Preparing machined gasket surfaces

-by dolsontire.com

When engineers design components for engines, drive line, transmission, or other critical sealed surfaces they calculate how wide, how much pressure, and how the gasket materials used will interact with their design in order to optimize the fitness of the system.

During the repair process many technicians spend a great deal of energy preparing surfaces. It is often the case the uninformed make this serious repair technician error. 

The use of pneumatic tools with abrasives is a well known risk to the longevity of the repair. Lets explore why any casting, whether cast iron, aluminum, alloys, plastics and more may suffer from the overzealous inexperienced hand.

Tools that spin with abrasives on them can remove a great deal of gasket, and most unfortunately metal during the cleaning process. Because these tools are round discs, they are most likely to remove uneven amounts of material. Because they spin around and must be held at an angle they will never be perfectly square with the surface.

Another consideration is the required finish. While its best to look it up in your machinists handbook, a fine texture flat file is a good choice.

Use a chemical to soften the gasket material and clean the surfaces. Then while the chemical is acting, use a plastic scraper or plastic razor blade to remove the old gasket materials without affecting the original surfaces. In extreme cases use the chemical again with a brass brush that will not scratch up the surface to remove stubborn gasket glued to the surface.

Then use the flat file with just a few even pressured light strokes in one direction, then turn 90 degrees and a few more, and so on. Just enough to clean the surface.

When experienced you will see this removes the high spots around bolt bosses where clamping torque can be limited and quickly shows you the low spots if any. Use a machinists straight edge or granite block to check the flatness. If the casting is within specifications you are ready for the next step of assembly. 

If not, you may have to send it to a competent machinist to restore the perfect finish, replace the part, or if you are good enough, flat file more and check the flatness again.

This is how we do it, you may have your preferences. We fixed a few engines over the years where the other shop or dealer tech said he had always used a "whizzer and I never had a problem before!" at least that he knew of. Its an expensive mistake to let a job go with a possible error. The job may run for a while but eventually fails due to the loss of gasket compression. Its worth sending the job to a competent shop or educating yourself and passing the ASE Engine Machinists exams. If you need any assistance in Middletown NY contact us on our web site or watch these videos about engines here engine educational video

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