Ariel Owners Motorcycle Club

On the 58 square four that I am rebuilding, are the connecting rod bolts even something to worry about? These are a high grade bolt with low torque loading on a low powered low compression engine. Am I being overly cautious?

The bottom end of Square Fours is flimsy at best and, an egg-sucking lesson perhaps, the
oilways need to be completely cleaned out.

If you don't know anything of the engine's history a set of new rods from the club is good
insurance as a broken rod will wreck the crankcases at the very least.

The impression I have is that the rods are fine as long as they have oil. Are old rods just false economy?

Aluminium fatigues more than the usual steel rods. You have no way of knowing for sure how hard the motor has been used. Loss of oil to the rear LH rod due sludge is he most common failure. IF you know it's history and it's not done a lot of miles you could just do a cracktest and not ride it too hard. (High Revs). Some people are revheads and I wouldn't do it on a SQ4. Nev

The aluminium will fatigue with use due to the strain of thrashing up and down thousands of times a minute. Over time this may cause failure of the rod, however I am hard pushed to remember an engine failure involving a broken rod that didn't show evidence of big end seizure. In other words the rods tend to break not due to the failure of the rod but a failure in the oil supply system, usually number 4 rod as it is furthest from the oil supply. If in any doubt I would replace the rods, an engine blow up will cost more than the rods and where can replacement cases be found?

Will I have to relieve the crankcases in order for the new rods to fit?

No - I have never needed to.

Thanks for your help!