924Board.org

[WEASEL149]

Had some time today so decided to take a few measurements and thought this may interest a few people (Ideola??), as the more confirmed data we get the better.

I managed to obtain a decent glass 50ml Burette and sorted out some plastic sheet.

The first head I measured was a spare I have from a scrap 931. This head is almost beyond saving and has had ~1mm skimmed off over the years by various ignorant people.
Suffice to say this head measured at 16cc.

I performed the same procedure on my own head. This head has been skimmed twice, removing max 0.2mm/0.008", so is approximately in the middle of the 0.4mm machining limit.
This came out at 21.1cc.
Both measurements take into account the 2 washers I used on the spark plug.

So machine ~1mm off your head and it reduces head chamber volume by over 5cc.

The block I'm using in my current build came from a never rebuilt Euro NA. This had exactly 0.1mm machined from the deck and now measures 231.2mm. By my calcs and also the CR calculator on Ideola's Garage, this should leave my pistons flush with the deck, but I have yet to confirm.

I did also confirm that the Omega piston dish measures 35cc.

All measurements will be double-checked and I'll repost if different.
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1979 UK 932

[ideola]

Awesome, thanks much for the data!!!!
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erstwhile owner of just about every 924 variant ever made

[WEASEL149]

Just an update but the forged Omega pistons I have with OEM pin height are sitting just 0.001" beneath block deck when squared in the bore using a DTI.

Cold temp piston rock with ~0.1mm/0.004" bore clearance leaves the piston proud of the deck by 0.0085" at the most extreme (measured with DTI).
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1979 UK 932