Cylinder Head Disassembly
Before disassembling your head, it's good to take some initial measurements. To measure the chamber volume, use a graduated cylinder and a clear plastic plate as shown to accurately measure the volume. Note, this is done with both camshafts removed.
Use a little bit of grease to seal the plate to the head surface. Once you know the volume, you can calculate the engine compression ratio with the below equation. We have an excel sheet with the formula to make this process easier. Once you know your comp ratio, you can decide how much you need to machine off the head to hit your target. For 1.8 heads for example, every .01" of material removed equates to -1.22cc of volume change. Keep in mind other factors can alter the final comp ratio, include valve shape (if you're getting new valves) carbon build-up that will no longer be present and piston shape (again, if you are not replacing parts like for like)
Once you have the measurements needed, it's time to disassemble! Remove the cams and lifters. For removing the valves, we recommend a valve spring compressor like the one pictured below. These are available for sale on our site.
Remove the valves, springs, stem seals and all external hardware. You're not ready to take the head to the machine shop! If you are replacing the valves, bring the new valves with you so the machinist can verify the valve angle. We recommend having the shop resurface the deck, and grind the valve seats.
Next you want to measure the valve guides, and ensure they are good to be reused. Using a set of micrometers and some go/no-go gauges, measure the valve to guide clearance. The OEM spec is as follows.
| Item | Min (Inches) | Max (Inches) |
| Intake Valve Stem Diameter | .2351 | .2356 |
| Exhaust Valve Stem Diameter | .2349 | .2354 |
| Intake Valve Clearance | .0010 | .0023 |
| Exhaust Valve Clearance | .0012 | .0025 |
While the head is gone, it's a good time to rebuild your lifters (if an NA engine). Below is a video tutorial on the process.
Component Selection
The two main items discussed for the BP heads are valves and springs. Let's start with valves.
If you're doing an OEM rebuild, usually you can reuse the valves that came out of the head. using some paint thinner, soak the valves for a couple hours then clean the carbon build-up off of them. once the carbon is gone, you can inspect the valve seats and decide if they are good. If they have large pitting, scoring on the sealing surfaces, or any bend to them, they should be replaced. OEM valves are available, but they are extremely expensive. We use SuperTech's OEM size valve for our standard rebuilds.
If you are going to more power, or a race application, then a larger valve is advantageous. Keep in mind, changing the valve weight brings us to our next item- Springs.
If you are using the stock valves, stock camshafts, and running the motor to the factory redline, then then OEM springs will work just fine. However if any of the above have been changed, you might need a stiffer spring to control the heavier, or faster moving valve assembly. SuperTech has several spring options depending on your needs. Keep in mind though, that going with a stiffer spring unnecessarily is just robbing you of horsepower. You want the lightest spring that will do the job of controlling the valvetrain.
