regalman4925

I am throwing together a L29 long block right now, cloning the previous motor I dropped a valve on to use while I build a stroker motor. I was assembling the short block and I had 1 rod bolt that kept tightening, I backed it out and it torqued fine, last bolt on rod 8 and the same thing happened except this time I snapped the bolt. I have spare stock bolts but ordered a set of ARP 3/8 rod bolts because I do not like what happened. so I start reading about people installing them in the pistons while the rods are still in the block as I planned to and I read a few things saying that when you install ARP bolts you need to have the rod resized? I personally have known people to just throw them in or go on street rod engines but as we all know marine engines see more abuse so I am not sure I can get away with it. do I replace the 2 defective bolts with stock or can I get away with the ARPS and no resizing.

Young Performance

If you use the ARP bolts, you MUST re-size the big end of the rods. Are you sure you are using the correct torque spec or if your torque wrench is accurate? The only other reason for the bolts to snap is that they are just plumb worn out junk, in which case they need to be replaced anyhow. I certainly wouldn't take the chance. Put the ARP's in and re-size the rods.
Eddie

regalman4925

I just replaced the bad one and calling it good. I went back rechecked all of the others and everything was fine. this is a temp motor and just to get me by till the end of the season, I am not throwing any more money at it than needed. I torqued them to 50. as far as the torque wrench it has never let me down and worked fine on all other bolts. I am wondering if the one that broke had a issue before hand.

regalman4925

by the way eddie, thanks for the input. you seem to always reply to my questions and are a great help!

Budman II

iTrader: (1)

If I wanted to sleep good at night, I would go ahead and invest in a rod bolt stretch gauge and measure the stretch on the bolts instead of just the torque. This will be something that you can use again on your "good" motor. Measuring bolt stretch is superior to torque values because it takes friction out of the picture. You can install the gauge on the bolt with the nut finger tight, and then torque it to the correct value and note the stretch. Then loosen it back to finger tight and make sure the gauge goes back to zero. I think the general rule of thumb is that it should go back to .0001 of the original length, or it should be considered overstretched and replaced. If I had more than one of these stretching like yours did, I would be very leery of it. You have a certain level of time and money invested already in this motor - rings, bearings, gaskets, labor, etc. I would hate to see you run it and then sling a rod out the side of the block over something like this. Just the hassle of being towed back in would be enough to make me go the extra mile on this. Besides, you will have a good backup motor or something that can be sold, versus a pile of scrap iron if it tosses a rod. JMHO.

Also, if it is an "off-brand" click type wrench that has not been calibrated, I don't know if I would trust it. I had one of those and broke a head bolt with it while waiting for it to click. Even the inexpensive Craftsman beam type wrenches are more accurate. Either way, I would find a way to verify and calibrate the wrench for the next motor. Good luck!

ezstriper

I can tell you this, If I had two act funny I would replace them all now....it ain't pretty if one cuts loose....the pin has been removed....

regalman4925

all new stock bolts in it now. I am not resizing anything on this motor for the arps. the last engine I am replacing was identical and had no issues with a stock lower end. im saving my money for the stroker motor, I already have H beams with ARP bolts in them for that build

Young Performance

That's great that you replaced the bolts, but personally, I would re-size the rods anyway. We always re-size rods that have had the bolts replaced. Some may think it's not necessary, but it's pretty cheap insurance. It's a little different for us since we are sending it out to a customer. We have to be able to remove any doubt that it will stay together. The other thing to keep in mind is that you need to torque and release those rods several times to be sure the bolts are completely seated. I use the press to put the bolts in and then torque and release them 5 times before re-sizing.
Eddie

Budman II

iTrader: (1)

I would at least run a quick check for bearing clearances on the rods before buttoning it up, just to be sure one didn't go out of round with the rod bolt replacement. I have always understood that any rod that has the pressed in bolt with a nut on top should be resized if the bolts are replaced. The aftermarket rods with the cap-screw bolts with no nuts have the dowels built into the rods to locate them, but the stock ones rely on the knurled portion of the bolt for locating the cap. If you do not have the proper crush on the rod bearings you will spin one.