NOT good......

The piston is resting on the spark plug electrode..

about 2mm to tall........

possible solutions?

shorter plugs?

Cut or mill domes so there is .050 clearance between the plug and piston, weigh pistons to make sure they match, and reinstall?

Find out the piston top/deck thickness and put in a fire slot in while you are deburring and smoothing the piston top.

How thick is your head gasket?

NGK BUR7EQP from a "7"?

http://www.autopartsbargain.com/ngk-bur7eqp-laser-platinum-spark-plug.html

gasket is .020... not enough.... but it might help...

Hmmm, shorter plugs isn't, yet might just be the answer... not shorter plugs, but less plug in the head.... using plug indexing washers(.064" from Moroso) along with the head gasket.... I went to Moroso's site and the .064" index washer backs the threads off 312 degrees, I backed the spark plug off, and somewhere between 180 and 270 degrees, the piston stopped contacting the plug...

I'm try NOT to cut down the slugs if at all possible, the head work was based entirely on a piston volume of 9.5cc, shrink that and the compression begins to tumble

My Father will tell you from his days of being a marine mechanic.. that sometimes marine plugs are longer or shorter than the land based ones for the same engine.

I may be missing something but without the piston in the block you have no idea how high its going to come up.It might clear.The dome does not go flush with the head.IMO :)

speedbiu wrote: I may be missing something but without the piston in the block you have no idea how high its going to come up.It might clear.The dome does not go flush with the head.IMO :)

I've only built (as opposed to rebuilt) one motor, but yes, in my experience, TDC isn't even flush with the block, much less the head.

That said, I've never used any of them fancy domed pistons.

Use rotary plugs

Spoolpigeon wrote: Use rotary plugs

I remember the first time I saw the plugs in my RX-7, mind blown.

What you're looking for is called a "retracted gap sparkplug".

They look like this:

...which are the kind of plugs RX-7s use

Or you can do what I used to do when I was too cheap to buy RX-7 plugs - use standard plugs and side-gap them. It takes a little bit of a knack to get the gap exactly right the first time, but it's pretty easy. Just cut the ground strap with a cutoff wheel approximately at the bend and then tap it down with a small hammer.

Downside - you can't re-gap the plugs. Upside - no more flame kernel shrouding. With a dome that tight and no "fire slot", you're probably going to need all the help you can get in that regard.

oldeskewltoy wrote: gasket is .020... not enough.... but it might help... Hmmm, shorter plugs isn't, yet might just be the answer... not shorter plugs, but less plug in the head.... using plug indexing washers(.064" from Moroso) along with the head gasket.... I went to Moroso's site and the .064" index washer backs the threads off 312 degrees, I backed the spark plug off, and somewhere between 180 and 270 degrees, the piston stopped contacting the plug... I'm try NOT to cut down the slugs if at all possible, the head work was based entirely on a piston volume of 9.5cc, shrink that and the compression begins to tumble

Make sure that you have enough clearance for carbon buildup on the plug and top of the piston. I actually have had plugs that are as close as we are talking about have their gaps closed by piston contact due to carbon.

.1mm not cool IMO. Plus there is a bit of thermal expansion when you are talking about a head that is a different casting metal then the block.

speedbiu wrote: I may be missing something but without the piston in the block you have no idea how high its going to come up.It might clear.The dome does not go flush with the head.IMO :)

I am missing this as well. Without a mock up piston/rod/crank/headgasket that you are maybe just not showing, we can't be sure of anything.

I believe the OP's second picture is the piston sitting with dome in the head, not the block:
"The piston is resting on the spark plug electrode.. "

erohslc wrote: I believe the OP's second picture is the piston sitting with dome in the head, not the block: "The piston is resting on the spark plug electrode.. "

And?

Why not just put a washer under the spark plug? Gap it a little larger, start with a larger flame kernel, and it won't take many degrees of travel to get where it was supposed to be anyway.

Fly cut the pistons?

I would definitely try a washer under the plug first. Conical or flat seat? Either way its not too tough.

Perimeter-electrode plugs are another possibility. They've been used in 2-stroke marine applications since the late 70s. They are generally a very cold plug, but from the looks of those domes it shouldn't be too much of a problem. They look like this:

Of all the GRM solutions, the extra washer under the plug seat is the best. Cutting pistons for a plug electrode can make hot-spots especially given its proximity to the flame front. Adding head gasket thickness lowers compression by adding volume all over just to get a small distance of clearance.

Ok,Assemble the bottom end.Once you have the rotating assm together place the head on the block WITHOUT bolting it down and rotate the motor with a socket.Watch for the head to move,If it does you have issues other wise put your head gasket on and go on.Make sure your plugs are in your head at the time of your test.Hope this helps.Those pistons are not going to come that hign in the cyl unless the block and head were both decked.

speedbiu wrote: Ok,Assemble the bottom end.Once you have the rotating assm together place the head on the block WITHOUT bolting it down and rotate the motor with a socket.Watch for the head to move,If it does you have issues other wise put your head gasket on and go on.Make sure your plugs are in your head at the time of your test.Hope this helps.Those pistons are not going to come that hign in the cyl unless the block and head were both decked.

Yes, this.

Just about every plug has an identical one with a shorter reach. Recently had to go that route with a custom built stroker Rover V8. Then we started messing with the heat range on the plugs. Again, identical plugs with different heat ranges.

EvanB wrote:

erohslc wrote: I believe the OP's second picture is the piston sitting with dome in the head, not the block: "The piston is resting on the spark plug electrode.. "

And?

tuna55 had posted: I am missing this as well. Without a mock up piston/rod/crank/headgasket that you are maybe just not showing, we can't be sure of anything.

I suggested that the OP had shown that such a mock up wasn't needed in the picture.