1996 Speedster one engine locked up

[estorm]

Get ready for prediction time!

1996 Speedster - recently rebuilt carbs on one engine and had to replace the tuned exhaust as part of the mounting flange broke off the original one. The boat ran great, the plugs were a lovely brown color when I checked them, and after the work I mentioned above I put about three hours on the boat and it ran perfect.

Took it out yesterday, it started right up, went for about three minutes and the engine I had been working on quit.

Brought it home, removed the plugs and it wouldn't turn over, but it does move a couple of degrees back and forth and goes clunk at each stopping point. I removed the pump, as the wear ring did have a small tear in it, which is new within the past month - not sure when that happened. The motor still doesn't turn over, just clunk. When I try to start it, it just goes clunk.

So, what do you think I will find once I pull the engine and explore? And, what would lead to it running great and dying without warning?

Thanks!!

 

[estorm]

Get ready for prediction time!

1996 Speedster - recently rebuilt carbs on one engine and had to replace the tuned exhaust as part of the mounting flange broke off the original one. The boat ran great, the plugs were a lovely brown color when I checked them, and after the work I mentioned above I put about three hours on the boat and it ran perfect.

Took it out yesterday, it started right up, went for about three minutes and the engine I had been working on quit.

Brought it home, removed the plugs and it wouldn't turn over, but it does move a couple of degrees back and forth and goes clunk at each stopping point. I removed the pump, as the wear ring did have a small tear in it, which is new within the past month - not sure when that happened. The motor still doesn't turn over, just clunk. When I try to start it, it just goes clunk.

So, what do you think I will find once I pull the engine and explore? And, what would lead to it running great and dying without warning?

Thanks!!

 

[jts32]

You said you recently had the carbs off. Check the flame arrestor base and see if all the bolts are still in place. It's very common for them to come loose and get ingested through the intake, jam the rotary valve, and strip the brass gear on the RV shaft. Unfortunately a complete teardown if that's the case.

 

[estorm]

The engine is unwell. One of the needle bearings at the top end of the rod exploded and then proceeded to scatter itself around. Some parts were stuck in the rotary valve as well.

Here's a link to some pics.

Top end would need new sleeves as one is cracked. The crank seems to turn smoothly other than when debris gets in the way. Rotary valve plate needs to be replaced and both surfaces need to be machined.

Questions:

Why did it blow up? It doesn't appear that it was running lean, oil was getting everywhere, and when I checked the compression a few weeks ago (three or so running hours) it was at 145/145.

What should I do with this engine? Rebuild it (how far do I go? ), buy a rebuilt one, or something else?

Really, my main concern is that if I fix it, whatever caused it to blow up will happen again.

Any thoughts would be appreciated!

 

[JeremyD615]

What’s the history of the boat? Did it spend a long period sitting? Sometimes you can get rust on those parts when they sit too long not being used and over time it will eat the bearings...

 

[estorm]

The boat lived in Boise, ID for most of it's life ans was used a couple of times each summer. I got it four years ago and have used it about 10 times per summer. So it never sat for more than a year, but its use has been minimal. It's never seen salt water.

I don't have a hard time believing that the bearing could have just finally failed after 24 years, but the timing of it, given the work I just completed, worries me.

 

[JeremyD615]

I really wouldn’t stress it if it was a needle bearing that let go. If you had a melted piston or signs of seizure then you have a problem to work out, but that doesn’t appear to be the case here.