They are unmistakeable. We switched all ours to Ti.

 

are Ti or 04 and up retainers better?

 

my problem was, on the intake side, ALL OF THEM were cracked, every single one so they all looked just about flush where they were supposed to be seated in the retainer, then I look at the exhaust side and I was like uh...they look a little different, although I did not know if there was a difference on that side, so I pulled it all apart and the picture you see that billman posted of the cracked retainer is what I had ALL on the intake side.

Also in my situation the tip of the valve broke off, and the valve was just sitting there, stuck open because the spring could no longer pull it back to close it, this guy drove home like this and parked it, even after that had a "mechanic" aka "idiot" start it up and rev it a little and it still did not drop that valve, extremely lucky. The cam lobe on that cylinder had started wiping out because of the hitting.

 

What is #11? And wouldn't this part keep everything together?

BTW, this pic is from a Honda engine, not necessarily an S2000 engine. Does ours differ from this?

 

As part of the check - would you also see grooves or wear marks on the cam lobes from striking the lowered valve stem - and possibly contacting the retainer?

 

Parts #11 are the valve keepers. They are wedges that slip into the retainer and hold the valve stem in place. When the retainers stretch enough they can't hold the keepers in place anymore, and when the keepers come out there is nothing left to hold the retainer in place. Without the ratainer and keepers there is nothing connecting the valve spring to the valve stem, so the valve will simply "fall" open. When the pistons hit the valves it's bad enough, but from some of the damages we've see it also seems that the keepers and ratainers can do a lot of damage as they bounce around under the cam/rocker cover.

 

Keep in mind that it is the retainer that is stretching. The valve stem length remains the same, so the valve clearance does not change when the keepers stretch. IOW, the valve stem isn't actually lowered; The retainers are simply riding higher on the stems and keepers.

 

MX-5, good explanation

To clarify a little more, the #11 split keepers a tab on the inside surface that engages the groove in the valve stem #6. When installed on the valve stem they form a tapered outside surface that engages a corresponding taper inside the retainer #9. The valve springs force these tapers together. To dissassemble, the retainer is pushed down against the valve spring, freeing the keepers. Often a knock with a hammer is needed to unseat the taper lock.

When the retainers split, it allows the taper of the keepers to pull thru.

What I don't understand is why the retainers split from the bottom... seems to me the higher stess from the taper lock is on the top surface?

 

Retainers are being pushed up on the outside edges and pushed down in the middle. So the upper side of the retainers is in compression and the lower side is in tension. It is tension that causes cracks.

 

So even though you check the retainers for overrev shortly after an overrev, everything may look sound. You might have to check periodically every couple thousand miles?