Block skim advice sought

[SGP]

This M20 block needs to be skimmed, due to corrosion.
Some of the pitting is over 1mm.
Do we know maximum permissible 1st skim / gasket options.
Any advice in the best way to go ?
Many thanks.

[Brianmoooore]

Skim limit is indicated by dimples on the head face, so I suppose the limit that can be taken off the deck, using the standard gasket, is the same as this.
The area of corrosion between the two water holes is of no great concern, but the area closest to the cylinder most definitely is.
I'd rely on the judgement and experience of whoever does the machining to judge the minimum amount you can get away with as he does it.

[SGP]

Thanks Brian. the engineer had a quick look and reckons .020" or 0.5 mm could be enough. Will the compression ratio be ok if I use a standard thickness gasket with .5mm shaved off ?

[Brianmoooore]

Head skimming limit is 124.7mm between the upper and lower faces, so measure your existing head and subtract 124.7mm from that figure. If the result is greater than 0.5mm. then there won't be any piston to head contact problems.
0.5mm will only reduce the combustion chamber volume by about 0.9cc out of about 47cc, so if you're starting with a 8.8:1 CR, then it'll still be only just over 9:1.

[Mitchen]

Or you could just get a good used one if all else fails.

http://www.ebay.co.uk/itm/181485871128? ... EBIDX%3AIT

[reggid]

you can take a fair amount off the block if you are changing piston and rod combinations requiring a lower deck height and /or using an MLS gasket which can be made quite thick for custom applications.

but on a stock rebuild get a good used block and OEM gasket is preferable. i think will clean up ok without going to 1mm you just need fresh metal between all the holes not to get rid of ever single trace of pitting near the edges

[DanThe]

As above, dont forget the anti freeze

[SGP]

Thanks all, some great info there .

[Quaser]

ive got an m20 block for sale if u need it

[SGP]

Thanks, but keeping the original block is the goal.