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Hey Engine Man: How High Should Valve Heads Protrude?
Successful Farming Engine Man Ray Bohacz has engine grease and field dirt under his fingernails from a life spent repairing vehicles and running a farm. When he’s not busy in the shop, he’s working on maintenance articles and videos for Successful Farming magazine and answering questions from readers. The following is a letter the Engine Man received from Steven J. regarding the valve specifications on an International Harvester model 560 diesel six-cylinder engine:
The actual repair manual at the dealer shows valve seat depth in the head, margin, and seat width, face width, stem clearance, etc. A very clear picture shows the head of the valve protruding from the surface of the head. As we are replacing all valves, guides, and seats, how can I determine how far the valve head should protrude or come up with an installed stem height? With adjustable rockers, stem height is not given and is not important.
Response from the Engine Man:
I have a few thoughts on your situation based on how I am interpreting your letter. If my assumptions are wrong, please feel free to correct them so that I can better answer your questions. A few thoughts, though:
- I feel you do need to be concerned and measure the installed height of the valve once done so that you can set the valve spring pressure correctly.
- If it were a gas engine with a combustion chamber, you could cc it to help determine the protrusion. Since it is a diesel and, if I am correct, has no chamber, that would not be relevant. When I built race engines, I would often do this to sink the exhaust valve seat for better low-lift flow.
- Since you know the rest of the dimensions, you should be able to work backward to determine the protrusion, if the seats are placed as they were originally. Often, as you know, the seat will be slightly different due to tolerance, replacement parts, and how true they were set into the head. But that should get you close. At first blush, I do not feel that it should be too much of a concern because I don’t anticipate clearance issues with the piston, but – and this is a big but – I am not visually familiar with that engine to that detail.
- In theory, to determine an unknown valve stem height, you should measure the distance from the bottom of the valve spring retainer to the end of the valve stem on a new valve. Then add this dimension to the specified valve spring installed height for correct stem height.
- To determine an unknown valve seat location, you can do the following by taking measurements from the old head before the seat is removed: If the old seat had a factory width of 0.070 inch and you dress it with a 45° stone to clean it up, and it is now 0.150 inch, it is 0.080 inch wider. Divide 0.080 inch by 2. This value is 0.040 inch. Multiply by the diagonal constant of 1.414. This results in 0.056 inch. The valve stem height would now be 0.056 inch down from its original location. In your case, instead of subtracting the dimension determined by multiplying the diagonal constant, you can add it since you are installing a new seat and the width will be at it narrowest.
Vilsack Looks Back
As an aside, most companies do not provide valve stem height since it is a production measurement that is established when each casting is machined. There are valve stem height measurement tools, and I believe Goodson may have one.
Do you have a maintenance question? Email Ray Bohacz at SFEngineman@agriculture.com.