Editing Pistons and rings

=Pistons=

==Parts of a piston==

===Diagram===
[[File:Piston parts diagram.jpg|1000px]]

{| class="wikitable"
|-
! 1 to 10!! 11 to 20 !! 21 to 30
|-
|1. Compression Height ||11. Pin Oiler ||21. Skirt Thickness
|-
|2. Crown (Dome, Dish, Inverted Dome) ||12. Pin Span ||22. SS
|-
|3. Deck ||13. Pin Tower ||23. Support Band
|-
|4. Dome Angle ||14. Plug Relief ||24. Tang
|-
|5. Dome Diameter ||15. Ring Band ||25. Valve Relief (VR)
|-
|6. Dome Profile ||16. Ring Groove ||26. VR Angle
|-
|7. Dome Radius||17. Ring Land ||27. VR C/L Out 
|-
|8. Lock Groove ||18. Ring Root ||28. VR Depth
|-
|9. Oil Return ||19. Side Relief ||29. VR Diameter 
|-
|10. Pin Bore||20. Skirt ||30. VR Stop
|}

==Piston designs==
Cast pistons are fine for engines that won't see nitrous or boost. Forged pistons are a better choice if the engine will see boost or nitrous due to the added durability. There are those who say using cast pistons and nitrous/boost is acceptable. And it is- providing the tune is spot on and the engine never sees detonation. If it does, the cast pistons will be the first thing to fail, and when they go they usually damage the bore and possibly the cylinder head as well. This is because cast and hypereutectic aluminum alloys are brittle and when they fail they tend to shatter into many pieces, where a forging will generally stay in one piece, with pinched ring lands or depressed crowns, etc.

The worst possible piston design if a dished piston is needed is a round dish with a 45 degree chamfer around the outer edge. That leaves a scant 1/2" band on the top of the piston to provide the squish/quench effect, and that's just not enough.

[[File:Round dish sbc piston.jpg|500px]]


A much better choice if a dished piston is needed is a reverse dome or D-cup type piston (the one below, left is for a SBC 383 stroker). 

The round 10cc dished piston shown below right is a compromise between the D-cup and the undesirable type of round dish (shown above). As can be seen, the squish band is wider and the dish smaller in diameter,but deeper. This maximizes the quench/squish effect, but retains the "one size fits all" economy because one casting/forging will fit either side of the engine.

{|
|[[File:KB P-N 135 SBC 383 PISTON.jpg]]
|[[File:H423NP.jpg|300px|center]]
|}

==Dish volume==
Most dished pistons have published volumes. Those that don't or with pistons that are unknown as to brand can be estimated by using the following formula:

{{Note1}}All measurements in inches.
*3.14 x [radius of the dish]² x depth of the dish x 16.4 (converts cubic inches to cc) = Volume in cc
**Add 2 or 3cc for the valve reliefs if they extend beyond and/or below the dish. 


=Rings=

==End gap==
Ring end gap clearance has to be checked and verified or severe engine damage can result. The following are general recommendations. Consult the manufacturer's instructions and use that if they vary from these recommendations.

==How to square the ring in the bore==
Place a ring in the bore, then use a piston inserted upside down into the bore to square the ring.

==Ring end gap clearances==
Unless otherwise instructed by the ring or piston manufacturer, a safe ring end gap clearance is:

===Top ring===
*0.0045" per inch of bore diameter for street/strip
*0.0050" for drag or road race
*0.0055" for supercharged or nitrous use
{{Warning|Be aware that there are pistons like some made by Keith Black that use a wider top ring gap than what is normally recommended by ring manufacturers or other piston manufacturers. So be sure to check and follow the '''piston''' manufacturer's instructions, if they differ from the ring manufacturer's instructions.}}

===Second ring===
*The second ring should be gapped 0.004" to 0.008" wider than the top ring

===Oil ring===
*Minimum of 0.015" for the oil ring rails, do not file oil ring expander or rails 
{{Note1}} See the info at '''SBC oil ring depth''', below.

==Ring gap examples==
===4 inch bore (SBC, SBF, etc.)===
*4.00" plus 0.030" overbore = 4.030" 
*4.030" bore X 0.0045" = 0.01612, or rounded off to 0.016" minimum end gap.

===4.125 inch bore (SBC 400, Pontiac 400, etc.)===
*4.125" plus 0.040" overbore = 4.165" 
*4.165" bore X 0.0045" = 0.0166, or rounded up to 0.017" minimum end gap. 

==SBC oil ring depth==
GM has used both a shallow oil ring and a deep oil ring on SBC engines. Up to 1985 the oil ring/piston groove was 'deep' (0.195" or thereabouts). From about 1986 to the end of the L31 Vortec production, the 'shallow' rings (around 0.165") were used- but there could still be deep groove pistons and rings being used from about '95-back. A page on what to look for is '''[http://www.hastingsmfg.com/ServiceTips/oil_ring_groove_depths.htm Oil Ring Groove Depths]'''.

The difference is enough between them that if a deep oil ring were to be installed on a shallow oil groove piston, that the ring would bottom out in the groove. This leaves a portion of the ring extending out past the piston and will prevent the piston from being installed. The piston can be damaged if it's forced, and if somehow the piston were to be installed in the bore with the wrong oil ring, the bore and piston could be damaged.

Using a shallow ring in a deep groove will function normally, but installing the ring on the piston and the piston into the bore will be a chore due to the oil ring trying to pop out of the groove.

===Metric rings===
And if that wasn't enough, there were metric rings (2mm x 1.5mm x 4mm) used from about 1992 to 2002 when the Vortec bowed out. If you have access to the vehicle VIN and the original engine is still there, the metric ring engine is VIN '''P'''. There may be other VIN's that use metric rings so this has to be checked, regardless.

==BBC oil ring depth==
The BBC engine from about 1991 to 2000 used a shallow oil groove piston and ring. 

{{Note1}}Info on this is incomplete at this time.

==Ring end gap location==
The idea behind staggering the ring end gaps in a certain way is to have the engine start up without any gaps being aligned. The rings tend to rotate on their own during the life of the engine, so starting them out as shown will prevent them from aligning, at least not right away.

Hastings has instructions if there's a problem with installing their rings on some pistons, located [http://www.hastingsmfg.com/ServiceTips/oil_ring_installation_problems.htm '''here'''].

While there are different thoughts on ring end gap placement, unless the manufacturer's instructions say otherwise, the following diagram will work fine:


[[File:PISTON RING END GAP LOCATION.jpg]]

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{{Develop1}}

[[Category:Engine]]
[[Category:Undeveloped Engine articles]]
[[Category:Undeveloped articles]]