Engine failure

[gearren]

After about 2 hours in my 97 Challenger jetboat(787 motor), I lost power on the MAG cylinder, I was able to putt home on one cylinder. Found zero compression on MAG cylinder. The engine is a SBT engine that I installed 2 years ago, had no probs with it. I converted to oil block off at that time, and premix using Bombadier oil. I rebuilt the carbs, installed new fuel lines, and selector valves. I try to maintain the boat meticulously. When I removed the rave valve, I discovered that it had been hit by something, I assume the piston. Since I own the motor,(warranty expired), I pulled the head to see the extent of damage. There were bits of metal on the head, with scoring of the cylinder wall directly above the rave valve. This is a very low time motor(less than 50 hrs), which of course I will have to replace. Is this type of failure common? Any suggestions?

[mully]

Re: Engine failure

Can you post some pictures. I have a similur problem look for my thread


http://www.sbtontheweb.com/forum/showthread.php?t=21615

I would be interested your outcome.

[gearren]

Re: Engine failure

I'm not digitalized, i'll see if I can borrow a camara.

[Bill O'Neal2]

Re: Engine failure

You must detirmine if it ran lean in that clyinder, for whatever reason.
When a clyinder runs extremely lean it over heats the parts ( like the rave valves and pistons. Aluminum grows a bunch when it is heated up. If it were too lean, I could easily see why the problem exists in your motor.
For instance, if the top ring land broke on the exhaust side of the motor ( that is where they usually break when too hot) it could collide with the rave valve and those bits of metal on the piston crown could be pieces of rings and piston.

Scoring above the exhaust port indicates a lean hot piston has scratched the clyinder wall.

It is difficult to tell without seeing it.

[gearren]

Re: Engine failure

This is the second SBT engine that crapped out the same way, only the last one (2 years ago) lost the PTO cylinder. Diagnosis then was lean condition. I have been out of town, but I plan to pull the engine and look at the piston to determine if it was too lean. Unfortunately, I'd be willing to bet that this one also died due to a lean condition. I can't imagine how I had a correctable lean condition. I have done everything possible to prevent lean ops. I have rebuilt carbs, replaced all the fuel lines & fuel selector valve, gone to premix, hitacked all gaskets, use Bombardier oil, cleaned raves, fresh plugs. I even ran the low jets alittle rich for fear of lean. You name it, I have done it.

I really think that the engine is just too small for boat use. When used for tubing, as this was, the engine operates at max power nearly all the time, with little forward speed. Both engine failures occurred during tubing. Is it possible that the cooling system was insufficient, allowing the engine to overheat?

I am frustrated, and tired of poring $$ into this vehicle. This boat is gourgeous, but my confidence has been rocked.

[John Kubiak]

Re: Engine failure

The engine is a SBT engine that I installed 2 years ago, had no probs with it.

No problems with it 2 years ago, last year, or what?

I converted to oil block off at that time, and premix using Bombadier oil.

Well, that eliminates the lube questions if it's only one cylinder that has problems....

I rebuilt the carbs, installed new fuel lines, and selector valves.

You rebuilt the carbs and redid the fuel system 2 years ago?? Did you do anything PRIOR to putting the boat in the water THIS YEAR?



Two stroke engines make awesome power when they are lean, in fact, They run their best right before they blow-up! Don't beleive it? ask a racer, or a race tech...Hello Bill O!!!!

What I am trying to say here is that restictions in a fuel system especially at high RPM's usually will not exhibit any type of symptoms until AFTER THE DAMAGE HAS OCCURED! Most folks don't realize that they needed to do a carb overhaul until they blow the engine..ask around!

[gearren]

Re: Engine failure

I winterized the boat/motor (North Carolina, so winters are gentle) Stabil in gas, fogged the engine, silicone the ouside. Started it in Dec, Feb, April...Ran great..Took it out in April, burned up old gas, put in new gas, cleaned Raves, changed drive oil, new plugs, the whole smack. My neighbors think I'm an idiot for the time and $$ I spend on this watercraft. It truly is a "Personal" watercraft.

[Bill O'Neal2]

Re: Engine failure

I have my own personal opinions of pushing around heavy boats with lightweight pwc engines. To me, they have never made a lick of sense from the very first pwc jetboats I ever saw, until Sugar Sand and Sea Doo and few lesser known companies started putting Merc's into their pwc jetboats.

You could help your situation by installing my rejetting kit with Prok filters and Outerwears and a Skat Tral Swirl impellor, but other than that, I still don't like the whole idea of a pwc powered jetboat.

[Technical Support]

Re: Engine failure

It's kind of like dropping a Harley engine...in an F150 :)

[gearren]

Re: Engine failure

I already have the skat trac impeller, it helped, but I have to agree, the single engine jetboat just doesn't cut it, unless you are just cruising. I like the idea of the Merc, with larger jet drive. I plan to make this boat right, and sell it, maybe look for a twin engine, or a Merc powered. Unfortunately I will need to let my coffers replenish before I get a replacement. Thanks for the input.