Piston Pin Retaining Clips
Piston Pin Retaining Clips
(OP)
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.
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.





RE: Piston Pin Retaining Clips
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://mo
Or, no ears, and s slot cut in the piston to pry them out?
h
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
RE: Piston Pin Retaining Clips
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.
RE: Piston Pin Retaining Clips
RE: Piston Pin Retaining Clips
RE: Piston Pin Retaining Clips
Michael
RE: Piston Pin Retaining Clips
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.