Grp Rods Pulled Threads

The intent of the rod stretch gauge discussion was to plot it out in the garage before the race and after the race when you have time so you can make a lookup chart based on number of runs and on how much torque is required with your lubricant to get .006". I didn't mean to use a stretch gauge between rounds.

The explanation on clamping force and pulling threads was more fror any other readers that may not understand it.

 

From what I have been able to find out talking to different rod makers is that it is not so much the bolt that causes the problem it is the ability of the rod maker to cut the threads correctly in the the aluminum rod itself and therefore the importance of a NO-GO thread checker on new rods.

 

Paul, from a well known rod manufacturer, he states that cutting the thread in the aluminum rod is not the same as cutting the thread in a steel rod and there is a difference in the process. He stated that some rod manufacturers know how to do it correctly and consistently and some don't. I do not believe they are using a standed industrial thread tap. I am passing on what I found out and I by no means consider myself a machinist or an expert in this area but since they make aluminum rods as part of there main business I assume he knows what he is talking about.

 

Paul, you might be right but I have no idea. He wouldn't tell me because it was a trade secret.

I do know that I have never found a broken bolt in the pan after a rod failure. Usually if the cap comes off I never have a burned bearing but have one bent bolt and one bolt with thread in it which indicates that it lost torque and pulled out and bent the cap back. I don't know if that failure was due to a bad torque wrench or not. I did go out and buy the best Snap-On after that. We never use Excaliber (the torque wrench because it is so long looks like a sword) on anything but the motor. We have had brand new rods break the shoulder area on the first launch right off the line. I swear to this day that it was a faulty rod but you will never have a rod company tell you that just because o the libility of saying it.

I have also seen rods actually split the beam lengthwise and I am sure that was due to detonation. I have also had some rod failures that have totaly mistified me. There was no clue why it went.

We had a brand spanking new Jon Kaase Ford hemi nitrous motor that kicked the rods out on the first burnout because we think the driver came up too fast on the rpm while in the bleach box rather than pull out a little. (nitrous style burnout). We found out it had an Oklahoma guarantee which we found to be only good in Oklahoma and we were in Georgia and so was Jon.

We currently use Brooks rods in the Ford and so far never had a failure but sooner or later it is bound to happen. Different racers swear by different rods. Racers never want to switch from what they have had success with. I have had a small rod company offer a new style rod that was cryogenically cooled and had tons of neat features in the beam area but couldn't find a blown alcohol racer usng them and we sure where not going to be his test motor unless he would pay for all rod caused damages.

 

few points

i'm not an engineer nor do i have any experience in mfg to definitively comment on some of the discussion here. however, i've done bottom end for a number of hard running teams that buzz the motor pretty good. the few times i've done bottom end on a car that kicked the rods, other causes were associated.

in looking at how some people do bottom end, i'll share some of my methods.

i use torco assembly lube exclusively. i also use it liberally, and apply it liberally to the rod threads. hot or cold. some believe in using engine oil on the threads. this is just what i've used, and we regularly took cannon's car over 10,500 without fail.

i think it's important to walk the rod cap up evenly when reassembling. i use an electric impact hit one bolt a little and then run the other bolt all the way in...never run the first bolt all the way in.

the same method on torque. i give the first bolt one decent pull with the wrench, then do the same on the other bolt. then i go ahead and pull the bolt to 90 and do the same with the other bolt. sneak up on the click and barely click it. no matter how hard the thrash, always double check the torque on the rods after your done. i think it's more of a fail-safe method to go back through 1-8 after you're done, rather than double checking while you're on a particular journal. whatever is going to make you forget to torque a bolt may make you forget to double check it as well. if you don't put the pan on until you've re-checked all of them, it helps eliminate chance of error. it's never too much of a hurry not to double check. when youre thrashing, it's more the reason to double check.

i also have pretty hard standards on what bearings i put in it. everyone concentrates on the bottom width of the rod bearing, but i think now days more people run the hard v bearing (if you're not, you should be) and you need to look at the end to end clearance. a bearing shouldn't measure less than 2.503 or so. if it measures 2.498 or so, you can gently try to work the bearing back out, starting at the base of the bearing. the bearing needs to be able to clamp itself in the rod, and if it's less than 2.5, it's not clamping.

i know this isn't directly related to the root of this thread, but it's just a few successful methods i figured i would share. one point is right - if you find something that is working, stick with it. i learned bottom end directly and indirectly from tom conway, so that's where i got my training working for shelly.

i still stand by my statement there isn't a better alcohol rod out there than grp. yes they advertise here, but i'm also picky on who i endorse. maybe it's going to bite me one day, but with the grp's, if i don't feel anything funny during assembly, i'm gonna sit behind them and send them down track.

my .02

 

TOL as far as I know there appears to be two ways to make the rods we all use. Somebody else may want to amplify on this. The traditional forged rod such as Brooks, BME, C & A and the billet rod by GRP. The GRP rod is actually cut out of a sheet of aluminum. then machined to the correct finish. As far as which one is best is really more of a personal choice. If you get five racers together they will all have different stories on which rod has failed them and which one they swear by and nobody will switch from a rod that is not failing them. I believe most BAE motors now come with GRP rods.

 

I am in total agreement with you. Since the rod is cut with the grain in the aluminum sheet probably running along the length of the beam it would make the grain in the shoulder area running across the shoulder making it the weak point and that is where we always broke our GRP rods.