Custom 300X driveshaft? Has anyone seen this?

**simpson_3** · 12-23-2021, 03:22 PM

I bought a 20" 300x this spring with only 200 hours on it. I'm doing a waterpump right now and I noticed this engine has a unique driveshaft setup. Has anyone ever seen this setup before? Were these sold as a kit at some point?

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**25two.stroke** · 12-23-2021, 03:28 PM

Thats factory OEM. First gen 300x motors came that way. So did early optimax 3.0L engines.

**simpson_3** · 12-23-2021, 03:35 PM

Originally Posted by 25two.stroke

Thats factory OEM. First gen 300x motors came that way. So did early optimax 3.0L engines.

Interesting! Did they sell a smaller upper shaft that would work with a 15" mid?

**FUJIMO** · 12-23-2021, 03:39 PM

...early years of 3 liter gearcases, both fleetmasters & sportmasters. also as a service replacement gearcase for a couple years. offshore multi-engine 3 liter boats it was nice, as they could then fit all the different shaft length motors if needed to swap, for what ever reason was needed...

**FUJIMO** · 12-23-2021, 03:41 PM

Originally Posted by simpson_3

Interesting! Did they sell a smaller upper shaft that would work with a 15" mid?

...no, upper shafts for 20, 25 & 30 inch only...

**vnemous** · 12-23-2021, 03:42 PM

Dont lose that spline piece I think they are about $800

**FUJIMO** · 12-23-2021, 03:43 PM

...not to say you couldn't easily cut & weld one for a 15 though...

**simpson_3** · 12-23-2021, 03:53 PM

Originally Posted by FUJIMO

...not to say you couldn't easily cut & weld one for a 15 though...

Do those upper shafts ever come up for sale? I'm thinking about putting that on a 15" mid.

**25two.stroke** · 12-23-2021, 04:08 PM

Originally Posted by simpson_3

Do those upper shafts ever come up for sale? I'm thinking about putting that on a 15" mid.

I just took out one that was on a 15" mid and swapped it out with a 1 piece...thats the easier route if you want to go to a 15" mid. Buy a new 1 piece 20" shaft and have it cut down to 15" for $150. With shipping and the cost of the shaft all said and done you get a brand new driveshaft for $550 or less. Of course, you could sent out just your upper shaft you have now and have it cut to 15"...but I personally don't like the slop that the connector introduces.

**Chaz** · 12-23-2021, 09:59 PM

Plenty of dead shafts out there to salvage the hardened end from and make a shorty - shorty upper out of. The coupler can't introduce harmonics .. but a weebly-wobbly shaft can ..

If your gonna buy a new shaft, get a single bearing 25". They are cheaper than a 20" and you just push the spacer off .. and you now have a two bearing shaft. (Keven K. @ Fuller taught me that trick)

Originally Posted by vnemous

Dont lose that spline piece I think they are about $800

$800 *^%^&*I)()&%$ dollars ... Are they out of their %^&**&% mind. Ohh thats right, it's a Mercury part .. well worth it @ twice the price ..

I found a great use for them little $800 dollar couplers.
I've had a few nice 3.2L cranks come thru my door that had the splines spun out of them from offshore banzzi running / racing. Yep, bore the end of the crank, turn down the coupler to an interference fit. Heat the crank, deep freeze the slug. Drop it in place, silicon bronze the tip of the stub .. Going off their track record. I think the case hardening might be stronger than the factory crank's splines ..

**H2OPERF** · 12-23-2021, 11:55 PM

I like the idea if they had just made the coupler a bit longer and put some orings in the ends so you could grease it. I have modified a few with omc crank end oring retainers works nice no rust.