I now this is a stupid question , but can shims be installed over these PRC one piece seal / spring seat?
The shims I have fit over them fine , but conventionally I believe the shim goes under the spring locator…

 

NO!

But you can put the seal/spring locator over the shim.

 

Thank you , that’s what I thought but I wanted to make sure. I removed one and it’s a little damaged on the inside. I do t feel good about doing all 16 so I need 16 new seals.

 

You can put the shims on underneath the seals if you want.

Be aware though, that raises the seals, and thereby reduces the clearance between the retainer and the top of the seal. Not a big deal if you're talking about .015" of shim, butt if your cam gives you ALTOTTA lift, then you could run into problems.

 

Well, I was doing a lot of math here for a couple weeks and I determined that because I’m using roller rocker lifters with bronze guides on these PRC heads, but I should probably shim a little bit to increase my pressure due to the extra weight. The biggest thing I want is better harmonic control at higher RPMs. So I’m trying to increase the coil bind distance. Currently, I was set up at 16% from coil bind in comp cam’s recommended to be within 10%. My math determined that a .015 shim would get me down to 11% which is super close good enough. I’ve learned a lot in this experience here I’m still thinking about just taking him to a head shop, but there isn’t any real good head shops around me. Plenty of machine shops, but nobody who I feel specializes in racing heads.

 

A 15,000 millionths of an inch shim would probably be OK. Not sure I'd want to move the decimal point even one place toward the right from there though. I don't think I'd go past about 60,000 millionths of an inch underneath the shim, without careful measuring first.

Although, the thing that would determine whether you can put the shim underneath vs on top of the seal, would be, the clearance from the bottom of the retainer to the top of the seal, at max lift, with a bit of room to spare. Coil bind might establish how much shim you want, butt that other clearance would limit where you can put it.

 

Well I worked it out using Wallace racing calculator and some algebra to determine open pressures. I can’t get as close as I’d like to with my lifters , pressures get too high. I’m thinking I’ll shoot for 1.77 install height which will net 442lbs over the nose and .125 from coil bind at .630

here’s the shitty spread sheet I made



I emailed my lifter manufacturer (Howard’s cams) and they defer to gatermens specs so I assume they are actually made by gatermen. They say 400 is recommended and 480 is max. So maybe I’ll step up 1.755 install height which, but at this time I think I will allow a head shop to set them up. I want them killer .015 still anyway. And I have learnt plenty.

 

How is everything now?

 

What's up with the 15,000 millionths and 60,000 millionths??? I have never seen anything dimensioned this way. What exactly does 15,000 millionths equate to in thousandths of an inch????.....

 

Divide millionths by 10, I think.

 

If I, or anyone else, used that terminology in a Toolroom or machine shop, and they'd have laughed me right outta the building.......

 

That would give you hundred thousandths. To get thousandths you divide by 1000.

 

Avoid the confusion, and just stop before the millionths. 15,000 millionths is = to fifteen/thousandths, or .015. Again, if I asked a machinist or Toolmaker to take 15,000 millionths off a part, he'd look at me like I'd just landed on the planet in an alien spacecraft. Much easier, and quicker, to say fifteen thousandths......

 

just got some shims yesterday todays my day off but I have to go to work anyway cuz I took the truck keys

 

this was an odd autocorrect , everything is measure to ten tho no more

 

Why not just get valve springs that are better matched to your cam? I feel like the Summit .630" beehives would save you from needing to destroy your seals.

 

Is there a compelling reason you can't run shims on guide seal assembly, rather than under them? Maybe the shim O.D. is too large to fit inside the seat I.D.? Just asking, because I don't know, because I've never run that type seal. Always had just the separate seal....

 

Beats me. I’ve put shims on top of the seal seat/locator more times than I can remember. Just be sure the ID of the shim is large enough to stay off the seal itself, or it could cut through. I could see putting the shim under the seal if the guide was a tad proud and the seal was kissing it. You just don’t want the top of the seal to come in contact with the retainer/locks, or even be close, as putting a shim under the seat could maybe cause. Always mock everything up and check.