Block Strength

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6

6T9 GTS

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Well I had a catastrofic failure three monday's ago in the dart. Out for a little cruise to see how the pinion snubber and a new set of shoes for the back was going to react before going to the track on wednesday. Rolled through water across the road really slow and lit the tires after coming out of it, right after hitting second she popped on me. That night pulled her down to the heads and ended up taking the driver side head off. When it popped she was blowing hard out that side. After that head pressure tested out just fine we pulled the motor on out and found a broken #6 rod. That was a suspicion but we were hoping for the best. After taking the broken rod and piston out of the hole we found massive block failure at the bottom of the cylinder towards the outside. There are at least 4 vertical cracks and one that is horizontal to the cylinder. Is my logic right to assume that the block failed causing the cylinder to hydraulicly lock, breaking the rod and the dual plane intake explains the majority of water in #1 and 7? I have always been under the assumption mopars were really stout when it came to their blocks. Could the addition of a 4" crank and a .030 over bore weaken the block that much to cause that kind of damage?
 
could you take some pic's of the damage?
where did the rod break? did it sieze?
i'd say if you rule out everything else it might be possible.
block failure is unusual, but not unheard of.
anytime a motor comes unglued above idle massive damage is not unusual.

a motor turning 6000 rpm = piston speed 100 strokes per second with a
direction change at both ends of the stroke
valve train speed 1/2 that.
it's really a hard to believe anything survives in that enviroment anyway :toothy10:

please let us know what you find.
sorry about your loss
 
The block may have failed due to the rod angle and side loading of the piston on a overbored block that was somewhat thin to start with. Was core shift check before boreing the block?
 
A rod is usually bent under hydro lock not broken, but it could break it. What makes you think it was hydro lock. Even if a cylinder wasn't firing it wouldn't hydro lock from the fuel. The only motors I have seen that hydro lock from fuel while running are blown fuel and alcohol motors or a mechanical injection motor that isn't "backed down" before starting. Without a pic or seeing the block it is difficult to tell. Could have been just a rod failure.

Chuck
 
340mopar said:
A rod is usually bent under hydro lock not broken, but it could break it. What makes you think it was hydro lock. Even if a cylinder wasn't firing it wouldn't hydro lock from the fuel. The only motors I have seen that hydro lock from fuel while running are blown fuel and alcohol motors or a mechanical injection motor that isn't "backed down" before starting. Without a pic or seeing the block it is difficult to tell. Could have been just a rod failure.

Chuck
Click to expand...


I think he means hydro lock with the coolant that was coming in threw the cracks. Cylinder walls bow so I imagine those cracks could have opened up alot.
 
If I was a betting man, I'd put my money on you over revving the motor in the water, snapped the rod, and took out the block with the shrapnel. there's probably as many engines blown up at the stirip by being overrevved doing a burnout as racing. If it had hydrauliced, there should be major signs of the rod bending before it broke. That cylinder didn't have time to fill with water. At 6000 rpm with all of the cylinder pressure in there there's no way it could fill that fast.
 
Sorry for taking so long to get back on here. I'm gonna track down a camera and take some pictures this weekend. The rod broke right at the cap. Dad got pictures to eagle and they told us the rod was a victim not the cause (who knows). That motor had seen regular trips to 6-6200 rpm pretty much at least once everytime it was driven. It looks as if the lower 2-3" of cylinder wall gave way. When it popped it was runnig around 42-4500 and getting traction hard. A local engine builder did mention something about too much cylinder pressure causing that and he also mentioned that if a wrist pin starts to sieze it could cause a failure like that. Still boggles the mind why that happened. That block had been bored .030 over for 22 years. Looking at how its gonna go back together, i think we are going to go stock bore with the 4" crank and up the compression from 10:1 to around 10.5-10.75:1. More details to come after the weekend.
 
when you stroke a motor you increase the rod angles.
this puts tremendous sideload pressure on a rod, piston and block wall.
you may never know for sure what part failed first, but I would guess that material fatigue in the rod at the crank started it, then took the cyl. wall out with the broken rod end. if I had to guess.
 
Eagle will never say their rod broke. But, if it broke near the crank, the rod failed IMO. Cracks from stress appear where stress is greatest, and then the amount of water is not much that gets in unless the wall broke out...and the rod would bend and then break (in a matter of milliseconds at that rpm) and up near the piston. Not the big end. Post good pics of the rod bits, and the lower section of block. What model eagle rods were these? What was done to the engine during the 4" conversion? Wals flex, then crack, but a crack is a long way from schrapnel. Mains crack. I have one (customers) who shows a crack running from the cam bearing down towards teh main..but doesnt reach the saddle. That is costing both of us some $$ to replace the block.
 
My 4" stroke failed the same way. but the rod did not break. I had eagle H-beams. the cyl wall failed -the piston wedged in the cyl- the rod bent-the main cap failed-the crank broke-the shrapnel caused damage in other cylinders.BTW i have 4 good pistons 4.03" ross 12-1 and 6 good eagle H-beams for sale. LOL
 
Starting to sound like it would be a good idea to do half block fills of the water jackets on strokers.


Chuck
 
Nah, it's called a sonic test... Or as I call it "Expensive insurance". "Cheap Insurance" is keeping the overbore to .030 max :)
 
I may be missing the point but sonic tests on blocks I have used showed the "thinest" area between the cylinders - the sides. The front/back of the cylinder (facing the intake or exhaust manifolds where much of the rod pressure is) had plenty of meat.

I am currently running a 4.1x4.0 on a siamese resto block and had seriously considered going to bigger on the bore ... there was plenty of meat on the block but not enough cash in the piston budget.

And yes ... I know resto blocks are not supposed to be siamese ... I know of one other one so there are at least two. I don't have a picture looking inside at the water jackets but here is the block ...

Kory

OnBoringMachine2 (Small).jpg
 
SWEET block. I'm trying to find one but no luck yet. Can you take some more pics of that beast(bottom end). I have also heard of siamese resto blocks. I think there is even a part number for them.
 
Here are 5 pix of a resto bock fitted with 4.1 pistons ... but this is not my current (or siamese block). Last picture shows the lifters.. the ceramic lifters caused a huge problem and ultimately cost me the block....but I digress (and need to stop crying). BTW - I used the carcus to try and see if I could get a set of rollers in it- I couldn't do it (that is an ugly picture I can shhare only after drinking!)

New block was identical if you didn't look in at the water jackets.

Engine from Hughes (Small).JPG


Tray on Engine Final 2 (Small).jpg


Degreeing Cam 1 s.jpg


CrankBlock1.jpg


Lifters in Guides 2 s.jpg
 
Thanks for the pics. Man that block looks tough. I take it that you sonic checked it. Can you post the numbers? Sorry about the hijacked post.
 
Thanks for the pics. Man that block looks tough. I take it that you sonic checked it. Can you post the numbers? Sorry about the hijacked post.
 
Yes - sonic tested both blocks. Let me see if I can find and scan them.

How about that wintage tray!! ... good thing I don't have a clear oil pan so no-one can see it!

Kory
 
moper said:
Nah, it's called a sonic test... Or as I call it "Expensive insurance". "Cheap Insurance" is keeping the overbore to .030 max :)
Click to expand...

mod5v and 6T9 GTS were only .030 over though. Could these blocks be failing when pushed over 450 hp with a stroker crank? What could account for this? I find it hard to believe that side loading would cause this. There's a lot of 4" stroke engines of all makes that have not experienced catastrophic failure of this sort. Porous casting maybe? Rust from 35 years of negligence?

69GTS, I'm very interested in your photos. I would like to see what the cylinder wall mics out at the point of failure, what the busted out cylinder wall looks like and I'd also like to see pics of the rod too.

modv5, do you have any pictures you would like to share?
 
Hmmmm....Good info but it appears that the problem (if there is one) is not with the MP resto blocks but with the factory blocks. Has anyone else had a cyl wall failure on stroker engine bored .040 over or less? Pictures and measurements would be appreciated.
 
I had a .040 340 1970 factory block sonic checked if I remember right The minimum thickness on a thrust side was about .138 I ran it with about 500HP no problems
 
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