96 challenger SBT engine died! What happened?!???

[manolocross]

Long time poster here but I haven’t posted in a bit. First off I want to say thank you to this forum. It has always been a great source of info for me. Hey @racerxxx !!!!
Quick backstory.
96 challenger single 787
Rebuilt carbs changed 2 stroke oil and filter and lines to XPS 2
Changed carbon ring
Changed wear ring
Ran great!
Winter came,owner did NOT WINTERINZE. CRACKED cylinders and head.
SBT engine ordered and installed by me. I have lots of old seadoo experience. Enough to do this for a living but do it as a hobby. Engine ran great for approximately 50 hours. PTO cylinder piston crown and rings blew to bits. SBT NO FAULT 2year warranty.
It was a LEAN RUN. In my investigation(lol) I found CHEAP Tcw-3 oil was used and mixed with XPs 2 oil. It was a “only thing they had at boat store” situation. I warned him about this. The boat store even recommended it! They obviously don’t know s**t about 2 stroke seadoos. But that wasn’t what killed it! It helped it die but was not the smoking gun.
Turns out THE GAS TANK WAS SHRINKING! I took one look in there and immediately saw that the gas tank had a huge VACUUM imposed on it and was semi collapsing!!!!
So the lean run happened and exploded the cylinder. So engine is on its way back to SBT AS I TYPE. So I need to remedy this problem. The only thing is I can’t find any info online on this boats (manual) and part numbers for gas tank purge and check valves. Also the boat is not at my garage so I just took a quick look in Hull and could not locate the purge valve in boat.( I just took a quick look)...
So my question is
Where is the purge and check valve located?
What are the part numbers?
Where can I download manual?
Pics you can show me?
Sorry for long post.... thanks boys!!

 

[Steve762us]

The 1996 Challenger has a fuel tank vent hose that emerges from starboard
side of hull, below the fuel filler cap. I never checked it for a check valve, but
mine doesn't act like it has one...just a big vertical loop in hose to keep water
from coming thru line to tank.

 

[manolocross]

That might be possible. I have to really look into it. But if there is nothing in line, why would the tank collapse like it had a huge vacuum on it. Anybody else have this issue?

 

[JeremyD615]

The fuel tank should have a vent line with a check valve on it. There is one that runs to the valve just underneath the rub rail that lets air out, and there is another that runs to a check valve to let air in. You’ve got something plugging that line up.

If you trace the vent line from the fuel baffle, you should be able to find where that valve is. I’m not exactly sure on your specific hull.

 

[Steve762us]

There's no need for a "check valve"--which would just introduce a failure mode and additional
manufacturing cost. Water intrusion is prevented with a riser loop in the vent line, routing it
from tank top to starboard hull, up toward the fuel filler cap, then back down to the thru-hull
vent fitting...similar to how bilge pump hoses are fitted.

AFA 'collapsing' the poly tank--no idea on that one. Maybe someone left the tank empty,
with all lines sealed, through a major seasonal temp change. I don't see engine fuel-draw
pulling anywhere near enough vacuum to do it.

 

[JeremyD615]

There's no need for a "check valve"--which would just introduce a failure mode and additional
manufacturing cost. Water intrusion is prevented with a riser loop in the vent line, routing it
from tank top to starboard hull, up toward the fuel filler cap, then back down to the thru-hull
vent fitting...similar to how bilge pump hoses are fitted.

AFA 'collapsing' the poly tank--no idea on that one. Maybe someone left the tank empty,
with all lines sealed, through a major seasonal temp change. I don't see engine fuel-draw
pulling anywhere near enough vacuum to do it.

I’ll have to get into my Speedster to see how the vent line is routed. I’m pretty positive that mine has a tee and a check valve just like the skis though... Now I’m wondering if that was modified at some point...

 

[Raven888]

I agree with Steve762us, there is no way the engine can pull enough vacuum to collapse the tank. The engine would stall first. This a common problem on motorcycles when the vent in the gas cap gets plugged. You're happily motoring along and paff, the engine dies.

 

[JeremyD615]

You guys are right, the vacuum on the fuel system is not nearly enough to collapse the tank, but a large temperature change with a plugged vent is more than enough... I still think he’s got a problem in the vent line or fitting...

 

[jts32]

The vent is on the starboard side, about 6" below the rub rail. It is an Attwood vent. I believe it is part # 1607-3. It doesn't appear to be a valve, just a vent fitting designed to keep water from getting in. I currently own two '96 Challengers, '98 Challenger 1800, and '98 Sportster 1800. All four tanks look like the top has collapsed, leaving a gap between the tank and straps. I think it's just the norm on these 20 year old tanks. I don't believe they collapsed because of vacuum, and I've never heard hissing when removing the gas cap

 

[manolocross]

Thanks guys... lots of good info. I thought that Atwood peice was the check valve but wasn’t sure because it looked nothing like what is on Jetski’s. Also I just did not have the time to investigate. But I’m gonna order it and replace it. Well as far as tank collapsing, it def was not like that when I replaced engine first time. So he had the engine failure and that is the first thing I noticed.

 

[Sportster-2001-951C-Stock]

Without reading all the posts, a check valve device for fuel tank makeup air is perhaps in the tank vent tubing. I don't think it's built into the fuel cap but might be? On mine the device I'm thinking of is called:

Vent Line Surge Protector

204560101

 

[Sportster-2001-951C-Stock]

I've never heard hissing when removing the gas cap.
/QUOTE]

I've never heard hissing on mine either.

Put a vacuum gauge on the fuel tank and pull a slight vacuum. Also pressurize the tank and make sure it doesn't go over spec, maybe 5psi?