pin lock ?

[Alan Roehrich]

Originally Posted by Dwight Southerland

Really?? Alan, I'm not criticizing or correcting that statement, but I would really like some evidence. I have been involved in several "exotic" European-based engine builds in the past few years and every one of them were factory designed with TruArc type lock rings. These were everything from turbocharged four cylinder to NA 12 cylinder that run over 10K+ rpm and cost over $100K. I think the quality of the ring and the assembly specs are important for integrity, but I don't see failures when properly done. The Japanese like the wire locks because they are cheap (but effective).

Dwight, I personally have not had any come out. But then I haven't used pistons and pins with double Tru Arcs for 15-20 years, when we stopped using Manley and TRW forgings in the majority of race engines. However, I have seen failures where the Tru Arcs did come out, and it happened to guys I know are every bit as good at building engines, and as careful and conscientious as anyone I know. I'm sure one of the problems is the poorer quality control we've seen on a lot of parts in the business, whether it be cheaper Tru Arcs, poorly machined grooves, or less than top quality wrist pins.

Of the top 6-7 piston manufacturers for race engines, none offers Tru Arc retainers on any off the shelf pistons. I don't think Spiro Locks are any cheaper (last set I bought for a freshen up cost near $50) and the groove is similar, so machining costs probably are as well. Whether they use Spiro Locks instead of Tru Arcs due to demand or due to technical superiority, or due to cost, is, I guess, a matter of opinion. I've never had a piston or pin engineer tell me Tru Arcs were better. I have seen various engineering studies on the round wire locks with chamfered pins, all of the finite element analysis and other data show the round wire locks retain the pin and distribute the load better than the other locks.

Feel free to ask the guys at JE, CP, Wiseco, Mahle, Autotec/Racetec, Diamond, Ross, etc, what they think, maybe they'll send you some documentation on engineering studies. I just looked at what some of their people showed me. The data and analysis looked sound.