I'm hoping that you guys can help me narrow down a knock in my neighbors engine. It's a 400 bored .060 over with an "RV" cam, in a '78 F350 Chassis cab. I recently rebuilt this engine and it has been running fine for about 2 months and probably 200-300 miles. Then 2 weeks ago my neighbor and I were hauling his 5th wheel from Reno to Winnimucca and got about 30 miles outside of town when a knocking started. For the next 5-10 miles the noise got worse and worse. Then is sort of topped out. It was still loud but not getting any worse. The engine was still running smooth, no miss fires or hesitation, but obviously it was disturbung to hear the knock. We turned back toward town not wanting to get stuck out in Central Nevada. The whole way home it was louder than S*** but still running good. All of the gauges read normally, good oil pressure, temp right in the middle, charging normally, but the noise is still there. It increases in frequency and volume with RPM, and is still there at idle. I just went over and started the truck up to check if the noise is still present and after about a minute at fast idle you start to hear it. I am a Automotive Technician so I checked it out with a Stethascope and the noise seems to be coming from the driver's side head area. My thoughts are a collapsed lifter or loose rocker but wouldn't that make the engine run rougher? The only thing that we changed between when everything was ok and now is we put Synthetic oil in it.
What I am looking for is any diag tips to narrow the problem down before I start removing parts. Any ideas or hints would be greatly appreciated.
Sorry the post is so long but I wanted to give you guys as much info as possible.
Thanks for any help,
Steve

 

Come on guys, I could use a little help. A test or direction to narrow this noise down. Any help would be great.

Steve

 

Sorry, some of us only receive digests that come once a day, not individual emails...

It could be that a ball has broken off a pushrod. Happened on my 351C once, and the car still sounded great when it ran (besides the hideous tappety-tap).
But if it is a knock, that kinda takes a large piece of metal to make that kind of sound.
I would pull the pan and check the condition of the bearings, but only after pulling the valve covers, since that is the easiest to perform, and as doctors say, least invasive of surgeries.
I would not have run synthetic oil this early in the engine's life. I would probably run it at least three oil changes before switching to synthetic, since it stops friction so much that rings and other parts don't wear-in properly, causing blowby, loss of power, etc.
I would not run the engine anymore at this point until you get to the bottom of it.
By the way, when you had the block at the machine shop, did you have the crank bore align honed, and new cam bearings put in?

 

Do you have an oil pressure gauge on it? It sounds like the oil pressure has dropped. The driver's side valve train is the last to get oil.
Try a heavier oil than synthetic. A 20W50 or straight 30W. See of it stops the niose.

Did you break in the cam with Diesel oil or other high zinc oil? Your cam may have failed. I don't think that Synthetic is recommended as break in oil.

 

He stated normal oil pressue during event.

 

trinogt- thanks for the ideas, yes it has new cam bearings but I'm not sure about the align hone. I was thinking the same thing about the synthetic and just told my neighbor yesterday that the first thing I'm going to do is drain the synthetic and put normal oil back in. Any suggestsions as to weight?

danlee- I didn't use synthetic right off the bat but like I told my neighbor we are going to drain out the syn and put in regular oil, cause like I told him if you change something and have a negative effect the easy starting point would be to go back to how things were before the change. Like I already said, any suggestions as to oil weight? I live in Reno at 4500ft and needless to say it's a wee bit cold right now

 

With the engine idling and a dwell/tach hooked up, start pulling the plug wires off and watching how much the RPMs drop. Put the wire back on before you pull another wire. If you have something broken in the valve train, the bad cylinder won't cause the RPMs to drop as much as the others.

Also, check to see if you've got an exhaust leak.

I hope you added something with ZDDP to the oil.

 

Use Rotella 15W40, or as pcmenten suggests add ZDDP to your oil. If the cam has failed, it is too late.

An intake manifold vacuum leak can also make a racket, but that would most likely occur at a cold start.

 

hate to say it, but its possible you lost a rod bearing...

 

Thanks for all the help and suggestions guys. I'm going to see what else I can get figured out this weekend and I'll let you guys know what I come up with.

 

Even though it seems to be running fine, id still pull the plugs, look for damaged straps on the plugs, signs of unburned fuel on the plugs, signs or pre-ignition maybe??

Pull the valve covers, make sure all valve retainers are on the top of the valve stem and seated correctly. Also make sure no head bolts backed out and are having a rocker hit it.

If its a knocking its probably in the bottom end or a wrist pin.

I dont run synthetic on anything with under 4500 miles.

 

Sounds like a cracked skirt on a piston,especially after it warms up.

 

Well once again, thanks for all the help and options. I went over last weekend with a friend that is a Ford Senior Master Technician and had another listen to try to isolate the noise. Unfortunately it sounds like either the main bearings or the rod bearings so it looks like I'll be pulling this engine once again, unless someone can tell me how to tell for sure which set of bearings is bad. Since there is about 4" of new snow on the ground right now it will probably be a while before I pull the motor again, so if anyone has a little extra advice I'd love to hear it.

Right now my plan is to pull the motor, take the crank, rods, pistons, flex plate, etc., to a machinist have it all rechecked out and balanced then replace all the bearings and hope that will be the end of it.

Let me know if you guys see something else I should be doing, and thanks again for all the help so far.
Steve

 

My guess is it will be a rod bearing.

 

Can you get the oil pan off without pulling the engine? May be able to pull the mains and rod bearing one by one if you cannot immediatly notice the culprit. If you lucky maybe you can put a new bearing on temporarlly till it gets warmer if the crank isnt to bad. Use dino oil in it till at least 10,000 miles on it before synthetic