Okay guys, been awhile since I have worked on the "pit" or posted anything due to recovering from surgery.

It's been driving me crazy thinking what is wrong with the truck.
After installing the new cam it runs good when cold. Once it warms up good, it doesn't idle as good and makes a rattle/knock sound. This sound is only when the rpm's are up. not at idle.
Acceleration and steady cruise above 40 is great. Low speed (0-30) cruise isn't very smooth.

This rattle/knock sounds as if it is coming from the lower intake area, if that makes sense and have been told it was a rod knock but it isn't a deep metal sound at all.

What has been done;
1)Every sensor has been replaced
2)Rechecked pushrods for proper tightness and to make sure they weren't bent.
3)Intake manifold and TB cleaned and new gaskets - checked for vacuum leaks.
4)New - distributor and module (thought the noise was coming from this at first), distributor cap/rotor, ignition wires and plugs.
5)Ignition coil tested good.
6)Water temp normal
7)Oil pressure normal
8)Fresh gas (91 oct. )
9)After running with new plugs they look very good

What this is not;
Not an exhaust leak
Not valvetrain noise (lifters/rocker clatter etc.)

The strangest things I have found;
1)When attaching a vacuum guage to the vacuum "tree" on top of intake the motor instantly dies. Remove guage before it actually dies (attached for only 1 second or less) it stays running. Whith the vacuum line disconnected for these attempted test's the idle smooths out but dies when you plug the vacuum leak?????

2)The compression check;
120 across the board (hot or cold). Unfortunately I do not know what it was before the cam swap.

Where I left it before my surgery I had tried to pull the oil pan to inspect the lower end but found I need to move the AOD back at least 1/2". I have the pan resting on the K-member with the oil pump and pickup removed, well the pump is out and the pickup tube is at the bottom of the pan.

What bothers me is the compression - The motor only has 40K miles since a rebuild. When I did the cam swap I didn't think about pushrod length. Could too long of a pushrod cause the low compression readings from leaving the valves open a hair and possibly cause some kind of ignition knock or rattle (not a ping) and that is what I am hearing after it warms up and causing it to run a bit rough at low rpm?

SORRY FOR THE LONG POST! But I have been down rocovering and thinking alot about it.

Thanks for any thoughts on this crazy truck. At least you know a Ford man when you see him - He'll be the determined one!

 

Unless you somehow spun the RPMs to 7500 then I highly doubt your pushrods are bent.

Was your block rebuilt with a roller cam?

Did you install guideplates when you did the cam swap? If so, those require hardened push rods.

Is the cam correct for your lifters (flat or roller)?

Did you break the cam in properly if it is a flat tappet camshaft?

Are you absolutely sure you have the rocker backlash setup properly? If they are too tight they make a ton of noise...this is what still suspect is not done correctly...

Are you still running the stock 1.6:1 stamped rockers?

120psi per cylinder seems a bit low for a 40K mi vehicle. I have seen 350 Vortec Chevy's with 160psi with 140K mi...

 

This is a flat tappet cam and lifters with the stock rockers. No guide plates and the pushrods are not bent. The cam was broke in correctly. I tightened the rockers to spec as they are non adjustable other than different length pushrods. I didn't do the clearance check with a bleed down tool, don't have one yet.

Another question, what is the easiest way to convert these stock heads to an adjustable valvetrain without too much hasle?

 

From what I reall about setting valve lash, you need to tighten them down until the rod stops turning then another 1/4 turn...I almost always use shaft mounted rockers on build ups as they are super-strong.

To convert to adjustable you will need: screw in studs, new rockers, and well I think thats about it.

 

These are the stock pedestal mounted rockers which all you do is torque the rockers down to 25 lbs.

I was hoping maybe someone sells adjustable roller rockers that I could just install in their place, oh well.

 

I think that is your problem being torqued to 25ft-lbs. Lash is usually not nearly that tight. Is that a published number from somewhere?

The rocker studs are like $30. ARP's 100-7101 that work with adjustable rockers...but I don't believe that you can convert the pedistal mount rockers to a stud mounted one.

 

I would check your oil pressure with a gauge. You may have low oil pressure when warm. Also, you may have too much lift for you valve springs and may be causing the springs to bottom out.

 

If oil pressure was low, it would have tons of valve train noise. But the stock gauge sucks so that is also a good idea to check it.

What are the specs of your cam?

 

Cam specs;
* Advertised duration: 270 intake/280 exhaust
* Duration at .050: 204 intake/214 exhaust
* Gross valve lift: 448 in. intake/472 in. exhaust
* Lobe separation: 112 degrees

This is a very mild cam and should work fine, it does great getting up to speed and holding a steady speed.

I have installed a good mechanical oil pressure guage and oil pressure jumps right up at start up and holds good pressure.

The problem is after it warms up. The noise isn't coming from the valvetrain, it is quiet. I don't believe it is a rod bearing due to the great oil pressure at all temps. Although I will verify once I am able to finish pulling the pan.

 

Bad rod bearing at 40K mi!? That is a pretty sad story if that is the case.

Are you running a high pressure oil pump or high volume?

 

Don't know what the one I pulled off of it is but I'm going with a standard pump with a heavy duty rod when I put it back together, depending on what the bearing clearances are. If they are on the large side then I will put a high volume one on.

 

bump

 

It could be a wrist pin. Pull one spark plug wire off at a time and see if it stops knocking.

 

I don't think it's a wrist pin, it's kind of an intermittent knock/rattle but I'll check the lower end soon. I hope.

I was hoping someone else has experienced a knock like this and found it to be a severe spark knock, because I'm almost positive those pushrods are too long from what the compression test revealed.

What does a burnt valve sound like, I've never had one and this could be the problem as well?

 

Anyone ever have a burnt valve? What were the symptoms?