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Author Topic:   knock/rattle
F-150Moneypit
Journeyman

Posts: 34
From: Oregon
Registered: Jul 2003

posted 07-26-2003 09:45 PM     Click Here to See the Profile for F-150Moneypit     Edit/Delete Message   Reply w/Quote
Okay guys, new to the forum and been awhile since I have worked on the "pit" due to recovering from surgery.

It's been driving me crazy thinking what is wrong with the truck.
After installing the new 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 )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 after it warms up, but when cold it runs great.

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?

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?

SORRY FOR THE LONG POST! But I have been down rocovering and thinking alot about it. Hopefully I'll be able to start wrenching on it again soon

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!

------------------
'90 F150 Super Cab XLT Lariat
5.0/AOD/3.55 275/60/15 BFG's
Latest Mod - 204/214 cam

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SteveLaRiviere
Administrator

Posts: 43151
From: Saco, Maine
Registered: May 99

posted 07-27-2003 07:31 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Here are my thoughts:

A rod rap only sounds on deceleration. You rev the engine up and as it slows you hear the rap-rap-rap... as the connecting rod catches up with the rod journals on the crank. Also, a rod rap isn't a lingering problem. It get quickly worse as you run the engine and the rod bearing quickly turns in the rod's bore and you lose oil pressure and BANG! So we can rule out rod rap.

A burnt valve is very noticeable. A burnt intake will backfire through the intake, an exhaust valve will backfire through the exhaust. This problem will also quickly get worse and progress to a no-run condition. So we can rule this out.

At first I thought of piston wrist pin noise or piston slap, but you said it is quiet when cold and noisy as it warms up, which are the opposite symptoms of those two problems. So I'd rule that out.

Since this problem appeared with a cam change, this might give us a clue. Here are what pops in my head:

*Did you break in the cam properly by running it at 2000-2500 rpm for a 1/2 hour immediately after first start up?

*Did you check to make sure you had proper rocker arm geometry with the different cam? You could have the rockers hitting the valve covers or rocker arm studs or tops of the retainers if the geometry is wrong. I've seen all three conditions before. You don't have much lift, but stranger things have happened.

*Are you running about 10 degrees of initial timing? Can you make the sound disappear by altering the timing?

*How did you adjust the valves?

------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150

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F-150Moneypit
Journeyman

Posts: 34
From: Oregon
Registered: Jul 2003

posted 07-27-2003 09:14 PM     Click Here to See the Profile for F-150Moneypit     Edit/Delete Message   Reply w/Quote
Thanks for the reply.
Yeah the cam was broken in correctly. The rockers aren't hitting the covers but I didn't check the geometry. Although I can't hear the noise coming from the covers, only from the intake. I just torqued the rockers down to spec (pedestal mount).

I think this is where it's at as I don't have a lifter bleed down tool to check the lash as the book suggest's.

Looking at the compression results of 120psi, I have a feeling the pushrods are too long causing the valves to stay open a hair.

I was very reluctant to drop the pan to inspect the lower end because of the great oil pressures hot or cold but I was desperate.

I'm am running 10* initial timing.

What are your thoughts on the strange behavior with the vacuum? I should be able to hook up a guage to it. I'm thinking this has something to do with the valvetrain geometry as well (valves staying open).

As soon as I'm able to get back to it I'll take a harder look at the valvetrain again.

THANK YOU!

------------------
'90 F150 Super Cab XLT Lariat
5.0/AOD/3.55 275/60/15 BFG's
Latest Mod - 204/214 cam

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SteveLaRiviere
Administrator

Posts: 43151
From: Saco, Maine
Registered: May 99

posted 07-27-2003 09:46 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
If the valves were being held open by longer pushrods, you would experience backfiring through the intake or exhaust or both.

120 psi isn't very far off for a low compression engine such as yours.

The engine dying when you plug the vacuum tree is very strange indeed. Do you currently run it with the port open?

How does the engine run with the distributor advance unplugged and that vacuum line plugged?

Can you get a vacuum reading from some other port other than the tree at the back?
I hope you feel better soon, recuperating from your surgery.

------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150

Please remember our sponsors,
Mustangs Plus, NPD, Osborn Reproductions, and FordRamAir.com

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F-150Moneypit
Journeyman

Posts: 34
From: Oregon
Registered: Jul 2003

posted 07-27-2003 11:23 PM     Click Here to See the Profile for F-150Moneypit     Edit/Delete Message   Reply w/Quote
It only dies when I pull the vacuum line off of it and either plug it or hook the gauge up to it. When the vacuum port is open with nothing on it, it idles up. Of coarse that's because I'm inducing a vacuum leak. When I hook the vacuum line back (not sure where it goes) the idle goes back down and continues to run. Only when that vacuum port is plugged it dies. Leaving it off isn't necessary.

There isn't a vacuum advance, that's controlled by the computer.

The vacuum tree is on top of the upper intake with a cluster of 3 hard vacuum lines and one single vacuum line. That is the one I disconnected.

I'll have to remove the cluster and use one of those ports next.

Thank you!
I'm starting to get around pretty good now, just not able to put any strength into anything, like moving the tranny back. Soon though very soon.

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SteveLaRiviere
Administrator

Posts: 43151
From: Saco, Maine
Registered: May 99

posted 07-28-2003 06:53 PM     Click Here to See the Profile for SteveLaRiviere   Click Here to Email SteveLaRiviere     Edit/Delete Message   Reply w/Quote
Another thing that occurred to me today is that the noise might be from a noisy fuel injector or two?

Why don't you follow that line and see what it leads to. If it leads to a MAP sensor that would explain it.

------------------
'70 Mustang Mach 1 - '72 Mustang Sprint - '94 F-150

Please remember our sponsors,
Mustangs Plus, NPD, Osborn Reproductions, and FordRamAir.com

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F-150Moneypit
Journeyman

Posts: 34
From: Oregon
Registered: Jul 2003

posted 07-28-2003 09:15 PM     Click Here to See the Profile for F-150Moneypit     Edit/Delete Message   Reply w/Quote
Just looked at the vacuum lines - The MAP sensor line is one of the hard lines in the cluster. The single line I pulled goes to something for emissions, a canister behind the drivers headlight. It's not the fuel vapor can, that's on the other side.

Yeah, I thought about injectors too but not sure how to isolate one to rule that out.

Well I'm giving it a shot now, a little sore from getting what I thought was all the bolts loose from the AOD. But she won't budge with my floor jack under it. There are only 5 9/16" bolts to the bellhousing aren't there? OHH yeah, time for a pain pill.

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MLariviere
Moderator

Posts: 3984
From: Biddeford,Me.USA
Registered: May 99

posted 07-28-2003 10:52 PM     Click Here to See the Profile for MLariviere   Click Here to Email MLariviere     Edit/Delete Message   Reply w/Quote
There should be 6. After you button the bottom up,try to find another source for vacuum,and see what you get.

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F-150Moneypit
Journeyman

Posts: 34
From: Oregon
Registered: Jul 2003

posted 07-28-2003 10:55 PM     Click Here to See the Profile for F-150Moneypit     Edit/Delete Message   Reply w/Quote
Will do, thanks!

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lyle29464
Gearhead

Posts: 962
From: Mt. Pleasant S.C.
Registered: Mar 2000

posted 08-01-2003 12:40 AM     Click Here to See the Profile for lyle29464   Click Here to Email lyle29464     Edit/Delete Message   Reply w/Quote
If it dies when you plug the line or put a guage (same thing) on it means what ever it goes to is open or letting some air in.

maybe that is 1/2 of your problem the other half is why will it run with that extra air coming in and die with it pluged off.
This is a total guess. I dont know if that port should have any "real flow".

If you know anyone that has a motor like it they might let you pull that one line to see what it does or maybe a m&m person will do it for you.

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