I just got my new 305 SR Torquers and I'm disassembling them in order to get ready for some port work. I see that each valve spring has a pair of round copper shims stacked underneath it. The thickness of the shim pair is different for each spring. I haven't measured them, but I'd say they range from about .050 to .080 thickness.

My guess is that they are intended to compensate for differences in spring heights. They may even be location specific...?

Does anyone know what's up with these shims? Are they matched to a particular spring, and/or a location on the head?

 

Typically, spring shims are used to correct for machining to insure proper spring installed height. Shims would therefore be specific to the head location, not the particular spring that is mounted. I would suspect that a new set of heads would be machined correctly and not require shims.

That being said, it is usually a good idea to use some sort of shim or centering cup on aluminum heads to prevent wearing the spring seats by the spring action and migration. The fact that they are all different indicates a lack of process/quality control in the manufacturing process.

 

Thanks for the response Vader. I did email World in regard to this. Their response was simply that it was to correct for spring height... No mention of head/valve location. I'm bagging and tagging parts as I disassemble the heads.

 

Keep 'em all separate and mark which valve they came off of. Valve spring recommended installed height for the springs in a stock/near stock application is almost always 1.70" on a SBC head. Typically the pockets are machined about .050" deeper than that (especially on an aftermarket head) so they can be shimmed back to exactly 1.70".

That installed height is difficult to get dead-bang perfect on a production head since so many things can affect it- valve seat location, spring pocket location, valve length, locks, retainers, etc. LOTS of opportunities for "stacking" errors to creep in. A hundredth here, a few thousandths there, pretty soon you're way off on the final spring installed height.

That's why you'll see shims in there. It's not a "crutch" for bad machine work, it's an indication that somebody cared enough to measure the final installed height and shim it until it was correct.

 

Keep 'em all separate and mark which valve they came off of. Valve spring recommended installed height for the springs in a stock/near stock application is almost always 1.70" on a SBC head. Typically the pockets are machined about .050" deeper than that (especially on an aftermarket head) so they can be shimmed back to exactly 1.70".

That installed height is difficult to get dead-bang perfect on a production head since so many things can affect it- valve seat location, spring pocket location, valve length, locks, retainers, etc. LOTS of opportunities for "stacking" errors to creep in. A hundredth here, a few thousandths there, pretty soon you're way off on the final spring installed height.

That's why you'll see shims in there. It's not a "crutch" for bad machine work, it's an indication that somebody cared enough to measure the final installed height and shim it until it was correct.

 

Keep 'em all separate and mark which valve they came off of. Valve spring recommended installed height for the springs in a stock/near stock application is almost always 1.70" on a SBC head. Typically the pockets are machined about .050" deeper than that (especially on an aftermarket head) so they can be shimmed back to exactly 1.70".

That installed height is difficult to get dead-bang perfect on a production head since so many things can affect it- valve seat location, spring pocket location, valve length, locks, retainers, etc. LOTS of opportunities for "stacking" errors to creep in. A hundredth here, a few thousandths there, pretty soon you're way off on the final spring installed height.

That's why you'll see shims in there. It's not a "crutch" for bad machine work, it's an indication that somebody cared enough to measure the final installed height and shim it until it was correct.

 

Keep 'em all separate and mark which valve they came off of. Valve spring recommended installed height for the springs in a stock/near stock application is almost always 1.70" on a SBC head. Typically the pockets are machined about .050" deeper than that (especially on an aftermarket head) so they can be shimmed back to exactly 1.70".

That installed height is difficult to get dead-bang perfect on a production head since so many things can affect it- valve seat location, spring pocket location, valve length, locks, retainers, etc. LOTS of opportunities for "stacking" errors to creep in. A hundredth here, a few thousandths there, pretty soon you're way off on the final spring installed height.

That's why you'll see shims in there. It's not a "crutch" for bad machine work, it's an indication that somebody cared enough to measure the final installed height and shim it until it was correct.