300/440/550 Old 550 modified engine in a 550sx

[ackrell]

Guys,

I bought a 550 a while back with a modified engine - a real find!!!! Paid £200 ($300USD) - skis are a lot more here than in the States so this was real cheap!


It is a bit of a strange one. The crank cases / bottom end is, I believe, from an old PP 550 but there are no engine numbers on the flywheel case.

The cylinders are old PJS ones, overbored 50 thou, with a westcoast head, PJS complete exhaust, mariner water box, dual keihin carbs, PJS dual intake manifold, total loss ignition and a K&N filter (plus PJS intake, ride plate, skat impeller etc etc).

I've changed the crank seals and given it a check over and it seems in an ok condition so I put it back in the old JS hull it came in and began to re-fit it.

The next morning I found a 550SX hull on ebay and bought it for the grand sum of £10.50 - $16 usd!!!

I only really wanted it for the hood and would give a couple of the other bits to my brother for his. It comes as a complete hull with:

Water box
Fuel tank
Good hull seal
Prop
Pump
Impeller
Side tubbies (original sponsons he means)
Uprated spring pole
All engine mounts
Steering cable
Throttle cable


Anyway! My old JS hull is a bit tatty, a greyish white colour and has been fibreglassed inside a few times (because of cracks or reinforcement I don't know). So - will the old engine fit straight in to the new 550sx hull with no adjustments other than the rear exit exhaust?

And would the 550SX pump be better than the 440 which it's currently mated up to? I don't know if it has a stainless impeller on the SX or what condition it's in as I don't collect it til saturday (600 mile round trip!)

I want the pump to have better low end grunt for playing in surf, wake / wave jumping etc.

Or...am I better leaving it in the old hull it came in and keeping the 440 pump and just giving it a paint and structural overhaul?

Could using the 550sx pump cause any problems? I read somewhere if the motor has a peak RPM of 7000RPM then it'll be ok for the 550sx pump, but if it has a peak of 8000 then it could start bashing chunks out of the sx and it would be wise to use a 440.



Obviously in the old days these 550 modified motors were built around using a 440 driveshaft and pump - my current idea is to drop the motor in to the new SX hull and use the 550SX pump, with the plan to be to bore out the nozzle and adjust the impeller to suit.

What I need is a definitive answer on the following as it is literally all I'm thinking about!!! - I haven't even ridden this ski yet and it's killing me:

• Stick as it is with the old tatty hull, 440 pump etc and do up the hull.
• Move the engine and ebox into the SX hull, bore out nozzle, change impeller if required and maybe get a different pump cone.

What will be best for surf riding and freestyle / wake jumps etc, and not cause me any problems in destroying my engine or pump!

 

[fastgtfairlane]

why not try to find another js hull?? its really hard to say if the 550 pump will work or not.. depends on the cylinder and pipe with the 550 pump.. the mixed flow 550 pump creates much higher load at low rpms which is good for surf and bottom end.. however, with that cylinder and pipe, the pump may put too much load on that engine at low rpms and create an rpm wall not allowing the engine to turn max rpms.. having the lighter driveshaft of the sx hull helps, a large outlet nozzle and maybe a short cone with maybe a 13/16 pitch impeller.. you may still want to go to a half pipe exhaust which is longer and will bring the power band down some.. does the bottom of the cylinder have a t1 2 or 3 stamped on the bottom of the reed housing?? i have a t1 cylinder and a with a 440 pump and it ran good. never tried a 550 pump with that engine.. the ski that my pjs engine was last in had a 550 pump and it hit the rpm wall i mentioned earlier.. his pump wasnt really setup for that engine though.. when i bought it and ran my exhaust and pump setup, the difference was night and day..

either pump wont destroy the engine or pump, it just may not run to its full potential..

 

[special fx]

The 550sx pump should be superior to the 440 pump. It uses the new style bearing housing at the bulkhead and the driveshaft weighs about half as much as the 440. The early 550 pumps were coaxial, but the 550sx pump is axial just like the 440 pump.

 

[fastgtfairlane]

the 550 pumps both js and sx are "mixed flow" and 440 pumps, like every other jetski pump is an "axial" flow pump.. the 440 pumps actually process more water than the 550 pump and was the common choice for the race boats back in the 90s.. 550 pumps work well at low rpm which is not where the OP's engine produces its power.. 550 pumps do not work well with high rpm engines..

 

[ackrell]

Guys, don't worry about this anymore. The cost of doing it isn't going to be worth it. The ski was built around a 440 pump so I'm going to keep it as it is in the old hull, unless I find a very tidy JS hull.

The SX is going to be cannibalised for the parts I need or are in better condition than on my JS and then I'll be building a cheap ski out of what's left and selling it ok next season