Long rod VS Short rod

[acecarlos]

Short rod engines have higher piston wear & failure rates than longer rod counterparts…the increased rod angle puts greater stress and wear on the piston & piston skirt.

You will see an increase in wear & failures occurring on the piston skirt intake side of bridged exhaust port cylinders, and both sides of the piston (intake/exhaust) non-bridged exhaust cylinders with short rod engines…

Shorter rod engines are also more prone to ring end or ring locating pin failure (pins backing out) due to the increased ring fluctuations (increased lateral & vertical forces) caused on shorter rod engines as the rings ride over the port edges…

Carlos.

[Lonewulf71]

QUOTE(acecarlos @ Mar 30 2011, 04:56 PM) Short rod engines have higher piston wear & failure rates than longer rod counterparts…the increased rod angle puts greater stress and wear on the piston & piston skirt.

You will see an increase in wear & failures occurring on the piston skirt intake side of bridged exhaust port cylinders, and both sides of the piston (intake/exhaust) non-bridged exhaust cylinders with short rod engines…

Shorter rod engines are also more prone to ring end or ring locating pin failure (pins backing out) due to the increased ring fluctuations (increased lateral & vertical forces) caused on shorter rod engines as the rings ride over the port edges…

Carlos.

Thanks for posting this as I really didn't understand it either. The 86 I just purchased has the longer rod, so this is good to know.

[diesel]

While I won't argue that there are wear issues associated with a short-rod setup, I will point out that the difference in rod angle isn't that dramatic.

Long rod, stock stroke = 73.92 degrees (crank @ 90 deg ATDC)

Short rod, stock stroke = 73.26 degrees (crank @ 90 deg ATDC)

Long rod, +4mm stroke = 73.00 degrees (crank @ 90 deg ATDC)

These are olds calculations, and I simplified everything by using 125.0mm & 130.0mm for the rod length, but the overall picture doesn't change. The short-rod is a good setup (think CR250R) and nothing to shy away from.

[jcs003]

While I won't argue that there are wear issues associated with a short-rod setup, I will point out that the difference in rod angle isn't that dramatic.

Long rod, stock stroke = 73.92 degrees (crank @ 90 deg ATDC)

Short rod, stock stroke = 73.26 degrees (crank @ 90 deg ATDC)

Long rod, +4mm stroke = 73.00 degrees (crank @ 90 deg ATDC)

These are olds calculations, and I simplified everything by using 125.0mm & 130.0mm for the rod length, but the overall picture doesn't change. The short-rod is a good setup (think CR250R) and nothing to shy away from.

agreed. im going back to a short rod on my 86 when the time comes since hot rods apparently got everything worked out.

[DareDevil]

The long rod connects higher in the piston making it harder for it to put too much pressure anywhere. if you have an 86 thats the first you should do is upgrade it to a long rod. makes it tons more reliable