dave1123

Okay, This question is for you guys that have extensive knowledge of the internal workings of the 4.0. When you see where I'm going, you'll understand.

For a couple of years, I've been researching the definitive answer to the old 4.0 valve rattle at idle. Everybody says it's a known trait and nothing to worry about, but being who I am, I just can't let it go. The closest answer I got was it's because the oil ports that supply the lifters aren't large enough to flow enough oil at idle to keep them pressurized. That seems kinda lame to me. I put a new set of lifters in my WJ when I replaced the head and they were quiet for a week, then the rattle came back. The rest of the valve gear is in good shape and the bolts are tight.

I'm quite familiar with the Chevy small block and know the oil galleries and lifter bores are "intersect" drilled, that is the oil galleries are drilled, then the lifters are bored close enough to break into the side of the oil passage, leaving an oval shaped hole. Has anyone looked at the 4.0 close enough to know how it's done? I'm assuming both these engines are "lifter priority" in that the lifters are supplied directly from the pump discharge first with the mains supplied off the same gallery? If that's the case, I don't understand. Has anyone messed around with adjustable rockers?

tony270

I haven't work or adjusted the rocker arms on this particular engine but I known about the sound. Yes adjusting the rocker arms will stop the lifers from rattling. You need to know the gap and adjustments need to be performed when the lifter is not on a cam lobe, when you do a head job you should take the valve covers off and readjust the valves, sometimes it takes a couple times for everything to lap back in, overtightening a lifter will close a valve.
I hated that, you can get some oil deflectors to clip over the end of push rods so you can run the engine with the valve covers off. Then everything can lap in with the engine running in the shop. I also think it helps to run 91 oct fuel.

dave1123

You must not know the 4.0 very well because there is no lash adjustment. The rockers are solid mounted to the head. My thought was if you COULD add an adjustment to the rockers somehow, that might fix the rattle. I've quieted Chevys by just adding a quarter turn to noisy ones, then taking down the rest of them so they'd all be the same. That positions the lifter plunger in a different less worn spot inside the lifter. What I'm saying is this may work on the 4.0 IF there was some way to do it. I guess you could use 1/16" longer pushrods to do it. I was just wondering if someone has tried this, or if it truly is a supply problem.

tony270

I guess you could shorten the push rods, lifters, cam or mill the head?

tony270

I was posting ways to tighten or loosen the valves.

dave1123

I thought you were a mechanic? To depress the lifter plunger, you have to lengthen the pushrods. The valve train geometry is preset by production tolerances with no adjustment designed in.

This may be the answer! These engines don't rattle when they are new, just after the parts get seated in! Wear in the rocker pushrod sockets, the pushrods themselves, and the pivots may change the factory geometry enough so the lifters lose their preload.

Here's something along the same lines. The 4.7 has a tendency to throw rockers because the lash adjusters stick. Some guys have placed a 1/16" washer underneath them to add more preload. I think I'll make a custom set of longer pushrods and see if it works! Everything should be all right as long as the lifter plunger doesn't bottom out. The only other way to accomplish this is to shave the bottom of the pivots. Where is my Bridgeport at a time like this? I just checked. New rocker pivots are only $1.76 each! I could buy 12, cut them, and try them out very easily.

Sometimes you have to throw an idea against the wall and see if it sticks! This is the second time this forum has provided me with an answer to an obscure question!

bigbadon

False: the main oil galley is inline with the lifters feeds oil to them almost immediately.

1. lifters are NOT PRESSURIZED by oil system. Lifter galley is flooded with oil and after the the lifter plunger is depressed by push-rod it returns by spring pressure to its up/extended position. As the spring pushes the plunger up it creates a suction and pulls oil in from the galley. Oil pressure may help some with the delivery but has nothing to do with pumping up the lifter.
2. Not having a way to adjust valve lash is the short coming of the 4.0
3. As the engine warms the push-rods and valve stems increase in length reducing or eliminating any lash.
4. valve clatter on a cold start is not a concern....the noise may be annoying but as long as it quiets down life is good.
5. Like the chevy, if you had the option to adjust valve lash the problem would be solved.
6. You can get longer push-rods. Thickness of head gasket plays a role too.
7. in theory once a lifter is pumped up it should remain pumped up after engine is shut off for a long time. An engine that sits a week may experience collapsed lifters but the rattle sound at start up should last no more than a second or two.
8. Lifters in good condition do not consume oil,they do not need to be replenished...once filled they pretty much stay filled. Lower oil flow at idle is not an issue unless flow completely stops.
9. In summary the ticking people blame on oil pressure is usually just a clearance issue until thermal expansion reduces the clearances.

dave1123

I agree with just about everything you said, however you're forgetting the oil supply for the rockers comes thru the lifter. This oil bleeds thru the lifter when the valve is closed. As soon as the lifter starts to rise on the cam, the plunger seals off the bottom of the lifter creating a solid pocket of oil. What I'm saying is the plunger is too high in the lifter so all the oil goes to the rockers and is not maintaining enough pressure to keep the lash closed. High mileage engines rattle all the time at idle, not just when cold. This is not a problem unless the rattle doesn't disappear above in idle.

Also, I'm assuming the entire oil supply to everything comes off a common oil gallery. In that case, the lifters are supplied with system pressure all the time. I have not been able to find a clear diagram of the oiling system for the 4.0 anywhere. The one I DID find was so small when you blow it up, it pixelates and you can't see anything.

I'm not trying to build a better mousetrap, just figure out why someone hasn't figured out this rattle before now and done something about it. I've had jeep salesmen tell me the reason people don't like the 4.0 is because of the rattle. They think the engine is worn out! We all know better!

It would be interesting to replace all the valve train parts with new ones and see if it still rattles. I don't think it will until these parts start to wear.

bigbadon

Lifters are fed directly from main oil galley....they get plenty of oil supplied to them. Yes a very small amount of oil is metered through push rods to lubricate rockers and it takes pressure to lift oil to top of head. In theory it would only take 1/2 psi to lift oil above the static oil level. On a cold start after engine has been sitting it can take as long as several minutes for oil to work its way up the push rods to the rockers. No big deal...the residual oil on the rockers protect the rocker assembly until oil flow is started again. The lifters,however, get supplied with oil right away. There are some web photos/diagrams of the AMC I-6 lubrication system that I have seen in the past that shows the main galley and lifters. I believe lifter preload on the 4.0 cold engine is marginal because of the design flaw.

dave1123

Precisely what I thought. At my first opportunity, probably not until spring, I'm going to try the lowered rocker pivots and see if that helps.

It was 10* this morning and it felt like driving thru a deep freeze! Jeep started with a little hesitation, but fired right up. Slow crank until the starter got warm.

dave1123

Okay, here's the latest on my valve train project. I spoke to a friend who owns a engine machine shop and builds race engines as well as normal repairs. He seems to think my idea has merit, so I ordered all new rocker pivots and a cover gasket. He said if it doesn't work, he can get precision spacer washers to go back under them, if I want. Either way, it can't hurt to try it.

Project reports will be forthcoming.

Cleman Simpson

I kind of like the lifter rattle in my 4.0. This thing runs so quiet that without the rattle you probably couldn't tell the engine is running. It doesn't seem to bother the deer either as I have more than once now had deer to walk up to within 20 yards of me while I was sitting in it drinking coffee with the motor idling.

wgebb

Any update on this project Dave? Curious to see how it turned out if you got around to it.

dave1123

Sorry, no. I did get new pivots only to find they are about 60 Rockwell C in hardness, so cutting them is out of the question. They would have to be surface ground or RAM EDMed. I WAS going to buy new rockers and pushrods, but other things got in my way for time and cash.

I'm beginning to think the most wear is on the rockers where they rub on the pivots. That's a hard area to measure. The rockers are stamped steel and case hardened, softer than the pivots.