For you folks that have been on this site for a while, you know I’m a pretty big advocate of never using a spray sealer on a new MHG. I’ve based my argument against using it mostly on the various manufacturers recommendations…none recommend using a spray sealer. I’ve also used these two articles on surfacing the head and installing MHGs:
http://www.aa1car.com/library/2003/eb30320.htm
and
http://www.babcox.com/editorial/ar/eb70228.htm
My contention has always been: You want to have a MHG seal correctly? The RA spec (or smoother) for the specific MHG must be met for both the block and head, the machine work must be precisely flat for both the block and head, and the proper torque spec for the fastener used must be applied in the TRSM sequence. Attention to detail on these is what ensures a proper seal.
I have also said (several times) that the use of a spray sealer (such as Permatex Copper, Brake Quiet, etc.) can damage the fluoroelastomer coating the MHG manufacturers use on their product. However, I've never really backed it up other than a single line in the first article. I decided to research this...first a little background:
Viton (by DuPont) is the most common fluoroelastomer coating; it is used to initiate the initial cold seal on a MHG. It is applied in a very thin layer and is an inert, tough, heat resistant coating. It is one of the more expensive fluoroelastomers out there, and actually is manufactured in four families…the one we are interested in is for automotive applications. It is highly resistant to oil, gasoline, nitro methane, and alcohol. However there are certain chemicals that will affect it. From a tech article on Viton:
“In general, low molecular weight ketones and esters will swell a vulcanizate of Viton and, in fact, ketones such as methyl ethyl ketones are used as solvents for uncured Viton®. Esters such as ethyl acetate are also used as solvents for Viton. The more polar a material the more likely it will swell Viton. Much work is being done in the area of solubility parameters to characterize the swelling behavior of various fluids by comparison of dispersion, hydrogen bonding and dipole parameters to the corresponding parameters of the elastomer.
Amines affect Viton® differently from the ketones and esters. Generally, amines will react with the polymer backbone and result in embrittlement of the vulcanizate. The elongation will drop off significantly and hardness will increase. Amines are just one kind of base. In general, strong bases such as sodium hydroxide at relatively high concentrations will degrade Viton®. In summary, a basic understanding of chemistry is helpful in judging an elastomer's resistance to swelling or degradation.”
Now...the question is are any of these chemicals in a spray sealer? If you read the back of a can of Permatex Copper Spray-a-Gasket, it contains methylene chloride (a simple chlorohydrocarbon), acetone (a ketone), and ethyl acetate (an ester). Take another look at the tech article quote above…since acetone is a ketone, it will attack Viton. I have personally used acetone to clean the old Viton off in order to re-use a MHG. Ethyl acetate is specifically mentioned above as a solvent for Viton...I do believe we have the culprit Dr. Watson! Acetone and ethyl acetate can cause Viton to swell, making its ability to seal very questionable.
The most common counter I hear for using a spray sealer is “I’ve always used it and never had a problem”. That’s fine…use it if you want, but realize that you are applying chemicals that can dissolve the fluoroelastomer coating designed and engineered for the MHG you are using.
I also hear “Cometic says it’s not required, not that it’s not recommended”. Well, I called Cometic and spoke to one of their engineers…his response was “our gaskets do not need additional sealer…we do not recommend using it.” Using a little common sense and knowing how the chemicals in a spray sealer affect Viton, it’s no wonder they do not recommend it. BTW…I couldn’t get HKS to talk to me
Everyone here is free to make their choice. After reading up on the chemistry, I’m not going to use a spray sealer regardless who says it’s ok. Chemistry does not lie...this is not based on hearsay. I’m pretty positive the engineers know what they are doing on this one
http://www.aa1car.com/library/2003/eb30320.htm
and
http://www.babcox.com/editorial/ar/eb70228.htm
My contention has always been: You want to have a MHG seal correctly? The RA spec (or smoother) for the specific MHG must be met for both the block and head, the machine work must be precisely flat for both the block and head, and the proper torque spec for the fastener used must be applied in the TRSM sequence. Attention to detail on these is what ensures a proper seal.
I have also said (several times) that the use of a spray sealer (such as Permatex Copper, Brake Quiet, etc.) can damage the fluoroelastomer coating the MHG manufacturers use on their product. However, I've never really backed it up other than a single line in the first article. I decided to research this...first a little background:
Viton (by DuPont) is the most common fluoroelastomer coating; it is used to initiate the initial cold seal on a MHG. It is applied in a very thin layer and is an inert, tough, heat resistant coating. It is one of the more expensive fluoroelastomers out there, and actually is manufactured in four families…the one we are interested in is for automotive applications. It is highly resistant to oil, gasoline, nitro methane, and alcohol. However there are certain chemicals that will affect it. From a tech article on Viton:
“In general, low molecular weight ketones and esters will swell a vulcanizate of Viton and, in fact, ketones such as methyl ethyl ketones are used as solvents for uncured Viton®. Esters such as ethyl acetate are also used as solvents for Viton. The more polar a material the more likely it will swell Viton. Much work is being done in the area of solubility parameters to characterize the swelling behavior of various fluids by comparison of dispersion, hydrogen bonding and dipole parameters to the corresponding parameters of the elastomer.
Amines affect Viton® differently from the ketones and esters. Generally, amines will react with the polymer backbone and result in embrittlement of the vulcanizate. The elongation will drop off significantly and hardness will increase. Amines are just one kind of base. In general, strong bases such as sodium hydroxide at relatively high concentrations will degrade Viton®. In summary, a basic understanding of chemistry is helpful in judging an elastomer's resistance to swelling or degradation.”
Now...the question is are any of these chemicals in a spray sealer? If you read the back of a can of Permatex Copper Spray-a-Gasket, it contains methylene chloride (a simple chlorohydrocarbon), acetone (a ketone), and ethyl acetate (an ester). Take another look at the tech article quote above…since acetone is a ketone, it will attack Viton. I have personally used acetone to clean the old Viton off in order to re-use a MHG. Ethyl acetate is specifically mentioned above as a solvent for Viton...I do believe we have the culprit Dr. Watson! Acetone and ethyl acetate can cause Viton to swell, making its ability to seal very questionable.
The most common counter I hear for using a spray sealer is “I’ve always used it and never had a problem”. That’s fine…use it if you want, but realize that you are applying chemicals that can dissolve the fluoroelastomer coating designed and engineered for the MHG you are using.
I also hear “Cometic says it’s not required, not that it’s not recommended”. Well, I called Cometic and spoke to one of their engineers…his response was “our gaskets do not need additional sealer…we do not recommend using it.” Using a little common sense and knowing how the chemicals in a spray sealer affect Viton, it’s no wonder they do not recommend it. BTW…I couldn’t get HKS to talk to me
Everyone here is free to make their choice. After reading up on the chemistry, I’m not going to use a spray sealer regardless who says it’s ok. Chemistry does not lie...this is not based on hearsay. I’m pretty positive the engineers know what they are doing on this one
