Originally Posted By 360view
http://www.enginebuildermag.com/2012/01/valve-seat-selection-finishing-materials/

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Chrysler has reportedly had problems with the exhaust valve seats loosening up and dropping out in some of its late model 4.7L engines. Seat failures have typically occurred between 60,000 and 80,000 miles, often after an overheating episode in which the coolant got above 250 degrees F.

Some engine builders say Chrysler didn’t use enough interference fit for the seats in these engines and recommend using an additional .002" of interference when the seats are replaced. Cutting the seat recess slightly deeper can also improve seat retention.

Some vehicle manufacturers use only a couple thousandths of interference when they install valve seats in a new cylinder head. They can get by with minimal interference because the heads are brand new castings that have been freshly and accurately machined. There’s been no wear, corrosion or motion to loosen up or distort the valve seat recess as is often the case with high mileage cylinder heads.
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This is right as I had a few drop valve seats in them. Many would come in with a rocker arm that fell off and laying in the head because the seat dropped and held the valve from closing all the way and the clearance let the rocker fall out. I also saw many that ran good for a long time but I would say our dealer would see a dropped valve seat maybe every 6 months as I know I did about 4 of them over a 2 year period one time. The other thing about them is they are overhead cam and they have a few timing chains on them going to each head and one to a dummy shaft where the in block cam would normally be. It has a gear on that shaft that makes it look like it has a cam in the block until you remember its overhead cams. But I know without the special tool to hold the chains in place on that gear on the dummy shaft its hard to do the chains on them. The tool holds the chains in place on that gear while you put the chains on. My point is it will cost alot more then a timing chain job would on say a 318 magnum eng would.
But I would want to look at the oil and coolant and drive the truck hard before I would consider buying it. If it looks to have been maintained right and runs fine then if the price is right I would buy it. But I can also do my own repairs if I had one and something did break. Good luck with it , Ron