Grp Rods Pulled Threads

Dave, sorry to hear about the clearcoat problem, the new color sounds good, can't wait to see the pix.

As for the threads, what you are referring to is the thread height. Threads are designed so that the main point of contact is in the pitch diameter area, the major and minor have to clear or you will get galling and parts will not mate.

Threads have different classes wich controls manufacturing tolerances and amount of contact area. Class 3 is the most common in aerospace and yields higher strength than the lower classes, 1 and 2. A common problem I've seen in non-aerospace is the mixing of classes, i.e. class 3 bolt into a class 1 nut, a bad design.

Imho, any shop that threads parts should be checking them. Just like there is a no-go gage for threads, there is also a go gage that is the minimum size for the specified class. The go gage must easily screw in, without force, the minimum thread depth needed. A shop that doesn't check their threads will have lousy quality and I wouldn't purchase from them.

 

grp rods with loose threads in the rod


NOTE: Torque wrench was o.k.
NOTE: Can check torque in backing rod bolt out with digital torque wrench
NOTE: Just on this website alone, there has already been one person who got a set of new grp rods that the threads in the rod did not have enough contact with the rod bolt causing the rod bolt to be loose in the rod.
NOTE: Take rod and torque bolt to infinity and I agree, rod bolt will break before the threads will give.
NOTE: Do you want to experiment? Rods not cold in the motor when the motor is running... Take rod....torque to 90 lbs...check as advertised with stretch gauge...put in oven...set oven to 90 degrees...leave in oven for 3 min and remove and let cool on its own..and then check torque with digital torque wrench taking the rod bolts loose. It's far from 90 lbs of torque. 3 out of 4 rods were 25-40 lbs of torque to remove rod bolt.
NOTE: Please xplain how very little thread contact with the rod bolt doesn't have anything to do with this problem.
NOTE: To my knowledge this is one of the only rods that the threads in the rod are that loose to the rod bolt. Cut thread, rolled thread, upside down thread, inside out thread, still comes down to thread contact with the rod bolt
Any ideas???????

 

Paul pretty well summed the thread deal up: With the internally threaded part of the rod, I'd feel much more comfortable with a thread that was NOT CUT with a conventional tap. The thread forming process does not cut into the grain structure of the aluminum, rather, it displaces the material, thus leaving a much stronger thread. As to the length of rod bolts, there must be a length/strength ratio, that once exceeded has no discernable increase in strength of the clamping force. I'd go along with the GO/NO GO guage, err on the side of caution.
Henry

 

I have a lot to say about this subject but I don't have a lot of time right now. I will come back later with my views. What we deal with in TAFC and BAD are some of the most extreme conditions that a connecting rod will see. 10,200-10,500 RPM is common almost every lap. In order for a rod to live, the clamp load holding the cap on the body has to be greater than the tension load pulling it apart. If the tension load is greater it will start stretching the bolts and cause the treads in the aluminum rod to fail in fatigue. The fatigue life of aluminum is less than the steel bolt so the aluminum fails first. The best way to prevent this is to make sure the clamp load is greater than the tension load. A torque wrench is not a very effective tool for checking clamp load but it is what we are all used to. According to the studies (NASA) I have read a torque wrench is only slightly more accurate than tightening by hand (with a experienced operator) the next in line was the torque angle method, then checking fastener stretch and finally actually checking the clamp load with a load cell. A typical tension load for a TAFC at 10,000 rpm is around 32,000 lbs. The clamp load on 1 bolt is 16,500 lbs at .0065 stretch. Total for both bolts is 33,000 lbs. No room for error. My suggestion is to verify your torquing method periodically with a bolt stretch gage.

Thanks, I'll be back
Brian Scollon
GRP Connecting Rods

 

Good info, can't wait for more.

 

Anybody else put rods in the oven....see VHBR post on page 4.

Try it you might learn something!!!!

 

Rod discussion

Before Brian gets back too us. No one has mentioned the stroke of the engine. TAD's have small stroke engines. TAFC's generally longer stroke's. I believe this will also have an effect. I believe you will have problems with a 4.500 stroke and 10,000 plus. Brian, what is your opinion on this?
My vote is GRP's are the absolute best rod ever.

 

But your from canada- can you vote? kidding, aah

 

They told me the same thing, and I doubted them, so i also went through the exercise.
The bolt broke at around 230 ft/lbs of torque.

 

GRP Rods and thread failure

I'm a Pro Mod racer from middle North Carolina. I have been running Pro Mod since 1990. We run Gene Fulton prepaired engines 706 cubic inches that turn about 8300 rpms we have done our own maintenance for 12 of these 16 years. I have used Rods such as Bill Miller, Venolia, MGP, & GRP. Here is my story. Last year at Norwalk (2005) we made it in the last session with a 6.26 thought everything was fine until we got back to the pit and found the motor with the rods knocked out they had 10 runs on them. After disassembly I sent 3 of the Rods #3 #4 & #8 from the motor #3 being the one broken to an Aero Space engineer in TN. for analysis. Rod #8 was untouched and Rod #4 was next to the broke one. When we took the motor apart there was 1 Rod bolt laying in the oil pan with the threads still on it. Here is what the engineer had to say. After checking all the pieces he concluded that the minor thread diameter was .389 and should have been .366 the minor diameter was .023 over sized leading to a 28% loss of strength. He went on to say that 90% of their threads were incorrect. Also GRP uses ARP 2000 bolts he said they had seen a 3/8 ARP2000 bolt fail @ 55 ft lbs of torque. MGP uses A-1 rod bolts which is a true Aero Space bolt with unsurpassed quality control.

 

we run Mike's rods also
very nice piece
I like his rod cap serrations
not one problem yet and we was plenty hard on it getting this new combo to work
lots of shake and hitting the rev limiter a few times

Ps. Thanks Jeff you were right

 

So now there are at least 3 teams on this site that have experienced GRP rods with thread engagement problems,(aka)rod bolt laying in the pan with threads around it. Do you suppose that all 3 of us didn't check the thread stretch or torque correctly or put the right amount of oil on the rod bolts? ...WHAT'S THE ODDS OF THAT!!!!!!!!!!!

 

we had the threads pull out of grp rods, but we think it was because th rod cap split after not getting on the clutch at the end of the run. when the cap split, it gave the crank room to build up speed before it hit the cap the next time around, puling the bolt out with the threads still on them. i don't think it was the rods fault

bryan brown

 

We spun 3 rod bearings due to an oiling issue on a 5.59 at Pomona. The bearnings were gone, but the rods stayed on the crank. I wouldn't have believed it if I didn't see it with my own eyes.

And yes, they were GRP's.

 

Still waiting to here from Brian on the GRP story. Pulled threads on a very Fat match race setup, and no it did not see 10,000-10,500......never got over 8800 EVER during the run. Did I mention MATCH RACE. Why kill it for a match race.
Still want to hear "The Rest of the Story"

 

Update
Fixed our rod problem!!!!
SWITCHED BRANDS!!! No more problems!
What do you think it was ! !? ? ? ? ?

 

what brand do you now run??
inquiring minds want to know...