300/440/550 550 to 750 conversion questions NEED ANSWERS!!!

Js550FTW

Js550FTW

Location
Anchor Bay, MI
Alright, I know this question is asked a lot, but this is my first conversion I want to do so here are the questions.

1. whats the differences between a small pin and big pin motor

2. Which one should I get

3. what do I have to do to the 750 crankshaft coupler to fit the 550 driveshaft coupler

4. Can the ebox on the 750 bolt on to the 550 mounts, if not, what do I have to do to fit it on there

5. Do I have to do anything to the pump? I want to put a 19 pitch impeller on there for speed

6. I want this geared more to the top speed end of the spectrum, but I do not want to lose all of the torque. I just want speed more so. What is the proper set up to do so?

7. Can I still use an oversized gas tank in it?

Thank you for anyone who puts time in to answer these questions. I really appreciate it!
 
Js550FTW

Js550FTW

Location
Anchor Bay, MI
tatronation said:
1. buy a superjet
2. buy a superjet
3. buy a superjet
4. buy a superjet
5. buy a superjet
6. buy a superjet
7. buy a superjet

In all seriousness im sure it will be a fun project. Sorry I can't help.
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Haha that's funny! But to be honest I'm going to get a sj in the next couple of years. Like for me right now, I think I have spent way to much time on my 550 just to let it go. I'm just passing one year year owning the thing so I want to do this project, use it a couple more times, then sell it and get a sj. But thanks for the info!
 
john zigler

john zigler

Vendor Account
Location
wisconsin
1 - Crank Pin size. Also cyl port timing. (height) A Big pin 750 has larger wrist pins, and bearings. Note, I have NEVER had a Small pin fail due to "too small of bearings". Small pin engines have lower port timing, and are better suited to making low end power. Big pin engines have taller port timing and make more power in the upper RPM range.

2 - Either is good.

3 - Early 750's have a 18mm thread on the coupler, and the 550 coupler will screw right on. Later 750's have a 20mm thread, and will need to have a modified coupler. We sell 20mm couplers here exchange.

4 - No. You will have fab up a bracket, mount, etc.

5 - No. Tall pitched impeller is needed, IE 19p etc. Make sure your pump install is perfect (silicone job, etc), and pump is in excellent condition. I also recommend boring the exit nozzle, which we can do here for you.

6- Depending on your pipe choice, yes, you should be able to fit an oversized tank.

We also have our own RCJS engine conversion plates in stock. ON SALE today, for cyber Monday, ONE day only sale;

https://www.watcon.com/engine/conversion-plate/engine-conversion-plate
 
Js550FTW

Js550FTW

Location
Anchor Bay, MI
john zigler said:
1 - Crank Pin size. Also cyl port timing. (height) A Big pin 750 has larger wrist pins, and bearings. Note, I have NEVER had a Small pin fail due to "too small of bearings". Small pin engines have lower port timing, and are better suited to making low end power. Big pin engines have taller port timing and make more power in the upper RPM range.

2 - Either is good.

3 - Early 750's have a 18mm thread on the coupler, and the 550 coupler will screw right on. Later 750's have a 20mm thread, and will need to have a modified coupler. We sell 20mm couplers here exchange.

4 - No. You will have fab up a bracket, mount, etc.

5 - No. Tall pitched impeller is needed, IE 19p etc. Make sure your pump install is perfect (silicone job, etc), and pump is in excellent condition. I also recommend boring the exit nozzle, which we can do here for you.

6- Depending on your pipe choice, yes, you should be able to fit an oversized tank.

We also have our own RCJS engine conversion plates in stock. ON SALE today, for cyber Monday, ONE day only sale;

https://www.watcon.com/engine/conversion-plate/engine-conversion-plate
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Thank you so much! I believe sbt sells a small pin 18 mil shaft 750 engine that'll work just fine for what I want. Can you guys fabricate a conversion plate for the ebox for me? If so, how much $? And also, do you guys have any impellers of that degree for a 550? Thank you!

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Js550FTW

Js550FTW

Location
Anchor Bay, MI
Okay, I heard a 650 conversion is much easier and more affordable, should I go for that instead because I think that project is easier to complete

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Js550FTW

Js550FTW

Location
Anchor Bay, MI
And plus, I think it's impossible to fit a decent sized gas tank in it with a 701. Not even making a close fit with a oversized tank

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john zigler

john zigler

Vendor Account
Location
wisconsin
Js550FTW said:
Okay, I heard a 650 conversion is much easier and more affordable, should I go for that instead because I think that project is easier to complete

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650 or 750 really are pretty much the same. I tell people to purchase a "donner" ski. Find a good running sit down (TS, 750SS, STS etc.) and use as much as you can from that for your build.
 
Js550FTW

Js550FTW

Location
Anchor Bay, MI
john zigler said:
650 or 750 really are pretty much the same. I tell people to purchase a "donner" ski. Find a good running sit down (TS, 750SS, STS etc.) and use as much as you can from that for your build.
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Thank you for the reply! Any words on the 701 conversion? The only downfall I can find doing that is the huge price to complete and the tiny gas tank. Any more pros and cons?

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Quinc

Quinc

Buy a Superjet
Location
California
This guy should have everything you need. https://www.rhaasproducts.com/

Go on craigslist and find a broken sit down ski with the engine you want for cheap. You should be able to find a complete running ski with a junk hull for a couple hundred. Go with a 701 so that you can put it in the superjet you are going to want 2 months after you finish the conversion. :)
 
Js550FTW

Js550FTW

Location
Anchor Bay, MI
Quinc said:
This guy should have everything you need. https://www.rhaasproducts.com/

Go on craigslist and find a broken sit down ski with the engine you want for cheap. You should be able to find a complete running ski with a junk hull for a couple hundred. Go with a 701 so that you can put it in the superjet you are going to want 2 months after you finish the conversion. :)
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Thanks man! Is there any pipe I would be able to fit in there with a oversized tank? If there is I'm AL set!

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Js550FTW

Js550FTW

Location
Anchor Bay, MI
Also, can anyone help me out with what sit downs have the standard 61x or 62t engines in them so I know what to look for

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ajmps1

ajmps1

Location
Pa
Tons of searchable info on donor skis but in short, waveraiders 701/760/1100, vxr 650, vxrpro 701, waverunner 3 gp 701. All are great donors for a superjet and should be under 1000 with a nice trailer and titles for both in any area. Sell the trailer for 250 plus, sell the hull for 100 and youve got a complete motor with electronics and any other parts you keep. Probly wasting your money on the 701 swap into the 550. Swap a cheap kawi 650 into it with a high comp head, lightened fw, 44m sbn and stretch the stock 650 pipe 4 inches. Theres a great thread on getting power out of the kawi 650 for under 250 bucks. You will be more than happy with the power you get especially in proportion to how much you spend.
 
Js550FTW

Js550FTW

Location
Anchor Bay, MI
ajmps1 said:
Tons of searchable info on donor skis but in short, waveraiders 701/760/1100, vxr 650, vxrpro 701, waverunner 3 gp 701. All are great donors for a superjet and should be under 1000 with a nice trailer and titles for both in any area. Sell the trailer for 250 plus, sell the hull for 100 and youve got a complete motor with electronics and any other parts you keep. Probly wasting your money on the 701 swap into the 550. Swap a cheap kawi 650 into it with a high comp head, lightened fw, 44m sbn and stretch the stock 650 pipe 4 inches. Theres a great thread on getting power out of the kawi 650 for under 250 bucks. You will be more than happy with the power you get especially in proportion to how much you spend.
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Thanks! I appreciate the feedback. But if I drop any Yama into the 550 hull, I'm gonna keep the ski. Just because this is my first ski and if I drop I nice engine like that, I want to experiment with what that ski is capable of. Plus, if I did sell it, I would just resell the hull and all the 550 engine parts separate, so I can get more $. Then keep the sj engine and drop it in a more modern hull.

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Quinc

Quinc

Buy a Superjet
Location
California
Js550FTW said:
Thanks man! Is there any pipe I would be able to fit in there with a oversized tank? If there is I'm AL set!

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Smallest pipe that I can think of (that is also a great pipe) is the coffman sizzler. Not sure if a bpipe will fit. Check out the RHaas 550 ski. It has a 701 in it.
 
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