1998 Challenger 1800 bad starboard side cavitation and other smaller issues

[PaulB84]

Hi all. Long time lurker, first post. Got a 1998 Challenger 1800. Used to ride an HX and XP as a kid, and still have both. Not a total noob, just enough information to be a hazard lol. I'm pretty decent with two strokes in general and rotax specifically, but don't know much about the pump/plate/shaft/impeller/intake side of things.

Largest issue on the boat I can find: simply put starboard side has more "rattle" going on than I'd like to hear. To be clear I don't mean internal engine noise, I mean pump/shaft/nozzle area. Noticeably louder and more metallic than port side. Also, taking off slowly, everything runs great and she absolutely zips. But from a standstill fast start starboard side cavitates badly and you need to lower RPM to keep from doing something dumb. Ditto on sharp turns to port, starboard pump looses it's grip.

Impellers appear good by visual inspection. Weed guards seem to be functional and don't rattle or play excessively. On the PORT side (non issue side) the blue plastic around the impeller shaft is broken off/missing above the seal.

I'll try and gloss over the myriad of other small issues any used boat has. Both motors start, run and drive well enough for now. Starboard side had a new starter, it appears to be cheap cause it simply doesn't turn over like the port side. Starboard side also runs a few hundred lower than port, you can compensate with throttle position but in N the boat turns in a circle. I'm hoping a simple throttle cable adjustment can solve that one. Speaking of which, with wheel Max to port, the port side motor revs a few hundred RPM. I've followed the steering and throttle cables as far as I can, haven't found anything damning. It happens reliably, every time, whether in F N R. Thanks in advance guys and gals.

I'm thinking carbs for sure on the starboard side, probably a pump rebuild but wanna get it from you gurus. Paul in Michigan.

 

[PaulB84]

Uh, I may have another problem.... SMH.

 

[wayneh]

Ignoring the compression issue for the moment, your one-sided cavitation issue could be as trivial as needing fresh grease in the PTO on that side. Plenty of grease there pushes the driveshaft slightly aft and this in turn tightens up the carbon ring seal. A loose seal there can cause air to get sucked in around the seal. You doo have that kind of seal, right? If it's the older bearing seal, this "fix" may not help.

The revving at full turn is by design. It's meant to increase maneuverability.

 

[noviceskier]

Ignoring the compression issue for the moment, your one-sided cavitation issue could be as trivial as needing fresh grease in the PTO on that side. Plenty of grease there pushes the driveshaft slightly aft and this in turn tightens up the carbon ring seal. A loose seal there can cause air to get sucked in around the seal. You doo have that kind of seal, right? If it's the older bearing seal, this "fix" may not help.

The revving at full turn is by design. It's meant to increase maneuverability.

they switched to carbon seal in 96 i believe except for the 95 hx

 

[PaulB84]

Thanks guys. I'll update as I go. Can't believe that starboard side motor ran as well as it did with one cylinder that blown. Haven't pulled head yet but I'm assuming total rebuild for starboard motor plus carbs and pumps.

 

[PaulB84]

Finally tore into the starboard motor. I've rebuilt a zillion chainsaws but this will be my first rotax. Still amazed it ran. Chunk gone from piston, ring broken (where's the piece?? That had to be the rattle I was hearing) and a thumb size burn in the top of the Piston. Head looks immaculate. Cylinder walls look really really good too but I need to inspect much closer. Is there any chance the lower end isn't trashed? I don't see how I could get away w just a piston and rings but that's what I'm hearing so far.

Any chance of a rebuild here or just yank and replace? Thanks in advance for your help. Pics coming. Compression in bad cylinder was 55, opposite cylinder very high 190ish.

Paul

 

[PaulB84]

Edit- derp my brother and I started threads on the same boat same time. Sorry guys. Mods, please combine

 

[H€PHÆ$TU$]

My rule of thumb in terms of economics for rebuild vs replace is, if the crank needs any work, you're money ahead to replace. The pieces of your piston are probably down in the bottom of the crank case or somewhere in your exhaust system. If I were in your position I'd pressure test the crank case and RV gear case, and if it passes, split the block and inspect. If the RV gear case doesn't pass the pressure test, order new engine.

With the piston in the condition you say it is, I would have to do some seriously close cylinder inspections and measurements before I re-used those cylinders.

 

[chipskittles]

That sucks about your motor. Even if you luck out and the only damage is at the top, you will still want to replace the mag and PTO crank seals and rebuild your carbs. Seals will require splitting the case but I would not skip this. Leanness from airleaks or carbs is what killed this motor in the first place.
When you get it going again, if you still have cavitation it might be as simple as adjusting the carbon seal boot to put more tension on the carbon seal. Also, the driveshafts have a bumper at both end, these get squished over time and will throw off the carbon seal assembly adjustment. It will also cause a pump rattle that you will notice when flushing the motors on land.

 

[PaulB84]

Thank you gents. I will proceed and report back. SBT generally the go to for replacement? I have a local guy who wants the same $ but no core. Also no warranty lol

 

[H€PHÆ$TU$]

One of my engines is an sbt. I'm happy with it but it's only been in there for about 20 hours.