Rod Bearing Wear

[Chris Hill]

Just curious, but when you disassemble an engine after a few or allot of runs, what part of the rod bearing has the most wear? The rod side or the cap side.

Thank you,

Chris

[Alan Roehrich]

Chris,
I see even wear on both sides. What I've seen on our stuff is a VERY light pattern, barely visible to the naked eye, that is almost all the way from parting line to parting line.

Try the Mahle Clevite website, they have a lot of really good stuff on bearing wear.

Are you and Larry doing an autopsy on the engine you lost at Belle Rose?

[Chris Hill]

Alan, thanks for the response. No autopsie yet, just reviewing my engineering text books on how pressure fed oil bearings work and how oiling systems are supposed to work.

The books only give generalities and only for production car clearances and engine speeds.

[Chris "drooze" Wertman]

Originally Posted by Chris Hill

Alan, thanks for the response. No autopsie yet, just reviewing my engineering text books on how pressure fed oil bearings work and how oiling systems are supposed to work.

The books only give generalities and only for production car clearances and engine speeds.

On that note, you may want to look into Motorcycles particularly Harley XR750 , the clearances are significantly different but they arent roller bearings a STOCK XR750 is 100hp, modified its not unusual to see 150+ They take a beating on the rod bearing at high RPM in a Flat Track application.

Or even Import stuff, particulary Mitubishi, they (the ricer types) are boosting those RELIABLY to 1000hp, the Mistu bottom end is a tank and that why it has the following, PLUS they are spinning the crap out of them.

Just a thought....

[Chris Hill]

I'm not really sure if rod bearing life is a hp or a rpm issue or a combination of the two.

My gut says it's more of a rpm issue rather than a hp issue, but I still need to prove it.

[Chris "drooze" Wertman]

Originally Posted by Chris Hill

I'm not really sure if rod bearing life is a hp or a rpm issue or a combination of the two.

My gut says it's more of a rpm issue rather than a hp issue, but I still need to prove it.

LOTS of things, lots lots lots, rpm, clearances, oil system, load, etc etc.

Ive had bikes spinning 12k+ for 90% of their track time with no appreciable bearing wear. Ive had Harleys same (XR750's) and other Harleys that ate bearings like they were crank food. Machine work, finsih. bearing material on and on and on.

Im still a bit sketcy on clearances with the H bearings compared to other stuff, and I think Im seeing some side loading on my bearings which well...that a biggie for certain failure.

Not the right guy to be answering it, I guess Im agreeing in part, basically there are a ton more things than even I normally think of.

[SSDiv6]

Originally Posted by Chris Hill

I'm not really sure if rod bearing life is a hp or a rpm issue or a combination of the two.

My gut says it's more of a rpm issue rather than a hp issue, but I still need to prove it.

Chris, bearing wear and life is defined by torque, rpm and hp. As you know, they are all related to each other. Go back and refresh on Mohr's Circle.

[Jeff Lee]

Consider the ability of the rod to stay round. OEM rods, when stressed in a racing application, will distort and elongate. The bearing will decrease the clearances at the parting line, creating a scraper and wiping the oil from the rod journal. Yes, I was very happy with NHRA allowing quality, aftermarket rods.