I am rebuilding a 302 for the first time (so far so good) and questions come up. Naturally I turn to y'all. I don't know any of the engines previous history other than I was told that it had been rebuilt prior to me buying it (yeah right). I was going to rebuild it again anyway. My question is: How do I determine which valve springs I need on the rebuild? Also, which valve stem seals are recommended. It's just going to be a weekend/local driver. THanks and I am sure I will have more questions later.

 

With a stock to mild cam (like an RV type cam) stock springs are fine. Your machinst that does the valve job can help you there too.

 

I was planning on doing the valve job. So I was trying to figure out which springs to order.

 

Do you have the equipment to do the valve job?

 

such as? I have disassembled everything down to the bare head. I just need to know what size springs I should go with in a 302 with a small cam. I haven't miked the springs to see what they currently are. Lifters are good, I plan on replacing valves, seals, possibly springs, etc.

 

A valve job typically begins by disassembling, cleaning and inspecting the cylinder head. Cast iron heads are "Magnafluxed" to check for hairline cracks. This involves applying a strong magnetic field to the head and sprinkling iron powder on it. Cracks disrupt the magnetic field and attract the iron powder, making invisible cracks easy to see.

Cracks are bad news because they can leak coolant into the combustion chamber damaging the cylinders and/or causing the engine to lose coolant and overheat. If cracks are found in any critical areas of the head, the head must either be repaired or replaced. Cracks in cast iron heads are most often repaired by "pinning" (installing a series of overlapping threaded pins). Cracks in aluminum heads are very common and can often be repaired by welding.

If a head has been repaired (pinned or welded), most shops will usually pressure test the head afterward to make sure there are no leaks. Some may also apply a sealer compound to the inside of the water jackets as added insurance against future leaks.

Once the head passes this point, it is also checked for flatness. The surface of the head must be flat to seal the head gasket against the block. Excessive warpage, roughness or any damage can cause the head gasket to fail. If the head exceeds the maximum allowable out-of-flatness specs, it must be resurfaced or replaced. Usually there’s enough metal in the head to allow for a certain amount of resurfacing. But on many import aluminum cylinder heads, the amount of resurfacing that’s possible is minimal.

Overhead cam aluminum cylinder heads are often found to be warped (usually the result of overheating). If the condition cannot be corrected by resurfacing, the head can often be straightened by heating it in a special oven and then bending it until it is straight.

Next come the valves, guides and seats. The guides are checked for wear. They’re almost always worn, so they either need to be replaced, relined or knurled (a process whereby grooves are cut into the inside diameter of the guides to decrease the bore size). Few shops knurl guides anymore. Most install new guides, guide liners or bore out the old guides to accept new valves with oversized stems. Aluminum heads have cast iron or bronze guides that can be replaced but most cast iron heads do not.

If the valves are to be reused, they will be inspected, checked for straightness then refaced. Many shops automatically replace all the exhaust valves to reduce the risk of failure (exhaust valves run much hotter than intakes and are much more likely to fail).

The seats in the head are either cut or ground to restore the sealing surface. If a seat is cracked or too badly worn to be refaced, the seat must be replaced. If that isn’t possible (as is the case on many late model cast iron heads because the casting is too thin), then the entire head must be replaced. All aluminum heads have hardened steel seats that can be replaced.

The valve springs are all inspected and tested to make sure they are still capable of maintaining proper pressure. The spring retainers, keepers and other hardware is likewise inspected. Any worn or damaged components are replaced. New valve guide seals are always used.

The valves are then installed in the head and shimmed to restore proper valve height. This is necessary because machining the valves and seat alters their dimensions. Valve height is important because it affects valvetrain geometry and guide wear. If it is an overhead cam engine, the cam is also installed and the valve lash adjusted prior to returning the head to the customer.

 

That was a lot of info. Thanks for taking the time.

 

And you said the lifters are good ? We talking about roller or flat tappet ? If they're flat tappets, and you failed to keep them in order as to what lifter bore each came from, you now need to go out and buy a new set. They HAVE to go back in the bore each came from, otherwise they'll eat the cam lobes. They wear in with the cam lobe they ride on. You can't mix them up after they've been worn in.