cold engine knock

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Feb 3, 2004 | 09:23 PM

deanc

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Joined: Feb 2004

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From: okla usa

cold engine knock

cold engine knock
Have 91 F=350 with 4.9/5sp.

Orginal engine had 105k and developed a cold rattle or knock that went away when warmed up. Figured the engine about gone so got a factory long block and installed. Engine ran good, but noticed it had the same knock as the old one. Replaced everything that even showed wear or tear outside the engine, NO HELP!! Talked to the rebuilder, told them everything that had been done and that I was not satisfied. They send me another long block and told me to install it and send in the first one, so I did. YEP YOU GOT IT SAME THING ALL OVER AGAIN, several people have been involved it this and its got us whipped. No way 3 engines has the same noise. Its got to be something external, but have replaced or swaped a lot of the external conponents. Engine runs and pulls great, but the noise is driving me nuts, not to mention the bucks spent and still there. Would appreciate any and all help. Thanks in advance

Dean

PS, Forgot to mention that the knock or tapping comes in at about 15 hundred and you can't hear it after about 22 or 23 hundred rpm. Has to be under load for it to show up, like it 3rd or 4th gear. Can hear it in the cab going down the road. Sounds perfect at idle.

Last edited by deanc on 02-03-2004 at 09:19 PM

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Last edited by deanc; Feb 3, 2004 at 09:43 PM.

Feb 3, 2004 | 10:49 PM

parks911

Cargo Master

Joined: Sep 2003

Posts: 2,543

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From: Georgia

Try running a higher octane of gas.

Feb 4, 2004 | 01:05 AM

Frizlefrak

Senior User

Joined: Nov 2003

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From: El Paso Texas

My only suggestion is to replicate the conditions when it occurs and use a mechanic's stethascope to locate the source. Start it cold, crawl under it and put the stethascope everywhere (chock the wheels of course)

The only other possibility that comes to mind is a stuck EGR valve or something in the smog pump. These are the only temperature related items that I can think of that would have been potentially reused when the new long blocks were installed, and might cause a bad noise if stuck.

It has to be something you are reusing, so let's start with the obvious.

Clutch and throwout bearing original?

Have you checked the exhaust manifolds for cracks or leaking?

Good luck, keep us posted. We love a good challenge.

Feb 4, 2004 | 08:16 AM

deanc

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From: okla usa

Smog pump was gone and plugged off when I got the trk and put in new ( not rebuilt ) clutch and pressure plate when the first engine was installed.

This is one of the times I wish it was auto, as its kinda hard to load the engine with a five speed in the shop, need a dyno!! Have the steathascope and have been all over many times, very hard to isolate the knock or tapping, hard to describe. It doesn't give one much time to listen, cause as when it get warmed up it goes away and doesn't return until its cold.

As was said above, its got to be something that is bolted to the engine, but you know that a pretty simple engine and theres not that much to it. Been everywhere but the distributor, but never heard of a distributor making that kind of noise and still run, muchless run good. As I said when it warms up, it sounds perfect. If you all like a good challenge, here it is.

Any more ideas, if there are lay it on me and we'll give it a whirl.

Thanks, Dean

Last edited by deanc; Feb 4, 2004 at 08:18 AM.

Feb 4, 2004 | 09:08 AM

carpe_diem

Fleet Mechanic

Joined: Feb 2003

Posts: 1,314

Likes: 35

No idea, but empathize. If you find out, post.
I had a similar bitchy problem, one of the belt driven devices sounds like its bearings wore out but couldn't find what it was and just started randomly replacing parts.

Feb 4, 2004 | 02:19 PM

Frizlefrak

Senior User

Joined: Nov 2003

Posts: 155

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From: El Paso Texas

Dean....Actually, I did once have a car back in the 70's that had a noisy distributor. The shaft bushings were worn out and there was a lot of play in it, and it produced a noise similar to a noisy lifter. It would go away at any RPM above idle, but occured without regard to temperature.

If you haven't poked the stethascope at the distributor, it's worth a shot. It has to be something that rotates, and that has been reused between engines. Just make sure you don't have any leaking plug wires or you will get a nice little high voltage surprise where you least want it.

I wish I could hear the noise, then I might have a better idea what to suggest. Have you checked for a stuck EGR?

Feb 4, 2004 | 10:34 PM

tinman57

Freshman User

Joined: Jan 2004

Posts: 47

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From: Tx

I had a knock in my 92 F250--351W--I couldn't find it anywhere.I took it to the Ford dealer and it turned out to be an injector. It cost me 80 buck to have them run an injector cleaning kit through it and wha-la no more knock.