R.I.P. OG 5 bolt Grayhound

[Daniel Coop]

What happens when your camshaft is capable of turning higher RPM's than your stock rod is willing to. CL3 peaced out my Grayhound. Surprisingly, with little warning outside a loss of power followed by a slight rattling noise. RIP little guy. Some of your reusable parts will become​ donors for other rippers.

 

[Harquebus]

Yep, when these little engines go, it's usually a contained little 'burp' and not the fantasy-realm of parts exiting the block at supersonic speeds and injuring the user or innocent passerby.

I knew you actually meant crankshaft. :laugh:

 

[danford1]

CL3. I heard that was a nice cam. How did you like it? Did it have more low end tq than the stock cam?
Would you use it again but this time with a billet rod?
Many questions...

Danford1

 

[Havasu Dave]

Sorry to hear this. Is there any chance that the rod bolt failed or otherwise came loose and caused the destruction? I've learned on the high rev two strokes, it's a common point of failure, so the kart racers use expensive 100,000 pound bolts, and use them once.

Man, she really took out some aluminum. Glad none of it bit you.

 

[Mariah]

Another pull start grenade! Glad it missed you!

 

[Daniel Coop]

Yep, when these little engines go, it's usually a contained little 'burp' and not the fantasy-realm of parts exiting the block at supersonic speeds and injuring the user or innocent passerby.

I knew you actually meant crankshaft. :laugh:

No, I meant rod... The stock crankshaft would be good up to 9000RPM. It's the stock aluminum rod (bearing) that failed. The way it was explained to me by my engine builder buddy, is that after 6700RPM, the stock rod bearing gets starved for oil and spun on the crankshaft. I may have held it past that or right about there, a little too long, trying to prove a point by smoking a buddy by a bus length or more in a drag race. And you are right, it did let go in a rather unspectacular fashion. A piece of the case hit me in my leg, but even wearing shorts, it didn't leave a mark.

 

[Daniel Coop]

CL3. I heard that was a nice cam. How did you like it? Did it have more low end tq than the stock cam?
Would you use it again but this time with a billet rod?
Many questions...

Danford1

Yes, the CL3 is a nice cam and pulls well all the way towards 7000RPM. This one was unscathed and will be now used in my Hemi Predator with a .020 longer ARC billet rod and to replace the original CL1 in it currently. If you desire a high torque cam, I would recommend that OG CL1. It's only downside is that it's all done before 6000RPM.

 

[Davis]

No, I meant rod... The stock crankshaft would be good up to 9000RPM. It's the stock aluminum rod (bearing) that failed. The way it was explained to me by my engine builder buddy, is that after 6700RPM, the stock rod bearing gets starved for oil and spun on the crankshaft. I may have held it past that or right about there, a little too long, trying to prove a point by smoking a buddy by a bus length or more in a drag race. And you are right, it did let go in a rather unspectacular fashion. A piece of the case hit me in my leg, but even wearing shorts, it didn't leave a mark.

The stock rods don't have bearings did you machine one into it?

 

[Phil1958]

you ought to find all those aluminum block pieces and mig them back in place!

a new rod and some cleaning and i'll bet that engine will run just fine.

:thumbsup:

 

[cheezy1]

The rod came apart? Wow this couldn't be. I hear all the kart guys and others claiming they use stock rods all the time and never have issue and that billet is senseless. Must be a freakish random thing. (*sarcasm)

 

[Daniel Coop]

The rod came apart? Wow this couldn't be. I hear all the kart guys and others claiming they use stock rods all the time and never have issue and that billet is senseless. Must be a freakish random thing. (*sarcasm)

Lol! No, I was clearly warned about the rod being the weak link. Especially with that cam. Hey I'm still a little green... But I am learning. I'm now sold on the billet rods for anything over 6500rpm Seems like cheaper insurance than dealing with these issues. Yeah, Davis you're right. No bearing? I know I had never seen bearing inserts for a stock rod, but I guess I assumed they were built into the rod or something... Ignorance on my part, I stand corrected. I've only actually dealt with one rod at this point, and I had just shaved down a Hemi Crank to clearance the camshaft and only had the cap off. I managed to screw that up somehow to, because the stock rod ended up coming loose and ruined the crank a few weeks later. Crank journal was then undersized... Im learning something new about this shit everyday. No expert for sure, but ain't scared of trying, and sometimes failing.

 

[cheezy1]

Lol! No, I was clearly warned about the rod being the weak link. Especially with that cam. Hey I'm still a little green... But I am learning. I'm now sold on the billet rods for anything over 6500rpm Seems like cheaper insurance than dealing with these issues. Yeah, Davis you're right. No bearing? I know I had never seen bearing inserts for a stock rod, but I guess I assumed they were built into the rod or something... Ignorance on my part, I stand corrected. I've only actually dealt with one rod at this point, and I had just shaved down a Hemi Crank to clearance the camshaft and only had the cap off. I managed to screw that up somehow to, because the stock rod ended up coming loose and ruined the crank a few weeks later. Crank journal was then undersized... Im learning something new about this shit everyday. No expert for sure, but ain't scared of trying, and sometimes failing.

Wasn't directed at you really...just to point out to others that billet is the way to go. Because there are many that still tell new people that the rod will be fine...lol

 

[noseoil]

From the picture of what's left of the rod, it looks like it did get way over heated on the crank journal. Look at the surface of the rod & galling from the heat.

When this happens, the gap closes up from the higher heat, the rpm's can't keep enough oil in place with the stock rod dipper design. It gets too tight, oil is starved completely out of the space it usually goes (15 thousandths, or whatever the factory managed that day, becomes "0" or minus numbers in a very short amount of time), the heat continues to build until the turning creates enough friction to try to weld the rod in place on the crank. Since there's all that shit turning so fast without any oil, something breaks.

Parts, dollar signs & a new learning experience is created!

 

[Daniel Coop]

From the picture of what's left of the rod, it looks like it did get way over heated on the crank journal. Look at the surface of the rod & galling from the heat.

When this happens, the gap closes up from the higher heat, the rpm's can't keep enough oil in place with the stock rod dipper design. It gets too tight, oil is starved completely out of the space it usually goes (15 thousandths, or whatever the factory managed that day, becomes "0" or minus numbers in a very short amount of time), the heat continues to build until the turning creates enough friction to try to weld the rod in place on the crank. Since there's all that shit turning so fast without any oil, something breaks.

Parts, dollar signs & a new learning experience is created!

Best explanation I've heard yet!

 

[Havasu Dave]

Theoretical analysis via internet photos and groupthink are great troubleshooting tools. So respectively:

Can anyone explain how, if heat expansion on a rod journal/rod bearing on an aluminum rod will cause failure due to lack of lubrication, how an aluminum "billet" rod is somehow "not" going to expand at the same rate and suffer the same demise?

If nose oil's analysis (and I like it) is correct, the addition of billet aluminum rod would not have made a difference.

This is why I postulated above that a working rod bolt would yield the same physical outcome. As soon as thread torque is lost, the gap required to maintain oil tension between the journal and the "bearing" is lost, which manifests itself as lack of lubrication, then heat, galling, failure at the weakest point.

 

[noseoil]

The billet rod will expand at the same rate as the factory rod, you're right, since the material is about the same. The difference is in the size of the rod (massive top, bottom & center section), a real bearing insert & most important, the oil "splash" system or dipper. Even though there's no oil pump, the arc rod has a proper oil passage which, combined with the dipper & bearing insert, will force more oil into the bearing & journal area. If it heats up, it will fail, but the extra oil control helps keep things cooler, since the oil is helping with film strength (& cooling) in that area.

Take a look at the image in this link to see what I mean. Hope this makes sense.
https://kartfab.com/go-kart-engines-predator-212cc/arc-billet-connecting-rod-installation-guide

 

[Havasu Dave]

Thanks nose oil. I have listened to the acolytes gush on and on about a billet rod, never understanding why. A slightly beefier bearing surface and thickness of the rod is not going to be the difference between catastrophic failure at a journal, and a smooth 9000 RPM acceleration in a splash system.

What I did NOT know, was these rods came with a bearing. "That" is the difference, not the fact that it's billet. I suppose a forged rod would not be cost-effective.

The addition of a bearing makes all the difference. Thanks for the education. :thumbsup:

 

[Phil1958]

that engine oil comparison link that was posted a few days ago covers this. it is a good, but long read.

he even covered rod bolts stating that engine power has no bearing on rod bolt requirements, they are
determined by the deceleration of the piston/rod mass as the piston hits tdc on the exhaust stroke.

failures like the one described in this thread are caused when the applied journal load exceeds the oil's film
strength in PSI.

cool.

:thumbsup:

 

[62civa]

Hi Guys,
Question here from a newbie. I only ask because I can see how much knowledge you guys have here. I noticed that you have an aftermarket aluminum plate over the top of the engine. It looks to be about 1/8" or maybe 3/16" thick material. Is this heavy gauge aluminum part used to strengthen the case/head assembly or is this used to provide a shield (like a safety bell housing on a race car) if the rod lets go under your seat? That aluminum plate seems too thick if it were only being used as a place to mount a throttle cable.
Ron

 

[Daniel Coop]

Hi Guys,
Question here from a newbie. I only ask because I can see how much knowledge you guys have here. I noticed that you have an aftermarket aluminum plate over the top of the engine. It looks to be about 1/8" or maybe 3/16" thick material. Is this heavy gauge aluminum part used to strengthen the case/head assembly or is this used to provide a shield (like a safety bell housing on a race car) if the rod lets go under your seat? That aluminum plate seems too thick if it were only being used as a place to mount a throttle cable.
Ron

That's just a standard ARC top plate/throttle station made for all (this was a Grayhound) clones. I don't think it's meant to strengthen the case, and it's​ not attached to the head in anyway. It did work as a shield a little bit, but is not designed as such, and once again, it's demise was rather unspectacular. The top plate is also used to mount a fuel pump. ARC doesn't make anything chincy.