hairline crack in speedster engine block

[jprice]

This is basically a continuation from this thread: http://forums.iboats.com/showthread.php?t=352865
But since the issue has become engine related, I figured I'd start over here.
.....
It's a 1996 Speedster with the twin rotax engines. Been having issues with the overheat alarm going off after only a short time on the water. So as recommended by a local seadoo shop, I should start by flushing both engines, which I just did.

At the end of the 2-3 min flush on the right engine, the overheat alarm starts going off. I check, and neither the engine or exhaust are even remotely warm.
So I'm pretty happy thinking it's a thermostat issue. But since I'm doing it, I go ahead and flush the left anyway. No problems there.

Replace the thermostat, and flush the right again as a test.
Then I peek in the engine compartment and see this... (it's a little hard to see, but there's a small stream of water coming out of the block towards the exhaust)

Here's a view of the crack (again, a little hard to see, but it's there)

Is there any way to fix a hairline crack in the engine block other than buying a completely new engine?
I've read about some successes with JB Weld. Has anyone used it in a similar situation? If so, how well did it work?

 

[Mark22]

Re: hairline crack in speedster engine block

I believe on those blocks you can have them welded. They can be welded unless the crack is through a gasket mating surface. If thats the case, your block is shot. If I was you, I would start by pulling the engine and get a closer look at it.

 

[Jeff Walkowiak]

Re: hairline crack in speedster engine block

there is a gasket in a channel where your engine is leaking sort of like a big square rubber o ring,, and the block corrodes a lot in that area but that is not your overheat issue,, the sending units on those engines are notorious for going bad,, as for the leak,, clean the area and for the time being just j b weld it,, and later on you may have to do it again,, but it isn't a big issue

 

[jprice]

Re: hairline crack in speedster engine block

...but it isn't a big issue

Man, I sure hope you're right.
Last night I cleaned it, v-grooved it with a dremel, and applied the jb-weld.
It's supposed to rain all day tomorrow, but I'm still going to pull it into the driveway and give it another flush test.
...we'll see if it holds.

...the sending units on those engines are notorious for going bad

When you say "sending unit", are you referring to the thermostat sensor in the middle of the block? Or some other electrical component?

 

[jprice]

Re: hairline crack in speedster engine block

Well, I gave it another flush test today, and the JB-weld appears to be holding. Woo-hoo!

I also decided to give it a compression test just to make sure there was no loss of compression on the cylinder near the crack. All cylinders in both engines show a compression of about 125-130, so I'm happy about the consistency, but I have no idea if this is within acceptable ranges.

According to the shop manual it says:
Compression ratio
Uncorrected 12.25 : 1
Corrected 6.2 : 1
But there's no mention of any psi number. I looked around online, but can't seem to find anything. I saw a forum post somewhere that said 145psi was ok, but nothing that's giving a range of values.
Anyone know what an acceptable compression range is for the 717 rotax engine?

 

[Mark22]

Re: hairline crack in speedster engine block

125 to 130 is good. It doesn't really matter, as long as both cylinders are within 10% of each other. That is the general rule.