[Mk2] [Turbo] Head skim

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blogsy
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[Mk2] [Turbo] Head skim

Post by blogsy »

I was just wondering how many times a head can take a skimming before you have to think about getting a thicker gasket than the original 1.2mm one. Say you buy a secondhand block and head and want to get them refaced, does it matter if this has already been done at some point.
androo007
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Re: [Mk2] [Turbo] Head skim

Post by androo007 »

Depends on how much material was taken off the last time.

Putting a thicker gasket is a bodge, personally I'd get a new head as they're dirt cheap
blogsy
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Re: [Mk2] [Turbo] Head skim

Post by blogsy »

Can you tell if it's been skimmed?
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Driftlimits Performance
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Re: [Mk2] [Turbo] Head skim

Post by Driftlimits Performance »

Using a thicker headgasket is not a bodge. It's standard practice in the tuning game.
mr2magic
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Re: [Mk2] [Turbo] Head skim

Post by mr2magic »

Using a thicker headgasket alters the squish and is generally not advised to alter CR
C35Rob
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Re: [Mk2] [Turbo] Head skim

Post by C35Rob »

They're not talking about using one to lower CR though, using a thicker gasket to compensate for a head that's been refaced is perfectly acceptable
EX MR2 owner, currently on a '00 Honda CBR600 Follow me on Instagram @c35rob
androo007
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Re: [Mk2] [Turbo] Head skim

Post by androo007 »

I guess Rob im referring to a good old skim rather than a reface - you saw the turbo head I had on that turbo that had been skimmed (i.e cheesegrated) twice..... :shock: My point there was (and perhaps my ignorance showing here) if it's bad to lower CR with a HG, why is it OK to bring CR up to normal (i.e lower CR) with an overskimmed head?

Natually here i'm assuming that we dont know how much material has been removed and it could / probably is OK to skim twice. But would you? that's where my 'bodge' thought train comes from.
C35Rob
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Re: [Mk2] [Turbo] Head skim

Post by C35Rob »

you can measure a head to see how much has been taken off, there will (should) be a "stock" thickness somewhere in the BGB

the reason it's ok to restore the piston-to-head clearance/CR with a thicker gasket on a skimmed head, and not a good idea to smash a fatty in there to lower compression on an unskimmed head is that the PTH (squish/quench etc) clearance on a skimmed head that has been 'corrected' should be restored to stock, whereas attempting to lower compression with a thick gasket/decomp plate instead of pistons increases the PTH clearance and thus the tendency for knock :thumleft:
EX MR2 owner, currently on a '00 Honda CBR600 Follow me on Instagram @c35rob
androo007
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Re: [Mk2] [Turbo] Head skim

Post by androo007 »

Ahh, I am once again educated. Perhaps i should pose my answers more as questions eh? :lol:

Thanks Rob.
blogsy
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Re: [Mk2] [Turbo] Head skim

Post by blogsy »

[quote="C35Rob"]you can measure a head to see how much has been taken off, there will (should) be a "stock" thickness somewhere in the BGB

Thats interesting Rob, Anyone out there with the Big Green Book able to have a look.
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