Yamaha F100 slightly bent rod
#1
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Gents,
I'm at my wits end with a 2000 Yamaha F100, long story short, after much investigating Shes had a cracked head due to corrosion, its now at the machine shop getting welded and surface grinded. Looking at the cylinder bores seems the cylinder number 4 which copped the water ingress from the cracked head sustained mild hydrolocking. Its now 5-7mm from top dead centre, so ive deduced the conrods kinda bent.
anyone here ever had a bent rod and the motor kept going? Im reluctant to pull the bottom end apart and replace the conrod for many reasons, time and money etc.
thanking in advance
I'm at my wits end with a 2000 Yamaha F100, long story short, after much investigating Shes had a cracked head due to corrosion, its now at the machine shop getting welded and surface grinded. Looking at the cylinder bores seems the cylinder number 4 which copped the water ingress from the cracked head sustained mild hydrolocking. Its now 5-7mm from top dead centre, so ive deduced the conrods kinda bent.
anyone here ever had a bent rod and the motor kept going? Im reluctant to pull the bottom end apart and replace the conrod for many reasons, time and money etc.
thanking in advance
#2
Admirals Club




Once you’ve bent a rod you have induced a stress riser to the metal. It is just a matter of time before it will fail premature compared to a rod without the stress riser. It is a question of how long that is.
In addition, if you are that far away from TDC when compared to the other holes, you will end up with low compression, incomplete burn, poor harmonics, and low power.
So in summary, if it really is that far off, I would change the rod.
JD
In addition, if you are that far away from TDC when compared to the other holes, you will end up with low compression, incomplete burn, poor harmonics, and low power.
So in summary, if it really is that far off, I would change the rod.
JD
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#3
Senior Member

If the rod is bent, what condition might the bearings be in? Or the piston? Or the crank shaft?
#4
Senior Member

5-7mm is massive. You run it, you will soon have a ventilated block.
#5
Senior Member

5-7mm is massive. You run it, you will soon have a ventilated block. The time and money to replace the rod and check the bearings and crank will be very low compared to a new powerhead.
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#6
Senior Member

A slightly bent rod is kind of like being slightly pregnant or slightly dead! it's bent, it's replacement time.
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#8
Senior Member
#11

If the rod is bent, at bare minimum the loads on the big end bearing are likely to be uneven and cause an early failure. That might be your best case scenario. A rod through the block is just as likely. Really no choice but to fix it now.
#12
Senior Member
#13

Once a rod bends its only a matter of time before it breaks and exits the block. Experienced this personally many times. Customer amazed engine runs again after hydrolock driving through deep water...then its towed back in a week with a huge hole and needs a short block. You have it apart now its a no brainer.
edit: to add, cost will obviously be way higher once the block is toast.
edit: to add, cost will obviously be way higher once the block is toast.
#16
Senior Member

5-7mm lacking on tdc piston height means the rod is REALLY bent. That is huge. Pull the short block, split the case and fix it right. Run it like that and it will "ventilate" or "window" the block.
#18
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Not worth fixing . The block will need to line bored, cylinder sleeved and I bet 100% you need a new crank, all new rod and crank bearings..$$$
#19
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Thanks Gents,
Appreciate the advice. Its a pretty daunting thought and at times overwhelming to think what the task ahead entails (I have two left hands). Pulling this motor apart was always going to be a steep learning experience, I've made it as far as the head off etc. but the bottom block, looks far beyond my capabilities and honestly motivation. The verdict is in - re-assemble and sell as a wrecking motor, thanks everyone!!!
Appreciate the advice. Its a pretty daunting thought and at times overwhelming to think what the task ahead entails (I have two left hands). Pulling this motor apart was always going to be a steep learning experience, I've made it as far as the head off etc. but the bottom block, looks far beyond my capabilities and honestly motivation. The verdict is in - re-assemble and sell as a wrecking motor, thanks everyone!!!
#20
Senior Member

Thanks Gents,
Appreciate the advice. Its a pretty daunting thought and at times overwhelming to think what the task ahead entails (I have two left hands). Pulling this motor apart was always going to be a steep learning experience, I've made it as far as the head off etc. but the bottom block, looks far beyond my capabilities and honestly motivation. The verdict is in - re-assemble and sell as a wrecking motor, thanks everyone!!!
Appreciate the advice. Its a pretty daunting thought and at times overwhelming to think what the task ahead entails (I have two left hands). Pulling this motor apart was always going to be a steep learning experience, I've made it as far as the head off etc. but the bottom block, looks far beyond my capabilities and honestly motivation. The verdict is in - re-assemble and sell as a wrecking motor, thanks everyone!!!