Automotive question(bent connecting rod?)

Christopher561 · Post by **Christopher561** » Thu Oct 07, 2004 11:34 pm

What does a bent connecting rod mean? What would happen if a connecting rod becomes bend and why would it become bent? These are questions My teacher in Automech has asked us to look up and I cant find anything on it. just that a bent connecting rod would make your bearing wear differently

downhill · Post by **downhill** » Thu Oct 07, 2004 11:37 pm

Christopher...I don't want to do all your homework for you so lets start by asking a few questions...

First, do you know what a connecting rod is?

ScottE · Post by **ScottE** » Thu Oct 07, 2004 11:37 pm

The rod that connects the Piston to the Crankshaft is called the Connecting rod.

Could become bent due to detonation or due to poor lubrication. Usually due to detonation though.

Christopher561 · Post by **Christopher561** » Thu Oct 07, 2004 11:37 pm

downhill wrote:Christopher...I don't want to do all your homework for you so lets start by asking a few questions...

First, do you know what a connecting rod is?

yes, It connects the piston to the crank shaft.

The_Lurker · Post by **The_Lurker** » Thu Oct 07, 2004 11:38 pm

you will always get a bent rod if you hydro lock the motor at high RPM.

blow a head gasket and suck coolant into a cylinder, then when it tries to compress, well liqued won't compress, air/fuel will.

so something has to give, and the rod is usually the first to go. i have built many Ford Cosworth engines. had one guy running 40psi boots on the engine. he blew his head gasket and hydro'd a cylinder. i have never seen a piston/rod/block so utterly destroyed.

brembo · Post by **brembo** » Thu Oct 07, 2004 11:38 pm

ScottE wrote:The rod that connects the Piston to the Crankshaft is called the Connecting rod.

Could become bent due to detonation or due to poor lubrication. Usually due to detonation though.

Or hydraulic lock. Marine engines fall to that alot.

downhill · Post by **downhill** » Thu Oct 07, 2004 11:38 pm

Scott covered the next part.......

So give this a thought, what happens if the rod is bent?

Christopher561 · Post by **Christopher561** » Thu Oct 07, 2004 11:40 pm

downhill wrote:Scott covered the next part.......

So give this a thought, what happens if the rod is bent?

The piston doesnt make it fully to TDC? and the air fuel doesnt get compressed like the other pistions would.

brembo · Post by **brembo** » Thu Oct 07, 2004 11:42 pm

Christopher561 wrote:The piston doesnt make it fully to TDC? and the air fuel doesnt get compressed?

Roger....and it would be not all the way compressed. It would reach a new TDC of sorts, in synch with the other cylinders. But at a diminished compression and .......

its yer homework

downhill · Post by **downhill** » Thu Oct 07, 2004 11:43 pm

Christopher561 wrote:The piston doesnt make it fully to TDC? and the air fuel doesnt get compressed like the other pistions would.

'

Of course there is more...like that bearing you mentioned..You can see how that happens also.

So, you also understand then how it could become bent?

Christopher561 · Post by **Christopher561** » Thu Oct 07, 2004 11:44 pm

brembo wrote:Roger....and it would be "all the way compressed" It would reach a new TDC of sorts, in synch with the other cylinders. But at a diminished compression and .......

its yer homework

wow. Just a little bit of thinking and I kinda answered all my own questions. I guess I just needed a little bit of interviewing someone :-D. In my dictionary thats doing my homework.

The_Lurker · Post by **The_Lurker** » Thu Oct 07, 2004 11:44 pm

Christopher561 wrote:The piston doesnt make it fully to TDC? and the air fuel doesnt get compressed like the other pistions would.

don't forget about skewed geometry piston to cylinder.

Christopher561 · Post by **Christopher561** » Thu Oct 07, 2004 11:45 pm

downhill wrote:'

So, you also understand then how it could become bent?

Yes I believe so. like air and fuel can compress. so lets say you have a blown head gasket and coolant get into your cylinder. Coolant doesn't compress. so this would bend your connecting rod?

ScottE · Post by **ScottE** » Thu Oct 07, 2004 11:47 pm

brembo wrote:Or hydraulic lock. Marine engines fall to that alot.

Not these babies. Gas Turbine ]http://www.globalsecurity.org/military/ ... ilton2.jpg[/IMG]

brembo · Post by **brembo** » Thu Oct 07, 2004 11:47 pm

[quote="The_Lurker"]don't forget about skewed geometry piston to cylinder.
]

Skewed to some extent....I dunno the dimensions of pistons all that well. I'd think a shorter skirt would allow for some bending and not ream the cylinder(correct me if I'm wrong). It would likely play havoc with the oil passages right?

brembo · Post by **brembo** » Thu Oct 07, 2004 11:49 pm

Christopher561 wrote:Yes I believe so. like air and fuel can compress. so lets say you have a blown head gasket and coolant get into your cylinder. Coolant doesn't compress. so this would bend your connecting rod?

Yep.

Top fueler dragsters run so much fuel one of thier biggest concerns is hydro(in this case nitro methane) lock on the cylinders. Each plug gets about 40 amps pumped thru it, melting them in the process. The engines are actually dieseling by the end of the run. To shut em down they cut the fuel.

The_Lurker · Post by **The_Lurker** » Thu Oct 07, 2004 11:51 pm

brembo wrote:Skewed to some extent....I dunno the dimensions of pistons all that well. I'd think a shorter skirt would allow for some bending and not ream the cylinder(correct me if I'm wrong). It would likely play havoc with the oil passages right?

in the cycle halfway between TDC and BDC your piston will be shoved more to one side of the cylinder compressing the piston rings and scraping the cylinder with the piston. seen this with rods that were only mildly bent.

downhill · Post by **downhill** » Thu Oct 07, 2004 11:51 pm

Christopher561 wrote:Yes I believe so. like air and fuel can compress. so lets say you have a blown head gasket and coolant get into your cylinder. Coolant doesn't compress. so this would bend your connecting rod?

Sure that would be one way. Others are listed above.

There is a point where the rod just can't take more pressure put on it and it bends to compensate.

You get enough pressure on it and it just doesn't bend, it breaks.....

Been there and done that....I once knocked a hole in the side of an engine block from a broken rod..My old 56 Ford F100.......I felt terrible....

Christopher561 · Post by **Christopher561** » Thu Oct 07, 2004 11:51 pm

brembo wrote:Yep.

Top fueler dragsters run so much fuel one of thier biggest concerns is hydro(in this case nitro methane) lock on the cylinders. Each plug gets about 40 amps pumped thru it, melting them in the process. The engines are actually dieseling by the end of the run. To shut em down they cut the fuel.

And also If you have bad rings on the pistson I believe they are called? Oil could make its way into the cylender and Oil doesnt also compress.

ScottE · Post by **ScottE** » Thu Oct 07, 2004 11:52 pm

metallurgy 101.

ScottE · Post by **ScottE** » Thu Oct 07, 2004 11:53 pm

Christopher561 wrote:And also If you have bad rings on the pistson I believe they are called? Oil could make its way into the cylender and Oil doesnt also compress.

No, but it burns sort of so it's not going to stick around very long.

The_Lurker · Post by **The_Lurker** » Thu Oct 07, 2004 11:54 pm

Christopher561 wrote:And also If you have bad rings on the pistson I believe they are called? Oil could make its way into the cylender and Oil doesnt also compress.

not likely. you'll get more a oil mist in the cylinders. not enough to cause a lock, but usually enough to give a cool James Bond style smoke screen as you pull over cursing.

brembo · Post by **brembo** » Thu Oct 07, 2004 11:54 pm

Christopher561 wrote:And also If you have bad rings on the pistson I believe they are called? Oil could make its way into the cylender and Oil doesnt also compress.

Not so much. It would be difficult to get that much oil around the pistons even if the rings were GONE. Pistons tend to move pretty quick, and the clearances that pistons have would pretty much rule that out. The "leak" needs to come from a pressurized source(cooling system, hyperactive fuel rails or a turbo that has lost its mind).

downhill · Post by **downhill** » Thu Oct 07, 2004 11:57 pm

The_Lurker wrote:not likely. you'll get more a oil mist in the cylinders. not enough to cause a lock, but usually enough to give a cool James Bond style smoke screen as you pull over cursing.

Years ago...72? I had a friend who had a VW bug that smoked like crazy...

It left a heck of a smoke screen. His fix? He mated it with an inch and a half hose and ran it up the back of the bus to just over the top of the van....

Oh man.....was that ever funny to see going down the road. It looked like a coal stoaked montrosity...

Thanks for the memory boost...

Christopher561 · Post by **Christopher561** » Thu Oct 07, 2004 11:58 pm

One other thing what would be the symptoms? I guess one would be hydraulic lock. Would another be like rough idol and a-lot of vibration?

The_Lurker · Post by **The_Lurker** » Thu Oct 07, 2004 11:58 pm

brembo wrote:Yep.

Top fueler dragsters run so much fuel one of thier biggest concerns is hydro(in this case nitro methane) lock on the cylinders. Each plug gets about 40 amps pumped thru it, melting them in the process. The engines are actually dieseling by the end of the run. To shut em down they cut the fuel.

a quick fact. top fuelers cannot run steel alloy HI PO rods. they will snap quickly.

they have to run aluminum rods just because they will give under the extreme cylinder pressures. ofcourse they don't last very long and are discarded frequently regardless of there condition.

brembo · Post by **brembo** » Fri Oct 08, 2004 12:01 am

Christopher561 wrote:One other thing what would be the symptoms? I guess one would be hydraulic lock. Would another be like rough idol and a-lot of vibration?

Think about it.

Cylinder is not compressing the fuel. The piston is prolly skewed. So it's in synch movement wise, but the balance is all wacked.

What are the other consequences of havin low compression?
What happens to the fuel?
What happens to the exhaust gases in the effected cylinder?
Imagine the poor bent rod and attached piston zippin back and forth in the cylinder and make some guesses.

poptom · Post by **poptom** » Fri Oct 08, 2004 12:28 am

Christopher561 wrote:One other thing what would be the symptoms? I guess one would be hydraulic lock. Would another be like rough idol and a-lot of vibration?

Probably. I've never experienced it but I expect it would be rough at any speed. Once it is bent, it will only bend further. It would not have to bend much to come in contact with the lower edge of the cylinder barrel. That's when things will break.

Incidently, I've had hydraulic locks with the old Ford carburetors when a leaky power valve drained fuel into the cylinders while not running.

--Tom

Mad_Haggis · Post by **Mad_Haggis** » Fri Oct 08, 2004 12:31 am

its a piece of metal that spin's?

Hey all, Speeguide is Great

The Canada Arm is not about masturbation!

Answer to the thread..

p.s. ( is this a good) type forum thingy that i'm doin now...?

SG Broadband Community

Automotive question(bent connecting rod?)

Automotive question(bent connecting rod?)

http://www.discovery.com/