Hi all,

My mechanic sent me this photo of my old retainer. Apparently all 8 were cracked. I don't see any "cracks" per se. My friend's opinion on the photo is that the circular mark (see zoomed) is a casting mark?

Keen to get the forum's thoughts.

Thank you.

 

Bump!

 

Are these AP1 retainers? If so, just change it anyways and get AP2 retainers

 

Those marks certainly are not the cracks that pretty much anyone else would see. I just took a look at some AP2 retainers and didn't see that casting mark though.

 

Those aren't casting marks. These retainers aren't castings. They're stamped parts. That looks like a shock line, which is an artifact of a multi-stage stamping process. In one of the first stages the part is drawn into a wider cup, then in a latter stage the center section is drawn into a smaller cup section and the perimeter is shaped into the final dimension. It's done this way to get the metal to flow properly, preventing excessive sidewall thinning which would occur if it was a single stage stamping. My guess is that this part is made on something like a 5- stage progressive die, with each stage shaping the part gradually into the final dimension. It's done this way to achieve the critical dimensions required. After the parts exit the press they are likely heat treated then tumbled in a ceramic bead media to remove surface oxides, relieve surface stresses and give the part a uniform surface texture.
As you can see, that line isn't straight, which is caused by the anisotropy (non-uniformity) of the microstructure, typical of parts stamped out of a rolled sheet metal. I've never looked at retainers before so I can't tell you if this is typical or not but my first impression is that this shock line is quite pronounced, and may be heavier than normal. But since this isn't a critical area for potential failure of a retainer, it was considered acceptable from a quality standpoint. For all I know all retainers look like this - I'm just saying it doesn't appear to be a defect. The shock line is located where the die contacts the metal on this subsequent stage. Shock lines are typical on parts stamped on multi-stage dies.

 

Thanks for the detailed response! I spoke to my mechanic and instructed him to replace the exhaust side as well as a result of freaking out once he sent that photo.

In any case I'm glad they were not cracked per se.

 

Not sure if I see any cracks either. Its best to replace them if you have any doubt. Especially on a high revving engine!

Jay

 

Those are indeed stress marks in the retainers. Likely suffered a mild over-rev at some point in the cars life.

Ap1 retainers should be smooth as glass on the underside.

 

Close up of the worst one. (The retainer itself actually looked a little different to the rest. See line around the section that usually cracks)


Nothing like the infamous Billman replying to your thread!
Thanks confirming. I asked for the old retainers when I took the car home:

 

Smart. Always ask for old parts. At tbe very least it (mostly) ensures they actually did the work...