What is the difference between 3 angle valve job and a 5 angle valve job?

[Highbredcloud]

Just wat it says...also can somebody explain to me what what exactly a valve job consists of and the benefits of one? Does it have to do with the actual valves (intake/exhaust) or the areas around it right by the bowl/pocket? Reason for asking is I have a chance of getting some heads that have a valve job...but I want to replace the valves...could I do that or would that defeat the purpose of a vavle job? Just curious...

 

[gearheadboy]

Well, "valve job" could mean many things. First of all, a "normal valve job" consists of grinding the valve seats with a special grinding stone, and grinding the valve itself on a valve grinding machine. It also means grinding the stem tops to a new true, flat surface. Typically anymore on a car engine you grind the seats and valves with three differant angles using three differant stones. Once you are done most people "lap the valves in" using a gritty paste on the valve seat called lapping compound. This just finishes the sealing surface, kinda like a polish. They also usually vacuum leak test the valves. And probably if parts (valve springs, valves, etc.) were replaced, the spring "installed height" would be checked and shims placed under the springs to change this.
Thats a basic idea. As for a five angle, use more differant angled stones.(better seal) And will changing valves defeat the purpose of buying heads that just had a valve job? ABSOLUTELY, new valves need a valve job too, to match your seats. (not the ones that your girl sits on)
My question to you is this: why do you want new valves?

 

[Michael Yount]

Properly done, the more 'angles' that are cut into the valve seating surface, the better they flow - it eases the flow around the perimeter of the valve. 3 angle or 5 angle should seal equally well.

 

[Highbredcloud]

Well, "valve job" could mean many things. First of all, a "normal valve job" consists of grinding the valve seats with a special grinding stone, and grinding the valve itself on a valve grinding machine. It also means grinding the stem tops to a new true, flat surface. Typically anymore on a car engine you grind the seats and valves with three differant angles using three differant stones. Once you are done most people "lap the valves in" using a gritty paste on the valve seat called lapping compound. This just finishes the sealing surface, kinda like a polish. They also usually vacuum leak test the valves. And probably if parts (valve springs, valves, etc.) were replaced, the spring "installed height" would be checked and shims placed under the springs to change this.
Thats a basic idea. As for a five angle, use more differant angled stones.(better seal) And will changing valves defeat the purpose of buying heads that just had a valve job? ABSOLUTELY, new valves need a valve job too, to match your seats. (not the ones that your girl sits on)
My question to you is this: why do you want new valves?

I should have explained this better and I apologize...The heads that I am interested in had a detination problem (too much N20) and it looks as if though there are marks like pin holes in the valves...not sure how far they go but definately noticalbe...I have been assured that the heads have been leak tested and that the marks are nothing more than cosmetic imperfections and will not hurt performance what-so-ever...I have never seen a valve job and I can't tell the difference between them but my real concern was what can the detination in terms of damage? The heads are iron heads and the combustion chambers seem to be O.K, hence was my question regarding the bowl/pocket area under the valves...could this be damaged as well? I have pix of the heads...not sure if I can post it...I will try though...Any input would be appreciated.

Thanks

 

[Highbredcloud]

Properly done, the more 'angles' that are cut into the valve seating surface, the better they flow - it eases the flow around the perimeter of the valve. 3 angle or 5 angle should seal equally well.

Michael...if I send you pix of the heads would you be able to tell if there is damage to the valves from detination? I don't think I can post pix here...Let me know.

 

[Michael Yount]

My 'guess' based on pictures as to whether or not they are damaged wouldn't be near as good as having a good engine-related machine shop go over them for you. With used heads, I always take them in and have them checked over - they can give you the low down on the springs/guides/seals, as well as the seats. They can check for cracks, look at the issue you're concerned about with the valves and look at the seats/valve seal, and take a quick clean up cut to be sure they are flat. Given what they're telling you about how the heads were used, unless there's something world-class special about these heads, I'd move on and look for another set. There are simply too many used heads of all types available to feel like you've got to take a set that have been abused.

 

[gearheadboy]

The imperfections are small, and what happens is this, they leak a little and the leaking gasses rushing past them in the marks make them become "burned" and it works like a cutting torch to melt away the material. Detenation will also "tulip" the valve, it looks like some one heated it and tried to pull the stem out of it. And mike is correct, 5 angles also flow better, people also "back cut" their valves for flow purposes, but I was trying to explain it and keep it simple

 

[gearheadboy]

I also agree, leave them alone.

 

[FoxChasis]

Don't forget that checking valve guides for wear is also part of a proper valve job. If any are worn, their replacement is also part of the job.

 

[PURESTREET5006]

Thats a good question...EDC cut a 5 angle valve job in my ps2 165's and it's not streetable for more that 20k Ed told me,be he does have valve jobs for street cars.