Technical 302 rod knock or piston slap, is it salvageable?

Well I learned a lesson the hard way. I learned not to take anyone's word that something is good, without checking it. From now on the FIRST thing I will do on any vehicle is cut the oil filter open and check the oil.

Bought it last August. I was trying to work through this vehicle in a methodical manner. Worked through the electrical, brakes, etc. Oil looked clean on the dip stick and showed within the marks. It sounded fine at idle, sounded good when revved. Exhaust was shot and noisy, lots of leaks including the manifold. Probably put 50-100 miles on it last fall. Rebuilt the carb over the winter and just cleaned the top of the motor up. Put a new exhaust on, took it for a test drive, and that's when I heard it. A slight peck, peck, peck. Thought it was the exhaust rattling on something. Went through all of that again. Still peck, peck, peck. Narrowed it down to cylinder 4.

It has to be at a specific RPM to get the noise. If I pull the wire on number 4, it knocks at idle but DOESN'T knock at the rpm it was when revving. Put the wire back on, knock goes away at idle but shows back up in the rpms.

I am leaning towards piston slap instead of rod knock, but would like your thoughts? It doesn't do it when the motor is cold. It only does it (or progressively gets worse) as it heats up.

The oil has a fine (really fine) metallic sheen, If it sets in a pan for a few minutes, it seems to settle out quickly and is hard to see with a light, but it is there. The oil filter however had quite a bit in it. With maybe 20 "chunks" think coarse salt size...pieces of metal.

When I drained the oil it was a quart low, only had 5 quarts in it.

Oil pressure is reading 40 psi on the gauge, with the new 10w30.

So having said all that:

1. Do you think it being a quart low had anything to do with it?

2. Do you think it is rod knock or piston slap?

3. This is a "take the kids to dairy queen" vehicle on saturday night....Is there any chance I can just go into that one cylinder and "fix" anything to keep it on the road for a bit longer? Maybe a new rod bearing, new rings and a ball hone, etc? and flush it with a few oil changes? Or am I looking at a complete rebuild?

At some point (years from now), this one was going to get a frame off and a good rebuild on the motor. However that time isn't now and it isn't in the budget...

 

The oil looks milky .

you can kind of see the sheen .

could it be a blown head gasket ?
Not necessarily a knock , but a miss ?
Maybe ?

could the chunks of been bits of piston ring ?

you would think if you had a bearing going on a main or con rod your oil pressure would be less .

do a compression test and leak down on that cylinder

I would yank the heads and the oil pan and inspect


A 302 ford is a pretty easy and cheap engine to build if it does not require major machine work.

 

My sister had piston 'rot' in a K-car, I think she meant piston ROCK (as told to her by some mechanic). It was heard when the engine was cold and went away as the engine heated up (piston grew in size slightly due to the heat and filled the cylinder better). If piston 'rock' is the same as piston 'slap', shouldn't your noise be going away as the engine heated up as opposed to getting worse?

I'd drop the pan and check the rod bearing on that cylinder. You might be able to get away with a light sanding of the crank (while in the car) and a fresh bearing (if that is what it needs). Due to your present budget, your only choice is to attempt to fix only what is wrong. If that isn't the problem, then the piston and rod probably need to come out and you could (engine balancing be damned), change just the rod and piston with a used one (assuming it is standard bore and easily sourced). I see no reason why you couldn't reuse the same piston rings (if they aren't broken) or used piston rings from the replacement piston rod (if you are able to get a complete piston/rod/rings unit). Ball hone if needed, and hand file off the cylinder ridge if there is one (so you can get the piston out). None of the suggested above is the 'correct' way but it may allow you a few years of enjoyment out of that engine. Again, get into the engine, find out what is wrong, and replace only what is damaged.

I'd also do a compression test and leak down test to determine if there are other issues/the overall health of the engine as it may also reveal head gasket problems if there is water in your oil.

 

As above, generally piston slap will get better as it warms up and the piston grows.

It’s really tough to diagnose mystery noises over the internet.

 

Here is a better look at the oil. To be fair, it is hard to tell how long it has been since changed, and it has set a lot over the last year.

I did not see oil in the antifreeze...nor do I see any bubbling.

However I do see quite a bit of condensate in the headers. Which I chalked up to sitting...and just normal condensate...

Compression test was about 100 psi across all cylinders...low but really even.

Vacuum is at 18" at 14 degrees.

Any chance it gets worse as the oil thins as it is heated? Maybe taking up a little more clearance in the bearing?

My first thought was chunks of rings...however I would think the compression would be worse...

 

"Piston slap" is a cold engine thing only. Described as piston skirts with excessive clearance or somesuch.

 

You didn't say what year 302, but I suspect from all the parameters you gave that the skirt on #4 piston has broken off. The earlier 302s (68-72 or so) were notorious for that happening. While it is true that the piston "expands" when hot, so does the cylinder. With the skirt broken, the piston rocks in the cylinder. The other thing I would do is replace the timing chain set.

 

If you have 40 psi at idle, you don't have any bearing problems.

Some year 302s were notorious for cracking piston skirts which causes a knock due to the piston rocking in the bore. I've never seen one come completely apart but eventually that cylinder will start to burn oil.

 

Usually only a cam/lifter going bad, will make that much metal...unless the oil has never been changed since it was rebuilt.

I'd drive it around for a while and then change the oil again, see how it looks. If the noise is faint, it's probably not going to throw a rod on the way to Dairy Queen. That Corvair I had a few years ago had a nice little knocking noise when revved, I ended up driving it 5000 miles, then my brother bought it. A few months later it ate a valve guide, so I did a cheesy overhaul, using a lot of parts from a donor engine. The rod bearings were down to the second layer of metal, but the donor engine had some nice ones...I put them in, it's quiet now, been running great for the past couple years.

btw rings don't make chunks of metal like that, in my experience. They wear very gradually. But a fresh engine will make some metalflake. And losing a cam will make the oil look like the finish on a lowerider...big sparkly metalflake...

 

It is a 74 block....

 

This is not a rebuild...

 

Yes the cylinder does expand as well, however not nearly as much…something about the piston being exposed to more heat.

a broken skirt will certainly make noise, as squirrel said that’s a lot of metal in the oil.

Still hard to diagnose over the internet.

To answer the original question, anything is salvageable. I suspect it’ll run until it doesn’t anymore.

 

I'm ignorant, so if you are saying that is A LOT of metal, I probably should be looking for a donor and set this one aside for a future rebuild?

 

Pardon me if it was said but is this a Ford 302? Change the oil and filter use straight weight oil and keep an eye on things.

Pat

 

If you just want to drive it around town, then just drive it around town. If it gets worse, then do something about it. Long term, you can take the engine apart and see what's wrong with it. Mean time, if you happen across another engine to build, for a good price, you might want to do that.

It's really hard for us to be able to tell the condition of an engine from far away...and for you to find exactly what's wrong without taking things apart.

 

Follow squirrels advice drive it, if it gets worse then deal with it.

 

I should probably expand slightly on my answer above ... piston slap/rock/rot due to regular wear in the cylinder and possibly the piston, should go away or lessen as the engine warms up. Since your engine is doing the opposite, your issue is most likely not what I would call 'regular wear'. I think you have more issues, one possibly being a loose rod bearing or you could have piston issues above and beyond 'regular wear', like a cracked or broken skirt etc.

It bothers you to the point of asking on this site so I'd be inclined to drop the pan and check that rod bearing. If the bearing looks normal, then it might be worth pulling the head and removing that piston/rod ... the cause of the noise may be obvious at that point. The pan has to be dropped for piston removal so you're already part of the way there.

As others have said, you could also simply change the oil and turn up the radio if this is just an around town ice cream getter

You appear to have isolated the noise to one cylinder so there really are only so many things that are related to that specific cylinder and repair parts don't have to be brand new (if they can be found used) to be better than what you have now.

 

I had a couple of early 302's(60-70's) that I had pulled apart, and found cracked skirts. Could be the issue. Keep running it for those short around town drives, until it changes, or you decide to pull it apart to get the full details.

 

When I worked at the Lincoln/Mercury dealership we got a new Pantera in that seemed down on power. It ran fine, but just didn't seem to have what other Panteras had. As Service Manager at the time I had to personally test drive all Panteras and Lincolns and put my seal of approval on them (tough job for a 25 year old). We had it for maybe a month and it came in from a test drive with a knocking noise. Pulled the engine and found a bent rod. The knock came from the part of the piston skirt that broke off. The engine has obviously had a hydraulic lock at some time. Ford replaced the long block.

With that said, I'm always very wary of engine noises that are cylinder related. The fact that you can pull a plug wire and make it knock at idle tells me there is a lot of play somewhere that is taken away when you load the cylinder. You can have a bad rod bearing and still have good oil pressure if it has spun in the rod and covered the oil feed. I would at least drop the pan and see what's going on.

 

Bore scopes for phones are cheap Pull the oil plug and spark plug and have a look @ number 4.

 

That is on my list, I have one, just haven't slipped it in yet.

 

Is there any chance at all that it could be an exhaust leak around the header gasket?

 

I was in the valve train when I changed the intake gaskets and switched valve covers, it looked REALLY CLEAN. Everything was nice and "snug" like it should be. No loose push rods, etc.

At some point I will pull the pan. Just trying to avoid it because I have to drop the front axle....

 

I'd check the end play of the crankshaft that can give you an indication of bearing condition.

 

I'd pull that valve cover off and check for any rocker arms rubbing on the inside of the valve cover....
I've had that happen on a 5.0L with roller rockers....

 

It would be tapping constantly wouldn't it? this only occurs around 2k rpms then dies. (Plus these have way more room than the old ones). Wont hurt to check though...

 

Okay...this is interesting. Are talking about front to back, or rotational. Because when I was setting the timing I noticed when I would rotate the crankshaft it moves maybe 10 degrees or more before it feels like I get good resistance.

 

I used to have a 302 in a Fairlane that was run really low on oil and had a rod knock. Warm idle oil pressure was like 5 psi, and would go down the road with about 40. If you hit the gas too hard from idle, it would hammer the rod until oil pressure came up to cushion it. It was a very distinct noise from a valve train tap or exhaust leak tick. It sounded like knock, like 2 heavy objects hitting each other. It was less of an issue cold, when the oil was thick, as opposed to operating temperature. Whenever I'd come off idle, I'd just lean into the throttle, bring up the oil pressure, and then accelerate. I drove the bastard for thousands of miles like that as a daily and actually never fixed it. It was sold like that as a good runner and the next owner, being apprised of the issue, found a good used 302 and replaced it.

That would be my test. At warm idle, jump on the gas. If it hits harder, it's a rod. If it doesn't it either isn't, or isn't bad enough to worry about.

 

Engine Noise - YouTube
Clacking while driving - YouTube

That sounds similar to mine...i could have sworn it was something external it was so pronounced.