Engine rebuilding: Valve seat cutting angles

[Supercharged Riot]

I got a question for all you engine rebuilders

The service manual recomends cutting the seats the same angle as the valve face angle of 45 degrees

One of my professors recomends that i add an interference fit to the aeat angle and cut at either a 45 1/2 or 46 degree angle instead.

Any thoughts on this suggestion??

[Challenger340]

What Heads ? What Camshaft Lift ?

[Supercharged Riot]

Cast iron 906 heads
2.08 intake valves
1.74 exhaust valves

Hardened intake & exhaust seats installed

Camshaft: 
Compcams  xe274h-10

Duration: 274/286
Duration @ .050: 230/236
Valve lift: .488/.491
Lobe separation: 110



One of my professors recomended that i depart from the service manual because modern cars have an interference angle of 1/2 to 1 degree

Since my new valves were already 45degrees i should cut the aeats @ 46 degrees.

Service manual (which was obviously published in the 60's)  say 45 degrees for valve face and seats.

[chargerbr549]

In most of the shops I have worked in we have always cut the seat angle and valve angle the same but we have also had very good seat cutting equipment like Serdi's and machines of that nature and always vacuum check to make sure the seats are making a good accurate seal, from what I understand the main reason for the interferance angle was it would help the valve job seal better right from the getgo if the valve job wasn't as accurate.  With that being said with some of these newer race heads which goto 50 and 55 degree valve angles some will have a 2 degree difference between the seat and valve angles.

Kevin

[Cooter]

I would think Sealing would be more of a concern on a blower motor than flow characteristics. Just me though.

[Challenger340]

"Theory", versus actual "practise" again.
Interference Angle seat cutting was a reccomended procedure to reduse carbon buildup, more prominently used on the exhaust side back in the day when carbon was more prevalent due to lower peak combustion temps, carburetors, and leaded fuels.
Rotators were also employed with many brands.
It can still be used, however, the valve and seat will bash themselves together anyways during operation.

More importantly to the multi-angle grinds, is the actual widths of each Angle used for a particular Head, aaccording to the LIFT being used.
No point chasing your tail trying to get all 5 angles, especially the top 15 & 30 if it means sinking the Valves on a 906 Head to do so, it just kills flow.
On a 906 Head at under .500" lift, keep the 45* as high to the chamber as possible, "just" breaking with a 30* for final diameter is about as good as you will get.
A 30* backcut on the Intake Valve down to seat contact will help immensely.
60* @ .100"
75* Throat the rest.

[john108]

Dumb Question:  Are these angles measured from the center-line of the valve shaft (where zero degrees would be a cylindrical hole with no chamfer)  or relative to the head face (where 90 degrees would be a cylindrical hole with no chamfer)??

[Chryco Psycho]

By cutting the seats at slightly different angles from the valve  you thin the contact area which increases the the PSi / seal , the only thing that sinks the valve is cutting into the 45* seat & raising or lowering the contact are on the seat , removing material in the throat behind the valve will increase flow .

[Supercharged Riot]

So it sounds like a good suggeation to cut a slightly different angle on the seats

I suppose the service manuals instructions are considered obsolete in this area

[Challenger340]

We don't use an Interference Angle in our Valve Jobs, because we feel all it accomplishes.... is to put a "wear point" so the Valve and Seat can BASH themselves together under Rocker Arm action with sloppy guides, and establish a happy running equilibrium on break-in.
If you are using stock cast guides that are "pre-fit" at .002" to .003", then really no "hotrod" style Valve grind, nor the Interference angle will stay that way for very long under operation anyways..... because the guide slop just allows it to wear off wider every time the Valve seats on the seat.
The interference angle should be considered mostly as a way to achieve a "break-in", so the seats establish a seal only with loose guides.


Interference Angles areNOT required, when using Hone-Fit Brodix style Bronze Guides, or even Bronze liners that are Hone-fit for that matter, that retain good Valve to Valve Guide clearance of .0010" Intake and .0013" Exhaust, that stays that way over time.
Tight, Straight, and Round Guides will stay that way longer, than loose Guides to begin with, because, less Rocker Action leverage is applied, and thusly allows the "Hotod" style seat grinding to live.

I went out a bugged Donny(my Cyl. Head guy in my Shop), he was doing a coupla sets of what we consider "Stock" type Jeep Heads for some 6 Cyl Strokers we're doing,(for a 4x4 Shop)....I took a coupla Pics of what should be considered a "standard" Valve job...... using "Angles"....as opposed to the "Radius" cutters we use for our High Performance work(COMPLETELY different)

It's not a 906 Head...But you get the idea......again, this is "standard"/Stock stuff even though we install Bigger Valves, and we still use Hone-Fit Bronze Guides with the above noted clearances, even though just stock type Seat Grinding/Angles are used.

The "grey" areas are the lapped seat contact area for landmarking before we backcut the Valves.
Also,
Note the Backcuts on the Valves, which are ABOVE the Seat contact(grey areas on the Valve). If you look closely, you can still see a small amount of the 45* "shine" on either side of the grey, before the 30* backcut.

I ain't saying it's right...just the way we do things on "stock" type stuff, to illustrate an "Angle" style(NON-Radius) Valve Job, with Hone-Fit "correct fit" Guide Clearance where we can set thin contact "seats" for better Flow, that do NOT need an Interference Angle. 45* seat/45* Valve.
Final Intake 45* width @ .039"
Final Exhaust 45* width will be @ .050" for added Heat transfer(only way the hotter valve cools). Pressure x Area.

Cheers, and good luck with your project.

[Supercharged Riot]

Thanks for the detailed response!

[chargerbr549]

Kevin

[BSB67]

Challenger340 and Firefighter Ron are the best!

Kevin

Good to know...the rest of us can stop wasting our time

[chargerbr549]

Oops and I mean BSB67 too and other peoples i can't think of right now, my apologies, no harm intended!


Kevin

[FLG]

Theres really too many to name.