Piston Pin and Rings
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Posted by: matin ® 02/25/2006, 07:14:15 Author Profile eMail author Edit

I need to know that whether during engine operation does the piston pin and piston rings rotates or not,because if they dont then during inspection one should always find marks on the liner and if they rotate how do they do that and at what rpm and why????????????????

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Re: Piston Pin and Rings
Re: Piston Pin and Rings -- matin	Post Reply	Top of thread	Forum

Posted by: randykimball ® 02/25/2006, 08:59:38 Author Profile eMail author Edit

Piston rings usually do not rotate much. While assembled, you should stagger the gaps according to the manufactures recommendations and when dissassembled they are usually fairly close to where you placed them. So the ring gap stagger of properly fitting rings is why you do not see streaks in the liners. No streaks in the liners is reason to be pleased, it is not a reason to seek out why there is no streak. Piston pins do rotate, this is because the actions during the different cycles exerts rotating forces which tends to rotate the pin. The pin should be a slide fit in both the piston and the rod allowing and causing oil to work between all contact areas. By rotating, the pin tends to wear in a more even pattern, but this is not the magic, continue reading. The speed of rotation is of no consequence and is a product of the RPM, friction, viscosity, and stroke forces. Rotation patterns on the used pin is evidence that the pin fits correctly and allows oil to get to all contact areas. When a pin does not show evidence of a rotation pattern in a disassembled engine that did not have a piston/pin/rod failure is of no consequence, since the engine is now disassembled and already did not have a piston/pin/rod failure. When reassembling the engine, be sure the pin rotates freely inside the rod and the piston. That the pin fails to rotate is rarely the cause of a failure, something else will ususally fail many hours before a stuck wrist pin. If a stiff pin fails it is because of major lubrication problems causing the pin to lock in the rod AND the piston or the reason below. Wrist pin rotation also assures that the rod can seek and maintain the sweet spot linerally (side to side) between the piston bosses, which should be perpendicular to the wrist pin and crank shaft. With rod journal bearing slop and slop at the crank shaft thrust bearings the rod will often tend to favor one end of the journal and become less perpendicular to the crank shaft and piston pin. This causes the rod to migrate diagonally towards one of the piston bosses and causes the pin to be pushed against one of the piston pin keepers. This may cause the pin to stick in the rod or the piston bosses. Realize this is not caused by a failure of the piston pin but is an evidence of journal bearing and thrust bearing being worn out. Such an engine is in serious need of a complete rebuild and would soon fail due to a journal failure bending a connecting rod and stuffing it out the side of the engine block. So proper lubrication is the key. If you are investigating wrist pin rotation and compression rings not leaving streaks you are chasing a ghost. You should be more concerned with the fit of the journals and thrust bearings because these are where upper rod and piston skirt problems tend to begin. .... IF the engine was properly assembled in the first place. /←randy→/ The worst suggestion of your lifetime may be the catalyst to the grandest idea of the century, never let suggestions go unsaid nor fail to listen to them. Modified by randykimball at Sat, Feb 25, 2006, 09:53:13

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Re: Piston Pin and Rings
Re: Re: Piston Pin and Rings -- randykimball	Post Reply	Top of thread	Forum

Posted by: matin ® 03/01/2006, 03:33:45 Author Profile eMail author Edit

Thanks for the reply but I investigated this issue on the net and I found some interesting website that do explains the movement of piston rings please check this website ???://???.sacskyranch(DOT)com/piston_ring_rotation.htm Modified by Administrator at Wed, Mar 01, 2006, 08:28:51

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Re: Piston Pin and Rings
Re: Re: Piston Pin and Rings -- matin	Post Reply	Top of thread	Forum

Posted by: D.Taggert ® 04/17/2006, 18:10:28 Author Profile eMail author Edit

Would it be possible to design a piston engine without piston rings?

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