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chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

I have a question about head gasket, if a thinner head gasket can increase compression why milling the head there are no compression increase? I don't understand, is the same than cut the block.
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Porsche 924 2.0 na 125hp (1979) euro
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Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

Cedric · Joined: 27 Aug 2004 Posts: 2807 Location: Sweden

Since there is no combustion chamber in the head there will be no compression ratio change by milling the head. But you should do it anyway to make the head perfectly flat if you have it all appart, so you dont get any more leaks.

To raise compression you have to either mill the block or use thinner gasket. Dont forget that your engine probably need 98octane after the CR increase.
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chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

Just thinner gasket is equal to cut minimal part from the head.
If I remove mm on block or on the head the result is the same, block and head are nearest.
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Porsche 924 2.0 na 125hp (1979) euro
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Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

Cedric · Joined: 27 Aug 2004 Posts: 2807 Location: Sweden

chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

Then even thinner head gasket don't increase cr.
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

Yes it does.
Head gasket is like an extension of the block...part of the combustion happens inside the head gasket enclosed volume.
If you use a thinner headgasket you increase CR...but not by a whole lot.
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chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

This part is correct for my car?

0,063"
Guardalo su eBay http://www.ebay.co.uk/itm/201604502412

Or better this 0,050" ?
Guardalo su eBay http://www.ebay.co.uk/itm/351759796733
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

MikeJinCO · Posted: Sat Apr 01, 2017 6:04 am Post subject:

I just paid about $95 + shipping for a .040 head gasket from Cometic. The standard Reinz head gasket is much less and seems to be about .066" thick. My machinist charges about $100 to mill the block, which will probably need to be surfaced anyway and it doesn't cost any more to take 1mm than .25mm. Surfacing by 1mm will remove about 5.8cc from the combustion chamber which should raise compression by approximately(I didn't do the math) 7/10 of a point which would be significant in a 9.3 euro motor.

If you did that the cam would get retarded a bit which is bad(again no math but I think about 3 degrees:. Summit Racing has an offset cam key kit which I believe is for an early 1980's 2.2 Dodge ??? which would allow for making that up and advancing it a bit. As I recall the cam key kit is about $65 but that includes 3 or 4 different keys for various offsets. Ideola has a better adjustable cam setup but it is more expensive also.

Look at Ideolas website for the compression ratio calculator and try using different deck heights (mill the block) and head gasket thicknesses.
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chris79 · Joined: 29 Jan 2014 Posts: 551 Location: milan

But I think no remove block, compression was good, I would like only replace head gasket and fix valve intake myself.
It's necessary mill the block?
_________________
Porsche 924 2.0 na 125hp (1979) euro
------------------------------------------------------
Alfa Romeo Spider "Duetto" 1.6 104hp (1986) euro

MikeJinCO · Posted: Sat Apr 01, 2017 9:36 am Post subject:

Probably not. When I first had my '77 apart with a blown head gasket I just got the head surfaced probably .1 to .2mm and lapped the valves and it sealed up well or reassembly.
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Mike

'67 MG Midget Dp
'71 Ocelot Dsr Kawasaki 1000(under rebuild)

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

Paul · Posted: Mon Apr 03, 2017 3:51 am Post subject:

Measure the block height and compare to the spec to determine if anything can be milled.
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924RACR · Posted: Mon Apr 03, 2017 10:40 pm Post subject:

+1 that the Dodge/Mopar offset cam keys work, and work well, for the cheap cam timing answer (again, not as good as the Ideola cam gear).

When just doing a headgasket on a street car, use a long metal straight ruler to check for warping. Place it lengthwise and also on the diagonals, and see if you can fit any feeler gauge more than maybe 0.002" through any gap. Same thing to the top of the block. If you can't fit a feeler gauge through there, then it's flat and can be reused without machining - which is in fact often the case, with these motors, in my experience.

It's a bit harder with the valves in the way, but...

In short - odds are you don't need to have the block or head cut...
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