Another example of why teenage girls and cars don't mix well. My daughter let one of her friends borrow her car. Apparently, a leak occured somewhere and she lost enough coolant to overheat the engine. Rather than pull it over, she ran it until it wouldn't run anymore (though she claims she shut it down immediately). Anyway....I'm looking for some expert advice.

The obvious problem is that I have four cylinders where the exhaust valves are tapping the piston heads. For what it is worth, the car did start once it cooled down, but I shut it down immediately after hearing the noise and had it towed back to my garage. I checked compression and had 170 on all but 3 and 6, which had 140. Though a little low, probably not low enough to indicate a blown head gasket. Also, I did not see any coolant/oil at the junction and no indication of oil in the coolant.

Next step was to pull the heads and look for problems. I'll mention here that I had the lower end re-built about two years ago, but put the original heads back on after some do it yourself valve work. I suspect that the heads are slightly warped, but putting a straight edge to them, they don't appear to be off the very small 0.002 inch tolerance much. The engine deck is still flat. A few of the cylinder head bolts appeared to come out a little wobbley (possibly bent), which is one more reason I think the heads are warped.

I checked the valves on one side and they all had free movement. The exhaust valve springs are slightly elongated compared to spec, but consistant. The valve seals still appear to be fine as do the guides (though not checked for anything other than valve movement at this point).

The disturbing observations I have are that the 3 and 6 pistons do not come flush to the deck as the other four do when turning the engine over by hand. Also, piston heads 1, 2, 4 & 6 all have slight nicks where the exhaust valves have tapped them.

The question is this - Am I wasting my time (and $$) putting new heads on this engine and expecting it to work?

 

You have two bent connecting rods......The head gaskets popped, allowing coolant into the cylinders......Since you cant compress a liquid, The next available space for the engine to take is Buckling the rods....

 

You could concievably Drop the oil pan, and remove the PISTON/Rod Assemblies from the motor...and replace them...I would seriously advise against it....but it is do-able.

I would assume this is a 3.5...????? These are PERFECT Wrecking yard candidates, and if you are capable of pulling heads and checking compression....And understanding what all that means..You can certainly swap a motor.

 

Yeah, it is a 3.5HO. A motor swap is an option I was considering, but I'm really bummed about dumping the time and effort in the the last re-build and taking a chance on a used engine. My experience with this engine is that it is definetly not built for abuse.

I wouldn't try changing the connecting rods with the engine in the car. There is simply no room to work under these. If I went that route, I'd pull the engine. Good call on the bent connecting rods BTW. That had not occurred to me but makes perfectly good sense. One note though, there was not a significant amount of coolant in any of the cylinders when I pulled the heads. Unfortunately, I wasn't observant enough to notice if the little bit that was in there came from the head as I was pulling it or if it was already there.

 

That really isnt your fault....Lifting the head up off the block is ALWAYS going to spill coolant no matter how hard you try.....

But....I'm willing to bet, that if you flip the heads over, the exhaust valves have been "Steam Cleaned" to a High polish.......And That
would be your dead giveaway that there was coolant in the cylinders prior to removing the heads....

 

I've never heard that.....And no, they aren't. I just went out to double check and they all have a 'normal' soot level (dark, but not caked or burnt), and they are all consistant in color.

I'm liking your bent connecting rod conclusion, but I'm not sure about the coolant causing it. What's the possiblilty that the connecting rods got bent by the valve tap. I would think the valve(s) would bend first, which they aren't.

 

Slim to None.......

Kissing, maybe.....But if they got HIT by the pistons......You would see it.....And the fact that you have somewhat Normal compression leads me to The conclusion that the valves are fine...

It is possible that the Smacking noise you heard was the rod hitting the Piston "Skirt" as it traveled up and down...If it is indeed bent...then there is nothing keeping it centered in the bore.

I am a Bit surprised at no discoloration on the exhaust valves......

 

Not to say that there isn't contact on the skirt, but there is definitely contact between the valves and the pistons. There are little nicks on the top of the heads where the lower edge of the valves made contact. The nicks are small, so they weren't smacking real hard, but any contact is obviously a bad thing.

I'm in agreement with the compression test indicating the valves were ok. I was actually thinking at the time that it also ruled out the head gasket, but now I am not so sure. To be honest, I can hardly believe that the warpage in the head that I may or may not be seeing (0.002" is pretty small) would even cause the valves to conflict with the pistons. It seems that the timing would have to be off but when I brought it to TDC prior to pulling the heads, the cam sprockets and timing mark were all in the correct position (I had pulled the timing cover early thinking maybe the water pump got bent), and I had a rod in No.1 to make sure it came up all the way. So timing was fine.

 

Ok...I understand now.....No that isnt valve contact....Its detonation, or Spark Knock...which can show up as anything from Mild scuffing, to a "PIE WEDGE" cut out of the valve.....

a 10 or 20 point drop in compression from a bent rod is a Normal expectation...
But a little Known fact.......MOST of the timing belts that break, dont bend valves due to Piston contact.....They bend due to contact between....INTAKE AND EXHAUST VALVES.... and it is possible that the head gaskets are intact, and your coolant entered thru a crack in the head, (Between Valve seats, or even Internally)

Another scenario could have been, out of time.......But the Marks Lined up???? I had a 3.5 pacifica a few weeks ago, with a sheared key in the cam sprocket....The marks lined up... but the cam was dragging behind...

The More I think about this .....This is going to turn into a PIT to throw your wallet into.....Start Motor hunting....

 

"But a little Known fact.......MOST of the timing belts that break, dont bend valves due to Piston contact.....They bend due to contact between....INTAKE AND EXHAUST VALVES...."


That is why I like this forum. I learn something new everytime I come here. Now you've got me thinking a lot differently. To clarify, the nick I am talking about is in the head not the valve. I'm not sure if that is what you meant. Wouldn't spark knock also be a timing issue though?

The timing marks all lined up as stated, but I did not check the shear key. I will do that tomorrow (I hated that little bugger when I put it together the first time). But I think No 1 coming up with the marks aligned should indicate the shear key in it's proper place. I was thinking that if there is any sort of timing issue to be had, it would be in the camshaft not spinning quite right (back to the warped head thought and maybe a bit of bind, though that would be tough to swallow the way it's fit into the camshaft sprocket.

Thanks for all your help. I was hoping I could get away with new heads but had concerns with that solving the problem. You have given me a few more things to think about.