Super Jet Midshaft Talk - Building, Rebuilding, SN vs. RN, etc.

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#62
Old thread... but has anyone noticed that old 90s midshafts have a double row bearing and all the new bearings from yamaha are only single row. I looked at sit down part numbers and the part number is the same as the superjet. Did they do away with the double row bearing? I like the idea of a beefier bearing.
 
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Feb 26, 2017
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#63
I have a 650 squarenose hull that I'm putting a 781 ish motor in. So that is the old style smaller midshaft housing and possibly shaft. @JetManiac says in the beggining of this thread the old style shaft is weaker and shouldn't be used for "big power builds"

That will be bigger power than a stock 650, but maybe not really "big power", it's nowhere near a big billet power valve motor or something of the sort.

Looking for an opinion if a guy should bother trying to piece together a newer beafier shaft with the old style housing or just run the 650 setup and it should be fine.
 
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#64
Not sure on the mid-shaft but I am pretty sure the 650 driveshaft out the back is tapered so you might want to have a heavier one cut to length by @sasquatchcrap here on the forum.
 

augustaf

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#69
Old thread... but has anyone noticed that old 90s midshafts have a double row bearing and all the new bearings from yamaha are only single row. I looked at sit down part numbers and the part number is the same as the superjet. Did they do away with the double row bearing? I like the idea of a beefier bearing.
B1 Blasters had dbl. row bearings in the mid haft housing- SJ's had sgl row.
 
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#70
So just to get this 100% right. If I have a 90-93 SJ mid-shaft housing, I can use a 94+ mid-shaft even though its a bigger diameter?

Also what tools is used to hold the mid-shaft, so you can remove the coupling? WR001?
 

JetManiac

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#71
So just to get this 100% right. If I have a 90-93 SJ mid-shaft housing, I can use a 94+ mid-shaft even though its a bigger diameter?

Also what tools is used to hold the mid-shaft, so you can remove the coupling? WR001?
Yes, you can use the newer design shaft. The shaft is the same diameter where the bearing and seals ride, but is bigger where the thrust washer sits and coupler threads and area are larger.

JetManiac sells a midshaft spline holding tool that is designed to be clamped by a vise.
 
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#72
Sorry for resurrecting such an old thread. Just to be sure then......A waveblaster 1 midshaft housing + midshaft will bolt straight into a pre 08 RN Superjet??
Thanks
 
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Nov 27, 2006
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West Hartford, CT
#74
Can you experts tell me if this is a small housing that will fit on my 91 Superjet. I bought this as a spare which the seller claims it is for the 90-93 SN Superjet, but mine does not have a grease fitting. measurements between bolt holes center to center, bottoms are 110mm, bottom to top are 100mm. thanks in advance.
 

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JetManiac

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#75
Can you experts tell me if this is a small housing that will fit on my 91 Superjet. I bought this as a spare which the seller claims it is for the 90-93 SN Superjet, but mine does not have a grease fitting. measurements between bolt holes center to center, bottoms are 110mm, bottom to top are 100mm. thanks in advance.
Yes, that is the smaller size housing for a 650. It is an a/m housing made by Lynx.
 
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Nov 27, 2006
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West Hartford, CT
#78
The old housing with worn bearing and seals turns easily by hand but with lots of play, don't think the seals are making 360 deg contact with the shaft anymore. where as the new housing with new bearing and seals feels smooth but tight. keeping in mind that its a 650 so any HP robbing will be felt. notice on the low end and off idle, top feels pretty much the same. everything is much smoother and less vibration of course. Over all much better and much needed.
 
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#79
Do you have an inch pound torque wrench? I bet you'll find the 'tight' shaft has around 1 or two inch pounds of resistance, which comes out to about .1 hp at 6500 rpm, and half that at 3200. You'll never feel .1hp, and remember your old shady still had some small amount of residence.
 

JetManiac

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#80
ok, here's another question, more like an observation... does anyone notice huge friction torque (horsepower robbing) with new seals and bearing comparing to a worn out seals and bearing in the housing?
Not an issue, the rebuilt assembly will turn easily after a ride or 2.
 
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