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Please HELP!!!

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KyleB

KyleB

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Hey guys I think I may have messed up something on my 96 XP. I rebuilt the carbs and while I had them off I wanted to check to see if the rotary valve were turning properly. I removed the plugs and while they were out I decided to check to make sure the cylinders where operating properly by placing a pencil in the MAG cylinder and hand turning the drive shaft until I found TDC. While doing this I noticed the rotary valves turned and I continued to turn the shaft a couple of times to see if the valve continued to turn and it didn't. My question is, how many revolutions does the engine make before the valve turns. I did notice a clicking sound about every 1/2 revolution of the drive shaft. I know this is probably not very clear but before I put the carbs back on I just to make sure everything is ok with the engine. Thanks for any and all responses.

Kyle
 
Thanks Dr. Does the valve continually rotate or does it have a point where it stops? Keep in mind that I'm just looking at the valve through the carb intake holes so I can't see the whole valve. If I have to replace the RV gears is that a big job? Thanks again for the reply.

Kyle
 
The RV should never stop... but the window is open for 147 deg.

As far as "#5"... you would have to post the schematic you are looking at.
 
The only picture I have is the parts section of the forum and the schematic they have there. #5 is listed as the rotary valve shaft, #12 is listed as the sprocket 14 teeth and the valve itself is part #25 rotary valve (l 590). From the looks of things the only gears I see are the shaft, #5 and the sprocket #12. According to SBT the valve is 159 degree.
 
Perhaps you might position where you can see it more clearly with a light and rock back and forth the pto before ya go tearing it apart. Was the engine previously working? put a magic marker blot on the rv plate and try seeing again.
 
Thanks Bill for the response. It was working erratically and I came to the conclusion based on the great info I got from you and others on this forum that I had a fuel delivery issue. The engine would start but only idle. When I applied more throttle she would die. I took the RAVE valves out and cleaned them. Checked the fuel water separator and cleaned it. Added fresh fuel. Cleaned and checked the fuel selector valve so my last step was to rebuild the carbs. While the carbs were off I thought I would hand turn the shaft to see if the RV was turning. It did turn to a point and then it appeared to stop. I didn't want to turn the shaft too much for fear of doing some sort of damage. Did I do damage to the engine or the timing by doing this. This was a used ski that I bought for my kids back in the spring and the guy I bought it from put a rebuilt SBT engine in year before last. The engine only has about 20 hours on it. She was running great until about a month ago when I was going to put her back on the trailer after a day of playing and she just died and hasn't run right since. I'm pretty much at my wits end with this thing. I'll try what you suggest and if it is turning I'll assume that the RV is ok but will hand turning the shaft cause problems? Hope this info helps. Thanks again.

Kyle
 
No, you didn't do any harm and it sounds like your rotary valve is working fine. It will appear to stop but that's only because you can't see it moving when only looking through the intake hole. put a mark on the pto flywheel and rotate it one complete revolution, each valve should be closed or covered a little more than half the time.

go through your carbs as planned, make sure to clean the internal carb filters. did you change the spark plugs when it started running bad(not just clean them)? sounds like you may have just fouled a plug.
 
Great news ski-d00. Thanks for the reply. Yes I changed and re-gapped the plugs to .023 as indicated in the shop manual. One of the plugs was fouled pretty bad when she died so my initial instinct was to replace the plugs. Hopefully the re-built carbs will solve the problem. One good thing that has come from this experience is that I know a whole lot more about the 787 engine than I was before. Thanks again.

Kyle
 
Checked RV yesterday afternoon and it works just fine. I took your advice ski-doo and put a small mark with a soft sharpie on the valve and turned the shaft and she turned just fine. So what is involved with a top end job? Is that just rings or will I need to take her to a machine shop and get the cylinders bored and larger pistons installed? Thanks.

Kyle
 
on a similar note when I checked the compression I'm not so sure I got the gauge fully seated on the plug hole due to the angle of the block and the size of my compression gauge. Would it be possible to rig up an adapter to screw into the plug hole and have that on a piece of soft copper and then attach the other end to my gauge? If it is what size are the threads for the plugs? Thanks again.

Kyle
 
Yep... most gauges have a thread in fitting. I have an old "Push in" style gauge... and I only use it on engines where I can get a clean shot at the spark plug hole. It works well... but you have to hold it tight to get a real reading.

So... was there another problem, or were we just worried about the RV?

As above... 130 ~ 135 is low, but still usable. Also, if your location is above 4000' MSL... then the pressure will be lower.
 
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No Dr. I don't think I have additional problems just covering my bases. I hope to finish the carb install this evening and see if she will fire up. I'll keep y'all posted. Thanks again for all the help.

Kyle
 
By the way that is the old style compression gauge I have also (push in). This makes me wonder if I'm reading correctly.
 
Ok I think I may have finally found the problem. When I went back and checked compression with a screw-in type gauge I found that I have 110 PSI in the MAG cylinder and 140 PSI in the PTO cylinder. The questions I have is this; do these things loose compression that quickly? This is a SBT rebuilt motor with only about 20 hours on it! Will I need to rebuild both cylinders while I'm in there or will rebuilding only the MAG cylinder be ok? Will having these compression numbers be the cause of the thing just not running? By the way I checked both cylinders 3 times and the numbers I quoted were averages although all three times the numbers were the essentially the same. Thanks for any and all help.

Kyle
 
ALSO, what could have caused the cylinder to loose compression in the first place? I could understand it if this was the original motor from '96. Thanks again.:thumbsup:

Kyle
 
if you lost compression in 20 hr's... something is very wrong. That engine should have lasted +400 hr's.

OK... why?

1) Lean run. (Pluged carb, air leak)
2) Lack of oil (did you put in the extra oil for the break-in? Did you verify the oil pump volume when you installed the new engine?)
3) Crank out of index.
4) Ignition timing too high. (did you verify after the install?)
5) Defective parts.


The only way to know, it to take the top-end apart, and see what the piston looks like. Also... if it only has 20 hr's... does it still have any warranty left?
 
Dr. Thank you for your reply. I went back and double checked the compression and it's 120 on the MAG cylinder and 140 on the PTO. As far as your questions I have no idea since I bought the ski used from an individual and don't know how he broke it in or how he set it up. I will say that she idles great but when I start to apply throttle she bogs down and dies. The fact that the ski idles tells me that there is enough compression for her to run but I may loose some top end right? It seems that after all the work I have done I'm basically right back where I started from. I took the fuel return line off and blew into the line and I finally got fuel coming through the fuel feeder line just down stream of the carbs. Re building the top end is not an option right now and I was hoping this is something I could do during the off season. Why would this thing run so good and then suddenly just quit? I'm confused and frustrated! Thanks for your help.

Kyle
 
Is the oil line to that cylinder intact, can you check that that injector is not clogged? You may have starved that cylinder for oil. I know when I ran my skis out of oil, the MAG cyl. is the first to go (low compression, followed by broken rings, then piston seizure etc...) I had a 580 that when the oil ended, the mag cyl rings just got eaten up. Compression went down to 70 while PTO was stilla round 140. This may have something to do with how the motor is cooled (cold water coming in from PTO). You MIGHT be able to get away with a hone and new piston, but I'd be careful. If you do go this route, when ordering piston kit keep in mind that SBT rebuilds their engines with a 1mm oversize (90% sure of this, double check with them).
 
Thanks IDoSeaDoo for your reply. What you describe sounds like that might be the issue with respect to low compression. How would I check the to see if the oil line is not clogged? One main thing that I don't want to happen is seize a piston. I am getting some oil on the plug when I remove it but from what I understand that would be somewhat normal if the only thing the engine will do is idle. Thanks again.

Kyle
 
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