Twin outboards with bent cranks, is this possible?

[sawtellrob]

Hi all
Sold my little Markham Dominator 4.3 with twin Yammie 40s late last year. Was a great unit with only 140 hours on the 2006 motors. Contacted the buyer the other day to check if all was good and he tells me both motors have had a rebuild because of bent crankshafts, apparently he didn't ask his mechanic the cause. Anyone have any thoughts on this, was great when I sold it, has he maybe hit something hard? Don't understand how two motors could have such damage. He has no come back on me, I'm just curious
Cheers
Rob

[Noelm]

Be pretty unusual to bend a crankshaft, let alone two, if it was caused by hitting something, you would sure know about it, sounds kind of sus to me.

[stevej]

prob hub rubbers should give first

he gave his mechanic serious coin with out asking some simple questions ?

[chris69]

2stroke or 4stroke ,even with a gut full of water the rods would bend before the crank I would expect and with 2 motors there's no chance that they were running the same fireing order if the props hit something so that's all a bit suss to me.

[Dirtyfuzz]

Hi all
Sold my little Markham Dominator 4.3 with twin Yammie 40s late last year. Was a great unit with only 140 hours on the 2006 motors. Contacted the buyer the other day to check if all was good and he tells me both motors have had a rebuild because of bent crankshafts, apparently he didn't ask his mechanic the cause. Anyone have any thoughts on this, was great when I sold it, has he maybe hit something hard? Don't understand how two motors could have such damage. He has no come back on me, I'm just curious
Cheers
Rob

Out of curiosity I googled “bent outboard crank” and a lot of unhappy Yamaha customer comments on various forums popped up, came back here and noticed you also were running Yams so possibly a manufacture fault but most of the comments were about the larger models


Sent from my iPhone using Tapatalk

[catshark]

if it was fine when you sold it, then it was fine period, people will do stuff that bewilders others, perhaps he wanted to rebore the cylinders. perhaps he wanted to put a k&n filter on it to improve horsepower. dont buy into it, sounds like the buyer is full of it...

[gazza2006au]

How does a crankshaft bend? Its balanced, since its both engines i bet he sunk them while running and bent the conrods due to hydrolocking them

[catshark]

yeah same , agree he watch one too many coast gaurd videos and lauched it of a wave and fell back in engines first..

[tunaticer]

I fail to see how a crankshaft can bend being mounted on end and mid journals with less than 2 thousand " clearance. You would have to bend the powerhead to bend the crankshaft. Snap them, yes that happens.
I suspect it is the driveshaft they are calling the crankshaft.

[Noelm]

Lots of motors have pressed cranks, meaning they are made in pieces, the rods and bearing are fitted to the crank "journal" and that is pressed into the other half, it's is possible to twist them, but it's very rare, and to twist both would be a really long shot.

[gazza2006au]

Tuna yeah because journals are hardened if over stressed they will break but bending the crank i have never seen that would need to be quiet tremendous forces

Sawtell none of your fault i am almost certain he has sunk the engines

[sawtellrob]

Thanks guys, Its just been a puzzle to me that two very low hour, well maintained motors could fail and need rebuilding without some sort of trauma. His words were 'all new internals', he drove from Melbourne to Sawtell (near Coffs Harbour NSW)to get the boat and seemed a really nice young fellow, hope his outboard mechanic friend is on the up and up.