pulled head and found....

[bockslanding]

This is a 360 in an 87 GW.

actually this started with aweird oil leak at the head gasket (former post).
I did a compression test and found 90 psi on two next to eachother right where the oil leak was at. I re torqued the head and the compression came up to the 120s. this did not fix the leak but did pinpoint it to the spot between the head and block.

Today I took everything apart to replace the head gasket. on the same two pistons Ifound small nicks or melts mabey, little holes, one each, on the edges of both those pistons. Great Googley MoogleyGreat Googley MoogleyGreat Googley Moogley:banghead:

SO it apeared like compression loss was due to head gasket...BUT BOTH have little dinks...BUT BOTH had good compression after retorque:mad:

everything in the engine was very clean, no glopy oil or anything exept one of the two former low comp cylinders had slight crud on valves. It was running strong when I pulled it in and has since I have had it, just tryin to stop the leakin.

Now my first reaction was to tear it out but...I have a 401 I am going to build when I have the $. Dont want to spen the cash on this one when I could do the same for the 401.

I am tempted to replace the gaskets put it back together and run it.
What do you all think?:huh:

[shackwrrr]

do you have a picture? could be parts of the blown gasket melting into the piston

[bockslanding]

gasket itself had evidence of oil leak, kind of crudy where the leak was, but didnt look otherwise bad, no tears or cracks that i could see

[bockslanding]

oh and it is a small hole, with good light I can see the ring. its a hole not something stuck to it

[Crazy_Jeepman]

Running it out of time (Pinging) will do that.

[Ristow]

the top of the piston will start to fragment,and pieces will start closing the spark plug gap.

[bockslanding]

could be it was something like that butnot since ive had it. could it (piston) be in this condition and still be okay tho? cylinders arent groved or anything there is a ridge but its got some miles on it. could oil have been getting past the rings and fouling up the plug?

Now That Im thinkin about it when I first got it, it was running rough so I did a tune up and one of those cylinders had a thick black gunk on it. couldnt have been sparking. timings fine, I didnt think to check for gap under the crud. Its been fine since then.

[HellCreek]

You didn't say which two pistons. Are they sequentially firing, adjacent cylinders? I had this happen on a 5.0L engine in my 86 Bronco. I had just completed a rebuild and installed the plug wires so they looked nice and neat (in the correct firing order, of course). After about 5oo miles the engine started smoking like a mosquito fogger. I pulled the heads off and the #8 piston had holes burned in it. Before I attempted another rebuild, I read an article in Popular Mechanics about this very problem. It seems that on sequentially firing, adjacent cylinders, if you run the plug wires together and parallel, you get what is called "inductive firing". This means that both cylinders fire at the same time resulting in burning the second piston in the sequence (in my case #8). The cure is to keep those wires seperate from each other. I have 200,000 miles on the second rebuild, so it must work.

[bockslanding]

its the front two on the passanger side or number 2&4 in firing order. Are those "sequentially firing adjacent cylinders"?

Engine never smoked not even at start up.

[HellCreek]

What is the firing order on a 360?

[Elliott]

Running it out of time (Pinging) will do that.

Detonation was the first thing I thought of...

[travisrda]

x2 that's the first thing I thought of also:fsj:

[HellCreek]

I just checked the firing order on an AMC 360. It is 1-8-4-3-6-5-7-2, so, no, 4 and 2 are not sequentially firing even though they are adjacent. I still think the cause of the holes in the piston is pre-detonation, but I don't know what caused it.

Tom

[bockslanding]

you mean pre ignition? like a hot spot. That seems more likely from the nice smooth hole. I havent a clue what caused it. This Jeep is fairly new to me.

sorry I never provide pics but im in the sticks and dialup is all I can get.

I just wanted you guys to say all kinds of great stuff like, "OH a hole in your piston, no problem there all like that". And "Mine runs better with extra holes" or "If your not going to use it with those nice holes, can I buy it, Ill pay extra for holes!

So I know what I should do, but like I said Im not throwing good money after this when I have the 401. plus it did have good compression after i retorqued the head before. so hoping this will, if nothing else, stop the oil leaking and give me good compression. if it does im happy.

this afternoon I got the head back on holes and all. Tomorrow if all goes well I should have it going again and will let you all know how it went.

[snoopy]

Sounds like the valve guide seals are gone on that cylinder if there's crud on the valve heads. Do you have a valve spring compressor? If so take that pairs keepers off and see if the valves will rock in the guides. If oil is leaking past there you will get detonation from the oil. Good news its not to expensive to just replace a couple of valve guides, throw a new gasket on and use it if you are going to build a new motor soon anyway. Torn, missing guide seals will do that to, they're real cheap.

[djongeward]

My old 360's pistons looked just like what your describing. Mine were #6 and #4, side by side, center pass side. My waggy had been overheated and pinged badly. I couldn't cure the pinging but I kept it going till I finished the rebuild, about a year in that condition. Only thing I found was a small suspect leak between the cylinders on the head gasket.

I suspect the cto smog system is related to the pinging.

[TooRisky]

Heck what a nice project....I would run the 360 and rebuild the 401, then replace and strat right in on rebuilding the 360 and sell it or shelve it for when the 401 needs to be pulled....heck it could be a life time project and make you da man of engine building...:eek:

Steve...:fsj:

[bockslanding]

[quote=djongeward]My old 360's pistons looked just like what your describing. Mine were #6 and #4, side by side, center pass side. My waggy had been overheated and pinged badly. I couldn't cure the pinging but I kept it going till I finished the rebuild, about a year in that condition. Only thing I found was a small suspect leak between the cylinders on the head gasket.

I suspect the cto smog system is related to the pinging.[/quote


REALLY:eek: with the leak and all!!!! unbelievable.
Did you replace the head gasket?
if so did it repair the leak?
Now with two identical issues I am starting to wonder if the leak could be caused by the piston? I guess ill find out.
its totally possable mine was overheated in the past, it has all sorts of stuff to keep it cool now, 4core extra fans etc. In fact it would barley get warm so im puting in a standard t-stat to see if that helps. oh my smog stuff is all gone.

I got both heads done and the intake yesterday. I also have a busted off dipstick tube I thought I could bandaid but its not going to work. so today im going to start on the oil pan, doin the rear seal while im there.
if I have any leaks after this.....um I guess there on the front:rolleyes:

[bockslanding]

as for that 401, I havent decided what to do. the PO got some of the work done for me. The crank is ground and there are a new set of speedpro pistons 40 over??? will those even work? I have read that 20 or 30 is as much as you can go. hopefully the block isnt that far out. it looks ok, I can still see cross hatch in there. I need a bore guage.

[djongeward]

as for that 401, I havent decided what to do. the PO got some of the work done for me. The crank is ground and there are a new set of speedpro pistons 40 over??? will those even work? I have read that 20 or 30 is as much as you can go. hopefully the block isnt that far out. it looks ok, I can still see cross hatch in there. I need a bore guage.

I have heard 40 to 60, but I think 40 is pushing it. It depends on the block. AMC castings aren't the best and they vary, however I think they are better then Chebys. Of course they don't come close to BB Fords. :D

I have a similar delema with a choice of 3 401's in my buddys shed. Bore again, sleave, etc. Still deciding. You could haul it in and have it tested to see what you have left.

We want to put a built max built 401 in the parts waggy and make it an offroad buggy only, but then I'll have 2 extra 360's floating around.

BTW - I ran the old 360 with nothin done to it for a year. I only noticed the crumbled pistons when I yanked it for the new 360. So how long it ran like that before I got it, who knows. These engines seem to take a beating and still run. Mine never died, just didn't perform well. I think the pinging was all the piston chunks and rubble flaring up.