First blown engine. =(

fastgtfairlane

fastgtfairlane

Location
Charlotte, NC
It was probably in need of a bore when you replaced the pistons and the new pistons caused the issue. Ill bet the cylinder walls are egg shaped if you were to measure with a bore gauge.. I bought a 750ssxi years ago. Cylinder walls "looked" ok so i put fresh pistons and a light home on the cylinder. I got just over 2 seasons out of it. Decided to have the head milled and put a lightened flywheel on. Got 3 rides out of it when it blew. Had a broken skirt on one of the pistons just like yours.
 
WFO Speedracer

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
Yep I ran a 650 Kawi motor like that for years , very noisy engine that I put together out of a bunch of spare parts, it never did let loose God only knows why.

I took it by my cylinder boring guy about a week before a freeride , he said it needed to be bored 2nd o/s , it was at std bore size , I didn't have the time to have it bored and get it back together so I installed a new set of std rings and went with it , it worked just fine till I replaced the entire engine about a year later.
 
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Quinc

Quinc

Buy a Superjet
Location
California
Last bore on the cylinder and figured after 10 years she could use some preventive maintenance. I did check the ring gap in multiple spots and give her a hone. Live and learn. Now do I drop in a oem 760 or go with a big boy engine? =)
 
yamaharider85

yamaharider85

Location
Socal
Sorry for your loss. Did it take the 62t cases with it or just the crank? How does the cylinder look?

Also do all 701’s goto heaven? Asking for a friend.
 
WFO Speedracer

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
harrymank said:
You put pistons in a worn out engine without doing cylinder work? How did the rings even seat?
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Who knows , it ran well enough till I got another engine put together , sometimes you just have to do what you have to do..
 
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Myself

Myself

manic mechanic
Location
Twin Lakes AR
I rebuilt a customers Seadoo 787 this past winter that was loose enough the first oversize piston would slide HALF WAY down into the cylinder!! Still didn't break a skirt.
 
WFO Speedracer

WFO Speedracer

A lifetime ban is like a lifetime warranty !
Location
Alabama
Myself said:
I rebuilt a customers Seadoo 787 this past winter that was loose enough the first oversize piston would slide HALF WAY down into the cylinder!! Still didn't break a skirt.
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The main issue here is it is a 760 , those from my experience are bad about breaking skirts and trashing sleeves , the sleeves are too thin in my opinion , at stock bore they are ok after that watch how far you bore them out , I don't go over 2nd O/S on those cylinders .

I have one in here now that is 1.00 O/S , it's an SBT engine of course and if you know about SBT you know their engine are std bore or 1.0mm O/S bore , that's all they offer ,if you get a std bore one you are good to go , if you get the 1.0mm bore when it breaks you are done , I have never torn into an SBT engine that was std bore and I have seen the inside of many of them..

The customer didn't understand why it couldn't be bored to 1.5mm O/S , my answer is it can be but I won't build a motor with it because I know it won't last.

Most here don't realize how Yamaha got the 760 and 1200 engines , they quite simply bored out a 701 and an 1100 as far as they would possibly go , you can take an 1100 Yamaha liner and drop it in a 760 or a 1200 and bore it to size, I have done this numerous times , pretty much the same with a 62T and a 760 liner , the 701 liner will go into the 760 cylinder just fine but there is an exhaust port difference on the 62T to the 760 , 1100 and 1200 there is not.
 
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kevbo

kevbo

Location
dfw
What is a big boy engine? Remember larger bores will always have higher fuel requirements. Standups can get away with really hot setups where the same engine would melt in a couch.
 
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