Crower Rod autopsy.

[McRat]

We pulled apart two pistons on our last run at Bonneville. The engine had many quarter passes, dynos, a sled pull, and 3 LSR passes before the pistons quit. So there was a good amount of abuse put to them.

I put the rods on a CMM machine, and found that even the damaged cylinders had acceptable eye to eye length. 6 were less than .0005" from original spec, and 2 were less than .002"

One rod twisted slightly on a damaged piston cylinder, which most likely happened after the piston came apart and the wrist pit hit the bottom the of the piston.

A stripe of burnishing was appearing in the little end bushings about .2" wide and 90° long on the pressure side. It is 1/2 way between the center oiling groove and the outside, so it's an oiling issue. Stock rods show this as well. Whether it would ever get to the point of failure, I don't know.

 

[malibu795]

sound like there is room for imporvement

thanks for the update. you cleaning them up and putting them back in or getting new ones?

 

[slowlmm]

Sounds like they held up well

 

[fast03]

Sounds like they held up well

And we all know what Pat means by abuse. Thanks Pat for updating us.

 

[Diesel power]

got any pics of the bushing issue?

 

[sweetdiesel]

are the crower a H beam and do you remember the wieght of them?

 

[McRat]

H-Beam? (I always get the two mixed up, standard design) billet rods, 1146.2-1146.7 grams.

Here's a picture of the burnished area. It is "polished" and discolored. The rest of the bushing retains the hone markings.

It is entirely possible this is normal and acceptable wear. The diameters were fine. All eight rods had the same burnished area.

 

[Stingpuller]

Rods

Pat, By chance do you know what the clearance was on the wristpin? Thanks Jeff

 

[duratothemax]

crowers/R&R's are I beam.

Carillos are H beam.

 

[Jared Duramax]

so this shows that under extreme abuse forged rods may not be completly necessary?

 

[slowlmm]

are the crower a H beam and do you remember the wieght of them?

mine came with a slip of paper with the weight of each rod i think there all diffrent but not sure

 

[Fingers]

That mark lines up with the edge of the small upper end. I would think is burnishing of the minor machining imperfection that can happen when you go from a complete hole to a partial.

But what do I know.

 

[Cornell]

Interesting

 

[EDP]

nice info good to know thanks Pat

 

[Diesel power]

H-Beam? (I always get the two mixed up, standard design) billet rods, 1146.2-1146.7 grams.

Here's a picture of the burnished area. It is "polished" and discolored. The rest of the bushing retains the hone markings.

It is entirely possible this is normal and acceptable wear. The diameters were fine. All eight rods had the same burnished area.

Is it like that on both sides of the rod? if so i think i can explain what is happeneing.

it looks like the load is so great in that area, that the outer edge or the rod or lip, is bending down or flexing with load, causeing a wear mark........?

the only other possible explaination is that there IS a size difference somewhere along the wrist pin OD, or the rod small end ID, and that slight difference is causeing a wear or polish mark.

another possibility that for reasons above the oil is being pushed out of that area by load or a eneven surface( rod or pin) and causeing a slight lack of lubricant where it is showing where.

I think that it's a OD and ID spec issue, in the rod or the pin itself.......