Piston slap, is it going to hurt my engine more?

[deadironrat]

I have an AMC 360 in my Jeep J10. When I bought the truck the guy said the engine was already .20 over and rebuilt not to long ago. I have since then put in a summit K8600 cam, edelbrock intake manifold, edelbrock four barrel carb, HEI dizzy, oil pump rebuild kit, SS midplate, bulltear dizzy and cam gears, and I believe thats it. The problem is during the cam break in I forgot to fill the radiator with water :(: and the engine got very hot. Since then its started making this very fast metal on metal sound. My grandfather (retired mechanic) told one or two of the pistons probably collapsed (he listened with an engine stethoscope) when it over heated and that is causing fairly severe piston slap. So my question is will this hurt my engine any further? I do plan a full rebuild down the road but I don't have the funds right now, I would like to be able to drive the truck a little with the engine the way it is.


Is this going to kill my engine?

[fifesjeep]

What's really hot?

Metal on Metal sound... anytime I hear that I instantly think mains/bearings etc... Does it increase with rpms?

Piston slap is when the skirt slaps the cylider walls... due to the piston to cylinder tolerances being out of spec... it'll only get worse with time ultimately causing more damage.... Does the noise decrease when it is at running temperature? etc...

If it is either or you have some issues and will need to rebuild that motor... No sense in driving it and creating more damage to the internal parts.

Then again if you're going to do a full rebuild and you have extra cash to blow... Drive it like you stole it knowing that it isn't going to last... AMC's are expensive to build just keep that in mind.

Just my opinion.

[deadironrat]

I don't know how hot it actually got because mine only has green/red to tell you the temp, it did go well into the red though. I don't think its rod or main bearings because I just replaced those. It also doesn't sound like a rod knocking, its not quite that deep of a sound.

The speed of the sound does increase with the engine speed but it really doesn't get any better with the engine warmed up. I think that is because I also have oil pressure problems (I know, its time for a rebuild) so once its hot the pressure drops alot.


I know its time for a rebuild and I do plan on doing one this summer once I get a little more money. What I'd like to know is if this will cause any extra damage that I won't already be fixing in a rebuild. I do plan on going up to .30 over.

[fifesjeep]

I don't know how hot it actually got because mine only has green/red to tell you the temp, it did go well into the red though. I don't think its rod or main bearings because I just replaced those. It also doesn't sound like a rod knocking, its not quite that deep of a sound.

The speed of the sound does increase with the engine speed but it really doesn't get any better with the engine warmed up. I think that is because I also have oil pressure problems (I know, its time for a rebuild) so once its hot the pressure drops alot.

Well, I'd recommend changing the guage out for something that has degrees... You mentioned that you have oiling issues.. What kind of "problems"... It sounds like there is excessive clearance with either the oil pump or the mains etc, possibly both... What is the pressure when you first start it? and what is the pressure when it's at the normal operating temperature?... Oiling issues, metallic noise, a little thumping noise... I'd point towards a rod or two and possibly a couple mains... Easiest way to tell is drop the pan and remove a couple caps... do it on the suspected cylinders... if you see metallic flakes in the pan then you know you have some issues.

Yes things can only get worse at this point... if your piston is slapping the cylinder and it breaks or shatters it could gouge the cylinder wall which would call for a larger bore... anything is possible...

Does she smoke when you start it or get on the skinny after she's warm?...

[tufcj]

You can drive it, but don't depend on it holding together. If there was no coolant, the only thing cooling the engine was the oil. If you're seeing a big drop in pressure when hot, especially with a new pump and mid plate, then you probably fried the rod and/or main bearings. I've seen plenty of spun bearings in overheated engines that were otherwise healthy.

If the engine is already .020 over, and it is piston slap you're hearing, I doubt it will clean up at .030 (remember a .010 oversize is only .005 off the wall) Expect to go .040 (if pistons are available), or .060.

If you're lucky, it's just bearings and you can save it if you fix it now before anything else comes apart. May be worth the time to drop the pan and pop a couple of caps.

Bob
tufcj

[deadironrat]

I don't think its rod or main bearings because I just replaced those.

The reason I think it is piston slap and not rod/main bearings is because it started after it over heated. I was told that when an engine gets very hot it can cause a piston to collapse making it a few thousands smaller and causing piston slap. It does have brand new rod/main bearings BUT I do not remember the engine ever making this sound BEFORE I put in the new bearings.


As far as the oil pressure goes I get about 60 PSI at cold idle and once the engine is fully warmed it drops down to right around 10 PSI hot idle. It smokes a little a startup but its not blueish oil smoke, its more like white steam, once its warmed up it never smokes even at WOT.

[fifesjeep]

Just drop the pan look at the suspected cylinders and check the mains etc.

[deadironrat]

I changed the oil today for what I thought would be the last time before the rebuild. I used 5qts 20w50, one bottle of STP oil additive, and one bottle of motor honey. The sound is now GONE, I also now have 15PSI oil pressure at 600RPM. If I do drop the pan what exactly should I be looking for, should I plasti-gauge all the bearings? The rod and main bearings have less then 4 hours on them, so unless I installed them wrong (which is a real possibility) I don't see how they could be making the noise. Could oil additives make piston slap go away? I'm no expert but I sure don't think it could.

[tufcj]

With all those thick additives in there, it could stop piston slap or a rod or main knock. Drive it a while and it may return as the additives thin and break down.

If you pull the pan, look for any bluing of the rod/main caps (sure sign of a spun bearing). Pull a couple of caps, look for scratching/scoring of the bearing or journal. Look at the bearing, if any copper is showing, replace it.

The only really noticeable and constant piston slap I've ever heard was in a re-manned Ford 351 we got that had std pistons in a .030 over bore. Heard later that that company was having a 30% failure rate on their engines under warranty. Wonder why with that kind of quality control?

We had a re-manned Toyota 22R engine once that came with a .030 under crank and .020 bearings. It only knocked when the rev's went above 2500, held good oil pressure too.

Bob
tufcj

[deadironrat]

Could there really be scoring or copper showing on a brand new bearing?

[jeepsr4ever]

What happens is the thick areas of the piston expand and you get some scoring at least on the sides of the pistons and if your lucky not on the cylinder wall. Depending on how long you ran it you could be looking at a quick hone and new pistons.

[fifesjeep]

Could there really be scoring or copper showing on a brand new bearing?
Well, you can lead a horse to water but you can't make him drink it. :idea: You have our thoughts, opinions and ideas... as well as your grandfathers who is a Retired mechanic. So IMO the only thing that remains is to crawl under the vehicle drop the pan, get a little dirty and inspect everything thoroughly. :? It could be something simple or it could be something a little more serious which we already described/explained... :t:

[deadironrat]

Thanks guys, I guess its time to drop the pan again.

[ironman_gq]

I had pretty bad knock on my 304 once that i thought was a stuck or collapsed lifter (sound was under the valvecovers) and she ran a little rough but I decided to just run her till she died cause a rebuild was planned. When I pulled the intake I found 4 bent pushrods 1 had a 90 in the middle of it and 1 that was broke in half. no bent valves no stuck lifters no stuck valves no broken rockers even. :shock:

[fifesjeep]

So is there an update?

[deadironrat]

No update yet, I just now got some more money to use on the engine. I'll probably be dropping the pan within the next two weeks to see what is going on.


The sound is a little more defined now, and it is starting to sound more and more like a rod. I think I must have done something wrong when I installed one of the new bearings.

[deadironrat]

I still haven't been able to get the oil pan off (too much other stuff going on right now) but I just remembered something. When I put all the new stuff in the I forgot to put that little cone shaped washer on the crank, I'm pretty sure its just an oil splasher. Since its right on the bottom of the timing chain is it possible that my timing chain is making the mystery noise? I've been listening to lots of different engine noises on youtube and mine is far higher pitched then any of them. I honestly do not think it is the timing chain but figured I'd throw something new out there.


Right now I'm running thick oil with oil honey and the noise is very very faint now. I still want to get it fixed right though.


Oh, one more thing, when I first start the truck up you can hear the sound very well, then as soon as it builds pressure (probably about 1-2 seconds) it goes nearly away. I think it must have something to do with either the lifters or rods bearings, but it really sound too high pitched to be either one.

[tufcj]

Doubtful. That is a baffle, not a slinger. It goes between the lower timing gear and the cover. It keeps the front crank seal from being overloaded with oil. Your chances are about 75% that the front seal WILL leak without it. If you're pulling the pan, might as well pull the timing cover and install it, or you could be doing it again later.

Bob
tufcj

[ironman_gq]

dry cylinder walls. the oil on the cylinders cushions the piston and prevents the piston and cylinder from touching. on cold start up after sitting overnight there is little oil there and splash lube coats the cylinders quickly

[deadironrat]

Sometimes I hate how smart you guys are. I guess I don't have any reason not to pull it apart now. Oh well it will be a fun spring project.