OEM piston rings quick question - Zilvia.net Forums | Nissan 240SX (Silvia) and Z (Fairlady) Car Forum

<^> ^_^ <^> · 06-24-2008, 09:57 PM

Ordered some OEM sr20det piston rings and was wondering if they come pregapped? searched and didn't find an answer

RedtopTech · 06-25-2008, 01:48 AM

All oem rings designed for stock bore will be tight out of the box. As with any part that has a clearance spec you shouldn't just pull them out and toss them in (even though many people due get away with it.)
The ring gap is crucial for a couple reasons. First, you have to consider heat expansion. If the gap is to tight, once the engine warms up the rings will expand which could potentially cause the ring end to touch. A few degrees later and the expanding ring will break the piston and or will push outward and first scar the cylinder wall and next lock the motor. Also it should be noted that a tighter ring gap will seal better which allows more pressure to push the piston instead of leaking past the gap.
That being said a larger ring gap is important on any forced induction engine. Since more heat is created there is more expansion. Also a boosted application can cause pressure build up between the rings which results in reduced sealing. The Top ring will require more clearance since it will experience higher temps than the second ring.
When planning my build i had to consider that i drive it daily yet it also had to deal with nitrous use at the local strip on a weekly basis. I didnt want excess blow-by yet i didnt want to risk being to tight. I decided on .0021 for the top and .0020 for the second. I ended up with less than 8% leakdown on all cylinders and have gone through many lbs. of nitrous with no issues.
Cylinders can develop a bell shape over time so it is important to check the rings at the top, middle, and bottom of the bore. Hone the walls first and use a piston to make sure the ring is "square" in the bore. Also keep track of which rings go in which bore. I would reccomend that you aim for the larger end of the factory spec to allow for higher boost/ power in the future.
No they arent pre-gapped, they are just close.

06-24-2008, 09:57 PM	#1
<^> ^_^ <^> Zilvia Member Join Date: Jun 2004 Location: Richmond Posts: 261 Trader Rating: (0) Feedback Score: 0 reviews	OEM piston rings quick question Ordered some OEM sr20det piston rings and was wondering if they come pregapped? searched and didn't find an answer __________________ http://www.zilvia.net/f/showthread.php?t=21036

06-25-2008, 01:48 AM	#2
RedtopTech Zilvia Member Join Date: Dec 2005 Location: Virginia Beach, VA Age: 40 Posts: 293 Trader Rating: (0) Feedback Score: 0 reviews	All oem rings designed for stock bore will be tight out of the box. As with any part that has a clearance spec you shouldn't just pull them out and toss them in (even though many people due get away with it.) The ring gap is crucial for a couple reasons. First, you have to consider heat expansion. If the gap is to tight, once the engine warms up the rings will expand which could potentially cause the ring end to touch. A few degrees later and the expanding ring will break the piston and or will push outward and first scar the cylinder wall and next lock the motor. Also it should be noted that a tighter ring gap will seal better which allows more pressure to push the piston instead of leaking past the gap. That being said a larger ring gap is important on any forced induction engine. Since more heat is created there is more expansion. Also a boosted application can cause pressure build up between the rings which results in reduced sealing. The Top ring will require more clearance since it will experience higher temps than the second ring. When planning my build i had to consider that i drive it daily yet it also had to deal with nitrous use at the local strip on a weekly basis. I didnt want excess blow-by yet i didnt want to risk being to tight. I decided on .0021 for the top and .0020 for the second. I ended up with less than 8% leakdown on all cylinders and have gone through many lbs. of nitrous with no issues. Cylinders can develop a bell shape over time so it is important to check the rings at the top, middle, and bottom of the bore. Hone the walls first and use a piston to make sure the ring is "square" in the bore. Also keep track of which rings go in which bore. I would reccomend that you aim for the larger end of the factory spec to allow for higher boost/ power in the future. No they arent pre-gapped, they are just close.