I know there has been almost rampant discussion about using cast iron cylinder liners vs. the Nikasil coating process in the Big Bore kits. [/emoticons/emotion-1.gif]
In my research, I've read a fair amount on the two processes as well as a number of forums and engine builder web sites. I found the following article to be very good in comparing the two processes and thought it might be instructive for those of you trying to decide among the various performance alternatives, Big Bore kits being among them.
I have edited some parts of the article to make it more concise and eliviate some text that does not add to our education needs at RSWarrior.com
I hope this information proves helpful to the membership and does NOT become a thread for personal attacks or arguments. [8D]
Thanks,
Gary
Source: Ward's Auto World, Apr 1, 1999 http://waw.wardsauto.com/ar/auto_boring_trutheverybodys_ideas/
"Wow. Little did we know what a fire-storm we'd start with a seemingly innocuous mention of aluminum engine cylinder-bore treatment alternatives in last September's materials issue (see WAW - Sept. '98, p.61).
There were plenty of letters and calls to point out we'd muffed our facts regarding the Nikasil treatment process.
…
All over cylinder-bore treatments, for gosh sakes.
…
… [A]luminum is an inherently "soft" metal, and cylinder bores of an engine block crafted purely from aluminum wouldn't long withstand the constant, grinding friction of pistons and piston rings scraping their way up and down the bore surface. Most aluminum engine blocks actually are fashioned from an aluminum-intensive alloy that contains other metals, primarily silicon. That helps, but that alone isn't nearly durable enough.
"It's pretty simple," says one OEM powertrain engineer. "You don't want aluminum-to-aluminum contact. You've got to have a bore with a high wear surface, and aluminum has poor wear characteristics."
Thus, the primary reason cylinder bores can't be aluminum. Once it's agreed the bore must be protected, the question is: "How?" Other factors such as cost, manufacturing consequences and performance requirements then must be squeezed into the equation. That's where the cylinder bore-treatment "factions" start to dig in their heels.
The Methods
Broadly, there are two ways to protect aluminum-engine cylinder bores: Either install iron liners or find a way to make the bore surfaces more wear-resistant, usually with some type of coating or treatment of the aluminum. Some approaches use rather exotic and elaborate processes to accomplish this feat.
Iron Liners: The utility infielder
Installing cast iron liners - or "sleeves" - equates to what might be called the industry "default" to answer the cylinder bore-treatment matter. Iron liners have numerous advantages:
- They are probably the most inexpensive method.
- They are delightfully durable.
- They are easily and inexpensively integrated into the manufacturing process.
Cheap and durable - the two words the industry holds most dear, right?
Well, there are problems with iron sleeves.
Sticking iron into your fancy new aluminum engine obviously negates some of what you're trying to do in the first place. Iron is heavy - that's why you switched to aluminum!
Perhaps more importantly, iron liners take up space. A common iron liner is roughly 3 mm thick. Multiply that by the number of cylinders you're dealing with and the engine starts to grow; there has to be a certain amount of block "webbing" between each cylinder to ensure structure, so the room that liners require can't always simply be chopped out of the space between each cylinder.
To now, that hasn't been a big deal in the U.S. One foreign castings supplier, who asks anonymity because he's wooing domestic business, explains: "In the U.S. you have the 'luxury' of displacement. Engines are large, so there is no particular need to use modern (bore treatment) methods. The car companies here always think first of cost and high volumes."
This source's emphasis on the word "modern" is inescapably scathing.
W. Gregory Wuest, vice-president-research and development at Sulzer-Metco, a New York company espousing cylinder-bore spray coating technology, agrees, noting that engines in Europe and Japan must be inherently smaller and more energy dense because fuel prices are so high. "In Japanese engines, for example, there's no room for a liner. They're driven (to other methods) by that factor."
Mr. Wuest notes that spray coatings usually can be applied in thicknesses of no more than 100 microns - one-thirtieth the space each 3 mm iron liner demands.
Iron liners typically are cast into the block as it's being formed. General Motors Corp. employs this method with its Premium V-6- and 8-cyl. OHC engines. Saturn simply presses in the liners. Ford Motor Co., for its Intech all-aluminum V-8s, heats the block and presses in the liners; when the block cools, it "shrinks" around the iron sleeves.
Iron and aluminum exhibit different thermal properties, though, which can be troublesome. And aluminum blocks and iron liners don't completely "bond," regardless of the joining method. That leaves gaps between the liner and the cylinder wall. The bonding and added-weight issues can be improved by using aluminum sleeves instead of cast iron - DaimlerChrysler AG likes aluminum sleeves for Chrysler's 4-cyl. and new V-6 engines - but aluminum liners are tough to cast directly into the block.
If liners are cast into the block - as in the GM method - scrappage becomes an issue. If the entire engine is built, only then to be discovered to be defective, the iron liners must be ripped out and are useless.
"We have some relatively high scrap costs," admits one powertrain engineer.
The Coatings: You pays your money, you takes your chances
This story was born when we first conveyed BMW AG's woes with Nikasil. So let's examine the competing cylinder-coating processes.
- Nikasil: An aluminum engine is dunked in an electrolytic "bath" of free-floating nickel, silicon and other junk. The electrolytic action causes these hardy substances to adhere to the aluminum surfaces.
"It does work very well in a lot of applications," admits one engineer philosophically behind iron liners. But Nikasil's main drawbacks are serious.
First, says Achim Sach, of VAW Motor GmbH, a part of the VAW Group aligned with Mexican casting giant Cifunsa SA, "Nobody wants to have nickel in the plants anymore." Also, as noted in September, high-sulfur fuels eat away at the coating, eventually rendering it useless. Result: ruined engine. And Nikasil has "throughput" issues: The block has to be labor-intensively "masked" before it takes a Nikasil bath, so that the particles cling only to the bore surfaces. And the block has to soak for more than an hour, claim some skeptical sources. Nikasil appears to be on the skids for these reasons. BMW has abandoned the process. Jaguar Cars and Ferrari SpA still like it, though.
There's plenty of industry dissension about the true cost [of various coatings, including {Alusil, Lokasil,- excerpted} and Nikasil], but Mr. Wuest is frank with his figures: He reckons iron liners cost about $1.50 to $2 per bore; plasma coating probably ranges from $3 to $5 per bore.
Meanwhile, Nikasil runs from $5 to $10 per bore, the cost largely dependent on volume.
In my research, I've read a fair amount on the two processes as well as a number of forums and engine builder web sites. I found the following article to be very good in comparing the two processes and thought it might be instructive for those of you trying to decide among the various performance alternatives, Big Bore kits being among them.
I have edited some parts of the article to make it more concise and eliviate some text that does not add to our education needs at RSWarrior.com
I hope this information proves helpful to the membership and does NOT become a thread for personal attacks or arguments. [8D]
Thanks,
Gary
Source: Ward's Auto World, Apr 1, 1999 http://waw.wardsauto.com/ar/auto_boring_trutheverybodys_ideas/
"Wow. Little did we know what a fire-storm we'd start with a seemingly innocuous mention of aluminum engine cylinder-bore treatment alternatives in last September's materials issue (see WAW - Sept. '98, p.61).
There were plenty of letters and calls to point out we'd muffed our facts regarding the Nikasil treatment process.
…
All over cylinder-bore treatments, for gosh sakes.
…
… [A]luminum is an inherently "soft" metal, and cylinder bores of an engine block crafted purely from aluminum wouldn't long withstand the constant, grinding friction of pistons and piston rings scraping their way up and down the bore surface. Most aluminum engine blocks actually are fashioned from an aluminum-intensive alloy that contains other metals, primarily silicon. That helps, but that alone isn't nearly durable enough.
"It's pretty simple," says one OEM powertrain engineer. "You don't want aluminum-to-aluminum contact. You've got to have a bore with a high wear surface, and aluminum has poor wear characteristics."
Thus, the primary reason cylinder bores can't be aluminum. Once it's agreed the bore must be protected, the question is: "How?" Other factors such as cost, manufacturing consequences and performance requirements then must be squeezed into the equation. That's where the cylinder bore-treatment "factions" start to dig in their heels.
The Methods
Broadly, there are two ways to protect aluminum-engine cylinder bores: Either install iron liners or find a way to make the bore surfaces more wear-resistant, usually with some type of coating or treatment of the aluminum. Some approaches use rather exotic and elaborate processes to accomplish this feat.
Iron Liners: The utility infielder
Installing cast iron liners - or "sleeves" - equates to what might be called the industry "default" to answer the cylinder bore-treatment matter. Iron liners have numerous advantages:
- They are probably the most inexpensive method.
- They are delightfully durable.
- They are easily and inexpensively integrated into the manufacturing process.
Cheap and durable - the two words the industry holds most dear, right?
Well, there are problems with iron sleeves.
Sticking iron into your fancy new aluminum engine obviously negates some of what you're trying to do in the first place. Iron is heavy - that's why you switched to aluminum!
Perhaps more importantly, iron liners take up space. A common iron liner is roughly 3 mm thick. Multiply that by the number of cylinders you're dealing with and the engine starts to grow; there has to be a certain amount of block "webbing" between each cylinder to ensure structure, so the room that liners require can't always simply be chopped out of the space between each cylinder.
To now, that hasn't been a big deal in the U.S. One foreign castings supplier, who asks anonymity because he's wooing domestic business, explains: "In the U.S. you have the 'luxury' of displacement. Engines are large, so there is no particular need to use modern (bore treatment) methods. The car companies here always think first of cost and high volumes."
This source's emphasis on the word "modern" is inescapably scathing.
W. Gregory Wuest, vice-president-research and development at Sulzer-Metco, a New York company espousing cylinder-bore spray coating technology, agrees, noting that engines in Europe and Japan must be inherently smaller and more energy dense because fuel prices are so high. "In Japanese engines, for example, there's no room for a liner. They're driven (to other methods) by that factor."
Mr. Wuest notes that spray coatings usually can be applied in thicknesses of no more than 100 microns - one-thirtieth the space each 3 mm iron liner demands.
Iron liners typically are cast into the block as it's being formed. General Motors Corp. employs this method with its Premium V-6- and 8-cyl. OHC engines. Saturn simply presses in the liners. Ford Motor Co., for its Intech all-aluminum V-8s, heats the block and presses in the liners; when the block cools, it "shrinks" around the iron sleeves.
Iron and aluminum exhibit different thermal properties, though, which can be troublesome. And aluminum blocks and iron liners don't completely "bond," regardless of the joining method. That leaves gaps between the liner and the cylinder wall. The bonding and added-weight issues can be improved by using aluminum sleeves instead of cast iron - DaimlerChrysler AG likes aluminum sleeves for Chrysler's 4-cyl. and new V-6 engines - but aluminum liners are tough to cast directly into the block.
If liners are cast into the block - as in the GM method - scrappage becomes an issue. If the entire engine is built, only then to be discovered to be defective, the iron liners must be ripped out and are useless.
"We have some relatively high scrap costs," admits one powertrain engineer.
The Coatings: You pays your money, you takes your chances
This story was born when we first conveyed BMW AG's woes with Nikasil. So let's examine the competing cylinder-coating processes.
- Nikasil: An aluminum engine is dunked in an electrolytic "bath" of free-floating nickel, silicon and other junk. The electrolytic action causes these hardy substances to adhere to the aluminum surfaces.
"It does work very well in a lot of applications," admits one engineer philosophically behind iron liners. But Nikasil's main drawbacks are serious.
First, says Achim Sach, of VAW Motor GmbH, a part of the VAW Group aligned with Mexican casting giant Cifunsa SA, "Nobody wants to have nickel in the plants anymore." Also, as noted in September, high-sulfur fuels eat away at the coating, eventually rendering it useless. Result: ruined engine. And Nikasil has "throughput" issues: The block has to be labor-intensively "masked" before it takes a Nikasil bath, so that the particles cling only to the bore surfaces. And the block has to soak for more than an hour, claim some skeptical sources. Nikasil appears to be on the skids for these reasons. BMW has abandoned the process. Jaguar Cars and Ferrari SpA still like it, though.
There's plenty of industry dissension about the true cost [of various coatings, including {Alusil, Lokasil,- excerpted} and Nikasil], but Mr. Wuest is frank with his figures: He reckons iron liners cost about $1.50 to $2 per bore; plasma coating probably ranges from $3 to $5 per bore.
Meanwhile, Nikasil runs from $5 to $10 per bore, the cost largely dependent on volume.
