AIR FLOW PISTON

[Boone]

The pic is from my 68 440. Ran my 1st 200mile trip after a rebuild. When checking out a timing change, I ran up to4500 between shifts. When I pulled from the stop sign I noticed heavy smoke from rt side. Found two things: #6 cyl spark plug had electrode completely closed at tip end and I had a blown head gasket. Mystery to me is where metal piece is. The ring is exposed and looks great and there is not a trace of scaring or scratching on cyl wall. I have not driven car much and thinking I might have bought it in this shape. Plug electrode could have been from my dropping plug and not checking. Very hard to install plugs on her. Will appreciate any insight. I'm just WAGing.

 

[1 Wild R/T]

Looks like a KB Hyperutectic piston?

 

[Kern Dog]

If you only have 200 miles on that engine, it has some problems. There shouldn't be so much carbon on the pistons and of course, the broken ring land isn't a good thing.

 

[33 IMP]

Inadequate ring end gap. Ring gets hot, ends butt, bye bye ring land. Probably file-to-fit rings..... that weren't filed.
Piston chunk went out the exhaust. May have damaged that exhaust valve, and of course that piston is junk. Tear the whole thing down.

 

[1 Wild R/T]

Inadequate ring end gap. Ring gets hot, ends butt, bye bye ring land. Probably file-to-fit rings..... that weren't filed.
Piston chunk went out the exhaust. May have damaged that exhaust valve, and of course that piston is junk. Tear the whole thing down.

And what pistons are most known for this sort of failure? KB Hyperutectics.....

You can run tight piston to wall clearance but you absolutely must loosen the ring gap to at least 150% of normal..

 

[33 IMP]

.... and that ring gap factor is a factor/inch of bore. So, at least .030 for a 440 with KB hypers. I'm guessing o.p. has more like .020..... or less.

 

[1 Wild R/T]

KB 237

 

[R413]

You didn’t do that to the plug electrode, it would have been running on 7 cylinders. Dropping plugs doesn’t close the gap all the way as they are not heavy enough.

Poor engine, tear it down and blueprint it, clearances are not right.

 

[Cranky]

That chunk of the piston probably hit the plug on the way out.....

 

[diesel_lv]

I have a 1250 CC Evo engine I built in my hardtail. Rear cylinder detonated once on a steep grade at full throttle. Then all of a sudden I'm running on 1 cylinder. Pulled rear plug and it's pinched closed. Regapped it and rode the rest of the night. Next day I pulled the rear head, piston broke off and apparently hit spark plug and went out exhaust valve.

 

[69Bee]

That piston requires about 0.026" to 0.028" on the top ring due to the "Heat Dam". There is increased heat in the head of the piston due to its design. The instruction sheet that came with the pistons stated this.

 

[Cranky]

And I don't really get what the love affair is with those hypereutectic pistons. Yeah, they are 'supposed' to be stronger than standard cast pistons and not as good as a forged one and priced accordingly but what good does it do to have the top ring so close to the head of the piston and then you need to gap them wider because of it? Is it supposed to create a better ring seal?

 

[1 Wild R/T]

And I don't really get what the love affair is with those hypereutectic pistons. Yeah, they are 'supposed' to be stronger than standard cast pistons and not as good as a forged one and priced accordingly but what good does it do to have the top ring so close to the head of the piston and then you need to gap them wider because of it? Is it supposed to create a better ring seal?

I agree... They can run tight clearances which means they are quiet on cold start up... So what, I like the noise forged pistons make as they come up to temperature...

Hypers can't take detonation, don't even think about a little shot of nitrous... Yeah some folks get away with a small shot but far to many don't, not worth it...

Their single saving grace is KB makes so many options.... But on a 440 there are good options with forged pistons...

 

[Cranky]

I agree... They can run tight clearances which means they are quiet on cold start up... So what, I like the noise fired pistons make as they come up to temperature...

Hypers can't take detonation, don't even think about a little shot of nitrous... Yeah some folks get away with a small shot but far to many don't, not worth it...

Their single saving grace is KB makes so many options.... But on a 440 there are good options with forged pistons...

I know a few that ran a small shot using factory cast pistons and did fine. IIRC, the top ring is a good deal closer to the top of the hyper piston than factory cast or forged? Been a long time since looking at one....

 

[33 IMP]

Stock driver engine, cast are fine. In my humble opinion, if you are building a hi performance engine.... stick forged pistons in it.
Never was a fan of hypers, never owned any.
Edit: and I think I would trust real original Mopar cast with a small shot, more than the hypers. Cheap replacement cast are a different animal.

 

[1 Wild R/T]

I know a few that ran a small shot using factory cast pistons and did fine. IIRC, the top ring is a good deal closer to the top of the hyper piston than factory cast or forged? Been a long time since looking at one....

It might be a little closer but not much, the thing is it has an open space just below the top ring that acts as a heat dam, trapping the heat in the piston head and around the top ring... The ring can survive if given enough end gap but if treated like a normal cast piston the ring ends will butt together & the ring will stick in the bore.. When the rod tries to pull the piston back down the bore the ring sticks & part of the ring land typically breaks off.... Which is exactly what happened with the O/P's engine...

And yes, cast typically will take a small shot of nitrous.... Just don't get to aggressive..

 

[Challenger340]

Inadequate ring end gap. Ring gets hot, ends butt, bye bye ring land. Probably file-to-fit rings..... that weren't filed.
Piston chunk went out the exhaust. May have damaged that exhaust valve, and of course that piston is junk. Tear the whole thing down.

Yep, pretty common failure when insufficient ring end gap is used on the KB Hypereutectics.

The BIG GAP on the KB Pistons between the Top and 2nd Compression Rings.... is intended as an Accumulator Chamber, to allow a large space/volume for the compression pressure leakage from the top ring to 'accumulate' and NOT build up too much pressure between the Top and 2nd Ring and UN-seat both.

Remember.... during operation
the Top Compression Ring is 'Positive' twist, and the 2nd Compression Ring is 'Negative' twist ?
If compression pressure builds excessively between them in operation we get reduced sealing efficiency and ring flutter.

 

[Boone]

1st thank you for the great reply. You're correct on the KB. I have 2 more questions this morning. I'm 200 miles from home and will haven't seen head gaskets on shortly. Can I drive it? Are pistons replaced only by complete set. I'm going to sell the car. Physically can't keep doing this. Not going to do this blindly; buyer will know. Thank you all very much.

 

[33 IMP]

1st thank you for the great reply. You're correct on the KB. I have 2 more questions this morning. I'm 200 miles from home and will haven't seen head gaskets on shortly. Can I drive it? Are pistons replaced only by complete set. I'm going to sell the car. Physically can't keep doing this. Not going to do this blindly; buyer will know. Thank you all very much.

I would drive it back, after the new head gasket is installed, but I would drive at reduced speed, to try to keep piston/ring temp down. Do not push it hard up hills or under load. The bad piston might give miss, it won't be working as well as the others.
And, you can replace just one piston, no problem....but....
the engine needs to have all the pistons pulled out and the top ring end gaps checked, and probably adjusted.

 

[1 Wild R/T]

1st thank you for the great reply. You're correct on the KB. I have 2 more questions this morning. I'm 200 miles from home and will haven't seen head gaskets on shortly. Can I drive it? Are pistons replaced only by complete set. I'm going to sell the car. Physically can't keep doing this. Not going to do this blindly; buyer will know. Thank you all very much.

You might get lucky, but that ring is unsupported & will probably come apart.... It is now taking full force compression & combustion plus when going down the bore it has a completely unsupported gap.... The question will be if it does come apart does it too just go out the exhaust or does it bounce around, get sucked into the intake & take out a few more cylinders?

Personally I wouldn't waste the effort to put that back together without correcting the problem... A properly built 440 should be trouble free, unfortunately whoever built your engine missed a known problem

I'd either trailer it home or dig out my AAA card... If you have Collectors insurance most policies include some level of towing...