LZ23 piston ring gap

[budsaipan]

Hey guys, I'm trying to install my piston rings and after checking the gap, it seems a little too big of a gap on the second ring. My bore is at 89mm and currently the top piston ring is .014 / .015 inches and the bottom is about .025 inches. Does the bottom one matter or should I get oversized and file to fit?

 

By the way, I was going off the "how to modify datsun/nissan engine". 

 

 

[datzenmike]

Top ring end gap should be about 0.004"  times the bore in inches. It's hotter and will expand more than the second ring

Bottom ring end gap is 0.005" times the bore in inches.

 

89mm = 3.5" X 0.004 = 0.014" gap or 0.355mm gap top

3.5" x .005 = 0.017" or 0.44mm gap second or bottom

 

 

The gap will close up from the heat expansion. A turbo or nitrous motor will run much much hotter and will need a correspondingly larger gap. More gap than you need will leak compression and too little will break rings.

[budsaipan]

Damn, so looks like I'll need to find an oversized piston rings to file them down...

[datzenmike]

I don't know why it would be so far out at 0.025" unless this is a well worn cylinder. Has this been bored? Has the wear been measured? Also, the ring should be pushed down the bore with the old piston top about 2" or so then the gap measured.

[datsunaholic]

The rings should ALL be checked at the top, middle, and bottom of their travel.   Approx. 1/4 inch from the top for the top ring, and 1/2" from the top for the oil rings.  Then mid-bore, then about 2" from the bottom.  

 

Top ring .010-.015", second ring .012-.020", and oil rings .012-.035". 

 

A ring that measures OK in 1 or 2 positions in the cylinder and slightly wide in the 3rd position is generally OK (though that indicates cylinder taper, which might become a problem later), but never, ever have a ring that's too "tight".  It needs to have at least minimum gap in all positions.

 

Also, check all rings in all cylinders before ever filing any of them.  A ring that's too tight for one cyl might be perfect in another, and a different ring might already have a wider gap.  Not too time consuming in a 4-cyl with 2 compression rings (I've done it on V-12s with 3 compression rings- and no new rings available, so basically had a coffee can full of various used rings and spent hours matching rings to cylinders)

[budsaipan]

The engine was bored out from a z22 to match ka24e pistons. And I forgot to mentioned that the piston and rings are for KA24e truck engines. According to the specs on KA24e, the bottom one gap specs are at .011-.027 in. So it seems it falls just within the max limit for bottom ring gap.

 

So should I go based off this and call it good? Any help would be appreciated. thanks.

[budsaipan]

Anyone?

[Stoffregen Motorsports]

Sounds like you found your answer.

[budsaipan]

Thanks,  Building my first engine so I didn't want to screw it up... Always comforting when hearing from people that has dealt with this sort of things before. 

 

 

 

Sounds like you found your answer.

[datzenmike]

KA24E ring end gap

 

Top compression...........................  0.011" to 0.0169"... maybe split the difference 0.014"?.

2nd or Bottom compression............  0.017" to 0.023"

Oil control...................................... 0.007" to 0.023"

[budsaipan]

Where did you get your specs from? I downloaded the FSM and it says for rings with "R" and "T" should be 0.017" to 0.023" and rings with "N" should be 0.017" to 0.027". Now I'm not sure what the difference are between those.

 

Wonder if those markings have to do with the material or shape of the rings. The other messed up thing is that the max limit of ring gap is 0.020in. WTF?!

[datzenmike]

I just realized that these are truck pistons and rings. Sorry Bud I was quoting S13 specs and there were 2 different makes of rings, early Nihon and later Riken. I have a truck and an S13 piston... I can measure the ring lands and see if the same rings were used between car and truck.

 

I can't compare pistons because the car used domed and dished with floating pins, the trucks all had the same dished piston with press fit pins.

 

I think the best thing to do is apply that formula for end gap based on bore diameter.

 

Top ring end gap should be about 0.004"  times the bore in inches. It's hotter and will expand more than the second ring

Bottom ring end gap is 0.005" times the bore in inches.

 

89mm = 3.5" X 0.004 = 0.014" gap or 0.355mm gap top

3.5" x .005 = 0.017" or 0.44mm gap second or bottom

 

 

The gap will close up from the heat expansion. A turbo or nitrous motor will run much much hotter and will need a correspondingly larger gap. More gap than you need will leak compression and too little will break rings.

[budsaipan]

I suppose I should go that route... Damn rings.. Thanks btw

[datzenmike]

Yeah I guess excessive blow by is better than broken rings. :) I'm going to be fitting KA rings to a fresh re-bored Z22 soon so....

[budsaipan]

This is also my second ring set and both set seems to be off for some reason. I'll be getting .20 oversize rings and see if I can file them down to size.....  :confused:

[budsaipan]

Do anyone know where I can get File Fit piston rings? I can't seem to find anywhere that has those rings. Would an oversize piston rings fit on a standard bore and pistons?

[datsunaholic]

As long as you only go one size up it should be OK.  Oversize rings have a different curvature and hence if forced into smaller bores, even if filed, will have too much spring tension and can break.  But going one step up isn't that big of a deal, especially if the bores are worn.  So, 0.25mm (0.010") rings in a worn standard bore would work.  Now, if those show too much gap, you dont' have standard bores anymore.

[budsaipan]

I actually got my Z22 bored out and honed to standard 89mm from the machine shop. So either they removed too much or my piston ring is defective...