Worn shims - - Why?

[ventura ace]

Take a look at the wear on these shims. These are 2 of 5 that I replaced whilst doing a valve adjustment check last week. The valve clearances were spot on, almost exactly where I set them 20K miles ago, but the pitting and scratches have got me puzzled! All 4 exhaust shims were pitted to some extent, with #1 being major pitted as shown in the first picture, and the second picture being somewhat typical of the other pitted shims. The intakes looked fine, except #2. The lobes all looked good to me, intake and exhaust, as shown in these typical 2 pics.

My guess is questionable lubrication. I should probably go back and read the threads about motor oil recommendations. I've been running 20W-50 and 10W-40, with no criteria on picking a certain brand, and changing every 5K miles, with most of these miles being put on the car with cross-country extended freeway driving at 75 - 80 mph.

Anybody had this type of wear on the valve shims? I've never seen it before it in the 100K + miles that I've put on this car (mostly 1438cc stock engine). The last 20K miles have been with a 1.8L modified engine with some mildly agressive cams. The intakes (40-80) are set at .011" per PBS engineering recommendations. The exhaust (70-30) are set at .019", also per PBS recommendations. Maybe the exhaust cam is missing the ramp at the .019" gap and needs to have clearance reduced to catch the ramp better?

Any thoughts? Thanks in advance. Alvon

[So Cal Mark]

that happened in one week? Did you use oil with sulferic acid additive? Those shims are hardened, it's hard to believe the lobes aren't damaged after riding on those shims

[ventura ace]

Not one week, silly! (sorry Mark, I probably didn't make it clear). About 2.5 years, and 20K miles on these shims. They were brand spanking smooth and shiney when first installed, and looked good the last time I checked them about 12K miles ago.

Do you think that the Rotella oil that's been recommended would have prevented this, or is it likely to be something else causing the pitting? There's no sign of gouges on the lobes -- they're all very smooth. Just some discoloration, but I believe I remember seeing those discolored patterns when I put the cams in originally.

Alvon

[Flyingthere]

That is really strange, I wish I could help but let me share this Vicks has a new thing where you can email the mechanics your pictures at (I believe) vickstech@gmail.com. You may want to give that a shot. If the email does not work give them a call I have it written down somewhere and will look tomorrow to confirm. Good luck.

[So Cal Mark]

lack of zinc lube is the only thing I could imagine. I'd like to fwd those pics to my cam grinder and get his opinion

[ventura ace]

Thanks for the idea, Bob.
Mark, I'll take some more pics to e-mail to you. The pic of the really bad shim was without flash. The reflection from the flash in the other pics makes it hard to see what's there. I'll try to take more shots without the flash.

Alvon

[pope]

Interesting. Alvon, the first shim pic looks dull. It should be as shiny as chrome. Is it just the angle of the picture that makes it dull?
20w-50 should have all the zddp you need, 10w-40 might be reduced. Is 20w-50 to thick? Dont know...I have heard some guys use it.
Dont us any oil that has “Energy Conserving” in the API circle...reduced ZDDP modern oil.

Dont know for sure. Hope Mark comes up with something,

[racydave]

I just wonder why the wear is'nt more symetrical. It makes me think the shims may be at fault. More Zink!

[baltobernie]

Ouch! That lobe looks trashed.

Were your valve springs within spec when you installed the new cams?

[ventura ace]

The valve springs are higher force racing valve springs -- so that might have something to do with it. I'm leaning to think that it is a combination of higher spring forces, little-to-none ramp on the reground cams, perhaps a questionable shim in the first place, and possibly not the optimum selection of motor oil.

I've swapped out the shims, of course. I may set them to smaller clearances to minimize slapping from lack of ramp. I'll make it a point to study all my shims closely for surface defects before installing. And I'll check into using the best oil for this old type of valve actuation (what is it that was recommended here -- Shell Rotella or something like that?).

Alvon

[Europa]

The shims show damage (looks like gouge marks), but the cam lobes look just fine. If that's the case, wouldn't the quality of the shims be suspect?

[ventura ace]

I found a few articles on the internet, and together with replies from Guy Croft and Mark Allison, confirm my suspicion that the problem is with high valve spring loads. I'm running a set of performance racing springs that I didn't really research well enough at the time I put them in the head, but after studying the section in Guy's Workshop Manual about valve springs (pp 75-77) last week, I'm convinced that it's got to be the stiff springs causing the shim pitting.

These springs were formerly used by a fellow in Chicago area that raced 1438cc powered fiats. It's a double spring arrangement, with slight interference between the springs for damping. It is a stiff spring. Here are the numbers:

Spring type ========Standard* == GC Performance* ==== Mystery Performance
F, valve closed----------110#-----------85#-------------------------145#
F at std 9.5mm lift ----185#-----------190#-------------------------228#
F at 10.4mm lift--------194#-----------200#-------------------------236#
spring rate, approx----200#/in-------254#/in---------------------221#/in

*From Guy Croft Workshop Manual, page 76.

Perhaps these springs were fine for building race engines that get maybe one season of racing before a rebuild, but not for 20K miles of driving.

I'll rebuild the head with new shims and either the GC performance triple springs or another set of performance double springs (slight interference between springs for damping) that I have, that have spring rates and forces comparable to the GC springs. Maybe a good project for a tech day at my house???

[SpiderHead]

You will certainly get a great turn out if you can talk Steve into cooking us some steaks!

[rlux4]

I'm ready anytime, Ace! Can we set up the work area around the hot tub?
Ron

[baltobernie]

Alvon, sorry to see your misfortune, but happy that you've found the probable cause. Are you going to replace the cams?