Bad things

[Toby]

Recently stroked out my 302 to 347. The car has less than 100 miles on it and while driving last evening, lost power, big lots of white smoke out passenger side pipes and engine starts clanking, so I shut her down. Upon inspection find #3 cylinder has mashed spark plug and stuck valve! After removing head notice absence of #3 piston and bent rod! plus 2 large holes in cylinder walls. Engine builder says cylinder walls look awful thin 1/8 ". This was an existing 0.30 bore that had run fine as 302, with about 4000 miles behind it. Any ideas about other possible causes?

[Ron61]

Toby,

When you stroked the engine out, did you just increase the rod length or have it bored a little more? You know the formula: Cubic inches= # of cylinders X .7854 X Bore X Bore X Stroke. And how did the other pistons and rods look? If all other cylinders are ok, you could have had a faulty rod. From what you describe, it sounds as if for some reason the #3 piston hit the valve and spark plug. If all the clearances are good, it could also possibly have been a valve sticking open for some reason and then the piston hit it and the rest was history. Sorry I can't tell you more, but I am sure some of the guys here will be able to.

Ron

[Toby]

Ron,
Since the engine was a fairly fresh already bored 0.30 engine builder just honed and went with stroker kit. no evidence of problems with any other cylinders. problem did however neccessitate an underwear change!

[Ron61]

Toby,

That was to bad that it had to happen but good that other cylinders look ok. Did you check your valve spring on #3 to see that it wasn't broken or something happened to it to let the valve stay down to long? Keepers have been know to come off and let the valve drop. Since everything else was ok, I would more suspect the valve as the culprit. Was the push rod bent? There have been instances of push rods not being correct and causing bad things. One that I know of here had a wrong push rod but just looking at it, you would not notice the difference. However it was just enough that it rubbed the guide and slowed the valve enough for the psiton to do it's thing.

Ron

[Toby]

Ron,
The first thing we checked was the spring, and keeper and were o.k. the heads are edelbrock and were on the engine before, valves and all. I can only assume the valves were the right length from before, but there appears to be no damage to valves just scratches and pitting on the aluminum recess in the head. I am wondering about the integrity of the new crank now, this kind of malfunction has to put a lot of stress on it! the rod was bent at about 70 degrees and #3 piston was disintegrated.

[Ron61]

Toby,

I think if it was my engine I would have the crank tested before using it. You are correct about it taking a big jolt. All that force has to transfer somewhere. If the rest of the valves are ok, then the length must be ok or they would be hitting. When you said stuck valve, did you mean it was stuck open or shut? For some reason, that piston had to have came up farther than the others do to have bent the rod and smashed the end of the plug.

Ron

[Toby]

Ron,

When we first pulled the valve cover and started checking the valve was stuck slightly open or slightly depressed and could not be moved. Builder says it could hve been water in cylinder that bent rod and disintegrated piston, but cannot figure where the water came from (before holes) as gaskets were all good and sealed. if walls had cracked first water would have been pushed out cracks, thus no overpressure to cause this.

[Ron61]

Toby,

The water theory is ok except for one thing. Just a lot of pressure wouldn't have smashed the end of the sparkplug. The white smoke sounded almost like water, but if the gaskets were good and there was no crack anywhere, then that most likely came from water pouring in after the big bang. Also something stuck the valve and that sounds as if it had been hit. With the piston gone there is no way to look at the wrist pin and see if it broke or gave way. From all that you have seen, it sounds as if you may have just had a bad bit of luck with that one piston. And the fact that it ran good for a while tells us that everything was clear and the pistons weren't hitting. If there had been any clearance problem, all of them would have had it and you would have known it immediately after starting the engine. This part from experience of watching a guy I knew when we were younger starting his 1958 Chevy after putting in a big cam and not checking his clearances. It ran almost 30 seconds and broke everything. Are you going to try to sleeve that block or get a new one?

Ron

[Toby]

Ron,

The engine builder say's he has a good 302 block to use. I sure hope that all the rotating assembly that's left are good. In retrospect, I agree that the logical choice is one bad piston. Thanks for the insight.

[Ron61]

Toby,

Maybe just one more suggestion. Have the engine builder really check that crank shaft and especially that journal. If it is even a few thousands off, it won't last long. Good luck and sorry you had to go through that. I just spent a fortune to have my big block 69 Torino Cobra engine completely redone and sonic tested.

Ron

[trularin]

The stroke of the new crank removed the clearance between the rod and the edge of the cylinder wall. Once the rod tapped the wall, the metal gave causing a crack to run up the wall and cocked the piston. The rest is history.

Or, the builder failed to grind the releaf correctly causing a thermal weak spot that allowed the wqll to crack when the engine heated up.

Or, when the new lower end was installed, there was excessive passage clearance which reduced the amount of oil to the top end causing the valve to gall and stick to which the piston struck it on the up swing and the rest is history.

Or, when the engine was reassembled, improper Valve guide clearances were allowed to be passed to the heads allowing the valve to stick and strike the head.

Then there are the several lists of part failures that could have happened.

Take it back to the builder and ask him to fix it.

Sorry to hear of your missfortune. Hope this helps.

[mr0077]

or a bad piston, top (or part of it) came off and got wedged between the head and the rest of the piston, bending the rod, mashing the plug, bending the valve and punching holes in the cylinder wall...and if they were the old pistons, is that the builder's responsibility? Granted, they should have been checked...
Toby, sorry to hear about this miserable experience...what a bummer.

[Toby]

these were brand new keith black pistons. this must be awfully rare (if it was piston failure).

[Mr.Fixit]

Where did the piston go? It's gotta have the bigger pieces in there somewhere.

[Ron61]

Toby,

It would be rare, but any part can fail no matter what it is or who made it. Not saying it was a piston failure for sure, but from all the evidence it sure seems to point in that direction. Trularin gave some good reasons this could have happened but if it was the rod hitting the edge of the cylinder wall, then all of them should have did it and there should be marks. The fact that only that cylinder showed any sign of problems would sure make one think it was a piston or valve problem. But the valve could have been stuck from the piston hitting it and bending the push rod. Most likely you will never be able to pin point exactly what happened as you don't have the piston or it's pieces.

Ron

[Toby]

Mr. fixit

As of yesterday evening the builder has not pulled the engine or pan yet, but when I asked to see the piston he told me when the head was pulled that was it. only what I saw(bent rod with wrist pin sticking up). I am sure there must be some pieces of piston in the pan somewhere, but nothing within confines of the cylinder. truly a bizarre sight.

[Ron61]

Toby,

I agree with Fixit, there must be some pieces of the piston somewhere in that motor. If you could be there when the builder removes the pan, it might be a good thing. Not only look in the pan but at the crank journal and the rod bolts. And when it did blow up, were you winding it up or just driving along at a lower RPM?

Ron

[Toby]

Ron,

As I was trying to break in the new stuff and seat the rings, had only gone to about 4000rpm but not for extended periods. I put about 100 miles on stroker. when catastrophy occurred was about 2500or 3000rpm from first to second gear(automatic trans).

[Ron61]

Toby,

It would seem that you did everything right. I think there must have been a faulty piston or part in that cylinder. If the rod bolts are still good and the rod is still attached to the crank journal when yuo get it opened up then I would really suspect something about the piston.

Fixit,

What do you think about this?

Ron

[Mr.Fixit]

I have seen pistons come apart cleanly into two big pieces, split right through the wrist pin hole. The top half gets crammed into the head, smashing valves and the sparkplug. The bottom half gets chucked down into the crank and rods where it gets chopped into pieces like it was dropped into a cuisenart. Rod bounces around in cylinder destroying everything and ventilating the water jacket. The top half of the piston, which is just a flat disk gets beat up and can come apart and have it's bits fall into the pan.

Never seen it happen at low RPM however, only after critical piston speed was exceeded (ex: 5th to 2nd downshift)