[CJRacing]

"trying" to piece together my first jet boat. Starting with a 18ft. '75 Gemcraft Southwind. I bought the hull w/ interior only; the owner said it had a 454 that turned a 12JC Berkeley. I bought the same pump that came out of it(12JC), and have been trying for the longest time to fit this 455 in it. I have Harding water logs with up and over transom boom tubes. with the engine as far back as the exhaust will allow, I'm still short of the pump by a solid 3". WTF? I never imagined I could be off this far... With the engine and pump mocked up out of the boat, the rear motor mount will be sitting over the intake flange of the pump body by about 2", does that sound right? My idea of an easy solution would be a longer driveshaft, but i heard that doesn't exsist. My current shaft if 6.75"... Any input you may have can/will determin my boating experience this summer. Thanks

 

[fleetimus]

Pictures will help!!!

 

[TRG]

not too sure but does the olds and BBC have the same type of mount location, is it on a three point system? my guess would be that you start there first.
I am no pro, but with the info given?...you might wanna check the differences between Chevy's and olds!

 

[CJRacing]

not too sure but does the olds and BBC have the same type of mount location, is it on a three point system? my guess would be that you start there first.
I am no pro, but with the info given?...you might wanna check the differences between Chevy's and olds!

I'm positive they have different mounting locations, but even so I'm a good 3" further back from the previous holes in the stringers. I don't have any pics that would show my problem, but i'll try to get some tomorrow durring daylight.

 

[Constant840]

Sounds like you need a driveline spacer or even an actual driveshaft.
Any custom driveshaft place should be able to build and balance one to spec.
Or if you have the tools and skills you can build your own and then have it balanced.

 

[Oldsquirt]

"trying" to piece together my first jet boat. Starting with a 18ft. '75 Gemcraft Southwind. I bought the hull w/ interior only; the owner said it had a 454 that turned a 12JC Berkeley. I bought the same pump that came out of it(12JC), and have been trying for the longest time to fit this 455 in it. I have Harding water logs with up and over transom boom tubes. with the engine as far back as the exhaust will allow, I'm still short of the pump by a solid 3". WTF? I never imagined I could be off this far... With the engine and pump mocked up out of the boat, the rear motor mount will be sitting over the intake flange of the pump body by about 2", does that sound right? My idea of an easy solution would be a longer driveshaft, but i heard that doesn't exsist. My current shaft if 6.75"... Any input you may have can/will determin my boating experience this summer. Thanks

Those OT pipes are not universal. You need to have the correct offsets in both height and length. Here's one suppliers pageRewarder OT Pipes For what it's worth, you may not find a combination that works. Not all rear decks leave enough room fot OT Pipes.

Sounds like you have a short driveline. If it bolts directly to the crank, it is probably designed for a 3-point mount set-up where the bellhousing clamps to the pump. If you have 4-point mounts(front and rear cast plates and mounting feet) you can use a more common set-up of a PTO and separate driveline. That should buy you a couple inches.Rex Marine Drivelines and PTOs.

 

[CJRacing]

Thanks for the info OldSquirt. I'm flying kinda blind through this whole thing. Used to 4 wheels, and not all of the techniques used on 4 wheels translates to no wheels. ha ha