787 Rotary Gear

[Themist456]

Hello,
I picked up a 97 GTX. Diagnosed it as a rotary gear issue fairly quickly. I have already split the cases and flushed and cleaned out all the brass shavings. I also replaced both the full rotary shaft and smaller bearing with WSM parts.
However, after putting the new parts in, I am still getting a roughness when turning it over by hand. After removing the rotary shaft, this roughness goes away. Keep in mind, it spins smoothly until I torqued the cases together as well. However, with rotary shaft removed the crank and counterbalancer spin smoothly.

What are the possible causes? My worry is the metal gear in the crank moved but visually it looks perfect and center (I did clean all the brass off of it but there wasnt really much on it. . Is there anything else it could be?

 

[etemplet]

How do the gear teeth look on the crank shaft? I have a crank where the gear is questionable for me to reuse. You can put some Dykem Steel blue on the gears and reassemble the cases and turn the shafts and disassemble. If the gear mesh is a problem you'll see shiny spots. You could have a bearing issue.... dirt in there or something. What ever is causing the problem will get worse at 6k rpm. I had a heck of a time getting all the brass out of the engine I disassembled.

I think the guy accidently put gas in the oil tank.




The damage isn't on the drive side of the gear. I also measured the outside diameter of the gear on the shaft and it is smaller than other gears I've measured. Not from wear, from manufacturing. Good Luck !!

 

[Themist456]

How do the gear teeth look on the crank shaft? I have a crank where the gear is questionable for me to reuse. You can put some Dykem Steel blue on the gears and reassemble the cases and turn the shafts and disassemble. If the gear mesh is a problem you'll see shiny spots. You could have a bearing issue.... dirt in there or something. What ever is causing the problem will get worse at 6k rpm. I had a heck of a time getting all the brass out of the engine I disassembled.

I think the guy accidently put gas in the oil tank.

View attachment 61635


The damage isn't on the drive side of the gear. I also measured the outside diameter of the gear on the shaft and it is smaller than other gears I've measured. Not from wear, from manufacturing. Good Luck !!
View attachment 61636

The gear looks brand new and centered. That's what's so weird to me.

 

[Themist456]

How do the gear teeth look on the crank shaft? I have a crank where the gear is questionable for me to reuse. You can put some Dykem Steel blue on the gears and reassemble the cases and turn the shafts and disassemble. If the gear mesh is a problem you'll see shiny spots. You could have a bearing issue.... dirt in there or something. What ever is causing the problem will get worse at 6k rpm. I had a heck of a time getting all the brass out of the engine I disassembled.

I think the guy accidently put gas in the oil tank.

View attachment 61635


The damage isn't on the drive side of the gear. I also measured the outside diameter of the gear on the shaft and it is smaller than other gears I've measured. Not from wear, from manufacturing. Good Luck !!
View attachment 61636

 

[Themist456]

Well, new update. If I do not torque the bolts but put the cases together, everything spins smoothly. However, once I torque the bolts, it brings back the rough spot.

 

[mikidymac]

Well, new update. If I do not torque the bolts but put the cases together, everything spins smoothly. However, once I torque the bolts, it brings back the rough spot.

It is most likely a bad gear on the crankshaft or something is bent. Torqueing the cases should never cause a rough spot and no good can come from it.

 

[Themist456]

It is most likely a bad gear on the crankshaft or something is bent. Torqueing the cases should never cause a rough spot and no good can come from it.

Okay. I guess I will be buying a crank. Doh. I did find slight damage on the crank gear that I did not see at first. I don't think it could be anything else at this point. It's odd to me that there was a failure on this one as it's such low hours and no sign of damage anywhere else.

 

[mikidymac]

Too much sealant on those cases.

 

[Themist456]

Too much sealant on those cases.

Okay. Is there a picture of how much I should put? It looks worse than it is in the photo but I thought the same thing.

 

[mikidymac]

I use Threebond 1184 and only a light skim coat on both case halves. I don't like the 515/518.
If you look at the older seadoo manuals they use a roller to apply the 518 with an activator but have switched to the 1184 equivalent also.
The thing that turned me off to the 518 is it is completely cleaned off with gasoline and is only gasoline resistant and gasoline is always in the cases. 1184 is fuel proof. Having said that others swear by 518 so take my $.02 for what it's worth.

 

[etemplet]

I would suggest you get a can of Dykem steel blue. ITWProBrands

This is a layout fluid, very thin, and will cover the gears. You paint it on. Don't gob it. Put it on both gears. Assemble the cases without sealant. Make sure everything is lined up, all the partings are even especially where the rotary valve seals. Turn the crank shaft a number of times. Disassemble and look for shiny spots on the gears. Do lots of checking. Crankshafts are too dang expensive to replace just to be replacing. Identify the problem.

You might not have to install all the bolts to get a reading. Seems to me like you have something "pinching." If the crank is bent you'll have a tight spot then a loose spot. If the resistance is steady and consistent I'd look elsewhere for the problem. You could have a bad gear on the shaft you purchased. That could be the whole problem... defective part. verify that. I'd buy a used OEM rotary gear to test with before I'd replace the crank... unless you see a problem. Good Luck.

 

[Themist456]

I would suggest you get a can of Dykem steel blue. ITWProBrands

This is a layout fluid, very thin, and will cover the gears. You paint it on. Don't gob it. Put it on both gears. Assemble the cases without sealant. Make sure everything is lined up, all the partings are even especially where the rotary valve seals. Turn the crank shaft a number of times. Disassemble and look for shiny spots on the gears. Do lots of checking. Crankshafts are too dang expensive to replace just to be replacing. Identify the problem.

You might not have to install all the bolts to get a reading. Seems to me like you have something "pinching." If the crank is bent you'll have a tight spot then a loose spot. If the resistance is steady and consistent I'd look elsewhere for the problem. You could have a bad gear on the shaft you purchased. That could be the whole problem... defective part. verify that. I'd buy a used OEM rotary gear to test with before I'd replace the crank... unless you see a problem. Good Luck.

I ended up finding damage on the gear on the crank. Couldn't see it from the top but after close inspection there was a small chunk missing and very slight bend. I already sent it out to get rebuilt. Already spent too much time on it and have other stuff to do.

 

[etemplet]

I know you sent yours off already but I'll put this out there for anyone else that needs a crank. @mikidymac recommends a crankshaft shop and I can't think of the name. Guy has great reviews and a good turn around time. What impressed me most was the a walk-in customer with a crank and the guy took the crank and fixed it on the spot. That'd be nice to have someone like that in the neighborhood. I have a crank I may send him. Good Luck !!!

 

[mikidymac]

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