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Discussion Starter #1
Bought a set of 1mm larger inlet and exhaust valves with 45 degree seating face. Subsequently I've read some information regarding valve seats falling out after changing from 30 degrees. I'm surprised about this, but wonder if anyone has experience of this mod
 

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The angle of the seat doesnt make the valve seat fall out. A 45 degree seat is a better flowing seat angle, but it also allows for a larger port size when using a os valve. Valve seats are not for ever. However, as long as the car has been maintained, doing a valve job at least 1x is a normal thing. Good luck
 

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Richard Jemison
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I have to point out that to justify using larger 45 degree seats the existing seats must be opened on the ID leaving only a 1mm wide seat on the outer margin of the valve (and seat). Using a 45 degree seat on a narrowed seat places much more outward force on the seat. Often swedging it open in many cases.
Alfa seats are not very hard alloy. Have your valves reground to 30 degree seats and open the seats as covered on many threads.

A bigger valve on a stock seat cut with a 45 degree cut is only a impediment to flow.
 

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For reference, static change on side force = spingforce(sin45-sin30); corresponding decrease in vertical load = springforce(cos30-cos45). Might not seem like much but it is, in small wall section areas
 

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Discussion Starter #5 (Edited)
I accept the radial does increase(by about 23%) but the seat is supported by the head. The twin spark engine has 45 degree seats, is the outside diameter of the seat larger on those?
 

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Why ask the question again when you don't like the answer?
 

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I'd also like to hear the answer to the question as stated in his last line.
Did someone get out of bed on the wrong side this morning??? :rolleyes:
 

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I dont have a head laying around so cant take a photo, but if you search on 'angle valve seat' or something similar, over the years there have been a lot of photos and discussions on this very topic. I believe the issue is that the valve seat is marginally supported radially in some spots - somewhat weak wall section in the head that supports the seat. Over time, it distorts with the added radial load from the angle change. If you do a search I think you will find tons of info
 

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Richard Jemison
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Twin Spark heads do have larger diameter seats AND the alloy used is far more durable than in ANY Nord engine. In the later engines the exhaust was a harder alloy but not the modern alloys in the TS.

My race engines (nord) have oversize intake valves but their seats angles are re-cut to 30 degrees.
 
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