I am working on a set of heads for my sbf and upgrading the valve springs. The new valve springs have an installed height of 1.800 +- .015. So in checking things with my height mic I find that the intakes average .070 over. So I am looking at a couple of different options. One option is just to use regular shims and stack them under the spring. Another option is to use valve spring "cups" on the intakes plus whatever additional shims they would need. The cups are .060 thick. I dont know that they offer any real benefit on an iron head. The last option is to use off set keepers to lower the caps down and use whatever shims necessary. I can find the keepers with a .050 offset. The exhaust is much closer to spec averaging .025 over. The cam is very mild and the lift shouldn't cause any issues with the caps hitting the valve stem if I use the offset keepers. The easiest would be to just use shims, just not sure if .070 worth of shims would pose any longer term problems.
A .060 thick cup or shim would put you within tolerance on the intake . And a .030 shim would put you in on the exhaust. Unless it is a fairly high lift cam on the upper end of the spring spec .,,,,,you should be good . Shims are easy to get,,,,and are reasonably priced as well . Have you checked the spring pressure with a tester at that installed height ? You might be good to go anyway . Tommy
It's my understanding the method to shim valve springs is to measure all 16 valves height, find the one with the shortest or minimum dimension, shim as necessary and then adjust the installed height for the remaining 15 springs to that same installed height +/- .020". You probably know this already. The idea is to have them all on the same sheet of music. I thought valve shims were limited in how many should be stacked, no more than .030"? I would use the .050" keepers for starters and keep the stack from looking like a roll of quarters?
Shims come in three basic sizes, .015", .030", and .060". Here is a list from Crower with all their valve spring spec's, http://www.crower.com/media/pdf/2008b/166-180.pdf if you look at the measurement steps they are around 14 lbs per .050" step. Thats about 3.5 lbs spring pressure per .0125" compression. Adding multiple shims is OK to get where you need them to be, offset keepers also work. Adding a .015" hardened shim keeps the springs from digging into the heads if no other shim is needed. .060 + .015 = .005" tighter then needed, just a .060" will be .010" looser then needed if shooting for 1.800" when measured at 1.870". Look at camshaft valve lift and compare that to maximum lift before coil bind and see which way you want to set the spring hight. Keep .060" for clearance as a safety.
The cup is actually a shim as well, although thats not its stated purpose. I would use a cup as it may provide a little extra stability. If that doesn't get you to a workable dimension, then add a shim under the cup.
Thanks for all the information and ideas. I have already reground the valves and waiting on a couple of stones to redo the seats. The seats look really good and it wont take much to dress them up. After I get that done then I can get the final numbers and figure out what works the best.
You are correct. Thats why I am waiting to get the final numbers. However the seats look really good and it wont take much to clean them up. Had considered lapping them but the seat face is a little wide so I ordered some stones to redo them. I'm guessing less than .005 added to the height when done. I was also planning to take some time and sort thru the valves and try to match them for the most consistent installed height. Doubt it will make much of a difference.
Not arguing. Just wondering. What would the downside be to a stack of shims? I just ***embled a set of aluminum heads that took .075" of shims plus the .060" spring cup to get the 1.80" required installed height for my springs and cam.. Haven't had any problems yet.
Yeah, I dunno. Seems to me it was just general advice "no more than three shims" iirc, instead use 050 keepers or spring cups + shims if there's more clearance to be made up than that.
Not trying to de-rail this thread, but I've often wondered if new springs were matched closely enough that the installed height and the installed pressure went hand in hand, or if a guy would be better off shimming for the proper installed pressure and not worry about the installed height. Maybe it don't make a hill o'beans, I dunno... Any thoughts?
I wouldn’t tell anyone how to do it but I don’t believe anything written on a box about valve springs. I’ve used this set up for years on my heads and can control pressure with shims and keepers with different placement of internals. Not much $$ here and all I use is a bench vice or my drill press.
That's more than close enough for me, I'm not drag racing anybody or spooling up to 7,000 RPM. I just "***ume" that a new valve spring shimmed to the installed height will at least be within spec, or near enough. This does noticeably improve idle quality. Guys who are picky will take the time to mix and match spring and shim combos and measure individual valve spring pressure till every valve is very close if not identical.
Seems like alot of extra investment for minimal return, atleast on a street engine. I guess one man's extreme is another man's standard.
Yeah, that's hard core racing stuff though. Or "balancing and blueprinting". I like to read a lot before I get into a task, even if I'm not going anywhere near to that level. It's just really interesting to me the attention to detail that goes into that kind of thing. It isn't necessarily minimal return, not for racing anyway, what people sometimes call valve "float" is usually valve bounce, which seriously robs compression. The engine will basically rev no higher than the weakest valve spring out of the 16 is the way I heard it. It will act as a natural rev limiter. So they spend a lot of time setting up the valvetrain with lightweight high $$ parts and insane valve spring pressures on engines that get spooled up high. But even stock/street engines, if they have tired worn out valve springs or incorrect installed height it will cause a noticeable power loss as low as maybe only 4000. Just runs out of steam. Another engine builder says correct spring pressures keeps carbon build up off the valve seats.
Downside of running to many shims is running into coil bind. If you keep stacking up shims you need to be aware of at least .050 clearance before coil bind. Depends on the cam your running also.
If your using the shims to reach the installed height for the springs, and the springs are matched to the cam I don't think you would have issues with coil bind. If your adding more shims to achieve I higher pressure and it makes the installed height shorter, then I could see a potential coil bind situation.
You could have made most of the adjustment with the keeper. After an inner or outer style shim on the bottom of the sprain an aluminum head I’ll look to keepers to get real close to a single shim. Time is cheap when you do your own ***embly .
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