I recently acquired a complete 74 f100 in pretty decent shape. The engine ran good, and trans shifted good. The steering, suspension, and brake systems were worn out. Drove it home and a few other places prior to the suspension rebuild and other than an occasional puff of smoke, you'd never know it was an older engine. Wednesday I drove it about 50 miles round trip to have a windshield put in it and run a few other errands. The last stop I made, I noticed the truck was making quite a knocking sound. Im guessing its a rod knock. I drove it home and parked it. Started it up yesterday to get gas for the mower and it was quiet other than for the first couple seconds on startup. The drive to the corner store didn't get it to full temp though. Does a rod knock usually get more pronounced with engine temperature and rpm? At operating temperature, I have around 10psi of oil pressure - per my mechanical gauge. I have fresh 10w30 in it with motorcraft filter and a can of motor restore in it to help with the smoking.

I plan to look at it tonight. My understanding is that if I disconnect plug wires one at a time, the rod knock will disappear when I locate the problem cylinder. If it turns out to be a rod bearing, has anyone ever had any luck dropping the pan and replacing a worn out bearing, or do they usually mar the crank?

I know its a tired motor, but If I could limp it along for a year, I'll rebuild at tax time.

Would switching to a 20w-50 oil buy me some time?

 

I was never a fan of patching an engine. See if you can find a cheap, rebuilt 360 or 390 that you can see and hear running. Replace your engine with the cost effective alternate engine. When you have time, tear down your original engine and see what needs to be replaced. 10-30 oil is not a good option for a well used engine. If you don't, you will likely do more damage to your original engine, costing you more at rebuild time.
10 psi oil pressure is BAD.... There are additives that will quiet "to some extent" a rod knock, but the damage will continue.
It is not fun to be sitting on the side of the road with a rod sticking out the side of the block.
jmho

 

Once a rod knock starts it doesn't get quite.
Change it over to 20w50 and see if the oil pressure will stay in the 15-20 psi range at idle.
These engines where never designed to run on 10w30, 10w40 was the thinnest oil one could find back then.
How much oil pressure does it have at cruising speed or say above 2000 rpm, these engines are well known to have low oil pressure at hot idle.

 

With that thin of an oil, on an older motor with what is probably a bunch of goo and broken-down valve seals plugging the head drain holes, and after a long highway run, it's possible you starved the oil pump for oil because it was all up in the heads (also leading to an occasional puff of smoke because the oil is all up in the heads and seeping down the valve guides).

At least, that's my theory because the knock went away the next day.

20W50 will buy some time, but yeah, all the suggestions above are good. Swap to a known-good-running engine, because what happened when it started knocking is, it was starved for oil and is now going to fail in some way sooner rather than later.

Once you got it running well enough, rebuild the original engine

 

Well you guys hit the nail on the head. Took the valve covers off yesterday and found the drain holes packed with stem seal material, the drivers side rear being the worst. Spent several hours cleaning the drains out. I used a piece of weedeater string to fish pieces out of the holes until they were clean. I followed that up with compressed air, in hopes I could push anything remaining to the pan. I drove it yesterday before tearing into it an it didn't knock at all. While apart, I installed new stem seals. On the upside, I would say my smoke is definatly caused by oil pooling in the upper end. Pulled the plugs to pressurize the cylinder and found them all to show signs of being lean and no signs of oil. I was expecting to see them covered in oil.

I had my suspicions that it wasn't getting enough fuel, as it was kinda a dog. Once this all goes back together, I plan to reset the timing with a vacuum gauge, adjust the off idle jets with a vacuum gauge, and look into changing primary jets/ power valve. I think it was set lean to pass emissions.

 

Very nice

 

If any bearings were damaged it'll be the #'s 4 and 8. both the rear cylinders. These are the last in line to receive oil from the pump. You might try running a can of CD-2 Alemite with a fresh change or 20-50 oil. Run it a couple hundred miles then change the filter and add another quart of oil removed with the filter. Run it another few hundred miles then change the oil and filter. This should clean up the internals and buy you time on a rebuild.

 

 

I don't necessarily believe that ; my '64 manual from ten years prior specs 10w-30 right there in black and white, or straight 30wt above 90°, 5w-20 for extreme cold. So it must have been available by 1974.

 

I'm running 10w30 synthetic with ZDDP in my 428 cj motor. Have been for years with zero problems and good oil pressure.

 

It all has to do with the bearing clearances in the motor.

 

If I'm remembering correctly you installed one of those high volume oil pumps in that engine, what do you thing your idle oil pressure would be if you still had a stock oil pump running 10w30?

 

Our '66 390 liked 10w-40 and the lifters stopped clattering after I started running that vs. the 30w Co-op stuff my dad had for the tractors. There was an oil upgrade issued for FE motors sometime in the late '60s, requiring, iirc, SE level oil.

FWIW.....

 

You're correct. High volume not high pressure. There's a difference. I also have to add that you have a very good memory. It slipped my memory till you mentioned it.
I never did have an oil pressure problem with the old pump but when I went through the engine because of sunken valve seats, unleaded fuel, my machinist recommended the high volume pump. He also stated to stay away from the high pressure pumps.

 

Trying to determine what is causing an engine to have problems is at best a hit and miss best guess, due to many factors including how the op's defines the problem when we are not there to do a thorough investigation. That is why I normally stay clear of making best guesses before more facts are brought forward. If it was a true rod knock, then it is not going to get better. If it was temporarily starved for oil, then that would be another issue.
So unless us older FE gurus are there doing a complete examination,,,,, then it is every ones best guess and not fact.
It is good that we give op's some best guess's so he has somewhere to start to resolve his or her problems.