tru arc piston locks

[SPARKY]

NUB ---being a rookie eng builder  I am getting conflicting advice:

I had some new 20 + yr. old stock Speed Pro BBC flattop blower pistons we are using with my first eng build for our mule motor.  If you use one set of locks you have about .100 piston pin side to side float.  I have been told that they should have had double locks which will elimimate the float. Should I order the second set of snap ring style locks and eliminate the side to side.

[gearheadeh]

Sparky, Something about this double retainer ring sounds all too familiar.

[Dynoroom]

Yes,you need "dual true arc's" AKA snap rings.

[BALS aSALT]

it takes two rings per side of the piston pin and make sure to install 180 degrees from one another.

[SPARKY]

Thanks guys,  I appreciate the quick comebacks

[Rex Schimmer]

Remember if you are using ID snap rings the sharp side goes to the outside. I thought that the preferred retainer ring was a spirolock?

I prefer the wire style retaining ring and a chamfer on the ends of the wrist pin. As the end of the pin goes against the ring it makes it tighter in its slot.

Rex

[racergeo]

   If they are old TRW or Speed Pro they require the double spirol lock. A bit of a pain but they won't come out like a snap ring can.

[fwillyj]

-from what I have found if you measure a brand new never been squeezed tru-arc lock and get an outside dimension on it---then just squeeze it one time with the snap ring pliers to install it---then remove it and remeasure it the OD---the diameter drops noticeably in size.

-a couple of points to make here is it might be a good idea to have a several sets of spares.

-and to never reuse a lock that has been squeezed more than the one time to install it.

-and if when you disassemble the piston from the rod say to just measure the pin bushing wear and you plan on re-installing the piston---don't remove all the locks from both sides---just remove the two from one side and then install new locks.
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-spiral locks are sized to fit with something like  a .006" press fit into the groove---and the grooves are pretty tricky to measure.

-common BBC pins are .984"---but piston manufacturers don't all use the same spiral lock OD's---there can be some issues when trying to use the wrong spiral lock in a groove that was designed for something other than what you might happen to have.

-spiral locks should be available thru most any decent bearing house and the catalogs list the groove ID dimension and the spiral lock's OD dimension and thickness etc---where you might not be able to easily find all that information from an automotive source.
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-one other detail with those old Speedpro pistons could be that the wrist pins may not be precisely bored all the way thru---some of those old parts had the wrist pins bored in from each side and although there is a hole clear through the pin---there ends up being a distinct rib in the center of the pins.

-if you happen to have those pins with the internal ribs you are asking for a broken engine because they are very likely to break right at either side of that center rib.

[SPARKY]

Thanks for the detailed information,  I will go check them and report back!!!!!!! again thanks