperature uniform throughout each individual part - head button temp at squish vs at the bowl, piston crown vs piston skirt, sleeve top vs sleeve at top of exhaust port vs sleeve vs where the piston crown is at TCD, then there is sleeve at Exhaust side vs Boost port side...........

I think that this debate is getting a little clouded by things that aren't as clear cut as they are being made out to be.

 

[Jeff Lutz]

Jack,

There are no specifications for expansion rates on plated alloys such as those used in our engines. Even the thickness of the plate will change the expansion amount. I am sure that aluminum & brass liners that are plated with .003" of chrome/wall, will expand in a larger amount than their silicon aluminum pistons. If this was not the case, the engine would seize as it continued to heat up. In our engines, just the opposite happens, doesn't it?

Jim

Jim, I'm sure Jack was wondering how you come up with an expansion of 8.3 on a 360 liner chrome plated just a couple of posts back? And, how thick was the chrome?

The number comes from the RSA-444 T6 alloy that is use for pistons. The information is listed in the RSP Technology Catalogue under RSP Piston Alloys. I have already explained that the brass or aluminum chrome plated liner must expand at a slightly greater rate as the engine heats up, otherwise the piston would sieze in the bore. The plating thickness on my liners is .003"/ side.

I did not see anyone ask why a piston does not seize in a liner, but you are so right! Earlier you said a 360 liner chrome plated had an expansion of 8.3. Now you are saying that expansion number of 8.3 is for the above piston alloy.

Even you should be able to understand if they have the same expansion rates the engine would never sieze. I have already said that the expansion rate of the liner with the chrome plate would expand a little faster. I guess the next thing that you will tell me is, you have engines that are seizing. LOL

8.3 on the plated brass was very specific. I was curious how you felt so confident in this number for the bimetal. I'm glad you let us know it is your best guess. And yes, I have stuck a piston! Make a straight piston, and it will remind you how easy it is!

 

[Andy Brown]

Plus is the temperature uniform throughout each individual part - head button temp at squish vs at the bowl, piston crown vs piston skirt, sleeve top vs sleeve at top of exhaust port vs sleeve vs where the piston crown is at TCD, then there is sleeve at Exhaust side vs Boost port side...........

I think that this debate is getting a little clouded by things that aren't as clear cut as they are being made out to be.

Tim asks a valid and important question. And the answer is...No, the temp is not uniform, especially in a boat engine.

Take an engine with an ice cold crackcase, then explode a very lean mixture of fuel on a very large bore piston....and you'll soon find the liniar expansion of the piston crown far exceeds the reactionary expansion of the case & liner. You will know this reaction occured the moment the piston seizes with the liner.

 

[Jim Allen]

Jack,

There are no specifications for expansion rates on plated alloys such as those used in our engines. Even the thickness of the plate will change the expansion amount. I am sure that aluminum & brass liners that are plated with .003" of chrome/wall, will expand in a larger amount than their silicon aluminum pistons. If this was not the case, the engine would seize as it continued to heat up. In our engines, just the opposite happens, doesn't it?

Jim

Jim, I'm sure Jack was wondering how you come up with an expansion of 8.3 on a 360 liner chrome plated just a couple of posts back? And, how thick was the chrome?

The number comes from the RSA-444 T6 alloy that is use for pistons. The information is listed in the RSP Technology Catalogue under RSP Piston Alloys. I have already explained that the brass or aluminum chrome plated liner must expand at a slightly greater rate as the engine heats up, otherwise the piston would sieze in the bore. The plating thickness on my liners is .003"/ side.

I did not see anyone ask why a piston does not seize in a liner, but you are so right! Earlier you said a 360 liner chrome plated had an expansion of 8.3. Now you are saying that expansion number of 8.3 is for the above piston alloy.

Even you should be able to understand if they have the same expansion rates the engine would never sieze. I have already said that the expansion rate of the liner with the chrome plate would expand a little faster. I guess the next thing that you will tell me is, you have engines that are seizing. LOL

8.3 on the plated brass was very specific. I was curious how you felt so confident in this number for the bimetal. I'm glad you let us know it is your best guess. And yes, I have stuck a piston! Make a straight piston, and it will remind you how easy it is!

I don't make straight sided pistons, not even for a gas engine. A straight sided piston will be hard to sieze if the liner has enough taper.

 

[Andy Brown]

As additional information, the following metals are listed in order according to their thermal conductivity amounts. It can be easily seen that brass & steel would not be the most desireable metals to use for a head. All numbers are BTU/in/hr/ft squared/deg F. All the numbers can be found on any available metal's specification sheet from Google.

1018 cold rolled steel - 360 BTU....

#360 brass - 804 BTU....

2024 aluminum - 840 BTU....

2017 aluminum - 930 BTU....

It doesn't take a rocket scientist to figure this out.

"Andy, I guess where the peppering can be seen should be expected since the brass has a thermal conductivity 1/2 of aluminum."

Jim, The truth of your statement above is not reflected in your list of Thermal conductivity.

I will say that when comparing brass to aluminum it is far from correct to make statements like, "Brass and aluminum expansion is close." ~ Jeff L. or "brass has a thermal conductivity 1/2 of aluminum." ~ Jim A.

Aluminum alloys will expand as much a 50% more or 50% less than many brass alloys. While the Thermal conductivity of many Aluminum alloys are within + or - 20% of each other, Copper alloys (brass) swing very widely, Some are in fact 1/2 of aluminum, but other copper alloys are more than double that of aluminum.

Therefore I think it would be proper to specfy the particular alloy one is refering to when making these claims.