360
Not to hijack but Krazykuda i reused the old bolts on the pressed-pin rods that came with my 360 when i rebuilt it. The cam currently in it tops out only just over 5000 rpm but i'm thinking of doing some bracket racing this summer; would there be a bad risk of me tossing a rod?
There is a risk. You have no way of knowing how many times that the bolt has been "clamped" (tightened).
When I worked in the engine factory, we only allowed ourselves to tighten the bolts twice on the engine assembly line.
The bolts get their first clamp when the rods are machined.
Then they loosen them up so they can install the piston/rod assembly into the engine. That is cycle #2.
We would only allow them one repair or one recycle on a piston/rod assembly and then we would scrap them. this is cycle #3.
We "saved" two clamp cycles for a dealer service (one cycle) and one rebuild. However they only assumed that a rebuild will tighten them once. If you do it right and check your clearances with plastic gauge, then you use 2 clamp cycles.
Realizing that, I tend to play it safe and prefer to spend the $300 to get new bolts and have the rods reconditioned. If you don't and the bolts let loose, you can damage the rod, crank, piston, and put a hole through the block.
Now, since you already have your engine together, it may be ok. I don't want to scare you. How long has your engine been together? How bad do you drive it? Has it held up for a while under "hard" driving conditions?
Like I explained earlier. The bolt typically will stretch approx .001" - .003" per clamp cycle, it varies, and you don't know how much unless you measure the bolts. If the bolts only stretched on the side of .001", then they will be fine. If they stretched more toward .003", then you may be approaching the critical point.
I saw a post where a guy claimed that he was measuring bolt stretch by measuring the bolts in the rods and comparing the length to the rest of the bolts. This is not accurate. You don't know how long the bolt was when it started. There are production tolerances and there is variation on the bolt length. Sometimes there is a lip or a burr on the end of the bolt, that could make it hard to measure accurately.
To measure bolt stretch is not an easy process, here's what is involved:
First I would get a box of connecting rod bolts and take 200 - 300 of them to the tool room to have a machinist grind the ends flat and then center drill them. You can't just "flatten" each end on a belt sander. It has to be ground flat and parallel on each end. Then the center drill is perfectly centered in the bolt on the head and tip at each end.
Then I would mark each bolt with a number and measure them with a ball micrometer. (Another guy in our group didn't listen to me and did his bolt stretch with vernier calipers. They weren't accurate enough and his results were meaningless - too much error in measurement). He ended up having to re-do his test with micrometers.
After marking and measuring each bolt, then I would bring them down to the rod machining line and have them installed on the rods and then chase those specific batch of rods all the way through the rest of the machining process. After they were finished, then I would take them and have the nuts loosened, so I could remove the cap and measure them to see how much that they permanently stretched during tightening on the rod machining line.
Like I said, typically I would see .001" - .003" of permanent stretch.
Next, I would have them assembled into pistons and installed and tightened on the engine assembly line. I would record the information from the machine that tightened them to look for correlation. Then we would pull those pistons and rods out of the block in a repair spur and I would measure the bolts again.
We would then remove the block and crank, and reload it before piston install to have it built into an engine.
I would then measure bolt stretch with the ball micrometer again.
I would then have the pistons removed from the rods and they would recycle the pistons and scrap the rods. We never sent out ground and centered rod bolts to a customer.
It would take three days typically to run a complete bolt stretch study after I got the ground and centered bolts from the machine shop. They would typically take a week to complete prepping my bolts for me.
Also the equipment that we used at the factory was much more accurate than what we use in a garage to torque our bolts. We used DC electric motors and monitored torque and angle. It would monitor the graph of torque vs angle and sense when the bolts started to stretch, then would stop. this is a more accurate way to control clamp load than just using torque only or going to a target torque and then 90° or so after reaching the minimum target torque. It would store the information I could look up the averages and ranges for torque and angle. I could also pull up the screen after the bolts were tightened and see the torque vs angle graphs from the last cycle.
So that's what is involved in doing a bolt stretch study on a connecting rod bolt. It's not very practical or economical to do at home in your garage.
If you have had your engine together for a while and spun it to red line with no problems, then you should be ok. I would recommend that if you take it apart again, to have new bolts put into the rods and then recondition the bore at a machine shop. When the bolts are changed, it can affect the alignment of the cap and rod. Any misalignment between the cap and rod from what it was originally machined may cause that rod to be tight or even not let the crank turn at all. That is why you have to keep each cap and rod with its mate that it was originally machined with.