Pitted Exhaust Valve....With Picture

I am in the process of changing all the seals/gaskets on a '99 4.0L. The motor was given to me torn down so I never had a chance to run a compression test. The previous owner was an old friend who said the motor ran fine before tear-down. I did have the head decked, magnafluxed, and hot-tanked and confirmed its a 0630 casting. I just hand-lapped all the valves and noticed some heavy pitting on all the exhaust valves. All the intake valves seemed okay. The valve seats in the head all seem okay without any pitting whatsoever. I assembled the valves with springs and retainers and filled the chambers with gas to see if the exhaust valves would leak. Sure enough, all the intake valves were fine but I could clearly see gas running out of the exhaust valves. What can I do?

I really need to assemble this motor and get it running for a DD until I am finished with my master's this May. I need this motor to last until then, at which time I plan to build a stroker. What is the most budget friendly solution to this problem? Can I just purchase new exhaust valves and run then with the current valve seats without having a valve job done at the machine shop? In May/June, I plan to purchase all new performance valves and have a valve job done at the time but I would really like to fix this for the time being as economically as possible.

Thanks for the help.

Looks like the engine may have been run without an air filter for a while in a nasty environment. Lap the valves and run it. I wouldn't worry. At most, have a simple valve job done.

old_man:

That exhaust valve has been lapped. I actually lapped all the exhaust valve twice trying to get rid of the pitting. You recommend trying to lap them again to remove more of the pitting?

Ideally it would be the cheapest solution to just run the valves but wont compression be adversely affected by the leaking exhaust valves?

Best solution would be to take the head to a good machine shop have them work it, then put in new valves, springs, and keepers. That should last the 6 months you need it to and not give you any trouble.

I understand that would be the most ideal solution and it's what I plan to do down the road. I guess I'm just wondering if I could replace the valves with stock replacements and get away with just lapping them until I do a complete rebuild in 6 months.

Well that should work till the rebuild. Just go easy on it the first couple hundred miles. Only replacing the valves could be hard on the seats n keepers, etc. How many miles are on this engine?

150k. The motor appears to be clean and regularly maintained. I didn't plastigauge the rod bearing or anything like that. I'm just replacing all seals/gaskets, water pump, timing chain, radiator thermostat/housing, plugs, wires, cap, rotor, oil pump, and fan clutch while the motor is on a stand. Money is tight till I finish school and I'm hoping this will get me by till then.

valve really are not that expensive. If you are really worried about them after another lap job or two and they still leak I would just replace them.

Put it back together and run it. It should be fine. The comment on lapping was just to make sure that the mating surface matched all the way around. The worst would be a slight loss in compression, but when you are running, you should not be able to even feel the difference.

Since you are planning on doing the head soon, I would personally just run it.

I say run it the way it is. A valve job is also not to expensive. Buying the valves will cost almost as much as a valve job without new valves.
Ron

you CAN use a coarse lapping compound first, then the fine compound. that should remove the pits. but it may also take away from the surface of the seat. you have large seat lines as it is. the intake line should only be about the thickness of a dime. the exhaust about a nickel. exhaust mating surface is larger because the valve cools as it sits on the head, so more surface there is, the quicker it will cool. as mentioned, you can run em they way they are as long as you are getting a surface cut all the way around on both the valve and the seat. those little holes wont see that much leakage at all. or just buy some new valves, lap them to the head and be good to go for a good long time. i do think the valve job in 6 or so months is definitely a good idea by looking at those lap lines.

what am i missing . where is the picture .

There is a pic at the bottom of the first post. If it doesn't display for you:
http://www.naxja.org/forum/picture.php?albumid=351&pictureid=2052

Put it together and run it. Most XJs on this site probably have worse leakage with the mileage thats on them.

i wouldn't even bother with lapping it. Most machine shops only use lapping to check the matting of the valve and seat, not to actually grind. You lap it at room temperature and it might seal up better. But, its not going to help once the head is hot and the seat moves around a bit, it may even make it worse. Excess lapping will also cause teh sealing face to become concave.

I'm no expert on this, but how much are new exhaust valves, and how much is a JY head, ready to use, one with good valves?

There is no way I would reuse those, just looking at the pictures, way too much time and work redoing a head 6 months later for me, but that is me.

I don't like fixing the same thing twice, especially something like a head.

Edit: But I have been known to use duct tape and snake oil, in a pinch, LOL!

What's your budget? I'm thinking reman'd head. $250 shipped to you, and when you do the rebuild you can just slap the entire thing back on. I run a JS one off eBay, no problems yet. Comes totally ready to go minus rockers and bridges. Valve job, decked, springs and seals, ready to rock.

Ecomike said:

I'm no expert on this, but how much are new exhaust valves, and how much is a JY head, ready to use, one with good valves?

There is no way I would reuse those, just looking at the pictures, way too much time and work redoing a head 6 months later for me, but that is me.

I don't like fixing the same thing twice, especially something like a head.

Edit: But I have been known to use duct tape and snake oil, in a pinch, LOL!

Click to expand...

If you read his original post, he is going to pull the motor in May and build a stroker. All will be fine until then. Yes you could redo the head now and it would be ready for the stroker, but he was looking for low buck since he is still in school. I have rebuilt dozens of engines starting at age 10 on the farm. It will be fine. If the valves showed heat discoloration or warping, I would be worried but the seats are fine and other than some pitting, the valves look great.

Thanks again to everyone for all the help. I decided to just buy some stock replacement exhaust valves to replace the pitted ones. I lightly lapped the new valves and installed them into the head. After a gas test, the new valves sealed tightly without any leaks. When I finally get the engine back in the Jeep, I'll let everyone know how things work out.