Using a stock animal crank...

spincycle

spincycle

Member
Wondering out loud on anyone's thoughts on using a stock animal crank in a limited modified set up...more specifically, if the stock crank design isnt capable of handling 8000+ rpm...like maybe starts having a little out of balance or wobble condition at those high rpms? Something is causing the rod bolts to come loose even after just 1-2 races...I've been told the ARC beefy billet stock length rod is designed to take up to 10,000+ rpm, is that with s stock animal crank, or with a billet ARC crank? I run mine at no more than 8200-8300 and keep having loose rod bolts after 1-2 races...and there is no issue with the torque wrench/bolt torque...I do torque the rod bolts wet at 110-140-170...it seems there is a weak link somewhere...trying to diagnose what/where...thx! dr
 
sounds like you have a crank issue. limited mod animals do 9000+ all day without issue ARC crank is illegal in that class. would turn my flathead stock crank to 9700 no problem. I've herd the arc crank braking before a stock will.
 
Have you checked rod stretch for correct bolt torque?

Or checked bolt length after finding bolts loose?

Most likely answer is something between the mating surface as the rod is torqued.


Arp will have specifications for the amount of stretch rod bolts will need to correctly support the loads required.

What are you calling limited modified?

Lots of 85-9000 rpm engines with stock cranks.

I believe somewhere in recent years, animal cranks received heat treatment, making these preferred for use in high rpm engines
 
Shouldn't be a problem turning them 9000.+ The newer forged cranks can handle it just fine. The balance on them leaves a bit to be desired, however. If you notice, they are static balanced at the counterweights by grinding to lighten them. If you simply weigh the cranks, they are all over the place on overall weight. I actually just had a customer call yesterday with a concern about the appearance of the grinding on his stock class crank. I suspect it was one of the lighter cranks that the factory has ground more off to balance it. Keep in mind that when you use an aftermarket rod and aftermarket piston (especially big bore) that the balance of your rotating assembly will have changed dramatically. It would be a good idea (especially since you're having issues) to get the rotating ass'y balanced.
If you're shaking rod bolts loose that quickly, something is amiss. Too much clearance on the big end of the rod (bearings) can cause this. You'll notice it by the hammering look on the bearings themselves. Obviously after the rod bolts have shook loose, you'll be looking at the damage caused by that.
FWIW, I wouldn't be re-using the same rod or rod bolts after they came loose. The stress on the parts would be unbelievable and render them useless at that point, in my opinion. Rod bolts should only be torqued a few times. Continual stretching of the bolts weakens them over time.


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🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
34 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
 
i will go down the rabbit hole of what lube did you use? oil vs a moly paste changes the torque values required. And i agree with Brian once rod bolts have loosened themselves it's all trash order a new one
 
Finally had time today to get the motor apart...here is the culprit....
20230718_143156.jpg
 
As I mentioned before this rod was on its third show, the rod bolts were torqued wet to 170in/lbs, motor was turning approx 8400rpm...and then CLAPOWIE! It's come to the point that checking rod bolt torque may need to be added to the WEEKLY maintenance schedule...😉🙂
 
CarlsonMotorsports said:
Shouldn't be a problem turning them 9000.+ The newer forged cranks can handle it just fine. The balance on them leaves a bit to be desired, however. If you notice, they are static balanced at the counterweights by grinding to lighten them. If you simply weigh the cranks, they are all over the place on overall weight. I actually just had a customer call yesterday with a concern about the appearance of the grinding on his stock class crank. I suspect it was one of the lighter cranks that the factory has ground more off to balance it. Keep in mind that when you use an aftermarket rod and aftermarket piston (especially big bore) that the balance of your rotating assembly will have changed dramatically. It would be a good idea (especially since you're having issues) to get the rotating ass'y balanced.
If you're shaking rod bolts loose that quickly, something is amiss. Too much clearance on the big end of the rod (bearings) can cause this. You'll notice it by the hammering look on the bearings themselves. Obviously after the rod bolts have shook loose, you'll be looking at the damage caused by that.
FWIW, I wouldn't be re-using the same rod or rod bolts after they came loose. The stress on the parts would be unbelievable and render them useless at that point, in my opinion. Rod bolts should only be torqued a few times. Continual stretching of the bolts weakens them over time.


-----
🏁Thanks and God bless,
Brian Carlson
Carlson Racing Engines
Vector Cutz
www.CarlsonMotorsports.com
Carlson Motorsports on Facebook
www.youtube.com
34 years of service to the karting industry ~ 1Cor 9:24
Linden, IN
765-339-4407
bcarlson@CarlsonMotorsports.com
Click to expand...
What's all involved in getting the rotating assembly balanced? Typical cost? Thx! DR
 
You would need to send the rotating assembly, flywheel, and starter nut to someone that offers crank balancing services. (Preferably someone familiar with balancing single cylinder engines.) Some shops will want the clutch or drive gear as well. Cost will vary by the amount of time that is spent balancing and the amount of weight needed. We do not have a crank balancer in our shop or offer that service to individuals. I do have use of a balancer but even then I have the fellow who owns it do the balancing for me and only for engines built by me through our shop.
 
I'm thinking there is something Wrong. there is a lot of debate surrounding crankshaft balancing especially single cylinders. lots and lots of people run Limiteds, Opens etc, never balanced a crankshaft, and do not have the issue of rod bolts coming loose all the time. something is NOT right as in bent, misshapen, out of aignment or excessive tolerances IMO.
 
You are going through the steps they suggest to seat the cap/rod and torquing it 2-3 times before install? I don't remember the exact procedure but i recall them wanting you to do that a couple times
 
racinnut15xm said:
You are going through the steps they suggest to seat the cap/rod and torquing it 2-3 times before install? I don't remember the exact procedure but i recall them wanting you to do that a couple times
Click to expand...
Starting with the rod bolts oiled, first go to 110, then 140, then 170....I've also been told to check edges of the bearing inserts, sometimes they have a real small edge on them that needs To be smoothed with some real fine emery cloth so the ends butt up to each other properly...
 
spincycle said:
Finally had time today to get the motor apart...here is the culprit....View attachment 29515
Click to expand...
Upon closer examination...the rod bolts that came loose has some aluminum threading in its own thread...like it pulled the threads from the bolt hole in the rod....is this a sign of something gone wrong? Like maybe the rod bolts had stretched, maybe from something gone wrong during the torquing process...or maybe some sort of defect in the threads of the rod? Sorry if I seem to be beating this one pretty hard, just trying to figure out what/where/how this happened, as to hopefully avoid it ever happening again...
 
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