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Do I need a valve job or any head work?

jeepboy381

NAXJA Forum User
Location
Gresham, Or
So I had to take my head of my 4.0 to replace a snapped off exhaust bolt on the very back of the engine. While the head is off I am also going to do a little head work and gasket match the head. The question is do I need to take the head in to a shop to have any work done to it while it is off? Everything looks fine to me and I bought new valve seals while I was at it but is there anything else that I should have done? Possibly a valve job? This engine only has about 130,000 miles on it. Thanks Josh
 
I would pull the springs off a couple valves, run the valve to max opened height and check side to side play. If you do need the seats worked on insist they not be knurled but actually replaced.
 
JJacobs said:
I would pull the springs off a couple valves, run the valve to max opened height and check side to side play. If you do need the seats worked on insist they not be knurled but actually replaced.

1) You're talking about valve guides - seats are never knurled...

2) It takes some machine work to replace valve guides in the AMC six - the guides (and seats, for that matter...) are integral to the head casting. So, you'd have to actually bore out the guide cast into the head to replace it - making it cost about twice as much as replacing a removable guide (which can usually be just pressed in and out.) Likewise the seats - you have to counterbore the area around the valve seat cast into the head and press in a new seat.

Not trying to put you off - if the work needs doing, get it done. However, it can end up costing you rather more than, say, putting bronze guides in a SBC head...

N.B. If you need one done, you may as well have them all done. No sense in leaving a mixed bag in place for you to figure out later.
 
I have everything taken apart right now, I will check for play in the valves when fully open tonight. I am guessing everything will be fine. I bought this engine 3 years ago and completely took it apart, cleaned it, and replaced everything that needed replacing. The only parts that needed replacing were the gaskets only because I took it apart. It had an insane amount of sludge when I first took it apart 3 years ago. The sludge was so thick I question if the oil was ever changed at 120,000 miles! Even though the engine looked as though it was denied oil changes it was still in prestine condition. The Cyl. walls looked as though they were just honed, all bearing surfaces were nice, and there was a hardly noticable ridge at the top of the cylinders. Runs great besides the horrible exhaust leak I will be fixing.
One more question, I have a renix factory header on right now that has a small crack in it that I will fix. I also have a factory header off a 1995 XJ that does not have any cracks in it because they are already fixed. Is the 91-99 header worth the extra work of swapping on to my XJ, I will need to have a new exhaust downtube made for it to work. What do you think, should I keep the renix header or swap to the 91-99 header? Thanks
 
Well, machining them out is a lot better than knurling the guides, and the only option from here- if they're worn. I have had terrible luck with knurling.
 
Last edited:
JJacobs said:
Well, machining them out is a lot better than knurling the guides, and the only option from here- if they're worn. I have had terrible luck with knurling.

Knurling is very much a "band-aid" fix. And, I have found that it works rather better on bronze guides than integral iron guides - knurling iron guides is just about useless. Bronze does a better job of retaining a bit of oil - which allows them to keep the knurl a bit longer.

If I were to knurl guides in a head, tho, I'd probably do it just because I had another head handy, and just had to get it ready to be installed (knowing that I'd need 4-6 months to do the job right.)
 
Since you have the head off, check it for warpage and vaccume test to see if the valves are still sealing. As well as a good visual inspection and search for evidence of cracks or other problems. Before you take appart the head, look down the ports at the valve stems for oil that leaked past the seal. If the guides are worn out and you need bronze guide liners, either the thick or thin wall liners. You will most likley need the seats cut, because the guides will not go in perfectly the valves will no longer seat properly. If you are going to reuse the stock valves you can just have the seats cut without needing seat incerts since only a few thou will be cut/ground off.
I would not go for the gasket match on the cylinder head. By only opening up the first inch of the port and intake manifold you will be causing rapid changes in the velocity because you are not addressing the most constrictive part of the port. You might want to check out a 99+ intake manifold.
I would suggest you port match the manifold to the head and the head to the header. One good way to port match is to use a few old folders and cut them out to the port outlines. Another is to use a staining dye that will transfer over from the head to the manifold. When porting the manifold make the mouth about .050 larger than the opening in the port.

~Alex
 
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