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Thread: Exhaust Valves, F head

  1. #1
    Member Nemo von Klepper's Avatar
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    Exhaust Valves, F head

    I figured out the zero compression in my number 4 cylinder. IMG_3454.jpg
    All of the other cylinders weighed in at >90 lbs. of compression and the no. 3 was even at 100, though the valve was the next most concaved. This is my first rodeo when it comes to engine stuff and so I'm bumbling around a little. The other two valves look really good as do the seats. I would almost think someone had done a valve job recently if it weren't for the number 4 and 3 valves. Interesting note here, the number 1 valve is Willys scripted and in very good condition. Obviously the valves are a mixed bag. I'm not sure what would cause such radical differences in the wear or burning of the valves.

    I plan to replace all of the valves with new ss, just so I don't have to worry about gas additives. I'm not sure what to make of the valve guides or how to determine if they too need to be replaced. The jeep hasn't run in about 30 years, so I can't judge by smoke from the exhaust, which is what advice on Google points to. One excellent Youtube video showed how I could pull the guides without pulling the engine, which suits my purposes for the time being. It said number four could be a problem because of overhang of the hood cowling.

    Anyhow, is there a reasonable way to figure out if the valve guides are too worn?

    Assuming they are too worn, what off the shelf valve guide driver would you recommend?
    And what valve guide reamer would you recommend.

    Thanks!

  2. #2
    Super Moderator bmorgil's Avatar
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    Nemo, a classic worn valve, eventually burning through. I would think since all others were "good" that cylinder was a little lean. Maybe a little vacuum leak on that cylinder. That seat will also be ruined. Replacing the valves with SS is always a good idea. They are stronger. However the wear caused by UN-leaded fuels effects the seats the most, the exhaust seat primarily. To combat this harden seats are installed. There is a discussion about this in the "Well the darn thing is out" thread. The Willys engine (Basically a Continental Industrial Engine) may have had harden seats from the start. The reason being the exhaust valve gets hot and pounds on the hot exhaust seat. Hardening and/or lubricating the valve and seat, and in some cases the use of valve rotaters, makes it last much longer. The lead in leaded fuels provided great lubrication. When unleaded appeared, many auto engines without hardened seats, had valve seat recession. The exhaust valve would pound its way right down into the seat. I would not put a motor together without hardened exhaust seats. There is no draw back only positive, contrary to popular belief they do not fall out when installed correctly. All aluminum heads have inserted seats. There are many who don't do it. They are not wrong for three reasons. If you don't put the motor under loads for extended periods it probably makes no difference. If the motor is loaded hard for extended periods it will make a difference. There may not be enough material to install them. And it is quite possible the seat area has been "hardened" already. If you clean up the exhaust seat area, you may see an insert or a "Hardening Ring" where the metal looks a little different, where the seat may already have been induction hardened. If the guides are bad so are the seats. The wobbling valve ruins the seat seal.

    The valve guide wear can be done by feel. The valve should fit smoothly with no perceivable side to side play.The valve should feel smooth with no side to side play. A VERY small perceivable amount of "play" indicates they are starting to wear. When they are "new" with a little oil on the valve stem, they drop slowly by there own weight. It is a .001" to .003" fit.

    The exhaust valve and seat probably needs to be ground or replaced on that cylinder. That means you are going to have to take it to the Machine shop anyway. You sure can see big time valve trouble in #4. the rest can't be far behind. On the exhaust guides in the block, I would be surprised if they are worn. The fact there is no rocker arm to impart side load to the guide helps here. In an installed engine, they could be done. Using the correct driver they are driven out and then driven in to the correct depth. They must then be reamed to fit. If you are clean and careful, why not! Go to the Jeep Universal Service Manual Section D paragraph D-58 for instruction on how to make drivers. Or you can go here for drivers and reamers https://goodson.com/collections/valve-guide-drivers . However I do think you are going to have to have that #4 exhaust seat reconditioned.
    Last edited by bmorgil; 10-04-2020 at 08:01 PM.

  3. #3
    Member Nemo von Klepper's Avatar
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    Thanks for your response.

    From what I can tell, I have hardened seats. I also took the good #1 valve with lapping compound on the #4 seat to lightly clean it up to get a better look. Both cleaned up nicely and the seat looks to have an even pitch and no pits. I did a graphite test on the seat as described in the shop manual and got a nice even line on the contact surfaces. The local machine shop wants me to pull the engine if I bring it in. I think I'd just rather lap with new valves, check for even contact and make a decision based on how they look. It seems to me I'm out the personal time of removing and refitting the head and gasket materials if I test my hunch, vs. the hours of time and bother to pull the engine and refit it. I'd also need a lot of additional resources to pull the engine at this point. Just a thought.

    Thanks again and for recommending a guide driver.

  4. #4
    Super Moderator bmorgil's Avatar
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    NvK, after you lap them, assemble the valves and springs and check the seal with a vacuum pump. A hand held Mighty Vac is perfect. I use a Mighty Vac hand pump and a port adapter I made up out of a rubber cup. If the valve will pull down vacuum and hold it for a minute or two, it will seal and hold compression. All good machine shops vacuum check the valves before they leave. It is the best way to know if it is going to seal.

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