I have a 1984 Ford F250 4x4 with a built 351 windsor in it. The engine has 500miles on it since the rebuild. This knock started yesterday. At first I thought it was rod knock but, It doesnt make ANY knock when its cold to 130degrees water temp. As soon as its ran for about 5 minutes a knock appears. The engine has been kept under 3000rpm for its entire life so far. I had everything machined and turned. I put in ALL brand new bearings in the engine and torqued everything to spec.

It rises with engine speed and falls with it. But at Idle none that I can hear. Im running 8degrees at idle so its not to high of ignition. Im running 10-30 GTX in it but my oil pressure has varied. Im using a HV oil pump and When I changed the oil 2 weeks ago I was pulling about 25lbs at idle (700 rpm). Now Im about 19lbs.

That isnt a substantial loss for me to suspect it being a rod. What could this knock be!?!?! I can only hear it when My head is directly in front of the water pump in front of the grill. The only other spot I can hear it is slightly below the balancer. When I stick my head to the pan I can hear anything except when next to or in front of the balancer. I cant tell where its coming from. It seems to be louder over the top of the dist.

The only thing I can suspect it being is when I swapped the ignition and put a duraspark dist in. I didnt have my truck this weekend so I cant exactly tell when it started. I ran the old TFI ignition with the truck so I had a worn dist gear and the cam was new. When I put the new dist in it had a brand new gear on it. Could this at all cause a knock? Please help!!!! The Truck runs AWESOME! But knocks are bad.....

 

Well... after reading your post and thinking about it... it isn't entirely impossible that you may have spun a bearing on the crank.

I had an 83 F150 with a 351 in it. When I bought it, starting it cold, it didn't knock. But the warmer it got, the more it knocked.

When we tore the engine down to see if it was rebuildable... holy crap. I'm surprised it didn't knock worse than it did. The crank was entirely shot and there were several bearings that had spun.

It's not impossible to spin a bearing on a new build. Your oil pressure, to me, doesn't sound right. Is this a high velocity pump? My new 351 and even most 289 and 302's would idle at 30-40 psi. And I only spun one bearing on one older 302, due to racing a dude when I still had winter weight oil in it. I used to be known to wind an engine out pretty hard. But after all the engines my brother built for me, that is the only one that I ever harmed in any way... and that was after a couple years of driving it and hot rodding.

Sometimes you can hear the fuel pump making a knocking sound, too. If you can get a stethoscope type listening device, I'd listen closely to the fuel pump. You can even take a small metal rod, put a paper towel or TP tube over the end of it, and use it like a stethoscope, to pick up all kinds of sounds and more directly where they come from.

If you have spun a bearing.. tear it down NOW. Do not drive it or even start it any more than you can get away with. It doesn't take long at all, to mess up a crank bad enough to make it NOT turnable.

Good luck.

 

I think I may switch oils. I have never EVER had my oil pressure stay up in the 30's long with the GTX. As soon as its changed I run 30lbs for a few days. Then it slowly lowers. Im not sure what it is with this motor but it kills oil! Not burning or losing it but just breaks it down. I thought it might be the fuel pump. Yes it is a HV oil pump.

I have taken excellent care of the break in period. Im not sure why this knock has started but I need to find out. I wonder If maybe somthing is not getting enough oil or one of the feeds is plugged. Should I dump the oil and put some new stuff in? I mean it only has 500 MILES ON IT! The knock seems to be just dead behind the water pump! Would a collapsed lifter do this? I kinda doubt it as Ive heard what lose valve train sounds like. I heard that if you unplugged a plug wire one at a time going to each cylinder that you could track down which cylinder has a bad bearing. I tried that and it didnt make even the slightest difference in the knock.

 

I agree with Fordlover55. My first thought was a main bearing. Is it a deep knock or a rattle type knock. A deep knock main bear. Main bearings as a rule don't knock at idle. Did you put a crank kit in? If so did you check to see all bearings matched the machining of crank journals. I had a Jeep J10 with an AMC 360 that had a main bearing knock. I changed the bearings to see if it was just a bearing or if it was an out of round journal. Well it turned out to be the later. I drove it for a year then sold it with full disclosure of the knock and the guy that bought it is still using it to make dump runs etc.

 

I had the crank in it turned .10 under, and used .10 over bearings. I had the machine shop check all clearences before a return back to me. Its not a DEEP knock and not a light one. Its like right in between. I need to go get a stethescope but it sounds like its behind the timing cover. The knock started yesterday and Ive driven it 500miles no issues. Maybe I can take a sound clip of it. Then we can all listen to it togethor! I plasty gauged the mains at about .0015 thousandths.

Not sure how to type that but less then 2 thousandths.

 

If it's a rod knock, you can usually pull the sparkplug wires off one at a time, and when you hit the offending cylinder the knock will lessen dramatically or go away.

I have had several chevies have a serious sounding knock up front, and it turned out to be the fuel pump. I have never had a Ford do that, but it's a possiblitity I guess.

 

I did try the wire method and to no avail. Still knocks and made no change in sounds. That is the general area that the sounds is coming from. If I take the pump out what would I be looking for on it as far as damage? I can almost make out that is where that sound is coming form. WOW, do u think maybe my new dist. could be hitting the fuel pump rod? Actually I dont think there in the same area but threw it in there anyway. Pretty sure the dist is inside the block.

 

My first thought was a broken piston, probably on the skirt. Sometimes they are complety quite until the engine warms up, most times they run fine. Second thought is a wrist pin, although not real common on V8's. I have had two different 6 cylinder engines with wrist pin knock. Drove both many miles with no problems, never got any better, never got any worse. Hopefully it will be nothing major.

 

I invested in new pins when I was at the machine shop with my pistons and had them put them in. Would a broken skirt end up in the bottom of the pan? Cause Im going to change the oil again cause the castrol GTX just isnt working for my engine. Also would a compression check tell me if a skirt was broken?

 

Most likely piston will only have a crack although it could have broken off a piece. If the engine is not missing it will probably have good comp. Although it is an easy check and if it isn't about where the other cylinders are you could have found the problem. The problem with a piece of alum. piston in the pan is you will need to drop the pan to find it. Good luck.

 

Is the elastomer in good shape on the harmonic balancer? I've had one of those go bad and it sounded like a bad bearing knock.

 

I used Castrol GTX for a number of years. Used 50 wt in my 500 Honda thumper. Never had a problem, but I did notice that the warmer the engine got, the more I heard rattles on the top end.

I used to use nothing but Valvoline 20w-50 for years in small blocks, but have recently changed over to full synthetic 15w-30. I really don't notice much for difference as for engine performance. The synthetic seems to remain a bit cleaner for a tad longer, but might be my imagination and hopefulness, due to the cost. Probably go back to Valvoline on next changes in all rigs.

I came back to mention that you could take the fuel pump OUT. Get a block for the hole..borry from a stock car buddy if ya have one. Then try out an electric fuel pump to see if the knock disappears. Kinda a hassle..but then, so's tearing everything down. And the worry would be enough to drive me up the wall.

Yeah.. some of the other suggestions sound like a possibility too. A real knock, has a "hollow" sound to it. Dang..hard to explain. A knock, you can hear reverbing off, say a close building or fence as you drive by it...if it's a loud enough knock. You shoulda heard that 83. OY!!! No idea why it just didn't toss rods in every direction. Probably would have if I'd tried to use passing gear. Didn't take but a couple days of driving it to decide it was outta there though.

I'll sleep on this and check back. Try the electric fuel pump thing. Always go the cheapest route ya can. OR.. take it over to your mechanic buddy and he's probably got an engine stethoscope.

Oh... and with a high volume oil pump, I still can't believe you've never had higher oil pressure. That just blows my mind. 19 pounds warm, with an HV pump sucks and suggests bearings.

Maybe I just always had faulty guages or something... but I do know that at highway speeds I'd average 40-45 pounds it seems. Idling..may have been a bit lower, but no less than 30 pounds. I know I'm getting forgetful in my youth, but not that bad...egad..at least I hope. I need a freakin' time machine.. a big one so I can go back and get my 68 Falcon before I sold it to Mr Idiot. That was the 302 that always had the greatest oil pressure. Anyway..'nuff. I'm off to bed before I start babblin' again.

 

I have never had good luck with the castrol GTX stuff. Just doesnt survive in my engine for some odd damn reason. It takes 10-40 before I rebuilt the engine and lucas oil stabilizer. After about a week of driving it turns thicker than 20-50W into water. Not Kidding the consistensy is literally like that. Im thinkin maybe its the amount of heat thats doing it. I can honestly say I cant keep my foot outa it so possibly it is all my fault. But this break in period I set the rev limiter at 3500rpm. No way it went over with my foot.

I have the heh EL CHEAPO oil pressure gauge set. Perhaps the tube has a pinch in it somewhere. When the engine is cold Im turning 65lbs of oil. After its good and hot about 20lbs. 3000rpm im about 50lbs. I think im going to try, I think its Delo? Ive heard good things but its dang expensive.

I believe I have tracked down the knock. I put my hand on the timing cover where the fuel pump is. I think my pump is bad. Ive read about 25 articles with people having fuel pump knock so I know it can sound like a rod. I think I know what you mean about the hollow thud. kinda like hitting a propane tank but very deep.

Ok maybe this info will make sense to somebody. For the past couple weeks on the break in periode. The engine has been running so rich I get raw fuel out of the pipes when the engines cold. Doesnt matter what temp as long as its below 60 outside. If its above no raw fuel. For the past few days before the knock ive had kinda poor performance like it was starving for gas. Now everytime I have started it stone cold with that knock being there Its running lean and Not a drop of fuel. So maybe its related to that pump. Ill take it out tomorow and investigate the carnage.

 

If you want to test the fuel pump run the motor for a few seconds to fill the carb up and then shut it off, pull of the pump, put some ducktape over the hole and fire it up and rev it a couple of times. That should tell you right away. Hopefully thats what it turns out to be. I bought an 85 that had a 351 that was just rebuilt. It had great oil pressure, but on the way home it started nocking. When we pulled the motor and sent it up to the machine shop they found a peice of plastic wedged in an oil passage.[ Hopefully nothing like this happened to you.

 

Running too rich...if way too rich, can leak un-burned gasoline past the rings and into the oil, thinning it. What's your oil smell like? If your oil is getting really thin, especially when warm, that could account for some loss of pressure. But pressure is measured only between the crank bearings, so I'm not 100% on that theory. I'd think that if the bearings have the right clearance, the pressure would remain constant. As long as you have good pressure at higher rpms, you should be ok though. I had a worn 223 that would drop to less than 15 pounds after highway driving and coming to an idle. But at crusing speed, the pressure was up in the good range.

I'm betting on your fuel pump making the noise, because I listened to mine do the same thing once and got all freaked about it. One listen to it with the stethoscope rid me of all fears. And what's wierd though..is the noise comes from the diaphram area of the pump...outside the block. The only think inside is the pump lever, which really isn't going to thump, as it's spring loaded really heavy, and rides the cam lobe.

If you continue to have a thinning problem with your oil, I'd consider running a single and heavier weight oil during the warmer months, then switch to the multi weight in the winter. I"d go with a 40 wt unless you are really revving the poop outta it when broken in. I'd not put the heavier weight in though, until you have the engine and bearings worn in pretty good. Stick with the multi weight for a little while.

I don't know about the Delo oil at all. Have you ever read any of the threads in the oil forums? Lotta opinions and factoids there, to think about. Some oils work great, some better. Some build sludge faster, some run really clean and have no sludge buildup over time. After looking at hundreds of blocks my brother tore down to rebuild, some of which, he knew the guy changed oil regularly and seeing the differences between oil brands and block cleanliness... that's why I switched over to Valvoline in the first place. Valvoline makes a good top of the line oil and also has mixed oil/synthetic or full synthetic. Some people swear by Mobile 1, but man is it spendy. All full syn oils are spendy to an extent though.

Gotta go work in the yard. Off like a herd of turtles!