Sounds like you may be on to something. You can make up a tool to compress a spring on the car to see what the keepers are up to. Can't quite envision how they could hit without things falling apart, but have never seen marks on the valve side, so definitely worth a look see.

 

Here are some pictures of the retainers I took before installing the latest cam housing, and a picture of a lifter that was marked.

The rubbing on the retainers is pretty obvious. I should have paid attention to this much earlier.

 

Those Ti retainers seem to stand a lot taller compared the top of the valve stem than the stock retainers.

 

Semi-solid lifters ... how exotic

Reverse engineering the retainers to titanium was apparently not 100% successful, but it should be fairly straight forward to correct.

 

I found 2 old pics of Lindsey Racing valve springs with chrome moly retainers for comparison.

 

Well then, looks like you found where the problem is. Are the retainers taller than stock relative to the stem top? On a stock head, do you know if the lifter would hit the retainer if the button gets pushed in all the way?

 

Are those retainers made for stock keepers?
If so the it seems pretty odd because the spring preload must be way low with the retainer that high on the stem.

 

...or the retainers are very thick

 

Is it the pics or is the top of the valve stem concave ? The retainers hitting the lifters explain wiping out the cam lobes and followers since the follower could not spin . Your real lucky a valve hasn't dropped.

Clifton

 

Let me see if i have pictures of my ti retainers.

 

I don't know, and because of that I am beginning to have doubts on this latest theory.

If you look at the pic below, the upper edge of the retainer supposed to hit the lifter is a fair bit beyond the top of the valve stem.

If the retainer hits the lifter, then for sure the lifter's button must be retracting excessively inside the lifter.

If the lifter is in good working order, then valve spring preload may be set excessively high for this to happen and/or valve springs are too stiff to begin with?

 

Thom

How are you measuring and at what height are you setting your valve spring preload?

 

I took some measurements for you to compare with. On a bone stock 951 head, the distance between the top ridge of the retainer and the top of the valve stem is "about" 3mm. On a spare soft lifter, the button stands about .7mm above the "deck" inside the lifter cup. I could not get a precise measurement about how far in I could push the button, but the travel distance seemed to be fairly limited, and certainly less than 3mm. Whether the button would go in further under heavy mechanical pressure, I don't know. But, if the distance from your retainer ridge to the top of the valve stem is less than 3mm, then your set up is giving you less margin for error than stock. If so, you might try using a set of stock retainers/keepers to increase the distance and see if that resolves the issue. While you have the retainers off, you can get the spring rates too...

 

If the seats and the valves have been cut a bunch then the stem over all length has to be cut to get the stem height back correct putting less stem above the retainer . The keeper area does not change.
May be time for new valves and seats or start over with another head and valves . However those retainers do not look like my TI retainers either.

Clifton

 

Nick, I don't think it is possible to get a very precise measure of spring preload with the springs installed.
I adjusted spring preload by putting each retainer and its retainers locks in place, holding the retainer upwards by hand, measuring the distance between the spring face of the retainer and the spring seat washer, then adding/removing shim(s) below the spring seat and repeating this process until getting the right distance between the spring face of the retainer and the spring seat.

Tom, thanks much for the figures.
I have a set of new stock retainers on the way.

Clifton, the valves were not cut.
Do you have pics of your Ti retainers?