How much rotational play is normal on the rotary valve shaft - t2000 720 GS

[cinejeff]

I have a new to me 2000 GS with the 720 motor. The previous owner claims it was running well then on day wouldn't start when leaving from the dock. I'm a first year seadoo'er but have a fair bit of experience with the older carbed rotax engines.

The engine has compression of about 125psi on both sides, has good spark, and the starter turns it over well. I can get it to sputter for a bit if I put gas into the carb, but feels like the timing if off. It sputters really rough and will only run when I hold the throttle wide open. It also seems to spit out from the carbs a bit which seems odd to me, but doesnt backfire. It had a some crud in the internal filter but is all cleaned out now and I plan and changing the grey tempo fuel lines. After cleaning, it still does the same thing.

I'm waiting on an RV degree tool to check the RV timing and plan on pulling the flywheel to check if the stator has moved or if the woodruff key has sheared. I've pulled the engine and noticed that the RV valve shaft has some rotational play in it. I would say it has about 5 degrees of play. I'm just wondering it that could be my issue? What amount of play is acceptable?

 

[cinejeff]

[video=youtube_share;2s6DqBalm0w]http://youtu.be/2s6DqBalm0w[/video]

 

[racerxxx]

Video is private

 

[racerxxx]

More than anything the RV gear has stripped. Can you dump oil from the oil in/out of the RV cavity? If so look for brass shavings. It's pretty common on the 720's. I have yet to see anyone here shear a key way on the crank, that would be my last check honestly, but that's me.

 

[cinejeff]

No brass shaving out of the oil that I can see. This thing was way off, at about 300 degrees vs 147. It seems to turn ok, no dead spots and it gears feel smooth, just a little sloppy. im wondering if the previous owner was having trouble getting it running. The carb filter was filthy so I'm guessing that maybe they pulled off the rv cover and didn't put the valve back to the correct timing. I just fixed the video so you should be able to see it now. How else could this have gotten so out of time? Thoughts?

 

[cinejeff]

I did some more research tonight and found a service manual. Apparently the Seadoo service manual doesn't specify how much free play is acceptable, they refer to it as backlash. Also I found a very tiny nick in the edge of the RV plate tonight. From online picts, i noticed that there is a spring that holds the brass gear in place on the rv shaft. Can that gear move enough to slip if something jammed the rv plate for a second when running putting it out of time?

 

[racerxxx]

What typically happens is the gear on the crank slides to the front or back of the crank and wipes out all or some of the brass gear. That nick in the edge is not sounding good either. Something spinning at does not like any thing in its way, so yes that could be enough to wipe it out. The back lash should not be very much.

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[cinejeff]

So if the gear on the crank has moved is there a way to wedge it back to its proper position? I'm going to pull the TV shaft/open the crank case tonight.

 

[racerxxx]

Can you post a short video or mark one of the points on the shaft and also the case then rotate the shaft and mark the case. That way you could do it with 2 pics instead of a video.

You might be able to slide it, but it's gotta be centered if not you'll wear the gear out.

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[cinejeff]

So I dug into this engine tonight and found a nice hole on the bottom of the case and a crack by one of the case machine screws. So obviously something hard got sucked into this engine and caused some damage. I also found two stripped gear tips on the brass gear. The gear on the crankshaft has shifted ever so slightly, just under 1/16" (1.5mm). I'm posting some Picts but its hard to tell in the photos.

Would you run it like this or how can I centre that gear on the shaft? I found a good lower case and complete rv shaft assembly locally.

I also had about half a cup of oil pour out of the stator/flywheel when I removed the cover, seal looked ok. It almost looked like motor oil which I found weird.

 

[racerxxx]

That engine has already been replaced once in its lifetime. That crank has been welded after it was rebuilt. The only place I know that welds cranks is SBT. I think at this point you should be looking for a complete replacement. Your not going to save any money by scabbing an engine together, trust me. I'd bolt that back together and see about the cheapest cases you can get and send them in with the core. I'd never trust that crank having to slide the gear back, if that's not perfect it will eat that brass gear alive in no time. It can happen to any crank from any rebuilder, it's just the way it is. It's always in the back of my head when I'm riding my HX. Not the news you're looking for.

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[cinejeff]

Ok thanks, good to know. If cash wasn't an issue I would just do that. Actually I probably would just buy a new ski. Would the sbt pistons fit into a stock crank as I have a line on one locally? I only put about 10 hours on my Gtx this summer, I'm thinking swap out the rotary assembly now and just change the brass gear yearly as preventative maintenance. Get it rebuilt if it blows again. Can the sbt engine even be rebuilt? Or do they just send you an exchange? It's funny, I bought the 720 thinking it was a bullet proof motor. I should have stuck to another 787.