The e30 or e12?oldskool wrote:Will you please fix MY car. I can't wait to drive it!
clongo wrote:The e30 or e12? (the 1985 545i in your shop. . . )!oldskool wrote:Will you please fix MY car. I can't wait to drive it!
Small update - the head was warped and they had to take .015 off. Luckily MLS makes a oversized .018 gasket so I will be running that. I also had them replace the valve guides and do a valve job. Parts should be here next week so I will put the motor in next sat if all goes well!
16clongo wrote:Duke, what was the RA that PB used to finish that head?
If the engine uses an MLS head gasket, the recommended surface finish may be 20 RA or less.
Ford specifies an unusually smooth surface finish for its 4.6L V8 engine. This engine, like a growing number of late model Japanese engines, uses a multilayer steel (MLS) head gasket. The recommended surface finish for the OEM gasket on the 4.6L V8 is 8 to 15 RA!
I hope so, better to wait a bit longer than have to do it all over again. You can come drive the E39 in the mean time (figured out it has the updated rotor).clongo wrote:Great. I'm curious to see what it is. He already took off .015 to make it flat. My gasket is .018 over. So hopefully he can do it.
OK....look at your head, and look at the pictures of mine and M. Holtmeier's. Does yours look close to a mirror? If "should be fine" is good for you, then install it. I am just going by your pic, could be different in person.clongo wrote:I called the machine shop and he said it was finished at 15 RA.
Yes and no. The iron does not expand near as much as the aluminum and thus does not need such a low RA. Thats why you hear some much about prepping Aluminum heads.clevertd wrote:Is the block side RA something to worry about/check as well?
For years, most aftermarket gasket manufacturers have said surface finishes with a roughness average (RA) of anywhere from 55 to 110 microinches (60 to 125 RMS) are acceptable. The preferred range they have recommended is from 80 to 100 RA. Even so, as long as the surface finish on the head and block end up somewhere between the minimum smoothness and maximum roughness numbers, there should not be any cold sealing or durability problems with the head gasket (assuming everything is assembled correctly and the head bolts are torqued in the proper sequence and to the specified torque, too).
But like everything else, these numbers have been changing. These recommendations were primarily for older cast iron heads on cast iron blocks. As castings have become lighter and less rigid, the need for smoother, flatter surfaces has become more important. Consequently, some aftermarket gasket manufacturers now recommend a surface finish of 30 to 110 RA for cast iron head and block combinations, with a preferred range of 60 to 100 RA for best results
For aluminum heads, the numbers are even lower. The typical recommendation today for an aluminum head on an OHC bimetal engine is a surface finish of 30 to 60 RA, with the preferred range being from 50 to 60 RA.
Smoothness has become a major issue with bimetal engines because the difference in thermal expansion rates between an aluminum head and cast iron block creates a tremendous amount of sideways shearing force and scrubbing action on the head gasket. If the surface finish is too rough (more than about 60 RA), the metal will bite into the gasket and pull it sideways as the head expands and contracts. The cumulative effect over time can cause a delaminating effect in the gasket, literally tearing it apart causing it to leak and fail.
