580 to 657 swap

[oldchevyscadillacs]

I tried looking through the search feature but didnt find it,
Are the 580 and 657 carbs, pto ect interchangeable someone put a 580 motor in my GTX and i want to swap it back to the 657. Hopefully SBT will take the 580 as a core:hat:

 

[timmyboy76]

hey...you probably have the same carbs,..all bolt on things, that went with the 657, they just swapped motors..but heres carb specs...1994 GTX 657 270500205mag 270500206pto BN-38 (SB) MAIN-125 PILOT-60 2.0n/s 22 - 29psi LOW- 1-1/4 HIGH- 3/8. These carbs have the 2 holes on top for intake, but with the bolts protruding from manifold to mount..

 

[oldchevyscadillacs]

Thanks!:hurray:

 

[derek]

you won't notice a lot of difference. i took a 720 out of a 97 GTI and put a 580 in. very little diff. if the carbs have allen head thru bolts they are the 650 carbs. if nuts on studs they are 580 or 93 650 carbs. SBT will not take the 580 as a core for a 650. they are very good about everything but their core policy. their core charge is off the scale. read it carefully. buy a dead 650 for a couple of hundred and send it to them. if you are gonna do this, you might as well go 720, though. wait till winter when everything is cheap. make sure you keep the stator that came with the ski.

 

[oldchevyscadillacs]

Back at it agian. do the 657 bores bolt right on to a 580 block? im kinda wondering if that is the case i have i cant tell what pistons i need, the tops of my pistons right now say 1.00 on them wondering if thats what its bored out to over standard. need to find out to see if i can rebore mine agian. Should i just have them measured?

 

[derek]

ok; what makes you think it is a 580? you removed the head. did you unbolt a ring of small allen head bolts around the edge of cyl cover to get to the head bolts, or did the head bolts go through the top cover. if small perimeter bolts-it is a 580. if 12 head bolts show when you take off the seat and look at top of motor, it is a 650. 1.0 on pistons means it has already been rebuilt. go to ebay. search personal watercraft parts. do a search for seadoo head. you will get pics of both types if in doubt. might be somebody used a 580 front cover because the bolts broke in his 650 cover. and the only 580 thing in your doo is a label. your bores will measure 77 mm if 580+1.0 79 mm if 650+1.0. now to your orig question. do jugs interchange? no. you might be able to bolt them on, but piston pin is diff diameter. then head bolt circle is diff size, so head doesn't interchange.

 

[oldchevyscadillacs]

You have hit the nail on the head. It has a 580 label but the jugs are 650, so im in good shape here . i can bore out to 1.5 correct?

 

[derek]

if it ain't broke, don't rebuild it. now, is it a 650 or a 650x? look on the back of the rear cyl. a part number down low. does it end with 380, or 382? if 382 it is a x motor. essentially equal in power to a 720. i am not sure about piston availability in 1.5 mm. i know they do 2 mm but some feel the sleeve is getting a little thin over 1mm. used jugs that are standard and needing bored are cheap. i know a guy with a set that don't need bored who wants $50 for them. and even if yours needs work, it may not need bored.

 

[oldchevyscadillacs]

My motor scattered half a piston ring in the pto cylinder, and my mag cylinder has signs of pre-detonation. I have a great guy that does my machine work so haveing them bored out im not afraid of and then some new pistons and rings and i should be good to go, gonna replace my impellar and wear ring while i have the motor out too bottom end is in good shape.

 

[derek]

i have done some looking. it is difficult to find anything but wisecos in 2.0 mm. buy a set of 650x jugs and get your friend to bore them to .5 or 1.0mm. they are better than regular 650's. they have the piston top, and therefore the ring recessed 1 mm down into the bores. stops the top ring from burning away. GTX is a heavy boat. the weight causes the crank to flex under load. the rear piston comes up 1 or 2 degrees late with the twist of the crank. the spark is still on time. makes it too advanced. burns up the rear piston. that is why the rear piston always goes in 3-seaters. you need a new head anyway. you put a ring out the exhaust. pieces of it made the head dome look like the surface of the moon. get an x head or an aftermarket one. i have a westcoast with 39cc domes. i get 155 psi. runs better than the stock 720 i just put back in it. i think i am going to re-time my GTI about 2 degrees retarded from spec. engine life is more important to me than top end.