Vavle stem height....

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danmc77

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Ok, I need some help.

A few years ago I took my J heads to the machine shop with the 360short block for some machining for a rebuild. My problem is with the heads...

I had new seals, valve guides, hardened seats and a valve job done on them. I bolted teh engine together with performance springs (appropriate for the cam) and stock valve train. It ram like a beast in my 89 Ramcharger for about 3 years (maybe 10k miles). Well, I've decided to sell the Ramcharger, so I pulled the engine to put into my Duster. (I rebuilt another 360 to put back into the RC).

Now, I have the engine sitting in the garage and my plans are to just refresh the engine with a more radical cam and an adjustable roller rocker setup. In addition, I'm going to mildly port the heads and gasket match.

Now - with all that said, here's my question. I took the time to look the heads over and noticed that the valve stem height is off on several of the valves. I laid a straight edge across the valve tips to determine this. It seems maybe that after installing the hardened seats that some of the valves are seated a little higher than the others.

- Shouldn't a reputible machine shop have accounted for or noticed this?
- Do you think I should take the heads back after 3 years and show them and complain?
- What can I or should I do about it? I will have adjustable rockers on it when i reassemble the motor. They are only slightly off, but almost recognizable to the naked eye without a straight edge across the tips. Honestly, I didn't want to invest more $ into this engine for this project. It is for a street car that might see the strip once in it's life, but I want to try to get into the 12's.

Sorry for the long-winded post, and thanks in advance for the help!
 
On an remanufactured engine w/10k miles the valve lengths are not gonna be identical. The tolerences were sort of loose when the engine was built, the very first time and since then you say the valves have been ground and the seats replaced? If the machine shop is very expensive and very methodical they may be able to rebuild, better than new, but most of the time it doesn't matter, that much. Did you pay for a rebuild or a blueprinting, because there's a big difference in the amount of time invested.
 
I guess i just paid for parts and machining. I certainly didn't pay for them to "blueprint" it. Although, I just assumed that when I had them install hardened seats and do a valve job, that it would be done the right way. I mean, if you are replacing the valve seat, wouldn't it go without saying that the newly installed seats would be machined to match the existing valve seats? I'm shocked that you would have to pay extra for it to be done the right way. Don't get me wrong, this guy wasn't particularly cheap, and has a decent reputaion in the area - I wasn't trying to take any short cuts.

Regardless, it's my fault for not noticing it when I picked up the engine. My biggest concern is if this varience can be rectified with the adjustment in the new rockers. I mean I know it CAN be done, but does it throw off the rocker geometry such that it will afect the performance of a street engine?
 
I have seen this on several heads also and it always bugs me. sst3193 has a point that if you don't pay for blueprinting you'll get this. If it's only a few thousandths (say no more than .030) the adjustable rockers will allow correct adjustment and it won't make much difference in performance. If it's over .030 it starts to make a difference on the geometry as you suspected. When it gets up to .060 it's getting pretty bad. I mentioned that because I had a set that were like that. I had to put lash caps on the intakes to make up for the shorter valve stem so it would have the correct geometry. Either that or take them back and pay for blueprinting or buy longer valves. The lash caps worked fine even though I know it's not exactly doing it the "right way".

I don't know why they don't sink the seats as far as stock but I do know that not sinking the seats in has a positive advantage on flow. The farther you sink the valves the poorer the flow. In my opinion it has to make a difference in power production from cyl. to cyl. when they are all uneven. Hope that makes sense.

BTW: I located a set of stock J heads to check the installed height because I couldn't ever find a figure as to what it should be. The stock heads measure 1.90" from valve seat to valve stem height. There was only .010 max variance with the stock heads.

Also if you disassemble them to clean them up you shouldn't need to worry about keeping the valves in the same hole they came from with no more miles than you have on them. You can try different valves in different holes to get the variance balanced out as close as possible because I'm sure the same amount of material removed from grinding the valves and seats are not always the same.
 
Thanks! That helps. I'll check out the actual varience when i get a chance.

as far as the difference from one cyl to another - I understand what you're talking about and agree - that's why I was concerned. Although, only the exhausts have the hardened seats, and it's the exhaust valves that are the culprit. So, as long as they are consistently off from cyl to cly, there shouldn't be that much diffenece from one cly to another (I'm guessing).

The engine ran great in the Ramcharger, so I think I'll just take some measurements and as long as it's not too far off, make up the difference with the adjustable rockers.

I guess I can always look at it as a slight bump in compression since the valve sits lower into the combusion chamber, right?:-D
 
Sorry, but if I picked up a set of (shaft mounted rocker) heads from a machine shop and the valve tips were not level, that would be the last set of my heads they would ever do. Hydraulic lifter preload can only compensate for so much.

Since you are planning to run adjustable rockers, you can set the preload anywhere you want. A reasonable work-around. You could also have the valve tips ground to level them out, run lash caps, etc...

If you feel you must level the tips, and performance is your main goal with this engine, consider oversize intake valves. This way the machinist can set them higher on their seats (good) as opposed to lowering the exhaust valves into their seats to raise the tips (not as good). This will provide the side benefits of a slightly reduced chamber volume, and some flow improvements (so long as you open up the bowl).
 
C130 Chief said:
Sorry, but if I picked up a set of (shaft mounted rocker) heads from a machine shop and the valve tips were not level, that would be the last set of my heads they would ever do. Hydraulic lifter preload can only compensate for so much.
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Yeah, I agree - that's why I think I might take them down there just to show them and see what they say.

Unfortunetly, I picked them up close to 4 years ago now and didn't know then what i know now. While I think I am relatively well informed, there's plenty I didn't and still don't know. I missed this one, but I won't make that same mistake twice.
 
Just use adjustable rockers. Most mopar heads come back from a valve job looking like this.
 
How about the varience in the installed spring height? If the exhaust valves are sitting lower (the stem), the spring pressures will be off from intake to exhaust, right? My plan was just to install shims under the intake springs to raise them up and match the spring height of the exhausts. Does that sound right? Right now, there are no shims installed under the springs. In addition, I'll use the adjustment in the rockers to compensate for difference in valve stem height. Will that work?
 
danmc77 said:
How about the varience in the installed spring height? If the exhaust valves are sitting lower (the stem), the spring pressures will be off from intake to exhaust, right? My plan was just to install shims under the intake springs to raise them up and match the spring height of the exhausts. Does that sound right? Right now, there are no shims installed under the springs. In addition, I'll use the adjustment in the rockers to compensate for difference in valve stem height. Will that work?
Click to expand...

It's a good idea to check the spring height and shim it accordingly. Stock spring height is 1.68-1.7" If the intakes are already at that height their ok. The exhaust may actually be less than that since the seats weren't sunk as far when replaced so shimming the intake valves to match the exhaust may just create another problem. You have to watch the installed height and make sure it don't coil bind at full lift. For instance if the installed height comes out to be 1.65 and you have a .500 lift cam you subtract the cam lift from the installed height and it comes out to 1.15 Now if the spring coil binds at 1.15 your in trouble. You need some tolerance there. Usually .050 will give you enough room so in this case a spring that don't bind until 1.1 lift would work. Using the adjustable rockers to adjust the preload should be fine unless they are way off.
 
dan, bad machine work, check for coil bind, you have to have seat retainers. the machine shop sucked. now you will have to go adjustable rockers,use the 3 position method , now you know next time to check the valve height and seat height with springs and locks in place anytime you pick up a set of heads from the machine shop,sorry to hear that. dont feel too bad, lot of new aftermarket heads have different seat heights ,sometimes the manufacturer compensates by grinding a few valves ,sometimes they dont bother. sorry to hear the piss poor job they did .025 to .050 is the #anything more than .050 or under .025you need a n adjustable pushrod and using the 3 position method set preload to .040 and get the right length pushrods.
 
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