Hi all,
I have a good one here that has me guessing. My 95 4.9 3.08 m5od at 175k has developed a noise at idle that only shows up when everything gets up to operating temp. Cold starts and drivability seem ok. Engine fires right up, idles high for a little bit and then comes down to about 800 rpm and is smooth. After about 20 minutes of running, the idle drops a little bit lower to about 750 and makes a rump rump clattering sound from the rear of the engine. I can feel it through the gear shifter and it doesnt change with the clutch pedal in or out. If I raise the idle up just a little bit, the noise goes away. Im thinking valvetrain issues for starters. I have 160 lbs of compression on all cylinders and replaced the oil pump when I put in an isky 256 cam about 10k miles ago. I also replaced the lifters, pushrods and smoothed up the ports in the head.
I put a long rod against my ear and different parts of the engine while its running to locate the noise. It is definately coming from the rear around the cylinder 5 or 6 valve cover location and lifter cover and seems to taper off as I move towards the front cylinders. I even releasd the tensioner to rule out any of the belt driven accessories.
Timing is dead on 10* with the spout disconnected and advances when installed. Vacuum is 21-22 inches. Fuel pressure is 55 psi and steady. I put a quart of thick oil treatment in it to see if that made a difference to steer me to a bearing issue but it made no change.
My guess is either lifters, rockers or bearings.
The thing that gets me is how it only shows up when the engine is all warmed up. I would think if it was something like a clearance issue it would do it all the time.
What do you guys think? Im open to all suggestions.

 

How's your oil pressure? Low oil pressure is usually indicative of a bad bearing. If your oil pressure is around 40 or 50 PSI, then I'd not worry about bearings for now. Especially with the vacuum and compression you've got, I wouldn't worry about the bottom end for now.

My father had a Jeep Cherokee with the 4.0 high output inline 6 in it. And the top of the motor would make a "plup plup plup plup" sound real steady, but you could only hear it inside the cab. When you started revving the motor up, it'd go away.

I'd pop the valve cover if you can, and pull each rocker and push-rod one at a time (make sure not to swap them between other rockers. Putting a rocker broken in for the #1 exhaust valve on the #5 intake valve wouldn't be a good thing, and can accelerate wear) and check each rocker on the inside where the ball sits (look for chips and uneven wear) check out the ***** and look for any uneven wear where the rocker contacts the top of the valve and the pushrod contacts the rocker.

I'd look into an oil additive. Add a little ZDDP to the oil, as well as something like Seafoam to get rid of any gunk that might be in the lifters/pushrods.

If I had to guess though, I'd say it's probably the lifters. You say it only happens after it's gotten warm, which leads me to believe that it occurs when the oil thins out. You might be able to go to a heavier oil and it go away.

Are all of your rockers torqued to the proper setting with the right length pushrods?

 

Thanks for the response.
I am going to check that hopefully tomorrow if the its not too cold out. I am going to put a tee with a gage in at the oil pressure sender and pull the valve cover to take a peek at the rockers. I am then going to pull the lifter cover and go from there. I always run 10w30 but this time I went with 10w40 and hadnt noticed a difference. I torqued all the rockers and replaced the pushrods with stock length because the head didnt need to be shaved. Pushrod geometry looked good with the rocker tip centered on the valve. I picked up an upper and lower intake, valve cover and pushrod/lifter cover gasket to have on hand just in case.

 

Well, after removing the valve cover it looks like the rockers could be the problem. I removed a few from the suspected area and the pivots seem to be worn a little much in the seat of the rocker. I can feel a click when moving the pivot through its travel on the three that were removed.
Hopefully this is the issue. The cam and lifters were replaced about 10k miles ago. Im going to check lift numbers to be sure though.

 

Sounds great, and thanks for letting all of us at FTE know what the issue was/may have been (won't know till you change the rockers and rocker ***** I suppose).

My rockers were worn well down into where the ball sits in the rocker arm too, and my rockers made a pretty good ticking noise even when adjusted right. So maybe you've found the issue.

If you have any more questions, let us know and we'll be happy to help.

 

Well, the new rockers are in and done. They were definately bad and the rump rump noise in now gone. Seems to idle better between the rockers and overall tune up being done.
While I was at it I installed a mechanical oil pressure gauge on a tee with the oil pressure sender. Oil pressure is right around 45 psi cold and 25 psi hot at idle with 55 psi max off idle.
Now Im chasing a minor rattle sound only at idle when warm. Ill keep everyone posted.

 

I think its time for a cloyes timing set because my stethoscope to the timing cover revealed the location of my rattling sound when warm. All accessories are good. I guess the Autozone timing set couldnt cut it. Im kind of anxious to see what it looks like anyway.

 

You can check out my recent cam gear fiasco.
https://www.ford-trucks.com/forums/1...-troubles.html

I would at least check the dist gear for wear and check for cam walk while it's out.

 

Several of my exhaust system heat sheilds have worked loose over the past 17 years and 239k miles causing a rattle at idle and while accelerating.
regards
rikard