Rough Mill job on heads
Teching In
Joined: Nov 2004
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with aluminum heads, the smoother the better. If you can catch a fingernail in the machined cuts, or if you run your finger with pressure in the same direction as the machining and your finger follows the machine marks I would take it back to the shop and get them to do a proper job.
That must really suck....now to correct it, they will need to mill it all over again causing you P/V clearence issues and really high compression. Don't believe all the BS they're going to give you about it being alright either, keep in mind they are not going to want to pay for a new set of $2200 heads!
Teching In
Joined: Oct 2004
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No, a smoother finish is not necessarily better!
The surface finish for most engines should be 54 to 113 RA (Roughness Average) microinches (60 to 125 RMS), with a recommended range of 80 to 100 RA (90 to 110 RMS).
Most importantly, the surface finish is dictated by the type of gasket used. For Multi-layer steel (MLS) gaskets (typical OEM) a 20 RA is recommended.
For aftermarket composite (typical Fel-pro) 80 RA is recommended. 60-80 RA can be felt by dragging your fingernail across the surface. The rougher surface for the composite allows the sealing surface to "bite" into the gasket, allowing the proper amount of movement during thermal dimension changes.
It sounds as though you have the proper surface finish for a composite gasket.
If in doubt, ask AFR what RA they mill their heads to!
The surface finish for most engines should be 54 to 113 RA (Roughness Average) microinches (60 to 125 RMS), with a recommended range of 80 to 100 RA (90 to 110 RMS).
Most importantly, the surface finish is dictated by the type of gasket used. For Multi-layer steel (MLS) gaskets (typical OEM) a 20 RA is recommended.
For aftermarket composite (typical Fel-pro) 80 RA is recommended. 60-80 RA can be felt by dragging your fingernail across the surface. The rougher surface for the composite allows the sealing surface to "bite" into the gasket, allowing the proper amount of movement during thermal dimension changes.
It sounds as though you have the proper surface finish for a composite gasket.
If in doubt, ask AFR what RA they mill their heads to!
Thread Starter
Teching In
Joined: Nov 2004
Posts: 29
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From: Baltimore
Thanks for all of the replies. Yes, the groves can be felt with you fingernail as will as the tip of your finger. The next time I will ask about the surface before any work is done. I was planning on using a set of cometic gaskets on the heads. So, I returned to the machine shop to ask if it they could correct the heads and the response was that was the best they could do and recommended another shop that had a better milling machine.
