Blew up new engine 657 (pics)

[Jris88]

Hey all, pretty discouraged here. Put a new SBT engine in my ‘93 XP at the end of last season. Took it out last week and blew the PTO piston. 145PSI mag, 0 PTO. Unfortunately for me, I’m a few months out of warranty. I followed the break in procedure last season on the first tank (even used the break in oil and mixed a small amount in the gas). I had just put in the second tank of gas before it blew (no oil mixed this time).

Trying to figure out what went wrong. I rebuilt the carbs, fuel lines were previously replaced. I replaced the oil lines (no bubbles in line) and tested the oil pump before reassembling everything last year. It did have a bogging/starting issue after it would run for 30 or so minutes. Figured it was the fuel selector valve since it was the only thing I didn’t replace. Replaced it and it seemed to start and run better - great actually until it died on me.

I attached some pictures of the damage, hoping someone can tell what went wrong - lack of oil, lean, overheat? Looks like a chunk blew out of the top of piston/ring. I have three theories:

Fuel
1) the hose I used to connect mag and PTO carb is garbage. Got the ‘fuel rated’ hose from Amazon. It looks like it shrunk - seems thinner than it was. It was also rock hard instead of soft and flexible. There’s a picture of this hose (cut) with a spare piece. Wondering if it was restricting flow and starving PTO carb?

Oil
2) when I disconnected the rotary cover to look at the oil pump I noticed the cable was missing it’s retaining clip causing the end of the jacketed cable to fall out of the retaining bracket creating slack in the steel cable. The arm of the oil pump was way off its match line. Thinking it could have not been pumping enough oil because of this? Although - I may have knocked the cable/clip out of wack when I took it apart.

Stupidity
3) pushed it too hard on second tank of gas rather than babying it? I figured I could drive it like I stole it after the first tank. Maybe I was wrong?

Any thoughts or advice would be appreciated!

Also, think the cylinder needs boring or could a hone be enough?

Thanks!

 

[mikidymac]

That thing ran super lean and melted down.

Cylinders can’t be saved and will have to be bored but a lot of the SBT engines are already bored to the maximum so your only option is to sleeve them or get different cylinders.

Also that lean I would check all crank bearings too.

With the fuel lines that hard and bad there is a good chance they were sucking air and causing the lean conditions.

Just buy standard automotive fuel hose from autozone.

 

[Jris88]

Thanks mikidymac. The other fuel lines are still nice and soft. It was just the line between the carbs and the pulse line (still soft) that I used that Amazon crap. I guess that makes sense why just the PTO blew. Will def replace with autozone.

 

[etemplet]

What do the oil lines look like? The ones coming from the oil pump and into the rotary valve intake.

 

[Jris88]

What do the oil lines look like? The ones coming from the oil pump and into the rotary valve intake.

I’ll snap a picture of them but they’re new, filled with oil no bubbles

 

[etemplet]

I’ll snap a picture of them but they’re new, filled with oil no bubbles

I had an issue with a new engine and the oiul lines were about 6 months old. I just posted on it. When an engine gets damaged like yours you have to check e everything and determine exactly what happened to avoid a repeat. I had one oil line that was not the proper material.

Just in case, I have 657X parts cylinders, mag, casings and such. Good Luck !!

 

[JC-SUPERJET]

The Intake Port Oil Injection Barbs might have Check Valves/Balls in them that can get gummed up and stuck preventing Oil from passing thru where it is needed. Did you see them both squirt Oil before you buttoned everything up?

Those Injection Barbs need to be cleaned too.

If the Single Pulse Line failed, the massive Air Leak would cause a major Lean Condition in the Cylinder next to Crankcase Pulse Fitting. Which would result in a roached Piston.

If the Oil Pump failed to provide enough Oil, both Pistons would have been damaged, unless one of the Oil Barbs was clogged.

Seems like the issue is located on the PTO side only.

Hard turns and donuts will stress the PTO Piston way more than the Mag Piston, so generally, the PTO piston tends to fail before the Mag Piston.

But the difference is night and day in this case.

Post a photo of both Spark Plugs.

 

[Jris88]

Thanks for the tips JC. The pulse fitting is by the PTO on this motor and it is that shitty hose.

The oil intake injection barbs - are those the oil holes in the rotary cover? I will double check but I believe I did see oil coming out of them. The rotary cover was new from SBT so hoping it wasn’t clogged.

I was doing several hard turns - the ones where you spin on a dime and create a huge wave in front of you. Is that not okay for the ski under normal conditions? Probably 4-5 but after that I was going straight 3/4 throttle before it blew.

 

[JC-SUPERJET]

The Oil Injection Barbs are the "Last Mile" of the Oil Injection System...

Donuts are fine on a Healthy Engine. Just don't do it when the Tank Fuel Level is low as the sloshing can allow Fuel Tank Air into the Fuel Lines and then into the Carbs giving a Lean Fuel Mixture.

In this case, your Ski had a pre-existing condition that killed the Engine. The Donuts just made it fail sooner because Donuts place a heavy load on the Impeller and Engine. The PTO Piston takes the brunt of this Load. The Crankshaft will even twist enough to cause Timing changes of a few Degrees. Some Skis come with staggered Carb Settings to counter this extra Load; thus the Rear Carb is set richer for added protection.

It would have failed soon enough.

 

[Jris88]

Just an update, re-tested oil pump (pumps fine - oil coming out barbs), went over carbs (settings match stock, pop off around 27, filter was clean, and passed leak test), replaced fuel line between the carbs, and the pulse line.

Replaced the piston with a used piston/cylinder with same bore as old one. Fired right up, 150psi compression. Going to get it back out on the water and try again.

Anything else I should check out? Maybe pressure test fuel system to be sure?