Feeler gauges are accurate enough. Alternatively you can CC the piston in the bore to measure dish at the same time

With pistons down in the bore, you won't be able to get adequate quench. No worries, it'll still run well, although not with optimum power

I just had a look at the link you provided. They seem to be mainly 79mm. Once I check all the cc's and get all my figures I'll decide on the gasket. Now checking the piston to deck height is a straight edge and feeler qauges sufficient enough or should I got a deck height gauge? My Pistons are def below deck height. Just by eye I would say close to 1mm but I guess I won't know until I measure properly.

Yes it matters, but not enough to tell. Most head gaskets are bigger than the original Nissan items, so they will fit a variety of engines (like A12 & A14 both, whereas original A12 Nissan gasket was different bore size from A14 Nissan gasket). So most of us use a commonly available gasket

For standard A15 pistons, you only need a 76 mm gasket, but can use a 78.5 or a 79

You could custom order a copper gasket from Cometic was around $100 last I checked but it's been a few years. Just depends on where you want to spend the money

Does the bore size matter. Should I be getting the 79mm gasket?

Bprojects sells both:
* GX head gasket 3780 Yen (about $38 USD)
* Nismo head gasket 12960 Yen (about $129 USD)
http://www.datsun1200.asia/category/select/cid/357

Sometimes you can find them on eBay, if a guy has one to sell, not every day. Kameira is the only other place I know of with regular stock, and they are very expensive. Ten years ago Nissan sold them but no longer

Looking at my Pistons they are offset dished. Now these nismo and gx gaskets, where do you get them from. I had a quick look and bprojects has a nismo for $300. Surely they are easier to get and cheaper than that.

Check this link

http://www.datsuncherry.ch/PDF/Rennteile75.pdf

The engine portion gives you compression ratios based on what combo you are using even down to how many CCs for the gap to the top ring. It's very useful, it also specs how much to mill the head.

On the subject of milling the head, I prefer to use varying thickness of head gasket. The issue with milling the head is it also brings the valves closer to the pistons as well as possibly necessitating shorter push rods.

Tom

* The GX or Nismo thicknesses (0.6 and 0.8 mm) are Multi-Layer Steel (MLS) gaskets
* The standard gaskets (1.6 mm) are composite and have various crushed thicknesses, you can measure the used gasket to see what it's thickness was and use as an estimate. These gaskets cannot be reused, but are inexpensive and are adequate. The A15 offset-deep dish is supposed to be better than the full shallow dish

Best head gasket may be one that puts the piston 0.50 to 0.75 mm from the cylinder head face for best power. Tight clearance means more power but any closer runs the risk of touching/breaking the piston at high RPMs. More than 0.75 and the quench effect disappears

10:1 with tight quench - more power
10:1 with loose quench - less power and potential engine run-on (dieseling problems)

Tight quench gains more power than 1/2 point raise in compression

Although dished pistons are inferior even if you up the compression ratio. Dished pistons reduce NOx pollution but also use more fuel and make less power. Even if you mill the head to raise the compression a dished piston still makes less power

When fitting a high-lift camshaft you'll want to measure the piston-to-valve clearance using clay but it shouldn't be a problem with dished pistons

Ok great. So the same way as you would do the combustion chamber. Thanks for all the info guys. Think I got it now.

So what thickness head gasket do you think will be best?

you need to measure. There are at least four different A15 piston dishes, all different

To measure the dish, see our tech article: CCing