Hey guys, I got a 351w in my '82 Bronco. I just bought this thing about 2 months ago and have been working on getting it trail ready. The engine seemed to be be running really smooth, not knocks or noises. No heistation, good power. I drove it around town a few times with no problems at all. Seems to be a good motor. Anyway, I got this thing prepped for the woods and took a trip up to my favorite wheeling spot (about 50 miles away from my home). Once I got off the interstate I noticed a tapping/knocking noise. I pulled into a service station as quickly as possible and started listening from all the angles that I could to pinpoint where the noise was coming from.

At one point driving the truck lost a lot of power when I got on the throttle, like it was starved for gas. I'm assuming that was because of the fuel pump, so I replaced that. Still had the same noise. I removed the valve covers and checked the rocker arms for lubrication and they all were lubed up pretty good. There weren't any dry ones. They were all tight.

Oil pressure in that truck (i have a manual gauge) has always been really good - 40psi @ idle - 60-65 psi @ 2000 RPM or more. After that trip I noticed the oil pressure was fluctuating a lil bit to like 50 psi @ 2000 RPM and 30 psi @ idle. So, I'm not sure, maybe the oil pump's going bad? I need to take the oil pan off anyway so I can clean that sucker up (its rusted bad and I have a grinder/wire wheel with it's name on it....).

You guys got any insights? Sound like the tapping will go away when I get on teh throttle, but letting off it starts knocking again.

I'd hate to have to pull the motor, but if I gotta, then I gotta.

 

Well you say there is oil flowing and the oil psi dropped when the knocking occured...my guess is a bearing is going. Good luck

 

How are you testing oil pressure? The factory gauge on your '82 obviously moves with pressure changes but as I understand it's not really accurate?!?!

 

If it's a rod, then it will get worse with a load on the engine. For example, if you hold the brake a little and give it gas at the same time, the rod will knock louder. Also a bad rod bearing will cause your oil pressure to fluctuate quite a bit. The same applies to mains bearings, but the sound is lower and deeper. Any loose bearing, including any cam bearings, should show fluctuation in oil pressure.

If it was a broken ring or compression blow by, it would also be louder with a load, than while decelerating. A broken ring will be worse with the engine cold, but get less noticable as the broken ring peices grow closer together with heat.

The fact that it's louder when your not loading the engine makes me think it may just be a lifter bleeding off a bit too fast, as the oil pressure drops slightly. However, worn valve guides can also cause this type of noise, because the valve stem may rattle a bit in the guide, with less load to help a seat it shut. Does it smoke a bit on acceleration after idling, or running a constant speed? That would indicate bad guides.

It may be a bit of piston slap too. However once again, it should diminish somewhat with heat, and be more noticable when the engine is below operating temp.

Take a long wooden stick and put up to your ear, and use it as a doctor would a stethascope(sp?) touching various points on the engine. Listen to different areas from the engine, and try and locate the source.

 

I had a thrown main bearing that dropped my oil psi, began knocking at 2000 rpm like clock work and went away with increased rpm...weird huh?

 

If you read closely I said I had a manual guage. Which means I swapped out the orginal junk ford gauge for a real one.

Ill give the long block of wood a shot to try and see if i can pinpoint the noise. I got underneath the engine and I could hear it under there too. It's weird. Sounds like it's coming from all over the motor. Mainly on top, but then again, it may be just resonations from the bottom.

How much of a pain is it to replace the bearings since I'm already going to have the oil pan/pump out?

*Edit*
I found a vid of this from this past weekend. You can hear the engine knock. Maybe by hearing it you'll see what I'm talking about:

Engine Knock

 

Well if replacing the main bearings were in my future, I would just plan on a complete rebuild, your gonna hate life if your changing the bearings laying on the ground under your truck, you'll hate life even more if replacing the bearings wasn't good enough and the crank/ or rods should have been machined.....since it would be easier to pull it and check the tolerances might was well rebuilt it while its out...

....hopefully that won't be your problem and it will be something simple. Good luck

 

I edited the post above. There is a link to a movie where you can clearly hear that knocking noise.

Do oil pumps ever make that kind of noise?

 

I couldn't tell you anything by watching/listening to the video...looks like your having fun with the truck though...good luck

 

I couldn't play the video on my old pos PC, and I'm no PC whiz anyway.

JW, I imagine the increased oil pressure at higher RPMs, would have helped quiet the knocking mains bearing some. To test if the knock gets worse under load he may need to load the motor against the brake, while keeping the RPMs down.

Crypton-I don't think the oil pump would make a knocking noise. It's probably a bearing, if it's down low and up front. Once it's started knocking, the crank will probably need to be turned, so a total engine out of truck rebuild is called for. A complete tear down and inspection may be needed to determine the exact problem.

 

On another note - lol - i used the stick on the engine trick. It really sounds like it's the loudest on the water pump? Ever hear a water pump tick/knock? I can see the oil slinging into the main bearings making the noise go away. I wonder if a fill up with 20w 50 would help me pinpoint the problem. I'm running 10W30 right now.

 

That's interesting. Take the belt(s) off and see if it's still making the noise, without turning the water pump or any of the other accesories. I once had a kind of knock that went away without the serpentine belt on. It turned out to be- the bolts for the pulley had loosened up. Another weird knocking noise, once, was a leaking gasket under the carb, were the egr gas came in.

At least you know the general area now, but sounds can be weird to locate since they can resonate through componants.

Heavier oil will help with valve train clatter and lifter noise at times, but if it's too much bearing clearance some where- it would be nothing more than a band aid, at best.

 

I was just pointing out that maybe if it were a main bearing, the tapping wouldn't necassarily increase with rpm....like you just mentioned. Wasn't trying to say you were wrong, just pointing out alternate scenarios.

After the last post, sounds like it might be something else altogether, will be interesting to see if the sound goes away with the removal of the belt. Oddly enough, going to the trouble of replacing a water pump or broken bolt, would be great news as opposed to pulling the engine and tearing the engine down in search of the problem.

later

 

Thanks guys. I'll give it a try tonight and see where I get.