I posted a month or so about the engine failure in my Z. Tore it down this weekend. Holy yard sale! It appears to me that the main cap came off followed by two rod caps. One of the rods came completely out of the block having separated from the crank and the piston. Very unexpected and it did not make any noise. Very mild vibration in the shift lever about 10 seconds before it locked up in third at 2500 rpms. I had my hand on the lever and said out loud "somethings weird" and ....... the guy behind me said he saw a puff of white smoke and brake lights.

The blue engine is the one going back in and am tickled to report it works perfectly.

That picture of the hole in your block brings back memories of mine. In '89 a girl I was dating drove my '76 Z. She said "it just quit", I thought the starter was locked up because it would click and that's it. Me and my Dad went to tow it home. He got down to look under the car for a tow hook and said "well there's your problem". There was a rod laying on the ground and a baseball size hole just like your picture.

I saw a similar hole in the side of the engine of a Z I looked at last year. The guy said he din't notice anything odd, he was just driving down the freeway and the engine stopped.

Are you going to pull the head? I'm curious about valve damage if a piston got pushed back up the cylinder after its cap came off.

What are the stories behind the three grenades above? Were the blocks rebuilt and rod bolts reused?

I was just looking at a used car, and the guy had just bought so knew little about it. It was in bad shape though, with an off-year AFM zip-tied in place and general poor maintenance. Someone had messed with it. The hole seemed to fit the general condition of the car.

My engine had 43K original documented miles.

I have not pulled the head, but I did pull the plugs. All were golden brown and none of the tips were bent which initially leads me to believe nothing got on top of the piston.

One of the main caps had come completely off, another has a bolt that dropped out. I can't think of an explanation other than it had sat for 20 years and maybe had drawn moisture rusting a wristpin and setting into motion the catastrophic chain of events. Or............?

Following up on the engine. Pulled the head and found five pistons more or less at TDC. The picture shows what is left of the #3 piston. It was about 1/2 inch thick, still was oriented correctly and had all the rings in place. There is not a mark on the cylinder wall. Also of note, there isn't a mark on the head.

Not that anyone would necessarily want to but could the engine be fixed? Interesting pictures. Would metal fatigue explain the broken rod?

Edited June 8, 201410 yr by Mikes Z car

I have a neighbor who is a certified welder. He said he could repair the block. We haven't looked at the journals at all so don't know what happened to them. There was a lot of trash get tossed around on the bottom end, it would need align bored for sure. I am biting my lower lip and driving 'just another 40 year old Z'. The replacement long block with the original carbs has a lot more 'zing' than the old motor so am guessing it was failing for a long time. I had the car for sale for a while and am glad it didn't sell, it would have been really disappointing for both parties.

The rod will clean up and make a really cool conversation piece as a paper weight however!

I've never considered the failure mechanism for a "thrown" rod but it looks like the wrist pin breaks free from the piston, leaving the piston pieces in the bore, then the rod is smashed through the side of the block by the crankshaft on the next up stroke. Is there any damage to the skirts at the bottom of the bore? It seems like that would be the fulcrum, or ramp, to redirect the rod sideways.

If the rod came off the big end first it seems like it would just get pounded up the bore and stay there with the piston. That's why I thought that there would be head damage.

I notice about 5 of the crank main bearing bolts broke wondering how far the crank flexed as it popped those bolts off but even so the flexing might not have hurt it?

Mike, look at the bearing cap in the middle of the pic (post #1, last pic). It still has a bolt in it that appears not to be damaged. If that's the way Leonard found it when he popped the oil pan off, that would suggest the bolt backed out. Perhaps the other 4 did as well? (Are they intact? It looks like some other intact bolts are hanging out in the bottom of the oil pan, pic #3. And didn't two main caps come off, not just one??? Or did you remove one for inspection?) This would have rendered the engine very much like a Triumph inline 6 (with three main bearings, as I recall), only a bit worse, so it still would have run, except with more vibration and less oil pressure. Then the vibration got the best of the rod.

Scary!

Edited June 9, 201410 yr by FastWoman