ARC Billet Rod Broke!

[BWL]

[MENTION=43506]trinik7597[/MENTION], no, I didn't torque again or check after that NR 230 cam went bad. Maybe that's where the problems started. Thx, man.
[MENTION=1406]minibikin'[/MENTION]. Na, man, I was was at full bore barreling straight toward the dam. Fortunately it blew about a mile before the dam or I'd be dead. Shows how good the casting on the BS motors are. There may be some unseen damage. My new powerhead should be in today.

I decided to buy a Champion Power Equipment replacement engine again. The one I had worked well and never failed. I used parts off it for the BS build, so it wasn't running at all. It was a long more time efficient to buy another one, knowing I have plenty of Champion part parts.

 

[OND]

[video=youtube_share;owahpOeLYaw]https://youtu.be/owahpOeLYaw[/video]

 

[BWL]

I was under the impression that these rod bolts were basically one time use. Not that you can't use them again, but shouldn't. Any fastener that is torqued obviously stretches and re using it can result in failure as well.


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The problem with that assertion is that it blatantly violates the instructions given by ARC themselves. They say torque outside the motor to seat the bearings. then torque them again to install in the engine. Jody even put together a video where he shows exactly how he does this. OND just posted that video above.

 

[minibikin']

Well, I for one really appreciate the documentation. I'm putting together an engine for someone right now and you're making me triple check every step![emoji23]


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[trinik7597]

Stretchable bolts .. 2 times max .. you see where i am going

 

[Moto Walt]

The bolts the ARC rod come with are TTY? No way huh? Pretty sure they are ARP.

 

[minibikin']

The bolts the ARC rod come with are TTY? No way huh? Pretty sure they are ARP.

And you reuse yours right? [emoji849] I usually break mine in without oil too...


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[danbur55]

BWL you say you torqued to 150 inch pounds, in the ARC video he says he is going to 170 maybe there is a discrepency there

 

[OND]

I think I read back a bit that BWL used moly lube instead of 30w engine oil... 150 in lbs with moly lube or 170 in lbs with 30w engine oil.

 

[minibikin']

I think I read back a bit that BWL used moly lube instead of 30w engine oil... 150 in lbs with moly lube or 170 in lbs with 30w engine oil.

Correct.


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[danbur55]

Curious if moly affects torque vs oil as far as grip. Also was it dry moly or grease. I am not familiar with characteristics of these when applying torque to two dissimilar metals. Thinking out loud that moly grease may not squish out enough and act as a lube that allows it to move instead of holding steady

 

[Moto Walt]

And you reuse yours right? [emoji849] I usually break mine in without oil too...


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Never taken a rod out of an engine so I've never reused one.

 

[danbur55]

After doing some searching I found several references to the different moly and oil torque specs although not directly from ARC. My apologies for the off the cuff post earlier. Thanks for understanding and have a great day

 

[OND]

Not a problem Dan....all help is appreciated ! :thumbsup:

 

[TheDullCarbide]

How many other people have had an ARC rod bolt back out on them? This seems like a first. How could the same exact procedure work for so many engines, but not give poor BWL a break. (pun intended if you get it)

 

[noseoil]

I think it comes from running wide open against an unforgiving pull (water) to find stuff that will break. This is basically like building race motors, finding the weakest part, replacing it & then finding the next weak part. At "normal" rpms & torque limits the motor is fine. Start adding more & more loading & things begin to happen much faster.

That motor on a mini bike might have lasted for years, since it won't get ridden that hard for long lengths of time usually. I guess riding on the freeway would do the same thing & finding things which would break & can be done the same way. Not so sure I'd want to ride next to a large truck hauling goods on a mini bike at 75 mph for 50 or 100 miles....

 

[TheDullCarbide]

I think it comes from running wide open against an unforgiving pull (water) to find stuff that will break. This is basically like building race motors, finding the weakest part, replacing it & then finding the next weak part. At "normal" rpms & torque limits the motor is fine. Start adding more & more loading & things begin to happen much faster.

That motor on a mini bike might have lasted for years, since it won't get ridden that hard for long lengths of time usually. I guess riding on the freeway would do the same thing & finding things which would break & can be done the same way. Not so sure I'd want to ride next to a large truck hauling goods on a mini bike at 75 mph for 50 or 100 miles....

So running WOT at a torque-y 6000rpm is alot harder on the engine than 8000rpm in pulls. That makes total sense, but how does that contribute to a bolt backing out? It's not like engine torque affects the strain on that bolt, or does it?

 

[SAS289]

I think it comes from running wide open against an unforgiving pull (water) to find stuff that will break. This is basically like building race motors, finding the weakest part, replacing it & then finding the next weak part. At "normal" rpms & torque limits the motor is fine. Start adding more & more loading & things begin to happen much faster.

That motor on a mini bike might have lasted for years, since it won't get ridden that hard for long lengths of time usually. I guess riding on the freeway would do the same thing & finding things which would break & can be done the same way. Not so sure I'd want to ride next to a large truck hauling goods on a mini bike at 75 mph for 50 or 100 miles....

I completely agree. What he's doing is like a 600 pound guy getting on his souped up 212 powered mini bike and repeatedly riding full out up a steep grade that lasts for miles.

At least part of the issue is the load placed on the engine. And there is no gearing! It's no wonder the engine is stressed.

 

[FirePowerMinis]

Speculation Ahead:
Rod bolt torque is just the easy way to get a particular amount of stretch/elasticity. Lubricant significantly changes the formula.
TTY bolts are mathed-out to do their job once. ARC likely added overage on strength, but if over stretched even once, they will not maintain clamping. Maybe they have an overall length spec?
I'm not a fan of aluminum rods for high-rev endurance applications(not that there are a lot of options). Thermal cycling of the rod may be an issue, expanding and constantly changing the clamping/stretch?
And, big guy may want to look at a big block? Steel rod GX390 maybe?

 

[Raskin]

.i love reading these threads ..thinking of high perfomance stuff I'll never do but love reading about....yeah new bolts i say w b way to go on high perf builds...these cheaply made engines w alot of vibrations also would loosen up things in high stress apps i guess..bigger eng like FPMinis said so you don't hafta drone along at high rpms w a little engine w less torque seems logical....best of luck..i mean you just wanna fish yeah..:shrug: