How to achieve correct surface roughness on block deck/heads
01-25-2013, 11:09 AM
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How to achieve correct surface roughness on block deck/heads Hello poeple , i was wondering if anyone can tell Me what the best sand paper grit # is for achieving the correct surface roughness for the best head gasket sealing characteristics when surfacing heads and block deck ?
01-26-2013, 03:20 AM
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A flat surface ,,,,,,,,,,,,,that's good ,,,,,,,,,,,,yes there is a certain amount of controlled roughness that is best for head gasket sealing and believe Me I realize that cloth-backed sand paper is'nt the same as using cutting bits but I'm sure there is a grit # ,,,,,,,,,say 220 or ? that could probably bring it to somewhere in the ballpark ,,,,,,,,,,,,,,the budget for this engine has just about disappeared . Were using graphite gaskets so probably not as important as compared to composite gaskets and this is a tame build . Just thought some of machinists might be able to offer some of Their knowledge
01-26-2013, 07:41 AM
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A flat surface ,,,,,,,,,,,,,that's good ,,,,,,,,,,,,yes there is a certain amount of controlled roughness that is best for head gasket sealing and believe Me I realize that cloth-backed sand paper is'nt the same as using cutting bits but I'm sure there is a grit # ,,,,,,,,,say 220 or ? that could probably bring it to somewhere in the ballpark ,,,,,,,,,,,,,,the budget for this engine has just about disappeared . Were using graphite gaskets so probably not as important as compared to composite gaskets and this is a tame build . Just thought some of machinists might be able to offer some of Their knowledge
What's with all the commas?
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01-26-2013, 10:35 AM
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Carefuldumrazor blade execution of the heavy stuff using the techniques already discussed....then (with the dowels out of the block) I use a medium length bodyman's longboard (about 3 X 10" or so) with 320-400 wet/drysandpaperdumusing WD40 as a cutting lubricant and a cleaner. The finished results dont come any better. I do it with even pressure (light) and work my way diagonally across the head trying to maintain the same stroke speed and amount of lateral movement. Then I go the other diagonal and do the same thing creating a very fine cross-hatch effect on the deck that the Cometics can bite into ever so slightly. I usually do two passes in each direction assuming a got the block pretty clean beforehand (no heavy stuff). Its impossible to warp the deck with the straightedge (longboard), not to mention it would take you quite awhile in the same location with that fine a paper so no worries and a beautifully prepped deck surface when your finished....Tony M.
Follwed tonys advice over on corvette forum, worked for me.
Follwed tonys advice over on corvette forum, worked for me.
01-28-2013, 02:09 AM
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Let Me start by saying thanx for You're replies and KCS I always use alot of commas when I write ,,,,,,,,,,I suppose sometimes it's just Me thinking about what I'm gonna write next and sometimes They're to provide a little time 4 the reader to fully grasp what I'm painting with words that is to say at least in My mind .
I've made 2 flat boards 1 12" by oh 18 or 20" that is adjustable so I keep it as flat as I can which have 2 pieces of 80grit belt sander belt glued and the other 1 is 6" by 22" with 1 piece of the same glued . the latter is'nt as easily adjustable being made of steel but is somewhat adjustable , then I've made a cpl smaller 1's for spot sanding . So far I've taken .010 or .011" off of My block deck and although difficult ,,,,,,,,not impossible to end up with a "flat surface" . But I still need more material removed . Up until now the plan has been to remove another .023" all so My slugs come out of the hole .023" for quench purposes . Now I'm thinking a set of Cometics that are .041" thick are sounding really good requiring only .006" more to bring quench to .035" . I live in Phoenix and although this build is mild ,,,,,,,My driving is not so much so with quench and an over-sized radiator I'm hoping to not create conditions where the ECM/PCM will need to retard ign much if at all ,,,,,,,,sorry 4 the mini-book
I've made 2 flat boards 1 12" by oh 18 or 20" that is adjustable so I keep it as flat as I can which have 2 pieces of 80grit belt sander belt glued and the other 1 is 6" by 22" with 1 piece of the same glued . the latter is'nt as easily adjustable being made of steel but is somewhat adjustable , then I've made a cpl smaller 1's for spot sanding . So far I've taken .010 or .011" off of My block deck and although difficult ,,,,,,,,not impossible to end up with a "flat surface" . But I still need more material removed . Up until now the plan has been to remove another .023" all so My slugs come out of the hole .023" for quench purposes . Now I'm thinking a set of Cometics that are .041" thick are sounding really good requiring only .006" more to bring quench to .035" . I live in Phoenix and although this build is mild ,,,,,,,My driving is not so much so with quench and an over-sized radiator I'm hoping to not create conditions where the ECM/PCM will need to retard ign much if at all ,,,,,,,,sorry 4 the mini-book
