I recently bought a set of used ported heads. They look really good, but my question is concerning the valves. They were supposedly using the stock valves with a full valve job, so I think it still has the stock seats. I called a local head shop to see about cleaning them and flowing them for me. They told me that I would have to get another valve job done if I went with new valves. I read here that even 2.0/1.56 valves would fit into the stock seats. I was told that they would have to ensure that the valves seated correctly, but couldn't they just shape the new valves to fit? Would it be easier to get larger valves so that they have more material to work with in getting them down to the right size? I know it might help to get another valve job, but I'm really stretching my budget as it is. Thanks.

 

You have to use the same size valves that the valve job was cut for, otherwise it will move the seat width placement. If the guides are still tight and the seats are not pitted or worn, you can stick new valves in and just lap the seats to make sure they are sealing. This will be better than sinking the seats farther and potentially loosing some CFM.

How many miles are on the heads?

 

I'm not sure about the miles, I think it was just one season. They are off of a world challenge camaro. Nothing looks pitted or worn, just coated with some carbon in the chambers. The runners still look clean. AutomotiveBreath, SStrokerAce, Injuneer???

 

My answer is basically the same as MachinistOne. I would lap the valves and if they clean up with no pitting or obvious sinking into the seat I call it good. If you do a valve job too often you end up sinking the valves into the chamber unnecessarily.

The stock valve size is all needed exception being all out applications. Our bracket race LT1's are running mid 10's with the stock valves and a mild clean up porting. If you add bigger valves with out resizing the ports to match, you could end up with little or no gain.

 

What exactly is lapping? Does it take off enough material to need larger valves to start with and then finish with the correct size?

 

When the last valve job was done the valve and the seat were cut the same size on the same angle so that they are a perfect match, that becomes the sealing surfaces. With run time these surfaces get carbon baked on.

Lapping the valves is done with a compound, think of it as polishing these surfaces. The spring is removed and the compound is applied to the valve sealing surface, the valves are spun slowly until the surfaces are clean, this will expose and pitting or wear.

 

Ok, thanks. Should I do this myself or get a shop to do it? I'm not sure if I could tell whether the valve was seating properly or not. How much should they charge?

 

You can do it yourself, but it is best to let the shop disassemble the heads and mark the valve locations - they do this all the time and will alert you if something is amiss. Have them check the spring pressures at the same time.

FYI here are some pics to illustrate the point. The lap line(grey) is the contact patch between the seat and the valve. Lapping compound is basically sandpaper in a bottle.

 

I think they will charge you 2.5 hours time to disassemble and clean the heads, inspect parts and check pressures, lap valves and grind if necessary, then reassemble. + $ for new seals

 

After laping ya can fill the ports with clean solvent to see if they are leaking. They need to be sprung back up and need to sit for an hour or more. Just barely damp is acceptable but no leak at all is the best.