pin lock ?

[rod]

for this 327, i am going to cut the pin bore for double Tru-Arc lock rings [each side naturally] the lock rings are .042" wide.
what i do not know is how much extra width to make the groove.
any help is always greatly appreciated.
rod in AZ

[Alan Roehrich]

Rod, the guy to call about that would be Erich at Rebco Machine. Very few people use Tru Arcs anymore, as they are known to fail. Most use at least double Spiro locks, and the best set up currently is the round wire locks.

[Dwight Southerland]

Originally Posted by Alan Roehrich

Very few people use Tru Arcs anymore, as they are known to fail.

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).

[Reed Granrt]

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).

I have been playing with engines since about 1962. In the early days, there was no such think as a spiral lock, double or single. TRW was the first high per piston to be made that was affordable fur us broke country boys. The first pistons had single tru arc rings. You know, I have heard a lot of people say how bad these clips were and I have been building engines on a regular basis since early 70's. If the clip is installed "correctly"(flat side out)--I personally have never seen a clip come out. And then later people went to double clips and I have never seen one of these come out either. Yes I have heard many stories of how they can come out but never seen one. Yep read many magazines about what not to do, but still no proof. Sometimes we are victims of our own wives tales. I just redid a chain saw for competition turning 21000rpm and it had tru arc and I said what the **ll. He cut 3 weeks ago and carried it a little past the rpm with no problem. And to tell u the truth my fingers hate spiral "wocks" and I'm sure every one will tell you they are better but-----
reed

[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.

[Dwight Southerland]

I haven't read much from the engineering side about pin locks, but what I have read says the round wire locks are the best. I do know, as you say, that all the American manufacturers use Spiro locks and that TruArcs are very difficult to get through them. I am not a TruArc bigot, so I just go with what ever, though Spiro locks are such a PITA. I personally have never had a lock come out so I cannot say anything other than they must all work pretty good.

I had a piston engineer at Venolia tell me years ago that clearance between the end of the locks is much more critical when using TruArcs; that excessive clearance contributes to pounding the locks and that TruArcs will give before Spiro locks. That seems common sense when you look at the difference in construction. Maybe that's where all this got started - the result of sloppy machine work and tolerances. I know that Chevrolet used a single TruArc in the '69 Z28 engines and that Traco used OEM pistons in their TransAm assemblies with no mods. The aerospace industry also uses single TruArcs in lots of critical assemblies that undergo similar stresses.

[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