Help!!! My engine blew and I need guidance, please!

[shawndoggy]

I bet we're gonna see a lot more of these blown engine threads now that Rotella T doesn't have the SN designation

[MadMan]

34 minutes ago, Ryan1776 said:

@MadMan "When the intake valve first opens, the pressure in the combustion chamber is greater than that in the intake manifold, so exhaust briefly flows into the intake manifold."
Correct, but for the pressure to be greater, the piston still needs to be moving upward. And therefore the exhaust gas that reverts into the intake port is not from exhaust already spent though the runner but what is still in the cylinder. Because there is still positive pressure expelling the spent charge out the exhaust as well. 

"Since the exhaust valve is still open, the exhaust briefly flows back into the combustion chamber, along with any water present. "

No way. Not enough time NOR strength. As I pointed out by the numbers, with a fairly aggressive cam, not what we have, the piston is only down in the cylinder 0.051" when the EV closes. And that VERY little volume of air/vacuum that exists before that E valve closes wouldn't be able to pull back water from THAT far down stream in the system. This is also not taking into account the fact there are other cylinders sending their burnt charge down the same pipe at the point of communion which will have significantly higher effect in forcing the water out than the extremely short amount of time the EV is open with the IV. 

 

The other thing is, we’re talking about VERY low RPM causing this issue (if it were high RPM, we know the overlap doesn’t cause reversion). At low RPM the throttle is choking off 90%  of the air flow.   Meaning… the cylinder isn’t even CLOSE to being full of air.  (it’s the basic principal of how a throttle works right?) So if the exhaust can flow well enough to empty the chamber at 5000RPM, it can certainly EASILY empty the chamber only 10% full at idle.

"but for the pressure to be greater, the piston still needs to be moving upward."

This is incorrect, the piston does not have to be moving, there is low pressure (vacuum) in the intake manifold at idle.

"As I pointed out by the numbers, with a fairly aggressive cam, not what we have, the piston is only down in the cylinder 0.051""

This is incorrect too, has nothing to do with the piston moving.

" At low RPM the throttle is choking off 90%  of the air flow.  "

This is true and is what is causing the reversion, because there is a vacuum in the intake manifold.

 

You might want to consider that people with aggressive cams in boats have been battling problem forever.  Your theories remind me of the old adage:

"In theory, there is no difference between theory and practice, but in practice there is."

 

[Ryan1776]

@MadMan Sorry I TRY to get off the grid on the weekend! :D 

I can assure you, I have plenty of "practice" to go along with my theory. 

So anyway, the old adage I subscribe to is "correlation is not causation." Just because you can measure the intake under vacuum, does not mean it's sucking water in the motor on overlap.

The piston has a significantly higher impact on what the air/fuel is doing in the cylinder than the vacuum created by the intake stroke of the other pistons.

The only time the piston wouldn't have a higher impact is at TDC, for that split second of time the piston has ceased to move, and therefore it has ceased it's impact on the air. But as air has mass, mass therefore has inertia it will continue along the path it has been sent.  The time at TDC is known as piston dwell. This dwell time is nearly zero (in truth it does hit zero but it's far too short a time to even argue about). In my example the piston is already moving 3.26 feet per SECOND at that 0.051" mark. Meaning it's time at true TDC is again, nearly zero. (SBC with 5.7 rod@ 800rpm-approx idle speed)

That doesn't leave a whole lot of time for the vacuum in the intake manifold to act on and PULL water and exhaust gas from the exhaust system up the the riser back down the manifold and though the exhaust runner on the head and into the cylinder. All while battling the exhaust gas forces of the other cylinders at the merging point. More on that later. 

On 5/18/2018 at 3:43 PM, MadMan said:

"As I pointed out by the numbers, with a fairly aggressive cam, not what we have, the piston is only down in the cylinder 0.051""

This is incorrect too, has nothing to do with the piston moving.

I hoping you missed my point with this comment, because you truncated it also, to finish my statement the piston is only down in the cylinder 0.051 when the EV closes. No matter WHAT force you want to chose on the exhaust gas stream, it's irrelevant at this point because the valve is closed. Again this is with a moderate cam. Again, not nearly what we have. I merely used it to show how minimal this effect is on a something larger. 

 

On 5/18/2018 at 3:43 PM, MadMan said:

You might want to consider that people with aggressive cams in boats have been battling problem forever. 

Which is why I specifically utilized a moderate cam to show how little of an effect there is and if the effect is that minimal on a moderate cam it's virtually non existent on our engines.  I did a quick search and the guys talking about reversion like was spoken about in this thread are on very modded engines with plus 600hp with cam specs in the [email protected] and narrow lobe separations, it's about exhaust duration.  Not to mention exhaust tube/manifold and riser design! Most likely bringing the mixing point significantly closer to the riser floor. 

I'm not saying it doesn't happen. I'm saying it doesn't happen on our stock-o engines. I'm also saying, it's not the vacuum in the intake causing it. Pretty sure Indmar figured that out. 

One last point. 

At 800rpm = 13.333 rev’s per second.  Meaning each rev = 0.075 seconds in total time.   Assume a cam has 20 degree’s of overlap out of the 360, meaning it’s only in overlap for about .0042 seconds.   If the water exit point is say 3ft away from the exhaust valve, that means it would have to travel 720fps (490mph!) to get back into the chamber on reversion.  No way is the intake manifold pulling enough vacuum to move the reversion at that speed. For reference… even when the throttle is wide open and the piston is moving mid stroke at 6000rpm, you only see around 300fps in the intake port!   

So answer one thing… how do you explain that the water can travel at 490mph in the opposite direction of the exhaust flow, considering it’s quite obvious the exhaust stroke completely cleared all water out of the port/manifold milliseconds before the reversion started?

Edited May 21, 2018 by Ryan1776

[JLickteig]

Craziest thing! I wasn't getting notifications on this at all. I thought no one ever responded... so I never came back.

SO here's the update. First of all, it was total milkshake city when the engine blew. The block cracked internally and externally ... rods flying everywhere. It was a mess and a nightmare.

We spent the summer of 2018 rebuilding the engine. Swapped the block and some other things that I literally did not/do not understand. I just did whatever I was told to do by my mechanic buddy. Took literally all summer but only cost $1,200 and lots of beer, tacos, and pizza. But she runs like a champ now.

Very expensive/hard lesson learned about what "draining water out" means when winterizing. Took her out twice last year and hit a sandbar 150 yards from shore. FML, right? So we had to replace the prop shaft and rebuild the prop twice... (it was pretty nasty). Only took her out those two times last year.

But this year! This year has been great. And she's basically down to only 50 hours. Thanks everyone for trying to help out. Sorry I didn't see it. 

 

[braindamage]

This thread is hilarious. @JLickteig, I gotta giv it to you for tenacity. A new engine and sandbar in successive years would’ve killed a lot of people’s enthusiasm.

[dlb]

8 hours ago, JLickteig said:

We spent the summer of 2018 rebuilding the engine. Swapped the block and some other things that I literally did not/do not understand. I just did whatever I was told to do by my mechanic buddy. Took literally all summer but only cost $1,200 and lots of beer, tacos, and pizza. But she runs like a champ now.

But this year! This year has been great. And she's basically down to only 50 hours. Thanks everyone for trying to help out. Sorry I didn't see it. 

 

Read through the thread and you can learn a lot about why your mechanic buddy had you do what you did......

Lost of good experience/knowledge relayed to all in this thread!