It is great to have a seat that is concentric to the guide and allows full valve contact (sealing) while not placing any side load on the stem/guide. Often what happens with a torqued down and hot cylinder head is different to what happens on the bench.
At least starting with a near perfect valve seat allows you to asses what may be going on in a running scenario after some run time and an inspection of the seats and valves. Not always practical unfortunately.
Sand and bearing grease
excellent !
I used to do 46* seats with Neway seat cutters a long tine ago. It was extremely easy to feel if the seat was concentric as the valve would stick on the 46 seat far easier than a 45 seat. Once the seat is true yes they seal very well in quick time so I see why the factory did it. 46 also seemed a little more forgiving to a slightly off seat.
With older style slow ramp cams and soft springs they last fine when done right. That said I think a good 45 seat is better than a good 46 seat.
I dont have a problem with using fine lapping paste for a very light witness lap.
Prussian Blue is great if you are gentle on the valve. On a big valve you can easily get a 'good' blue impression if you clap the valve onto the seat with any sort of force. Use light finger pressure only.
To start with as good a VJ as possible you need to forget the springs. You can have a seat so far off that you dont need light to see tha gap and put a spring on it, the valve flexes oves and it will seal. Think of that with a solid roller spring pulling on that flexed valve when running and the impact on valve fatigue, the seat, the guide etc.
1972ho wrote: ↑CJ just a question about a light clap of the valve to the seat for a impression,isn’t the valves working harder than that when the engine is running I mean when the valve closes with 150 to 450# of seat pressure seems you should be able to slap the valve down harder to see the impression.Just a thought?
If you aim for a seat that is as concentric as possible and centeres in line with the guide centerline AND certainly no more off center than half of the valve guide clearance then you are off to a good start.
When i say light clap onto the seat, that light! As in 'just' enough to get a transfer of blue. You should be able to blue the valve, touch down on the seat , clean the valve, touch down again and get a reimpression of blue back from the seat. When the seat in not concentric, you can actually feel it without even using blue.
^^^ yes as above.Keith Morganstein wrote: ↑Quoting an old post about Prussian blue
Keith Morganstein wrote:
Check seat to valve contact with Prussian blue paste. Clean the seat and valve. Apply a thin smear of Prussian blue paste to the valve face.
Position the valve in the guide and drop the valve into the seat. ( A tap with the finger will help it hit the seat) Do this once , with NO rotating of the valve. Pop the valve out pushing from the stem end and carefully remove the valve so as not to smear the paste. This will give you an accurate contact patch.
Important: DO NOT rotate the valve when checking contact!
On that point, if the valve is say out by .001" and the seat is out by .001" and you rotate the valve you would think the seat was perfect. Even if the seat or valve were concentric and the other was a little off the blue will be swiped across the seal face and can be misleading.