Broke connecting rod?

[lance flake]

Lance

The wear patterns and marks in that cylinder bore tell me that something was going on in THAT CYLINDER well before that rod cutloose! Can you post a couple of other pics of a couple of the cylinders that have not broken or been damaged from debris.

The skirt wear does not indicate any major issues from what can be seen in the pics, but those ring wear patterns and what appear to be stepping in the ring top of cylinder areas in the pics indicate some NOT good wear patterns.

I will try to get some better pics. The bore is beat up pretty good from shrapnel. If you could explain the wear pattern you are talking about I would appreciate it. I'm all ears wanting to learn more. The bores to me look like any other one that has run on alcohol/methanol. They always look bad to me way worse than gasoline. I have freshened up engines that I have built and ran on gasoline that still looked new after a couple race seasons. 200-300 passes

[Newold1]

Lance it is not perfectly clear from those pics you posted, and the damage from debris is not the issue. It looks as though the rings are putting a stepped pattern at the upper area of the bore almost as though the rings are shifting up and down like they would if the rings in a piston are to loose as though the ring groove heights have open up and allowed the rings to shift a lot in their grooves. Could be an effect of light and reflections from the camera pic.

That discoloration or heat marking on the right bottom corner of that piston skirt could be another issue also.

It's not common after a rod blowing like this to have the engine still operating for any length of time and generally not long enough to generate a heat discoloration on the piston like that or the ring to bore wear patterns that appear to exist.

If we can ask what ring sizes and types were you using here and the ring gaps if they were measured?

That's why I asked for some more pics of the other bores to see if this pattern was occurring more in the broken rod cylinder.

What type of piston to bore clearances were running here and what was the piston deck height on your set-up?

I know these may seem to be some questionable questions but if you really want to isolate the final cause idea for that rod it's important to eliminate and define other issues that may have been going on.

Another great old saying "Dumb questions are easier to handle than dumb mistakes!"

[kosky racing]

This ring marks are from the cyl. firing at the wrong time -that is what broke the rod-flame on

[Kevin Johnson]

This ring marks are from the cyl. firing at the wrong time -that is what broke the rod-flame on

Looks like the rod was in cylinder 7 and 5-7 misfires are common with sbc.

[lance flake]

Lance it is not perfectly clear from those pics you posted, and the damage from debris is not the issue. It looks as though the rings are putting a stepped pattern at the upper area of the bore almost as though the rings are shifting up and down like they would if the rings in a piston are to loose as though the ring groove heights have open up and allowed the rings to shift a lot in their grooves. Could be an effect of light and reflections from the camera pic.

That discoloration or heat marking on the right bottom corner of that piston skirt could be another issue also.

It's not common after a rod blowing like this to have the engine still operating for any length of time and generally not long enough to generate a heat discoloration on the piston like that or the ring to bore wear patterns that appear to exist.

If we can ask what ring sizes and types were you using here and the ring gaps if they were measured?

That's why I asked for some more pics of the other bores to see if this pattern was occurring more in the broken rod cylinder.


What type of piston to bore clearances were running here and what was the piston deck height on your set-up?

I know these may seem to be some questionable questions but if you really want to isolate the final cause idea for that rod it's important to eliminate and define other issues that may have been going on.

Another great old saying "Dumb questions are easier to handle than dumb mistakes!"

I think the discoloration you see is a shadow from not so great pic taking.

I’ll answer what I can off top of my head and I’ll look at spec sheet tomorrow.

Ring side clearance is still as built .001-.0015 was lapped on a piece of 1200 laying on glass. Rings were .043/3mm conventional ring end gap .022 top .024 second. No sign of ring butting

Piston to wall clearance was wiseco spec plus .0005-.0007. I’ll get exact number tomorrow and piston was .005 below deck with a .041 gasket I do believe

Rings could be used in the next build! Lol

[pdq67]

Fwiw, I am having a hard time thinking about a GOOD forged rod creating Shrapnel?? Powder rod, yes...

Or was the forged rod tempered out of spec so that it was so hard that it broke like a plate of glass??

pdq67

[MadBill]

This ring marks are from the cyl. firing at the wrong time -that is what broke the rod-flame on

Looks like the rod was in cylinder 7 and 5-7 misfires are common with sbc.

Good point. Inductive crossfire on a conventional Chev FO engine fires # 7 90° early.

[In-Tech]

Is this a std firing order? Was that cyl 7?

I would be putting the entire ignition system from the car on a distributor machine with a pressure chamber to simulate cylinder pressure. I bet you find rotor phasing to be wrong and it jumps to the next cylinder in the firing order(path of least resistance, next cylinder doesn't have near the cylinder pressure as the one you are trying to fire) and causes a situation similar to the death wall of preignition.

My $.02

[lance flake]

4/7 swap

It was #7

[lance flake]

Fwiw, I am having a hard time thinking about a GOOD forged rod creating Shrapnel?? Powder rod, yes...

Or was the forged rod tempered out of spec so that it was so hard that it broke like a plate of glass??

pdq67

When there is a piece of it left swinging and beats the block up it makes shrapnel

[Baprace]

lance , was the piston a solid dome or hollow ?

[lance flake]

lance , was the piston a solid dome or hollow ?

Hollow dome

[MELWAY]

What were 3 centre main bearings like?

If there was an ignition problem with not firing or burning the methanol you would think it would flex crank and hurt:wipe the centre main bearings

[blackflag]

Lance I’m pretty sure the rod just broke. I’m not claiming to be an expert but I’ve seen the same problem with just about every brand rod made and I’m talking about rods with big ends still on crank and pins still round. No burnt bearings all of these rods that broke had one thing in common. They were getting the hell run out of them. They all will break. Just hope it’s not on your watch when the do.

[lance flake]

What were 3 centre main bearings like?

If there was an ignition problem with not firing or burning the methanol you would think it would flex crank and hurt:wipe the centre main bearings

Will look tomorrow. Been trying to finish up other stuff while thinking abou this time one!