Haxle

My shop is telling me I have three broken valve spring retainers in my '79 SC 3.0 they just rebuilt. They say they have never seen this before. The only difference between my engine and stock is a 964 cam from MotorMeister -- which is a drop-in replacement for the stock cam. What is this greater community's opinion on this?
(Yes, the cam has higher lift than stock. I don't know about duration. The rest of the geometry of the valve train is supposedly the same as the 964 so that *should* not be a problem.)

Bill Verburg

The break on 964s also, usually from over reving, here's one from a 964 Cup car that broke at Lime Rock a few weeks ago;

BryanMD

I have seen everything else in the valve train fail, but not retainers. Were these original new, old or aftermarket? OE springs?

Steve Weiner-Rennsport Systems

Hi:

Its not common, but I've seen plenty of these valve spring retainers fail from the same reason that Bill V. mentioned; valve float.

These are all sintered metal, not machined from bar stock and have been that way through the 3.2's to the 3.6's. This is just one reason why we always install titanium retainers in engines that that see extensive and sustained high-RPM operation.

As everything is always a "cause & effect" issue, one needs to know that these items fail from simple fatigue and/or excessive loads imposed by the piston striking a valve that is hanging open due to float. Factory valve springs are no great shakes anymore, and slowly lose strength and tension over time that results in a steadily lowering threshold of valve float.

When valve springs are new and setup properly, the threshold is at one RPM; as you stack on the miles and run the engine at or near redline, (such as in DE events, racing, or even AutoX), the springs slowly lose tension that will result in valve float occuring at a lower and lower RPM.

We use and recommend valve springs & retainers that are better than OEM for engines that will see some hard use. This helps prevent bent valves caused by missed shifts,...

You know that old saying,..."An ounce of prevention is worth a pound of cure".

LOL,..there are also some tell-tale signs of over-revving left on the tips of the valve stems.

Tom F

I'd like to know whether anyone has seen this kind of failure using the standard 3.0/3.2 camshafts. Also, whether the valve spring tension/height is set the same in the 964 as in the earlier motors. Steve, do you mean that the retainers were different for the 3.2 and 3.6 motors? I thought that the retainers were the same for 2.0 through 3.2. I don't know about the 3.6 at all.

I am a little puzzled by why striking the piston would lead to retainer failure. I would have thought it more likely that the spring would have bottomed out during valve float, and that this impact is what would split the retainer. Or, is it that striking the piston causes the retainer to work free of the keepers momentarily, and then to shatter when it goes back in tension? How can one know for sure? How about burrs in the keeper grooves causing the keepers to sit unevenly, thereby stressing the retainer to split as shown in the photo?

Re. titanium retainers, I thought that titanium was roughly the same strength as steel, just lighter.

Haxle

Thanks for all your replies. More detail: three are cracked -- they don't seem to be completely broken yet. So far as we know, retainers and springs are OE. Shop tested the springs during the rebuild.
The engine was not overrevved and has only a few thousand miles on it since the rebuild a year ago. I have no intention of racing it, maybe a little DE sometime.

Steve Weiner-Rennsport Systems

Hi Tom:

Porsche changed the material for the valve springs retainers from a machined steel part to a sintered metal one during the 3.0-3.2 production and all of the ones in those (and 3.6's) and replacement parst are made this way.

Titanium ones are not just lighter, these are machined from barstock and are lots stronger than these sintered metal pieces.

Although I must say that I've not tracked this real closely, as these events are relatively rare,
I would say that cams with more lift would be more prone to this with OEM retainers than milder cams. I'd use titanium retainers over the OEM ones anyday, even if the springs were not changed in an engine that would be run hard.

A coupla missed shifts is all it takes and the results are not pretty nor cheap.

Tom F

Steve, thank you for the highly infomative reply.

Can the sintered retainers be identified by a visual check next to teh early retainer? Have you seen any failures of the early style retainers?

Steve Weiner-Rennsport Systems

[quote]Originally posted by Tom Frisardi:
<strong>Steve, thank you for the highly infomative reply.

Can the sintered retainers be identified by a visual check next to teh early retainer? Have you seen any failures of the early style retainers?</strong><hr></blockquote>

Hi Tom:

My pleasure Sir, happy to be of service anytime.

It takes a practiced eye to spot the differences between the early steel machined retainers and the later sintered ones. Side-by-side, you can see the subtle finish differences.

The early ones are far more durable IMHO, and these do not fail as easily due to these events. The only failure I've seen are in race motors where the owner repeatedly missed shifts or ran the engine to the rev limiter every time.

Haxle

Just to wind this up.
Shop says definitely overreving. Seems that a valve stem has a diagnostic ding in it. I guess I have to have a chat with Junior.
Stock springs will stay in and the OE retainers and keepers will be replaced with OE. The reasoning is that using titanium will just shift the damage elsewhere, mostly likely to the valves which will be more expensive to replace.
Thanks for all the advice.