Piston Pin Retaining Clips

[buns]

I am rebuilding a 1957 Ford 312 which has very low miles on it and the original pistons are in excellent shape, hence , I would like to re-use them. These pistons came with full floating pins held in place with a round wire "G" shaped clip. For obvious reasons I do not want to re-use these clips but I have had no luck finding new ones (I have searched everywhere).The pin diameter of the 312 is .912", and as luck would have it, Ford decided to use this same diameter on it's new small block engine, the 289 and 302.

These engines did not come with full floating pins, but luckilly, aftermarket performance piston manufacturers used the same diameter of pin with their full floating pins, hence, spirolox and tru-arc locks are available. The problem is that the retainers I found are .042" wide, as opposed to the .055" of the original retainers.

With the original clips, there is .035 'end play' between the pin and the retainers. With the new clips, there is .065". The questions are ,how much gap is too much? What causes the pin to exert pressure on the clips causing them to pop out?

There must be a lot of force at high RPM as race car engine builders like to use 2 spirolox per side. The car that this engine is going into is going to be a "parade queen" and will probably never see this side of 2500 RPM.

Any thoughts or comments would be appreciated.

 

[Tmoose]

In the 70s every Chevy racer was striving for 0.000/0.010 inch endplay. The Ford SAE report on the big block FORD GT engine development claims they needed 0.005 tp 0.010 to avoid retainer failure that ocurred with less than 0.005 inch endplay.

I don't think Endplay is the biggest problem. A round wire circlip properly is mated into a round section groove, machined with a tool with a round nose, 055 inch diameter or so. A spirolock or truarc belongs in a rectangular groove of precise dimensions, especially "depth" or outside diameter.

Do your lock rings have one or 2 ears or tangs for removal?

http://motorcycleproducts.co.uk/catalogue/images/930000.jpg

Or, no ears, and s slot cut in the piston to pry them out?

http://www.rivayamaha.com/RivaStore/images/prox_pistonkit.jpg

For a while Chevy moved away from occasionally troublesome truearc/spirolock, and adopted round wire locks sith no tangs, and a bevel on the wrist pin to positively capture the circlip. They may be available for a 0.927 diameter pin, which might be close enough if the wire diameter is the same.

For passenger use I would not be averse to carefully tweaking the old rings to full diameter, and checking them for full and tight fit in the groove. Some engine builders advocate positioning the tangs inline with the cylinder centerline to best resist loosening during hi rpm acceleration

Bent con rods are a great wrist pin ejector. Whether good used or rebushed I'd find a shop with one of these to check them.

http://www.allstates.com/SUNNEN TN-111 ROD ALIGNER.jpg

 

[buns]

Thanks for the info, Tmoose. One thing that I forgot to mention is that the groove in the piston for the retainer appears to be rectangular. Apparently Ford used round wire clips as well as square edged "E" clips on these engines. I have tried without success to determine if the grooves were cut differently to accomadate the style of retainer.
The round wire clips that I have are shaped like a "G" and hence there is only one tang for removal. My concern is that they are too easy to remove. I just grabbed the tang with needle nose pliers and out they came with little effort.
As you mentioned regarding the use of round wire clips with a bevelled pin, I see that many piston manufacturers are still using these. My pins have a slight bevel, but I believe this is only for ease of starting the pin into the piston.

 

[SMOKEY44211]

You may want to consider rebushing the small end of the rod and running an interfearance fit. Find a shop with a rod heater oven makes it a simple task. I've done this many times not so much to get rid of the retaining clips but to increase the load capabilty of the wrist pin. In a heavily loaded engine the bushing is the first to go. In your case it will achieve ridding any concerns about retainer failure.----Phil

 

[Tmoose]

For the beveled pin to capture the wire circlip the clip must be tang-less, and the bevel must be significant to start to ride over the circlip.

 

[stout1]

Why do you want to change something that isn't broke? I always have reused the retaining clips in race engines and in antique cars and tractors. I am about to redo a 55 t-bird and if everything looks good I'll use them again in there. Especially in this application there isn't going to be much acting on the retainers. You have to really be careful when trying to re-engineer some of the old designs, sometimes there was a good reason that things were designed way and sometimes there wasn't, you just need to be careful. Good Luck

Michael

 

[buns]

Thanks to all who replied. I found some info at

http://www.kb-silvolite.com

that answered my question. Here is an excerpt ( in case anyone else had the same question).

Occasionally lockring trouble is incorrectly attributed to a piston pin being either too short or too long. The fact the lockrings can be installed in their respective grooves with the pin in place is an indication in itself that the pin is not too long. It should be understood that under operating conditions the clearance between the end of the pin and lockring can never be less than it was during installation because the thermal growth of the piston, by virtue of both its greater coefficient of thermal expansion and its higher temperature, is much greater than that of the pin. On the other hand, a short pin should not have any adverse effect because in a properly assembled engine there is nothing to impart axial motion to the pin. If conditions are such as to cause the pin to slide back and forth, excessive end clearance will permit the lockrings to hammer out sooner; however, in such a case reducing the end clearance merely serves to delay but not prevent the inevitable pounding out of the lockrings. The lockrings must not be relied upon to restrain axial vibration imparted to the pin by misalignment.