Disassembled my dads 340 today and had the bolts fall out of two rods. The engine has very few miles on it since rebuild. I am taking it apart to clean it up, check the work, and paint it. So the rod bolts. They fell out when I very lightly tapped the cap with a hammer to get it off.
I am guessing I’d be an idiot to try to reuse them?
The shoulder on the rod bolts is what locates the cap to the rod.. if the cap is not properly aligned to the rod and the bore for the crank is mis-matched, it can cause an interference with the crank which can cause the crank to be harder to turn or even lock it up...
Whenever I change rod bolts, I have the crank bore of the rod refinished so they are aligned properly...
I would check the holes for the rod bolts in the rod for size before trying to go any further to make sure they are not enlarged... If they are ok, then I would get new bolts and have the rods refinished and install new bolts and re-machine the crank bore...
Also, how many times have the bolts been tightened??? If they have been tightened more than 5 times, I would recommend replacing them and re-machine the crank bore.... Keep in mind that if the rod bolts have never been replaced, they come out of the factory with at least two clamp cycles on them ---> which gives you only three left... If the rods were reused, and plastic gauged for the last rebuild, then you already have 4 clamp cycles on them... If you use them again, to plastic gauge and then reassemble them that will give you a total of six clamp loads on those bolts.. There can be a chance that they would be over stretched and weaken them... I would not recommend using them with that many clamp cycles on them...
The best thing to do if you want the engine to hold together, is to replace the rod bolts and have the crank bore re-machined... Otherwise you risk throwing a rod....