About time..........................

[Tom Foley]

I lost a rod in a Nova Rossi 46 DD which appears to have started to crack at the oil hole then gradually egg shape the bushing bore till it broke away . Bushing was intact as was the rest of the rod . Plenty of lube and no signs of a lack of lube . The engine had maybe a gallon of fuel through it . Very disappointing .

 

[Jim Allen]

I lost a rod in a Nova Rossi 46 DD which appears to have started to crack at the oil hole then gradually egg shape the bushing bore till it broke away . Bushing was intact as was the rest of the rod . Plenty of lube and no signs of a lack of lube . The engine had maybe a gallon of fuel through it . Very disappointing .

Tom,

The unknown factor here is what metallurgy & what heat treating processes were used to make the rod???????

JA

 

[Tom Foley]

Yes , stock NR rod , aluminum with nice serrated bushing bore etc , I think I will at least try to radius the edges of the oil hole , maybe that will do something to stop further cracking in the new rod .

 

[Jim Allen]

Yes , stock NR rod , aluminum with nice serrated bushing bore etc , I think I will at least try to radius the edges of the oil hole , maybe that will do something to stop further cracking in the new rod .

We have not had any rod problems with the long stroke .45 pylon racing engines thus far. Our data logger tells us that the engine reaches 29,000+ RPM in the air down the straights with a drop to 28,500- RPM around the turns. On the test bench we push the engines to 29,300+ RPM without any rod problems. However, at 31,000 the connecting rod begins to show signs of wear in a short amount of running time. At 32,000 the connecting rod will fail in a short amount of time. All of these rods are made of 7075-T 651 aluminum with #510 phosphor bronze bushings. The test run fuel supply amount is 14 ozs. We use a special tolerance amount in the bottom end with a single .032" oil hole drilled at an angle from the top of the bottom hole, off to the side. Our extensive testing at high RPM's tells us that the metallurgy & clearance in the bottom end are critical.

Jim Allen

 

[Glenn Quarles]

That too bad Tom! This is a very rare thing to have one of those rods fail! In all the time I sold them I only heard of a couple (2 or 3 if I remember right) that failed and each of those happened a few runs after soon other failure that put major stress on the rod. At least one happened early on before they changed the piston taper and after a bunch of full throttle piston sticks the rod bottom end did just as you described. The other ones happened after the early intake crank failures. I have never heard of a single rod that has failed as a result of normal engine running so I'm not thinking it is a design or materials problem. Ron may have further insite since I have been away from it for the past year.

GQ

 

[Andy Brown]

That is the most common place for an aluminum rod to fail when it has an oiling hole at the top. I've seen it happen on all brands of rods. The crank pin is acting like a splitting wedge and the hole at the top, along with the long groove that runs up the beam of the rod, provides a weak point that is full of stress risers.

I've seen a lot of rods that look like they were run through the log splitter.

Jim Allen is correct. The best place for the oil hole(s) is off center line. Maybe the major engine manufactures will figure that out.....someday.

 

[Tom Foley]

That is the most common place for an aluminum rod to fail when it has an oiling hole at the top. I've seen it happen on all brands of rods. The crank pin is acting like a splitting wedge and the hole at the top, along with the long groove that runs up the beam of the rod, provides a weak point that is full of stress risers.

I've seen a lot of rods that look like they were run through the log splitter.

Jim Allen is correct. The best place for the oil hole(s) is off center line. Maybe the major engine manufactures will figure that out.....someday.

Not only that the rod has a groove leading to the oil slot creating a target lol ! Wait ...you said that already !!!

 

[Tom Foley]

That too bad Tom! This is a very rare thing to have one of those rods fail! In all the time I sold them I only heard of a couple (2 or 3 if I remember right) that failed and each of those happened a few runs after soon other failure that put major stress on the rod. At least one happened early on before they changed the piston taper and after a bunch of full throttle piston sticks the rod bottom end did just as you described. The other ones happened after the early intake crank failures. I have never heard of a single rod that has failed as a result of normal engine running so I'm not thinking it is a design or materials problem. Ron may have further insite since I have been away from it for the past year.

GQ

Glenn , literally just running around the course ,upon disassembly the bushing slid right off the crankpin still round with the pieces of the rod sticking out the new windows in the case .

 

[dwilfong]

Tom just be glad it was not the 2.5 Merc..................I have dreams about it all the time.........LOL

 

[Tom Foley]

Tom just be glad it was not the 2.5 Merc..................I have dreams about it all the time.........LOL

 

[Andy Brown]

Tom just be glad it was not the 2.5 Merc..................I have dreams about it all the time.........LOL

Now that rod failure cost some big money!

 

[Danny King]

Dam that guy in the picture is small. Must be the angle.

 

[Brad Christy]

Andy, others,

For the 7075 rods I've made for Picco engines, I've always put two oil holes at 4 and 8 o'clock, with none at 12. I have had no failures to my knowledge (feel free to correct me if I've forgotten) since moving to that configuration (initially, they were at 2 and 10, with some failures due to ripping the bottom lobe apart through one of the oil holes) . Upon receiving ALOT of requests for an oil hole at 12 o'clock, I finally conceded and added it, but have still had no problems that I recall, with the two oil holes at 4 and 8, and a slight groove in the bushing, front to back, at 12 o'clock to allow for distribution of the oil? I'm not here to promote my parts, I'm just wondering about the need for the top center oil hole. I can definitely see where it would put a fracture initiation point right where the pressure is highest.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

 

[Andy Brown]

Andy, others,

For the 7075 rods I've made for Picco engines, I've always put two oil holes at 4 and 8 o'clock, with none at 12. I have had no failures to my knowledge (feel free to correct me if I've forgotten) since moving to that configuration (initially, they were at 2 and 10, with some failures due to ripping the bottom lobe apart through one of the oil holes) . Upon receiving ALOT of requests for an oil hole at 12 o'clock, I finally conceded and added it, but have still had no problems that I recall, with the two oil holes at 4 and 8, and a slight groove in the bushing, front to back, at 12 o'clock to allow for distribution of the oil? I'm not here to promote my parts, I'm just wondering about the need for the top center oil hole. I can definitely see where it would put a fracture initiation point right where the pressure is highest.

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

Model Machine And Precision LLC

Many years ago I was questioning Dave Richardson, of RPM rod fame, about the hole at 12 o'clock. He said it was there to "serve as a vent, not for oil to get in".

The way I see it is that in low nitro (20 -30%) engines which is the major market for .21 engines with aluminum rods, the hole at 12 o'clock is not an issue, but when the engine is used with high nitro ans high compression the hole at 12 becomes an issue.

However it is relatively rare to break an aluminum rod these days.

I have use the stock Picco 45 rod with the single hole at 6 o'clock and never had an issue.

Heat is the biggest enemy for 7575. At 300 degrees F it's strength is reduced to 50% of it's room temp strength. A little too much friction and skinny fuel/lube flow and that 300 degree temp can be reached in a heart beat.

 

[dave roach]

Andy

With the nitro -alc going into the crank case and being cold would that not keep the bottom end from over heating.

 

[Jim Allen]

"Heat is the biggest enemy for 7075. At 300 degrees F it's strength is reduced to 50% of it's room temp strength. A little too much friction and skinny fuel/lube flow and that 300 degree temp can be reached in a heart beat." This is a true statement! In fact 2024, would be stronger at 300*F. Maybe some questions to be asked are; can the friction & the resultant heat be reduced to a safe level with metallurgy, a particular radial clearance number, a lubricant in the fuel, the amount of lubricant in the fuel, or all of these things? Is there any engine induction system (front or rear) that favors good bottom end lubrication? How many engines are running at WOT (29,000) from the start of the race to the end of the race?

JA

 

[dwilfong]

I had some time to talk with Andy at the last race and induction systems where one thing we talked about.

There is a reason he used the system he did on the MAC engs.

May be he will share some insight on this ???????????

As for my self my finger is planted in the trigger all the time.........................LOL

 

[dwilfong]

Well back at it need a break from the Vector this week. That and after doing a few eng for some friends I got the itch.

Started to look at the VAC 1.05 and did a full disassemble of the eng.

Low and behold found the wrist pin locked up..............................

Looking at the rod that broke and the new rod I have. The oil holes in the pin boss are different.

The new rod has much LARGER holes.

So I will start over again on my quest .........................

Also found a billet piston from the first run Scott made me that was 3g lighter than the last one I used.

Rebalanced the crank also for the weight change.

So may be the 3rd time will be the charm.

I will use liquid Devcon to fix the hole in the block this week.

HERE WE GO AGAIN...........................................more plugs and nitro to buy..................

 

[Ain'tSkered racing]

Well well that didn't take long coming back over.. hahaha

 

[dwilfong]

It's all Julian's and your fault................You two are a bad influence on me.............