45* valve on 45* seat

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AC sports
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45* valve on 45* seat

Post by AC sports »

Some car makers manuals and indeed cutting equipment manufacturers specify an interference cut of say 46* on the seat and 45* on the valve. Logic being when hot the angles will pull together for a better seal.
I recently cut some seats with neway cutters at 45* and lapped them to a 45* valve contact face of close to .0 80'. It was a bit on the wide side but in manufacturers spec.
What can I expect long term from the 45* / 45* combo?
Will I have sealing issues?
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Re: 45* valve on 45* seat

Post by ProPower engines »

Most HP engines use the 45 and 45 angle on the seat/valves. The intake is normally narrower then the exhaust by more then half.
Most heads use an intake seat about .030 to .040 wide where the exhaust would be happy with .050 width.
Imports benefit long term from a narrower exhaust seat to keep from pounding carbon into the seat and valve face.
Some diesels use a wide seat on both valves but some use a 30 degree intake/valve and 45 on the exhaust.

The interference fit valve job the factory uses will seal because of the difference between the two angles but during the
painful break in period the valves and seats will mash together creating a wider valve seat contact area and the other reason is the factory guide clearance is greater then a HP build is. If you look at guide clearance spec's for a stock engine they are
very loose as in .002+ on the intake and .0025-.003 on the exhaust. It will run and seal with the difference between the two valve and seat angles and surprisingly last 250k miles but as time goes on valve and or seat leakage is increased causing a compression drop.

In any HP type cyl. head the valve job is done 45 and 45 to seal instantly and perfectly right out of the gate.
That is of course depending on the machinist to get the seats and seat face's concentric to seal.

as we know run out in this area of the job can cause leaking valves and compression loss oil useage low vacuum signal on computer controlled systems making them run like shit [-X

As for your dilemma depending on the engine I am guessing the exh. seat width is what you are talking about but regardless unless the valve gets really hot I would consider narrowing the seat to .045-.050 for an exhaust and carry on. :D
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Re: 45* valve on 45* seat

Post by modok »

I don't think the 1 degree difference will make much difference long term.
Lapping may shorten the life of the job tho. Putting a groove int he face of the valve is ok at room temp, but if you believe that the valve changes shape at running temp then you should also clearly see how the groove on the face of the valve won't line up when it's running.
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