Questions and Answers
Machining Blocks And Heads
Q. Hi. I am in the middle of a project car, part of which is doing a lot of engine work. I have a metal head gasket from HKS (1 mm stopper type) that they say needs a 6-8 micron roughness on the block deck and head surfaces.
The engine shop I used put what they call an R115 finish on the block and head. I am trying to find out if this R115 finish is acceptable, but I haven't been able to find any reliable sources that will tell me and the engine shop seemed a little too busy to worry about it and just told me 'yeah, yeah, that will work'.
Please help me as I now have the engine mostly assembled and am worried that I will have to take it back down to bare block and have the head and block resurfaced for a smoother finish. Also, could you tell me what the ratings mean, are they standardized, and what the correlation would be to a micron rating?
Thanks!
EricA. I'm not an automotive machinist, but I do know a little something about this. A head gasket has to work under very adverse conditions. Heat and pressure will try to push it out of place. Okay, let me see if I can explain this right. To prevent this, the block and head are machined with a tool that will leave a controlled "scoring" pattern on them.
This scoring is what the head gasket grabs onto to stay in place. If the block and head were perfectly smooth, the head gasket could slide out much easier. The machine shop has a book that has the specifications for each auto manufacturer for this finish.
I'm not sure of the ratings so I'm not even going to try to explain them. This is something that I trust my machine shop to do for me. Personally I think if the machine shop is too busy to spend a few minutes answering your questions, I'd find another shop.
Additional Information provided courtesy of ALLDATA
