Thread: 4tec driveline conversion GPRP
01-24-2015, 12:15 PM #1
4tec driveline conversion GPRP
Hey Gprxp guys! Im in an uncharted area here. Is there any know maximum legth on driveshaft? Rxp is 23 inches. Just wondering why you guys put a intermediate shaft in your conversions. Can you run a 30 inch shaft and just make a center bearing support?
01-24-2015, 12:41 PM #2
Let me find beerdart's post. I think the longest is the rxtx at around 25 1/4.
The intermediate shaft is a Yamaha design. Seadoo is unsupported in the middle with basically the same carbon seal setup since forever.
Here is one.
01-24-2015, 08:17 PM #3
That helps lilmam. Thought 23 was longest. Im thinking 30 inches with bearing carrier support in middle. Sure a lot easier duplicating previous builds than doing rengineering of nothing. Thanks again for donor block for alignment.
01-26-2015, 04:08 AM #4
I sent a drawing for an extended shaft to several machinists in the sport and got nowhere with it. It seems there is a real reluctance to extend the Doo drive shafts more than a couple of inches. The shaft I wanted was 30.81" OAL. I was willing to pay the cost ($1000+) but gave up, knowing there have been a lot of broken extended shafts over the years. Also, I have to believe these guys know what they're talking about. Hurts just to think of a project ski sinking due to a broken shaft.
01-26-2015, 07:39 AM #5
That extra 5" is going to be a stretch though. Not sure how you will make that up. Here is where I start to overthink things.... You could just slide the motor back and hope the trim and some adjustable sponsens help your handling. Or you could do what Beerdart suggested, find the COG, and get pretty close and then get a custom shaft built from there. I wonder how different it will be adding 100lbs to the motor. maybe that 4-5" back is beneficial.
That's actually why the mounts in my other MSX hull aren't done yet. I started thinking about the alignment, motor pitch, the through hull... and with not having a ton of experience with glass I didn't want to screw it up.
01-26-2015, 08:40 AM #6
Thanks Ziggy and Lilman helping me think through this most critical stage of design. I have studied and analyzed what few photos and videos of the three known xpl 4tecs for hours. based on visual measurements this photo represents pos of previous builds. All things considered the boat weighing 100lbs less is no issue in engine pos since weight loss is equal distribution. Watching Nico ride his boat in video seems at idle he is leaning back on seat a bit. I wonder if previous builds chose engine location based on cramped working conditions . If I slide motor way back , assembley and service negated...unless.. I can solve that problem.. clamshell XPL!
01-26-2015, 08:49 AM #7
So my plan is set back motor to 25 inch drive shaft length. Motor mount " landing pads " with aluminum rail inserts will be glassed in and extend 8 inches . This means when done if there is a handling failure, I can slide mtr forward, retap engine mounts, and re engineer driveline in a two stage design. All without scrapping entire project.
01-26-2015, 08:58 AM #8
I know that especially with the MSX conversions, depending on the shaft length that was used, its so tight in the rear you might have to split the charger casings just to get it in and out without taking the motor out.
01-26-2015, 09:43 AM #9
Awww.. good info. Forgot about intake clearance. Considered flipping exh manifold upside down and routing exh and water box in front of motor. Whats diff about 08.. why is there a J in pipe? Water back flow security? Im so cluless on 4stroke.. but I learn fast. Really need complete mtr. Just waiting for a,"deal" donor. What is best choice on donor boat year?
01-26-2015, 10:05 AM #10
I believe different pump sports move the pump forward and backwards. Might give you an extra 2 inches if you get the shorter pump support.
and if you use a carbon seal setup, the drive shaft doesn't have to be all the way in the impeller. That might give you another inch
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