Hello, I have a motor I just recently got and got running again. A 69 351w. 10.5 compression. I finally got it running but I have a knock in it. At idle there is no knock. If I hold it at a higher rpm I hear nothing for a couple seconds then I start hearing what sounds like a rod knock. My understanding is you always hear a rod knock it doesn’t go away. But this one come on like I said. And disappears at idle. Any clue?
Check your oil pressure Fuel pump possibly Balancer separating ? Auto or manual trans? Torque converter bolts loose? Oil filter collapsing ? rod knock is a pronounced loud hollow knock that’s rhythmic and follows rpm Knock..knock..knock..knock Like a hammer hitting a steel beam. what did you do? How long was it sitting? How long have you run it? more to the story please. but one of those cheap mechanics stethoscopes and poke around see if you can find the source of the sound?
Psi is 40 at idle. Seems to have a high flow pump. Sounds like it’s in the front of the motor as well. Sent from my iPhone using The H.A.M.B. mobile app
idle it up where it knocks and remove plug wires one at the time and you can usually determine which cylinder is knocking. Turning the timing back can quiet it also. No one has ever bought a car with a miss in it and find a plug tapped shut ? open the gap and now it knocks
Is it 1/2 way between a rumble and knock ? Back in the late 60s/early 70s Ford produced a lot of "soft cranks" that were famous for their bottom-end rumble. I had one of these "rumblers" (302ci) in my '40 Ford pickup...ran great, 60lb oil...just learned to live with it, put 35k miles on it in the truck. Also, remember these engines are externally balanced, A mis-match balancer and flywheel/flex plate will make it much MORE noticeable.
I bought a new flywheel for it and the front balancer is the correct one. Sent from my iPhone using The H.A.M.B. mobile app
My first thought would be to check the oil pan isn’t dented from hauling, storage, whatever. I wouldn’t rip it apart and throw rings and bearings at it, they might be perfectly fine. You need to try to pinpoint what area of the motor it is and go from there. Sent from my iPhone using H.A.M.B.
I would pull the pan and look at the bearings, one by one. For the cost of a pan gasket, you could thoroughly clean the pan, and eliminate that suspicion.
One of my Bandit TAs had a similar issue a few years back. Ran great, sounded great...until I bolted up the exhaust. Once it was quieted down I could make the mains talk with a little rev. I knew I had a rebuild on my hands and the sooner the better. We don't always want to hear what they are telling us, but they are talking all the same.
Get that fuel pump off of there and block off the hole temporarily. It’s the easiest thing to rule out before “digging in deeper” Sent from my iPhone using H.A.M.B.
Does the knock get louder when you blip the throttle? Or can you put it under load in gear and give some throttle? My experience is a rod knock will get louder under some load, either revving up or against the trans. It will quiet momentarily when you let off from higher rpms. Unless the bearing is really bad. You can also carefully open the oil filter and look for metallic shiny bearing material. Sent from dumb operator on a smart phone
Obviously you want to try the simple things first. So far I think the suggestion by Vandenplas is the best starting point. Get a stethoscope and when the noise starts, go over the engine and maybe the bellhousing and you should be able to at least get close to the origin of the noise. Since you have good oil pressure, I would consider opening the engine is probably not necessary. You might have some piston slap or rocker arm problems. If you have a rod problem it should be easy to find with the stethoscope.
I'd investigate the fuel pump, then torque converter bolts, before I started tearing it apart. Had an OT once that I woulda swore was history. Loose T/C bolts...
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