Don Terrill’s Speed-Talk

What can cause a connecting rod bearing to be pounded into as thin as shim with no signs of heat are black oil starve just flattened.This is on a 351 cleveland and all the other bearings look as good as did when installed.First failure was #5 rod and now #8 and only after 1 are 2 1/4 mile drag runs.

What side of the rod? Detonation comes to mind.

Gday,
Post up some pics of upper and lower rod bearings and mains that feed that cylinder
And engine details, clearances, fuel, comp, timing etc,
What do the plugs look like out of that cylinder?
What crank? How is the oil system set up?
Pm me if you like?
Cheers

If it gets no oil. Because it gets shoved up against the crank cheek by it's neighbour. Oil quickly overheats because it's escape route is closed off, no fresh cooling oil getting to brg. Cause? Bent rod, bore not perpendicular, could be a few things. Rod gets 'worked' to one side.
I grind three small scallops on the rod cheeks, so that should the rod become 'trapped' the oil has an escape path.

When you get things running again you need to confirm that your total timing up at 5000 rpm is not topping what you have intended to have it set at.

Unexplained rod bearing failures can many times be traced to this !

I’ve only pulled the 2 rod bearings 4 and 8 and I’m not sure when I’ll take the engine down but it looks just like the same problem as when 1 and 5 failed 5 was smashed down upper and lower until it looked like shim material without being oil starved 1 was down to the copper but not burned and intact upper and lower.At that time the timing was at 39 degrees and this time it was at 43 degrees running VP C12 race fuel the first time I was running Sunoco standard race fuel.

That is about 8 degrees too much timing for a clevo, even with open chamber heads.
At least 10 deg too much with closed chamber.

There's your answer.

If it needs that much timing something is wrong - find it, fix it.
If you need more than 34 with closed chamber heads something is just not right.

1972ho wrote: ↑Sat Aug 14, 2021 9:32 am I’ve only pulled the 2 rod bearings 4 and 8 and I’m not sure when I’ll take the engine down but it looks just like the same problem as when 1 and 5 failed 5 was smashed down upper and lower until it looked like shim material without being oil starved 1 was down to the copper but not burned and intact upper and lower.At that time the timing was at 39 degrees and this time it was at 43 degrees running VP C12 race fuel the first time I was running Sunoco standard race fuel.

What KnightEngines said.

I have never had the need to run that much timing on a Stock, Super Stock or even a Comp Eliminator Engine.
The last time I saw engines that required that much timing, the camshaft was degreed incorrectly or they had the incorrect camshaft for their application. C12 was not designed for that amount of timing, that amount of timing would require C25.

As said, way too much timing

Both failures are the outer cylinders on the same bank, what manifold are you running ?

First thought would be running into a lean situation with that side of the manifold outer cylinders and, combined with the excessive timing, rattling the bearing out

BCJonny I run a factory ford dual plane intake D1ZX-CA and the engine goes through the lights at 8000 rpm with a 5:57 gear and 9 inch 29.5 radial slick.

As the guys have said miles too much timing, distribution will be terrible with a dual plane, do you read plugs or know how to?
They will have told you a story,
Cheers

Chances are you have a combination of factors

The excess timing suggests a very inefficient combustion event ...... CCs or OCs with pop ups ?

If the latter, that's at least part of the problem, the D3ZE small valve OC heads generally allow a better throat but the 'chambers' end up a terrible shape ...... end gas detonation etc ...... and don't burn near as well as the CCs

I guessed it may be a dual plane ...... the shorter runners may be bleeding the longer ones on each level at certain (higher) revs, leaning them out, probably leading to higher rpm detonation, which can be difficult to hear

If a shell gets battered out in a blink and you shut down quickly, the rods don't always go black

Not an answer, just something to maybe look at ..... and all IMLE

I’ve been running the timing like this for about 6 years now running the same fuel and timing mark on the plugs are just over the bend in ground strap using open chamber heads with the bigger valves and the bearings have never looked great after a few races but they for the most part weren’t failing like they are now and it’s mostly on the 5 are 8 cylinder.So I’m not really sure why now I can’t get a 2 runs out of them with out one going bad.

If you could list what you have for parts, clearances, deck height, quench, etc, we might see something jump out

Have you checked the rod (mag, shape and size) and have you had the crank magged? Haven't seen any Clevelands break cranks, but have seen the result of a cracked journal on a Poncho.