I have a '79 F-150 4X4 with a 351m. I have owned it for almost 3 years but I did not start to drive it daily until last fall and before that I had only driven it around the block(had to tow it home when I bought it). When it would get up the highway speeds there would be a noise coming from under the hood, and I thought it was the engine. So I replaced the 400 with a 351m with about 12k on it. After I replaced the engine I took it for a test drive and it made the exact same noise. It mostly makes the noise above 2000rpm when it's warmed up. I thought it was rod knock, but wouldn't it knock at idle(mine doesn't)? The noise is extremly difficult to discribe, its kinda between a knock and tick(best I can do). At cruising speed(60-65mph) its more like a metalic buzz. Also, it's more likly to do it under load than while coasting. What the hell is this noise?? Its driving me nuts.

 

Sounds like your rocker arms are knockin to me. Take the valve covers off and see if any of the lifters are loose. If no, start the motor up and just let it idle. DONT rev it up!
Make sure all of the arms are getting plenty of oil. Thats the best I can do without hearing the noise.

 

Hey Ben_E, if you changed engines and hear the same exact noise, i would'nt suspect the engine. Have you checked your front bearings? They can make a very annoying sound when they are worn. How about your transfer case? Tranny? Is your front hubs locked in? how about rear end? Rear bearings? I would give all these components a thorough checking and grease every thing while i was at it. Just some thoughts, Good Luck. Rob

 

>Have you checked your front bearings?

New bearings on both sides and new hubs.

>How about your transfer case? Tranny?

The noise is definently coming from under the hood, but could be the tranny. The tranny has new fluid and filter and shifts good. What should I check for in the tranny?

>Is your front hubs locked in?

Makes the noise either way.

>how about rear end? Rear bearings?

Their all in good condition, but the noise is coming from the front of the truck. I figure it has to be either the tranny or the engine. But how would the tranny be able to make this noise? I think the noise is from something rotating or moving with the engine. I figure it has to be something either broken or has too much clearence wich allows the mystery part to make the noise at 2000rpm and up. As for what stryder said, since it doesn't make the noise at idle what should I look for with the valve covers off while the engine is running and with the engine not running. Also how good do the oil deflectors work? I hope good enough to keep oil from spraying everywhere while doin this. Thanks!!!!

 

Hey Ben_E, if you are sitting in the drive way, and rev your engine up to 2000r.p.m. can you here the noise? If you dont hear the noise in the drive way, i would look elsewhere. As far as checking the tranny, automatic i assume, i dont know of anything that would make a knocking sound, except the torque converter, even that, i dont see how it could knock. One more question about bearings, did you check your spindle bearings? I'm convinced it's not your motor, i've NEVER seen two different motors do the same exact thing. I think what stryder was saying is, take your valve covers of and run your engine at idle and see if all your rockers and push rods are moving properly. You will get some oil, but if you find the problem its well worth it. Well, hope to help, keep us posted and Good Luck. Rob

 

Ben, by any chance did you put the same fuel pump on both engines? I had an engine rebuilt once because the fuel pump lever tapped on the cam, sounded just like a rod had come loose. Other than that, check the front u-joints. Don

"Nothing lasts forever except natural stone and old Ford trucks." (Willie Nelson)

 

Thanks for all the suggestions. I'll post back with my findings.

 

I've got some new info and some corrections on old info. I just took it out of storage yesterday. So all the previous info was from memory. It makes a ticking noise at idle, and at 1800rpm it starts to get louder. And yes it does make the noise while in park and reving it up. But it still isn't noticable until it warms up. I used a long screw driver and held it up to my ear and tried to pinpoint the noisy area. It's coming from the drivers side at the front of the motor. It's not the fuel pump. With the screw driver I could hear it on the front valve cover bolts, head bolts, and the intake bolts. So I took the valve cover off and fired it up. I placed the screw driver on the very first rocker bolt and could feel it. The rocker is getting plently of oil and was moving just fine. I took off the rocker assembly and checked the fulcrum for wear but it looks fine. I reasembled it and torqued to 22lb-ft. Still makes the noise. So I'm guessing it's the lifter. What do you think??

 

I had a 351M that did the same thing. I put about a half a quart of tranny fluid in it with the next oil change(left out a half quart of oil of course). In about 1500 miles no noise. I don't know if this will work for you but it's worth a shot. I've seen this work more than once.
Jeff

 

i still agree with some of you guys in saying, it makes no sense that two different engines would make the same exact noise...what all did you reuse off of the old engine? the distributor for example, a missing tooth or something like that could cause the noise and in that area. thats all that would make sense to me is maybe a reused part from the old one, unless that is by some freaky coincidence they both had the same problem. anyway, let us know what you find out.

 

I re-used the dist. and it has the same p.s. pump that was on the other motor. I checked the dist. before I installed it though. I remember cause I didn't like they way the dist. that came with the motor turned too hard. The other thing, Before installing both motors I installed high volume oil pumps. Both motors run 18-20 psi when warmed up at idle(800rpm). It wouldn't suprise me if the old motor had the same problem. When I bought that one it had been sitting for about three years in the back of a truck in a barn. And it was pretty nasty inside, I spent a couple of hours scrapping off crud from the lifter valley and from under the valve covers. The engine I have in it now was sitting on a tire in a garage for several months. It supposedly has 13000 miles on a rebuild. I saw the receipts but one problem was that it was returned to the rebuilder due to rod nock and but was fixed. The reason the guy was selling it was because he did a 460 swap.

But after hearing the ticking at idle wih the valve cover off, and after talking to a few people I think it has to be a lifter. If it is the lifter what would cause it to make noise? Is it due to a mechanical defect in the lifter or could it just be gummed up? I need to change the oil anyway so I think I'll add something to the oil. I've used an additive called "Restore" before with noticable results.

 

I have a 1978 T-Bird with the 351M and it's doing the same thing as your engine, although probably not to the extent that yours is. My noise is more of a click, but other than that it has the same symptoms you described. I added a full quart of CD-2 oil detergent at oil change which is supposed to quiet noisy valves and lifters and unstick them. I've only put a handful of miles on the engine since then, so I'm not surprised that the noise is still there.