Cranks Between Ring Lands

[SRS_Chris]

There should be other obvious signs of detonation, such as piston top erosion (sand blasted look) or erosion of the side of the top ring land, pepper on sparkplugs, etc. if that were the case. That looks to me like it was hydraulic locked. Stuck injector? Flooding carb? Water got in it somehow? Check that rod for being straight and square.

That's what made me scratch my head. The tops and chambers don't show any obvious signs of detonation. The tune looks extremely rich though in all holes. I didn't see the plugs as the engine was brought to me without any. I will take a closer look at the rod and bearing shells to see if I can see any obvious connecting rod folding.

This is something I've seen with nitrous engines when the tune up is way too rich. The fuel gets down into the ring groove and detonates down in the groove. I'd bet the rich condition and pump gas did this in. Did the second ring look like it was butting together?

Top ring was conventional type. The second ring was a lap joint style ring. It did have a broken "lap" when I removed it from the piston. I too have seen excessively rich tuneups play havoc. Generally though I see it pop the top land (presumably because fuel is building up behind the top ring). As you suggested, I suspect fuel built up between the top and second ring. Either way, someone didn't build this shortblock right for the application.

[DCal]

Good thing you tore it down, any time the oil ring is doubling as a compression ring disaster is soon to follow. We forget sometimes that the 2nd land is supporting the cylinder pressure and when it breaks/cracks the 3rd land has to do it. That piston wasn't designed for boost so I suspect that the crown of the piston was oil canning which doesn't help ring squareness in the bore. Not a poorly made piston just the wrong one.

[Geoff2]

Joe 90,
There you go again with your nonsense.

Since the ring gap was not stated, the problem could well be caused by insufficient ring gap.

[user-23911]

It's really simple.......take a look at the specs of pretty much any jap turbo engine and take a look at the specs of it's non turbo equivalent.

The ring gaps are always the same.


If the engine starts detonating, the pistons always break in the ring lands.

Stock jap turbo engines can make incredible HP when tuned correctly without detonation.

Stock as in un opened and stock ring gaps.
Just because you don't hear it detonating and just because there's no obvious signs, it doesn't mean it's not detonating.

That's what modern electronics are for.
Far better than anyone's ears.


Tooners who can't toon properly blame the engine builder.
Engine builders who can't build engines properly blame the tuner.
When you do both yourself you do it properly .........eventually.


Reading the title again, the cracks are not "between" the ring lands, they're between the ring grooves which are AT the ring lands.

[user-23911]

Joe 90,
There you go again with your nonsense.

Since the ring gap was not stated, the problem could well be caused by insufficient ring gap.

Is it better to fix the cause of the problem or the effect of the problem?

The cause is detonation.
The effect is too much peak cylinder pressure.

2 wrongs don't make it right.

[ptuomov]

I think that the ring gaps are the same in Japanese non-turbo and turbo engines because the rings are designed to run at about the same temperature. The way they got them to run at the same temperature was to increase piston mass, increase the top ring land width, keep the skirts long, add piston oil squirters, etc. in the turbo engines. Which, in my opinion, is the properly engineered solution. And they did leave a huge margin of safety.

That doesn't mean that if you run the same piston with the same piston cooling in a turbo and non-turbo engine you should keep the ring gaps the same. My logic dictates that since the turbo engine rings will run hotter, the optimal ring gap will also be a little wider.

No argument on using "modern" electronics for tuning. I put the modern in quotes because the factory engineers have been using knock sensors on turbo cars since the 1980's.

It's really simple.......take a look at the specs of pretty much any jap turbo engine and take a look at the specs of it's non turbo equivalent.

The ring gaps are always the same.

If the engine starts detonating, the pistons always break in the ring lands.

Stock jap turbo engines can make incredible HP when tuned correctly without detonation.

Stock as in un opened and stock ring gaps.
Just because you don't hear it detonating and just because there's no obvious signs, it doesn't mean it's not detonating.

That's what modern electronics are for.
Far better than anyone's ears.

Tooners who can't toon properly blame the engine builder.
Engine builders who can't build engines properly blame the tuner.
When you do both yourself you do it properly .........eventually.

Reading the title again, the cracks are not "between" the ring lands, they're between the ring grooves which are AT the ring lands.

[n2xlr8n]

If the engine starts detonating, the pistons always break in the ring lands.

Stock jap turbo engines can make incredible HP when tuned correctly without detonation.

Any Subaru EJ I've torn down (prior to catastrophic failure), the presence of detonation was evident in the rod bearing(s).

By the time one breaks the ring lands one usually has a pile of rubble.

[modok]

I disagree. Seen it 3 times

[user-23911]

I've torn down lots of Subaru engines too.
Either the head gasket fails first and it pressurises the cooling system, it eventually cooks...because lots of hills where I am.

Or


The owner turned up the boost, it detonated, broke the ring lands, no obvious signs apart from excessive oil consumption, eventually it overheated or spun a rod bearing, broken ring lands were found along with the bottom of bore(s) rusted.

Catch cans fix everything.



got a head ache?
Go to the doctor.

Take paracetamol..

It fixes everything?

[n2xlr8n]

I disagree. Seen it 3 times

Which part? That the evidence is in the rod bearings or that when the lands break rubble is shortly after?

Not arguing- everyone's experience is different.

[modok]

I read it to mean, the rod bearings the in a subaru engine will compromised before ring lands.

(Imagine Al Borlin voice) "I don't think so TIm"

Of course it depends on the YEAR, and I don't recall, they even had a recall on some.
Certainly detonation, in any case. No question.

[Xnke]

It's really simple.......take a look at the specs of pretty much any jap turbo engine and take a look at the specs of it's non turbo equivalent.

The ring gaps are always the same.


If the engine starts detonating, the pistons always break in the ring lands.

Stock jap turbo engines can make incredible HP when tuned correctly without detonation.

Stock as in un opened and stock ring gaps.
Just because you don't hear it detonating and just because there's no obvious signs, it doesn't mean it's not detonating.

That's what modern electronics are for.
Far better than anyone's ears.


Tooners who can't toon properly blame the engine builder.
Engine builders who can't build engines properly blame the tuner.
When you do both yourself you do it properly .........eventually.


Reading the title again, the cracks are not "between" the ring lands, they're between the ring grooves which are AT the ring lands.

Not correct, Joe. The pistons are not the same between the two, for example in Nissan engines, the top ring sits lower on the piston, and has the same gap as the N/A engine. When you run the same jap turbo engine (L28ET, FJ20ET, SR20DET) with N/A pistons, you DO need to change the ring gap. The rings are higher on the piston, the top ring runs hotter, and the ring ends will butt if you do not adjust the ring gap to suit.

Things like piston oil squirters, which are usually found in the same turbo engines but not always found in the N/A examples also contribute to not needing to open up the ring gaps.

Basically, if you can keep the piston ring temperatures the same, you do not need to change the ring gap. When you can't expect to keep the piston rings the same temperature, you DO have to change the ring gap.

[user-23911]

If you look into it a bit deeper you'll find that in the early 90s a lot of jap engines had the ring packs raised on the pistons for emissions purposes. Same for both turbo and N/A applications.

The earlier pistons with lower rings break between 1st and 2nd compression rings where the later pistons with higher rings tend to break above the top ring.


Just because you can't see the breakage doesn't mean it's not broken. Need to remove the pistons to find the damage.

The one and only thing that breaks them is detonation.
Nothing else.

No detonation, no breakage.

Increased temps cause detonation.
Ring butting doesn't factor into it.


If you've got good knock monitoring, you can see it and prevent it before it happens.
If you don't have good knock monitoring you're blind, or rather deaf because ears are useless.


But everyone likes to think that their ears work when in fact they don't.
Dreams are free?

[tt 383]

So they raised the ring packs in the "Jap" engines.... Is it possible the second ring gap would see more heat and needed a wider gap? Second rings are usually tighter anyway yes no?

[user-23911]

No change in the factory ring gap specs in the workshop manual.


OK, so how hot do the rings get?
Not very?


The piston gets most of the heat from combustion.
Some of the heat flows through the piston walls to the block.
Some of the heat flows from the piston to the rings then to the cylinder walls of the block.

Do turbo engines really run hotter than N/A engines?
No.
They make more heat.
That's not the same as running hotter.
So long as you can remove sufficient heat, the temp is the same.

Assumption is the mother of all f ups.