Connecting rod bolt stretch advice needed
Posted: Tue Oct 10, 2017 12:41 pm
I installed a pair of new rod bolts using a stretch gauge and stretched each bolt alternately in 4 stages to 0.0014", 0.0028", 0.0041" and finally 0.0055". They are ARP L19 3/8" bolts and the spec. that came with the rods was stretch to 0.11 to 0.15mm (0.0043 to 0.0059") and DO NOT GO OVER 55 ft/lb.
After stretching them I decided to go over them with a torque wrench set to 50 ft/lb. One bolt didn't move but the other one did. Before assembly all threads and head undersides were coated with ARP lube.
I then backed off the bolts completely with the intention to just stretch them again and forget about the torque wrench. Once I had backed off both bolts however I found that each bolt without tension had now stretched 0.0005" compared to what it was originally. I was surprised and would have expected them to return to the same length they were originally. ARP set a limit of 0.001" stretch before bolts need to be replaced but these were new bolts.
So my questions are:
Is this normal/expected?
For each tightening should I do the stretch twice so that initial 0.0005" baseline stretch is allowed for in the second stretch tightening?
After stretching them I decided to go over them with a torque wrench set to 50 ft/lb. One bolt didn't move but the other one did. Before assembly all threads and head undersides were coated with ARP lube.
I then backed off the bolts completely with the intention to just stretch them again and forget about the torque wrench. Once I had backed off both bolts however I found that each bolt without tension had now stretched 0.0005" compared to what it was originally. I was surprised and would have expected them to return to the same length they were originally. ARP set a limit of 0.001" stretch before bolts need to be replaced but these were new bolts.
So my questions are:
Is this normal/expected?
For each tightening should I do the stretch twice so that initial 0.0005" baseline stretch is allowed for in the second stretch tightening?