Pistons and rings

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===Diagram===
 
===Diagram===
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[[File:Piston parts diagram.jpg|1000px]]
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[[File:Piston parts diagram1.jpg]]
  
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{| class="wikitable"
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{|table border="1" cellpadding="4" cellspacing="0" bgcolor="#ffffff" style="margin: 1em auto 1em auto;" 
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|-
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|+'''Diagram Key'''
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|-bgcolor="#CCCCFF"
 
! 1 to 10!! 11 to 20 !! 21 to 30
 
! 1 to 10!! 11 to 20 !! 21 to 30
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|-
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|-bgcolor="#f9f9f9"
 
|1. Compression Height ||11. Pin Oiler ||21. Skirt Thickness
 
|1. Compression Height ||11. Pin Oiler ||21. Skirt Thickness
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|-
+
|-bgcolor="#f9f9f9"
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|2. Crown (Dome, Dish, Inverted Dome) ||12. Pin Span ||22. SS
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|2. Crown ||12. Pin Span ||22. SS
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|-
+
|-bgcolor="#f9f9f9"
 
|3. Deck ||13. Pin Tower ||23. Support Band
 
|3. Deck ||13. Pin Tower ||23. Support Band
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|-
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|-bgcolor="#f9f9f9"
 
|4. Dome Angle ||14. Plug Relief ||24. Tang
 
|4. Dome Angle ||14. Plug Relief ||24. Tang
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|-
+
|-bgcolor="#f9f9f9"
 
|5. Dome Diameter ||15. Ring Band ||25. Valve Relief (VR)
 
|5. Dome Diameter ||15. Ring Band ||25. Valve Relief (VR)
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|-
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|-bgcolor="#f9f9f9"
 
|6. Dome Profile ||16. Ring Groove ||26. VR Angle
 
|6. Dome Profile ||16. Ring Groove ||26. VR Angle
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|-
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|-bgcolor="#f9f9f9"
 
|7. Dome Radius||17. Ring Land ||27. VR C/L Out  
 
|7. Dome Radius||17. Ring Land ||27. VR C/L Out  
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|-
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|-bgcolor="#f9f9f9"
 
|8. Lock Groove ||18. Ring Root ||28. VR Depth
 
|8. Lock Groove ||18. Ring Root ||28. VR Depth
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|-
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|-bgcolor="#f9f9f9"
 
|9. Oil Return ||19. Side Relief ||29. VR Diameter  
 
|9. Oil Return ||19. Side Relief ||29. VR Diameter  
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|-
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|-bgcolor="#F9F9F9"
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|10. Pin Bore||20. Skirt ||30. VR Stop
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|10. Pin Bore||20. Skirt ||30. VR C/L
 
|}
 
|}
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<br>
  
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==Piston designs==
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==Piston design and material==
 
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.
 
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.
  
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==KB ring gap and piston to wall clearance instructions==
 
==KB ring gap and piston to wall clearance instructions==
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{{Note1}}The following info is for the KB Icon/Icon FHR (Forged Head Relief) series and various KB hypereutectic pistons. Refer to manufacturer's instructions to verify these specs as revisions/redesigns may cause them to vary, and for other brands and types of pistons.
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*[https://www.uempistons.com/index.php?main_page=install_instructions United Engine & Machine (includes KB, Silv-O-Lite and Icon) piston installation instructions]
 +
 
 +
{{Note1}}The following info on the KB Icon/Icon FHR (Forged Head Relief) series and various KB hypereutectic pistons used to be on the KB site but has been replaced w/the above link. Refer to manufacturer's instructions to verify these specs as revisions/redesigns may cause them to vary, and for other brands and types of pistons.
  
−
;[http://www.kb-silvolite.com/kb_car/clearance_pop.php Suggested Ring End Gap and Piston to Wall Clearance]<nowiki>:</nowiki>
 
 
KB pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better and seals the engine for maximum power. When a loose fit engine is desired the rigid skirt design of the KB piston allows the builder a choice without fear of piston damage. See the clearance chart below for minimum and realistic maximum loose fit clearance for KB pistons.
 
KB pistons can be installed tighter than other performance pistons. A close fitting piston rocks less, supports the rings better and seals the engine for maximum power. When a loose fit engine is desired the rigid skirt design of the KB piston allows the builder a choice without fear of piston damage. See the clearance chart below for minimum and realistic maximum loose fit clearance for KB pistons.
  
 
===Special notice on Keith Black piston top ring end gap===
 
===Special notice on Keith Black piston top ring end gap===
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{{!}}The Keith Black pistons unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage. Safe top ring end gaps can be found by multiplying the bore diameter by the appropriate ring end gap factor from the clearance chart below.
+
The Keith Black piston's unique thermal conductivity, ring location and varied end use requires special attention be paid to top ring end gap. KB pistons make more HP by reflecting heat energy back into the combustion process and, as a result, the top ring runs hotter and requires additional end clearance. Increasing ring end gap does not affect performance or oil control because normal end gaps are realized at operating temperatures. Failure to provide sufficient top ring end gap will cause a portion of the top ring land to break as the ring ends butt and lock tight in the cylinder. The broken piece may cause further piston or engine damage. Safe top ring end gaps can be found by multiplying the bore diameter by the appropriate ring end gap factor from the clearance chart below.
  
 
'''Example:''' 4" bore "Street Normally Aspirated" = 4" bore x 0.0065 = 0.026 top ring end gap. NOTE: Second ring end gaps do not need extra clearance. Dyno and track testing has shown that 34 degrees or less total ignition timing makes the best HP and time. Excessive spark advance, lean fuel mixture or too much compression for the fuel and cam used will make heat sufficient to butt piston rings with as much as 0.060" ring end gap. The entire top land can expand enough to contact the cylinder walls, when close to melt down temperatures are reached.
 
'''Example:''' 4" bore "Street Normally Aspirated" = 4" bore x 0.0065 = 0.026 top ring end gap. NOTE: Second ring end gaps do not need extra clearance. Dyno and track testing has shown that 34 degrees or less total ignition timing makes the best HP and time. Excessive spark advance, lean fuel mixture or too much compression for the fuel and cam used will make heat sufficient to butt piston rings with as much as 0.060" ring end gap. The entire top land can expand enough to contact the cylinder walls, when close to melt down temperatures are reached.
 +
  
 
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     <td bgcolor="#FFF8DC" rowspan="3" class="table_label_two" align="center" valign="center" width="180">'''APPLICATION'''</td>
 
     <td bgcolor="#FFF8DC" rowspan="3" class="table_label_two" align="center" valign="center" width="180">'''APPLICATION'''</td>
 
     <td colspan="3" class="table_label_two" align="center">'''HYPEREUTECTIC'''</td>
 
     <td colspan="3" class="table_label_two" align="center">'''HYPEREUTECTIC'''</td>
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     <td bgcolor="#dddddd" colspan="3" class="table_label_two" align="center">'''FORGED'''</td>
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     <td bgcolor="#F1F1F1" colspan="3" class="table_label_two" align="center">'''FORGED'''</td>
 
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     <td bgcolor= class="row_a" align="center">0.0015" - 0.0045"</td>
 
     <td bgcolor= class="row_a" align="center">0.0015" - 0.0045"</td>
 
     <td class="row_b" align="center">0.0020" - 0.0045"</td>
 
     <td class="row_b" align="center">0.0020" - 0.0045"</td>
−
     <td bgcolor="#dddddd" class="row_a" align="center">0.0040"</td>
+
     <td bgcolor="#F1F1F1" class="row_a" align="center">0.0040"</td>
−
     <td bgcolor="#dddddd" class="row_b" align="center">0.0035" - 0.0070"</td>
+
     <td bgcolor="#F1F1F1" class="row_b" align="center">0.0035" - 0.0070"</td>
−
     <td bgcolor="#dddddd" class="row_a" align="center">0.0045" - 0.0080"</td>
+
     <td bgcolor="#F1F1F1" class="row_a" align="center">0.0045" - 0.0080"</td>
 
   </tr>
 
   </tr>
 
   <tr>
 
   <tr>
Line 266: Line 270:
 
     <td bgcolor= class="row_a" align="center">0.0025" - 0.0045"</td>
 
     <td bgcolor= class="row_a" align="center">0.0025" - 0.0045"</td>
 
     <td class="row_b" align="center">0.0030" - 0.0050"</td>
 
     <td class="row_b" align="center">0.0030" - 0.0050"</td>
−
     <td bgcolor="#dddddd" class="row_a" align="center">0.0060"</td>
+
     <td bgcolor="#F1F1F1" class="row_a" align="center">0.0060"</td>
−
     <td bgcolor="#dddddd" class="row_b" align="center">0.0080" - 0.0100"</td>
+
     <td bgcolor="#F1F1F1" class="row_b" align="center">0.0080" - 0.0100"</td>
−
     <td bgcolor="#dddddd" class="row_a" align="center">0.0090" - 0.0110"</td>
+
     <td bgcolor="#F1F1F1" class="row_a" align="center">0.0090" - 0.0110"</td>
 
   </tr>
 
   </tr>
 
</table><br>
 
</table><br>
Line 280: Line 284:
  
 
===Metric rings===
 
===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.
+
Metric rings (2mm x 1.5mm x 4mm) were 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==
 
==BBC oil ring depth==
Line 296: Line 300:
  
 
[[File:PISTON RING END GAP LOCATION.jpg]]
 
[[File:PISTON RING END GAP LOCATION.jpg]]
 +
 +
===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/applications that use metric rings so this has to be checked, regardless.
 +
 +
==Changes to popular rings, including Sealed Power E251K rings==
 +
[[File:Ring dimensions.jpg|400px|right]]
 +
As of about 2011, the Sealed Power 4" nominal bore (including oversizes) x 5/64" width top compression rings have changed. The ring is now thinner, '''''radially'''''. Instead of a ~0.180" radial thickness to fit a 0.200" deep ring groove, they now have a ~0.140" radial thickness. So when installed in a "normal" piston, the ring backspace is now 0.060"-0.070". Sealed power claims this was an engineering change to improve bore conformability. <br style="clear:both"/>
 +
 +
To address concerns regarding the increases backspacing, the following bulletin was released by Mahle (Mahle also makes Sealed Power, Federal-Mogul, and Perfect Circle rings):
 +
 +
;TB-7001 Issued July 27, 2011 (also released March 20, 2012 as AERA Technical Bulletin TB 2588)<nowiki>:</nowiki>
 +
<caption style="margin: 1em auto 1em auto;"><h4>'''Steel Compression Rings with Reduced Radial Wall Thickness'''</h4></caption>
 +
 +
MAHLE Clevite Inc. is transitioning its popular MAHLE Original ring sets from a grey cast iron top ring to a carbon steel top ring. The advantages include; 35% more strength, 30% less weight and double the resistance to side wear which is a common problem on late-model engines.
 +
 +
Since the steel is 35% stronger than cast iron, we can achieve the same ring tension with 35% less weight. That weight savings is made by reducing the radial wall thickness of the steel ring.
 +
 +
The net result is a ring that's lighter, so it has a higher effective RPM potential, stronger - so that it weathers the abuse of today's high output engines better, and actually seals better because the reduced radial wall allows it to conform to the cylinder wall better.
 +
 +
Having said all that, there's some additional explanation needed when it comes to back clearance - that area behind the ring which is calculated by subtracting the ring radial wall width from the root depth of the ring groove in the piston. For example; if I have a ring radial wall of .170” and a groove depth of .195” then my back clearance is .025”. Reducing the radial wall of the replacement carbon steel rings does increase the back clearance because they are going into piston grooves designed for the thicker radial wall of the cast iron rings.
 +
 +
It's been a well-accepted piston/ piston ring engineering design criteria, that for optimum performance, ring back clearance should be minimized. This comes from the fact that the top compression ring needs the pressure from the combustion gases to get in behind the ring and push out on the ring to maintain proper seal on the high pressure, or combustion stroke. The logic was that the smaller the area created by the back clearance, the quicker that pressure would build to push out on the ring, and the quicker the ring would react to its sealing requirements job. That logic is all good but what about the reality of the concept?
 +
 +
Since MAHLE makes both components in this equation - pistons and the rings, our MAHLE piston ring R&D lab did some testing in conjunction with one of our OE customers to see if engine testing could tell us what the right amount of back clearance should be. What the lab folks found surprised most all of us! The engine wasn't nearly as sensitive to ring back clearance as it was to ring side clearance.
 +
 +
The reason was the gases have to get past the top side of the ring in order to get around to the back of the ring to push out on it. When we tightened up the side clearance to less than .001", the ring went unstable even at normal operating RPMs. Blowby, which is gas leaking past the face of the ring, increased dramatically. Changing the back clearance didn't show us anything, negatively or positively either direction. We realized it was all about having enough side clearance to let the gases flow back to the back of the ring not how much back clearance we had!
 +
 +
We came to the realization that in any cylinder, you have hundreds of CC's of gases available to fill that relatively small volume behind the ring (0.4 cc's), Those gases are at a very high pressure, several hundred, or even thousand PSI, so they will fill the small space behind the ring very quickly if you give them enough room, a.k.a. side clearance, to get there.
 +
 +
Most OE and aftermarket side clearance specs are in the .0015" - .0025" range. For our regular, non-racing, customers; changing from a cast iron top ring to a steel top ring won’t cause any adverse effect at all from the increased back clearance because the side clearance is adequate to allow the gas movement. Remember, we have hundreds of cc’s of gas to fill the very small amount of space change.
 +
 +
The performance engine builders are a different story, but they take care of the issue with custom groove specs. The MAHLE Original performance ring catalog supplies radial wall specifications for every ring for just that reason. Many of the true high performance engine builders specify ring grooves with less than .001" side clearance, but they add gas ports, small channels drilled in the piston, either from the top or side of the piston, to give a direct path for those combustion gasses to get directly to the back side of the ring. The engine doesn't care how the gases get back behind the ring, it only cares that it does, and in enough volume and pressure to do the job.
 +
 +
In summary, you can replace cast iron top rings with carbon steel, get all the benefits we’ve talked about in this bulletin, and rest assured we’ve done our homework on the engineering side!<br>
 +
'''End of TB'''
  
 
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Latest revision as of 18:57, 25 September 2013

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