pin lock ?

[Adger Smith]

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? :~)

[Reed Granrt]

Originally Posted by Adger Smith

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? :~)

Hello Adger
I still have my home made pin oiler also. Back in those days, I feel that was what gave clips their bad rap. As pistons were made back then, this industry was going thru growing pains. We were doing things with pistons that these companies had no thoughts of. Since most pistons did not get adequate oiling, they would partially seize and batter out the clips. Hell we could have pushed any type retainer out. And if you ask any piston manufacuter to day about clips. most of these engineers dont even know what a clip is therefore they will tell you it aint no good cause they aint even seen one must less tested one. I have worked in industry for 34 years and have worked with some super high dollar pistons in cylinders and not one has ever had a spiral lock in it. Most either had tru arc or wire clips.
reed

[Run to Rund]

I used double tru arc 30 years ago and was surprised to see round wire locks supplied with Mahle pistons I got several years ago. Tech at Mahle assured me they are the best nowadays.

[rod]

my TRW pistons are old, bought new in 1968. i bought these for $39.00 for the set of 8 !!! this is the truth.
and yes, they did have pin oiling problems. i have since built a fixture to hold them and drilled them myself. i did contact the Tru-Arc tech, and .003" clearance between the lock ring and the groove is acceptable. doubling the locks does not double the clearance, it remains at .003". also the cold end play should be at 0", as Adger said. the piston will swell long before the pin does. [however that will remain to be seen, when i race at the new Lake Havasu City drag strip, where it regularly gets to 120 degrees!]
thanks for the replys, especially Adger and Reed.
rod in AZ

[rawhide]

the flathead Ford's that I have worked on have round wire locks so old is again new.
All of the Ford Cosworth engine parts I have seen have used the round wire locks from the 1960's up till now. I have only seen I engine pound out a tru-arc and I felt that it was an assembly error.
regards, Roland