pinellas50
New Guy
Has anyone ever had a good running motor with a bent rod? If so, what were the symptoms? How did you diagnose the problem? If there was a vibration to the motor, when did it occur?
Bent rod
- Thread starter pinellas50
- Start date
Syclone#2960
What ever it takes!!
Re: Bent rod
i heard a tapping noise...the bent rod was hitting the block on the down stroke. Kind of like the card in the bicycle wheel sound.
i heard a tapping noise...the bent rod was hitting the block on the down stroke. Kind of like the card in the bicycle wheel sound.
pinellas50
New Guy
Re: Bent rod
Was there a noticeable engine vibration to it? Did it show up on a compression test? Did it cause any KR?
Was there a noticeable engine vibration to it? Did it show up on a compression test? Did it cause any KR?
Syclone#2960
What ever it takes!!
Re: Bent rod
The motor detonated from overboost & immdediately heard the noise. I knew right away what had happened.
No engine vibration. Just the noise. I did not bother to do a compression test cause I knew it was a bent rod on a stock motor.
The motor detonated from overboost & immdediately heard the noise. I knew right away what had happened.
No engine vibration. Just the noise. I did not bother to do a compression test cause I knew it was a bent rod on a stock motor.
pinellas50
New Guy
Re: Bent rod
Thanks for the info. Anyone else? Anyone ever had a bent rod on an otherwise good running motor with no noise and good compression test results?
Thanks for the info. Anyone else? Anyone ever had a bent rod on an otherwise good running motor with no noise and good compression test results?
pinellas50
New Guy
Re: Bent rod
New distributor with ignition module, new cap/rotor, new plugs Autolite 23(the old ones all looked fine but since I was in there....), new wires, new coil, new harmonic balancer, compression test, check for codes in computer--none. DM shows no knock retard once I replaced the balancer...the old one was about 4 degrees off. Checked the flex plate for cracks and there are none. Ran the motor without the mechanical fan.
Unbolted the converter and ran the motor. Right after bolting everything back up I found a bad plug wire. So that kind of invalidated the unbolt the converter and run the motor test.
The only noises from the motor are at first start up there is an unusual noise. Not a knock or a banging. I'm not sure how to describe it though. I have found the noise described as piston slap in several threads. It goes away rather quickly once the motor starts to warm up. Once warm, the only noise I hear is a slight lifter tick as far as I can tell and of course the injectors. No noises that others have reported along the lines of a bent rod. I had rod knock with the last vehicle I had and there is nothing remotely going on that resembled that noise.
Oil pressure looks great on the stock guage with the motor both cold or hot.
Vibration is present in neutral. Much more prominent while under throttle up around 4K.
New distributor with ignition module, new cap/rotor, new plugs Autolite 23(the old ones all looked fine but since I was in there....), new wires, new coil, new harmonic balancer, compression test, check for codes in computer--none. DM shows no knock retard once I replaced the balancer...the old one was about 4 degrees off. Checked the flex plate for cracks and there are none. Ran the motor without the mechanical fan.
Unbolted the converter and ran the motor. Right after bolting everything back up I found a bad plug wire. So that kind of invalidated the unbolt the converter and run the motor test.
The only noises from the motor are at first start up there is an unusual noise. Not a knock or a banging. I'm not sure how to describe it though. I have found the noise described as piston slap in several threads. It goes away rather quickly once the motor starts to warm up. Once warm, the only noise I hear is a slight lifter tick as far as I can tell and of course the injectors. No noises that others have reported along the lines of a bent rod. I had rod knock with the last vehicle I had and there is nothing remotely going on that resembled that noise.
Oil pressure looks great on the stock guage with the motor both cold or hot.
Vibration is present in neutral. Much more prominent while under throttle up around 4K.
Re: Bent rod
i also had some metal in my oil filter when i cut it open and had lost a lot of power.
bret
x2.
i also had some metal in my oil filter when i cut it open and had lost a lot of power.
bret
pinellas50
New Guy
Re: Bent rod
I just got out from under the truck while it was running. That piston slap noise and a noticeable tick both seem to be coming from the torque converter or the transmission itself up by the pump. I'll finish this up in the drive train section.
I just got out from under the truck while it was running. That piston slap noise and a noticeable tick both seem to be coming from the torque converter or the transmission itself up by the pump. I'll finish this up in the drive train section.
Re: Bent rod
don't quote me, jsut a thought but almost sounds to me like you just have piston slap from aftermarket pistons of some type. i know my honda and other cars i've owned that had low compression forged pistons have done this since day 1 along with all other new motors with forged pistons that i've been around
if you know for a fact this motor is stock internally then disregard this, otherwise maybe some previous owner had built it :dunno:
just my :2cents:
don't quote me, jsut a thought but almost sounds to me like you just have piston slap from aftermarket pistons of some type. i know my honda and other cars i've owned that had low compression forged pistons have done this since day 1 along with all other new motors with forged pistons that i've been around
if you know for a fact this motor is stock internally then disregard this, otherwise maybe some previous owner had built it :dunno:
just my :2cents:
pinellas50
New Guy
pinellas50
New Guy
Re: Bent rod
As always, thanks for the information.
As always, thanks for the information.
pinellas50
New Guy
Re: Bent rod
I'm still poking at my problem. The best I can describe this imbalance I have is that the motor feels like a washing machine that has its load out of balance. Kind of a wiggle wiggle at low rpm, it kind of smooths out during normal rpm operation, and then it shakes violently at higher rpm.
I thought I had it narrowed down to a bad torque converter. I replaced the flex plate and converter but this made no change.
A good friend of mine, who is an excellent mechanic, seems to feel I have something like a bent rod going on. To go back in time, I had unbolted the converter and run the engine and I had no vibration. He believes that the slight extra load of the converter spinning would be enough to let the problem with a bent rod show itself.
So far, everyone who has posted with bent rod expierence doesn't say anything about any kind of engine vibration.
I don't have any kind of noticeable blow by coming out of the valve covers.
My latest compression test results:
1) 150
2) 152
3) 154
4) 138
5) 155
6) 155
The only things I can think of that would cause low cylinder pressure would be a bent rod, valve issue, or some kind of piston damage. Granted that 138 is in the 15 above or below the rest of the others but I don't like the look of it given how close all the others are.
I pulled the plugs and they look like they are new out of the box. Granted they only have a few miles on them but I was expecting to see some kind of evidence that they had been used in a running engine before.
I am being told that there really isn't anything in the transmission itself that could be causing this. The transmission still shifts great with nothing weird about it at all.
At idle, the exhaust note seems nice and smooth. Like it is firing on all cylinders.
Given all of this, is it time to pull the motor and tear it down for inspection? Or might there be something else I am missing like an injector not firing or something?
I'm still poking at my problem. The best I can describe this imbalance I have is that the motor feels like a washing machine that has its load out of balance. Kind of a wiggle wiggle at low rpm, it kind of smooths out during normal rpm operation, and then it shakes violently at higher rpm.
I thought I had it narrowed down to a bad torque converter. I replaced the flex plate and converter but this made no change.
A good friend of mine, who is an excellent mechanic, seems to feel I have something like a bent rod going on. To go back in time, I had unbolted the converter and run the engine and I had no vibration. He believes that the slight extra load of the converter spinning would be enough to let the problem with a bent rod show itself.
So far, everyone who has posted with bent rod expierence doesn't say anything about any kind of engine vibration.
I don't have any kind of noticeable blow by coming out of the valve covers.
My latest compression test results:
1) 150
2) 152
3) 154
4) 138
5) 155
6) 155
The only things I can think of that would cause low cylinder pressure would be a bent rod, valve issue, or some kind of piston damage. Granted that 138 is in the 15 above or below the rest of the others but I don't like the look of it given how close all the others are.
I pulled the plugs and they look like they are new out of the box. Granted they only have a few miles on them but I was expecting to see some kind of evidence that they had been used in a running engine before.
I am being told that there really isn't anything in the transmission itself that could be causing this. The transmission still shifts great with nothing weird about it at all.
At idle, the exhaust note seems nice and smooth. Like it is firing on all cylinders.
Given all of this, is it time to pull the motor and tear it down for inspection? Or might there be something else I am missing like an injector not firing or something?
Last edited:
etriebe
New member
Re: Bent rod
A buddy of mine put an engine in a frito truck, after it was all done he had a vibration. we unbolted the torque converter and the vibration went away. The engine was balanced so I pulled out the trans and replaced the converter, fired it up still had a vibration. pulled the tranny back out. I had a th400 out of a 3/4 chev truck sitting there that I had pulled out to do a rear main in and slapped it in the frito truck and the vib was gone. maybe something in your trans.
A buddy of mine put an engine in a frito truck, after it was all done he had a vibration. we unbolted the torque converter and the vibration went away. The engine was balanced so I pulled out the trans and replaced the converter, fired it up still had a vibration. pulled the tranny back out. I had a th400 out of a 3/4 chev truck sitting there that I had pulled out to do a rear main in and slapped it in the frito truck and the vib was gone. maybe something in your trans.
syclone2003
New member
Re: Bent rod
My engine had 2 bent rods and still ran. I bought it like that crank was hiting the bottom of the piston. I know because I just took it appart.
My engine had 2 bent rods and still ran. I bought it like that crank was hiting the bottom of the piston. I know because I just took it appart.
pinellas50
New Guy
Re: Bent rod
Was the vibration similar to my imbalance feeling I am trying to describe?
I just can't decide if the next logical step is to pull the tranny out and have it torn down or pull the motor out and tear it down.
Was the vibration similar to my imbalance feeling I am trying to describe?
I just can't decide if the next logical step is to pull the tranny out and have it torn down or pull the motor out and tear it down.
pinellas50
New Guy
Re: Bent rod
Did it have an imbalance or vibration to it when the motor was running?
Did it have an imbalance or vibration to it when the motor was running?
pinellas50
New Guy
Re: Bent rod
Well, I unbolted the converter again and ran the motor. Now I feel the vibration in the motor but it is much less than with the converter hooked up. So it seems the vibration has gotten worse since I began looking for it.
So the motor is going to come out for inspection. I already pulled the tranny out of this thing to get my feet wet. How hard can the motor be.:roll:
I already warned the wife that this operation may very well lead to the addition of things like Eagle rods and such.
It will be quite a few months before I do anything as far as fixing this. I have to put a roof on the house, carpet in the house, and a few other things before the Ty gets any $ thrown at it. I will be sure to update this with the results of my tear down.
Well, I unbolted the converter again and ran the motor. Now I feel the vibration in the motor but it is much less than with the converter hooked up. So it seems the vibration has gotten worse since I began looking for it.
So the motor is going to come out for inspection. I already pulled the tranny out of this thing to get my feet wet. How hard can the motor be.:roll:
I already warned the wife that this operation may very well lead to the addition of things like Eagle rods and such.
It will be quite a few months before I do anything as far as fixing this. I have to put a roof on the house, carpet in the house, and a few other things before the Ty gets any $ thrown at it. I will be sure to update this with the results of my tear down.
Don W.
Stab it and steer it
Re: Bent rod
Especially since you said it might be a while, take lots of pictures. Before and during the removal.
Especially since you said it might be a while, take lots of pictures. Before and during the removal.
pinellas50
New Guy
Re: Bent rod
The motor is out and I have the top end off of it. No sign of a bent rod or obvious signs of piston damage. The only thing I can think of now that would explain this nasty vibration is something like a bent crank or damaged block.
Further bulletins as events warrant.
The motor is out and I have the top end off of it. No sign of a bent rod or obvious signs of piston damage. The only thing I can think of now that would explain this nasty vibration is something like a bent crank or damaged block.
Further bulletins as events warrant.