Driveshaft won’t engage powerhead

[Hamboat Captham]

That’s what I thought as well, something is wrong with the crank it seems. The leg is fine. It won’t lock to the crank, like it’s sheared. There’s no evidence of that, completely clean and unmarked driveshaft end that goes up into the crank. The water pump quit too, brand new so know it’s good, the crank just stopped spinning the driveshaft. I can see the driveshaft not spinning through the slot.

Wenched it up on deck and onto the boom gallows, going to tear it down tomorrow am and find out what’s going on. Yamaha guy said it sounded like the crank went, must be a defective one he said. Only 2k to fix it he said! It’s only 4 months out of warranty!

[Hamboat Captham]

Like the title says the driveshaft wont engage the powerhead, I thought there might be some new setup in there but seems it’s just the regular driveshaft straight into crankshaft, or supposed to be.

[99yam40]

keep us informed on what you find.
I never heard of anything like this.

[Hamboat Captham]

Rajah that, me either why i asked. Thought there might’ve been a shear pin or something easy I was missing before I tore it down

[Hamboat Captham]

Got the powerhead off, wallered out crank snout. Anyone know if the earlier gen (90something to 06) will fit the later gen? Yam 9.9t 4stroker

[TownsendsFJR1300]

Got the powerhead off, wallered out crank snout. Anyone know if the earlier gen (90something to 06) will fit the later gen? Yam 9.9t 4stroker

The crank shaft splines are stripped out / gone??

How are the splines on the LU drive shaft that would engage the engine?

[Hamboat Captham]

Male splines are great on the d/s look perfect, it’s almost like the guy that we got it from changed it out and cleaned the crank slot. So much for a “great little motor”. Know if the last gen cranks fit these new ones?

[Masonmobilemarine]

Male splines are great on the d/s look perfect, it’s almost like the guy that we got it from changed it out and cleaned the crank slot. So much for a “great little motor”. Know if the last gen cranks fit these new ones?

This exact same thing happened to a motor I was tearing down. Crank was wallered out, but driveshaft was perfectly fine.

Guy had low/no oil pressure for a bit intermittently (mostly higher rpm). Took it to mechanic for water test and the mechanic punched it and suddenly only had neutral.

The lower unit driveshaft splines are somehow in mint, perfect condition.

[TownsendsFJR1300]

Male splines are great on the d/s look perfect, it’s almost like the guy that we got it from changed it out and cleaned the crank slot. So much for a “great little motor”. Know if the last gen cranks fit these new ones?

No idea about the crank, Boscoe should know and will post...

A NEW crank is about $400... https://www.boats.net/catalog/yamaha...nkshaft-piston

First I've heard of those crank splines "going away"....

Mason, was your above stripped engine a small engine or?


Hamboat, probably be a waste of time, but worth a try.
Contact the seller and see about at least a partial refund. With NO remnants of the splines (per post #1) the issue would have known by the seller (as debris WAS CLEANED AWAY when sold to you)and NOT disclosed...

[Hamboat Captham]

Thanks guys, wonder if this is a common yam problem. Seems the crank could be stronger or have a pressed sleeve would be nice, could be done at home possibly. Talked to he guy said it was dealer serviced (warranty) so he didn’t touch it. Plenty used cranks around from the last gen, haven’t seen one for the new ones yet

[TownsendsFJR1300]

Thanks guys, wonder if this is a common yam problem. Seems the crank could be stronger or have a pressed sleeve would be nice, could be done at home possibly. Talked to he guy said it was dealer serviced (warranty) so he didn’t touch it. Plenty used cranks around from the last gen, haven’t seen one for the new ones yet

I've NEVER heard of the spines stripping out (rusting and seizing up from lack of grease, YES). I've been on this forum about 9 years, again a first I've read about..

I'm curious how many Rodbolt and others have come across this and what size motors...

[Hamboat Captham]

Wonder if it’s a new gen thing, like the cars that fail just out of warranty now. Might see this becoming common as they start to slip out of warranty and fail.


hey mason was that one of the newer gen motors?

[zenoahphobic]

Sounds like poor hardening of the crank, and that might imply the crank has weaknesses elsewhere.
Because you didn't find any spline debris on the shaft clearly means that it had been taken apart before, and therefore you have reason to ask for some redress.
I hope that this doesn't mean quality is reverting back to the bad old days, when metallurgy, treatments technology and machining was not as good as it can be today.

[99yam40]

he!! how about welding some on the drive shaft or the crank and machining or filing to get things to fit tighter.
some JB weld might hold up but could be a problem getting back apart

[TownsendsFJR1300]

JB weld isn't that strong..

Agreed thou that that crankshaft likely wasn't hardened correctly from the factory....

Even if he tagged a rock with the prop, the prop hub would let loose first....


The only fix is a new crankshaft unfortunately..