When I was in high school and was having my MO block 302 Z28 engine rebuilt, the man doing the rebuild got me set-up on his lathe and taught me at the time to cut the three angles on my valves using the lathe.

Recently when I had a three angle valve job done on a set of #5 heads, the machine shop told me that they didn't cut them on a lathe but ground the three angles. In the end is it exactly the same result or is one method preferred for some reason? - Steven

 

My machinist told the the other day that they are ground, (and that is the only kind he ever does).

 

I have seen work climb up on a lathe bit and it gets ugly
I would think grinding is the preferred method, and the only way to get a proper face surface finish.

 

What exactly is a 3 angle valve job and can it be done at home

 

It's a process to finish a valves edge to seat it properly in the head. Although I'm sure some people do it themselves with their own equipment it's not a very expensive procedure to have completed by a machine shop. I paid $180 not long ago to have it done to my head set.

 

Ahh ok

 

Actually, it is more about the air flow. Instead of one wide flange, they break it up into 3 small flanges, thus the 3 angles. The air flows more smoothly over the valve. The middle section that actually seals the seat to the valve is quite narrow, but if done properly is fine.

 

I always wondered that
isn't every valve job at least 3 angles?
Otherwise how do you get the seat the right width and diameter?

Seems to me you need three angles:
the seat or face &
the two surfaces on either side of that.

Is "3-angle valve job" like a "full race cam"?

Bill- that's something you need your machinist to do, and it's no place to skimp. you will want to price the job first. They will tell you you "need" all new valves, guides, seats, etc. Total bill on the order of $1000 isn't unheard of.

 

The three angles are on the SEAT, not the valve, so you'll be hard pressed to cut them on a lathe. The purpose of a multi-angle valve job is to smooth the airflow through the valve seat by approximating a radius and minimizing sharp corners that upset subsonic flow.

 

Joe I appreciate your expertise but I distinctly recall sitting in front of a lathe and cutting on my valves with a lathe. Why would that have been done to the valves? Same reason?

 

Joe that is a good illustration. From the factory our engines basically came with a one angle valve job. You can have a five angle, or more valve job. This is something that can not be done at home. A valve grinder works somewhat like a lathe. It spins the valve in a chuck that can be moved to specific angles and pulled into a grinding wheel. When a modern machine shop performs a valve job they cut all the angles into the seat simultaniously with a special cutter bit. The old school way of doing it uses grinding stones cut to specific angles. Grinding valves to these angles and maintaining the width of the specific angle is not that hard. Matching those angles with stones into the seat is extremely difficult. That's why nobody does it that way any more. I recently was given an old valve grinding machine and seat grinders and a bunch of old stuff hat nobody uses any more. Call around to some local machine shops to see if they have any old equipment like this, they're not using. chances are they do have some old crap sitting in the corner, collecting dust, they would be happy to get rid of. The new machines they use are huge coin and make the work so much faster, why would they go backwards. By the way in your diagram Joe, the blue line where it shows 60 degrees on the seat, I do a 30 degree back cut on the valve for better flow. I now this is common practice. By the way for anyone interested, I started a thread about home porting that I will go into your basic valve job when the time comes.
https://classicoldsmobile.com/forums...echniques.html

 

There is a machine that "resurfaces" the valve so that it seals up against the seat, but it is a single angle. I suppose you could do it on a lathe. Then, like cutlass freak mentioned, you can take a little bit off the inside corner (back cutting) to ease the transition.

 

What you are describing we used to call back cutting the valves, it narrows the valve face to try and gain some air flow.

 

The man that did the rebuild back then (1980) had won a couple of national titles in J-Class drag racing and new exactly what he was doing. I recall that the "decking" of the block removed the engine ID numbers and he had a set of stamps to put the same numbers back on. On a 68 z28 the numbers on the block mattered even back then, I think like some of your more desirable Olds cars there wasn't a clear title notation as to what the car was. I do remember that my Z28 was only considered a "1968 camaro" on the title. The engine components, a mandatory choice of a four speed, and I think posi-trac and front disc brakes were all that were required for a z28. Even the stripes were an extra. Real 67, 68, and 69 Z28's were all four speeds with the first offering of an automatic being on the 70 1/2. I did have the fastest car stoplight to stoplight in high school. There were some cars that would have beat me in the quarter but I was so far ahead by the time I shifted out of second they would quit. Mine had the M21.

 

Ok, since we're talking about 3 angle valve jobs, I've been hearing about 2 angles and 5 angle valve jobs. Which is better, 2, 3, or 5? Or its just marketing BS?

 

Just my opinion, but 3 on the seat and 2 on the valve is fine. That is what we called a "race valve job" and should run around $350 +/-

 

Great information, thanks for summing it up.

 

The five-angle valve jobs smooth the airflow even more by further knocking down the sharp corners at the valve seats. You probably don't need it for a street car but if you're looking for every last HP, it helps.

 

Just wondering after looking at the last post, would it not be possible to have a rounded valve-seat mating surface instead of the angles, to maximize flow?

 

The problem is how do you physically machine it? The multi-angle valve jobs use a series of cutters at the correct angles. In addition, you do need a seat that's not radiused.