I have a 1989 Georgie Boy 29ft Motor Home with a 460 with 46,000 miles. Lately I have been hearing a knocking noise coming from underneath the motor. Kind of loud. It’s hard to tell for sure where it’s coming from. It sounds like around the back of the oil pan & flywheel area but definitely from the bottom of the motor. I was crawling around under there for about 10 mins just trying to pinpoint it the it started getting quieter until it just stopped all together. That was a few days ago so I went out this morning & fired it up & it was fine until it got up to normal temperature then the noise came back. One thing I noticed was that when the noise started the oil pressure would go down. I have an electronic gauge. Lets say on a scale from 1 to 10 on the gauge the oil pressure normally would stay at a 9 to 9.5 but when the noise starts it goes down to about a 8. Not a very big drop. At first I thought it was a rod knocking but would it come & go? Or is it possible it could be the oil pump going out? I’m not a mechanic & know very little about motors. Any help would be appreciated.

 

anything is possible but it is not likely the pump is bad after only 46k. is this on a john deere chassis?

 

just a silly thought, but could it be a loose torque converter?

 

Try to pinpoint the noise with a stethescope. It doesn't sound good, no matter the size of job to correct.
If you can pinpoint it, you know where to look first. You might have to pull the oil pan, or maybe the trans has to be pulled back from the motor. I noticed a slight knock today after starting my truck. It sat only about three hours, and it is the first time I ever heard that. I am thinking rod bearing almost done, so I have to drive it easy until my 76 s/c is on the road. No complaints outta the ol' girl: Over 500,000 miles on her, and she starts like a jackrabbit! Totally stock 351M, circa 1978. Leaded gas motor, but never got lead for years!. I might rebuild the motor after the body gets replaced. I gotta see what made this one so special...
Anyway, good luck on the listening! It is better to check it out than to leave it to go away. Chances are it will only go away when it isn't running anymore!
Mark


Ford started it; Ford will finish it!

 

I went through a similar experience with my '92 F250 HD 7.5L at 51K miles (I tow an 8500 lb trailer). The noise I was experiencing was somewhere between a knock and a rattle. The key was that it was not consistent in sound and did not appear the be ocurring regularly as with each revolution of the engine like a rod knock would. The only time you could hear the noise was to crawl under the truck. It was right where you describe your noise. I also had pinging under heavy load and at times even when unloaded. It was more pronounced when the engine was warm or after an extended pull.

After replacing the the flywheel,torque converter and finally the transmission, the Ford dealership found that the problem was carbon build up in one or more of the cylinders. The carbon had become loose and was rattling around in the combustion chamber. They decarboned the engine (twice) and the noise disappeared for about 6K miles. After a second decardon treatment, I keep the thing clean by using 89 octane fuel and treat the engine with a combustion chamber cleaner every 3K miles. So far (6K miles) there has been no more knocking/rattling.

I'm guessing some of the guys on this site will tell you that the 7.5L does not carbon-up. That's exactly what the dealership told me at the beginning of this saga. If you need more info, the dealer that did the work was Mills Ford in Anaheim CA. 714 776 1330 ask for the Service Manager, Glenn Scott. Good luck.