pin lock ?

Adger Smith · 09-21-2012, 09:25 AM

To help answer Rod... The clearance in the groove is not real important with Tru arcs. It is as Dwight says, The total clearance with the pin. Years (& years) ago I cut them in some pistions we used for Dirt racing engines. Because the piston grows more than the pin I always tried for "0" clearance in the pin to lock. I never cut them with more than .004.... When the piston gets hot and clearance develops and the tune up isn't right, (unhappy engine) the pins can batter the locks out. Another important thing about the Tru Arc is proper installation.
As stated in earlier posts the flat/square side out. If doubled install the rounded together. You should always put the open ends of the Tru Arc at the 3:00 o'clock or 9:00 o'clock positions. With the opening at the top or bottom the lock can crawl/slide up or down in the groove at high Rpm. That movement will close the open end just like you had a set of pliers pinching the ends together. When the piston stops (dwells) at TDC and BDC The Tru Arc can flip it's self out.
That last tid bit is why they got a bad rap as being no good....
BTW I also built a fixture to hand drill the pin oilers in those older TRW pistons. That was another problem we had to work around back in the golden/olden days... What about it Dwight? :~)

09-21-2012, 09:25 AM	#7
Adger Smith VIP Member Join Date: Dec 2001 Location: Texarkana Ark/TX Posts: 2,446 Likes: 575 Liked 880 Times in 311 Posts	Re: pin lock ? To help answer Rod... The clearance in the groove is not real important with Tru arcs. It is as Dwight says, The total clearance with the pin. Years (& years) ago I cut them in some pistions we used for Dirt racing engines. Because the piston grows more than the pin I always tried for "0" clearance in the pin to lock. I never cut them with more than .004.... When the piston gets hot and clearance develops and the tune up isn't right, (unhappy engine) the pins can batter the locks out. Another important thing about the Tru Arc is proper installation. As stated in earlier posts the flat/square side out. If doubled install the rounded together. You should always put the open ends of the Tru Arc at the 3:00 o'clock or 9:00 o'clock positions. With the opening at the top or bottom the lock can crawl/slide up or down in the groove at high Rpm. That movement will close the open end just like you had a set of pliers pinching the ends together. When the piston stops (dwells) at TDC and BDC The Tru Arc can flip it's self out. That last tid bit is why they got a bad rap as being no good.... BTW I also built a fixture to hand drill the pin oilers in those older TRW pistons. That was another problem we had to work around back in the golden/olden days... What about it Dwight? :~) __________________ Adger Smith (Former SS)