Thread: do i need a new crank?
04-15-2009, 05:01 PM #1
do i need a new crank?
finally got to split the cases on my 720xp. got the crank out and all looks good except the silver ball barriering in the center of the crank (the one closest to the rotarty splines. they all turn freely with minamal effort but that one. so, the question is, can i replace that barrieing or do i have to replace the whole thing?
04-15-2009, 05:18 PM #2
Well, if all you want to do is replace the middle bearing then you can have someone press the crank apart and then press the bearing off. You can do this yourself but you need a couple special tools. Also you would have to make sure it is lined up correct.
If the rest of the bearings are truly good, you can save some money for sure. That being true I would find someone local that does it and pay the labor and for one bearing. You will save on shipping and the rest of the parts.
The real question though is if one is bad, why is that one bad and all the others are perfect? Just a thought
04-15-2009, 06:05 PM #3
get a re-doo crank and be done with it. reman crank or hot rods. I prefer the re-doo
04-15-2009, 08:43 PM #4
Hold up, I believe you have a major problem there!!! The helical gear on the crank is supposed to be centered, not to one side. The gear is pushing the seal into the bearing and that is why it is hard to turn. The bearing is probably still good, but I bet the seal is bad. I am also betting that the oil from the rotary cavity was leaking into the cylinder like crazy. I hope you didn’t hyrdolock your engine and bend a rod. The gear is press fit on and can slide over when forced too hard. Something probably got stuck in your rotary valve and jammed the valve.
Things to verify:
Brass gear – Usually strips when something like this happens
Rotary Shaft – Sometimes can bend when this happens
Rotary Valve Plate- If something got jammed between it and one of the ports, the plate might have a huge dent in it
Connecting rod- The engine may of hyrdolocked, with the possibility of oil entering the cylinder, so check the rod for bending on the side where the seal is presses against the bearing and gear.
Crank- The crank is totally repairable, I had the same thing happen on my skidoo and got the crank fixed for $100. All I needed was a new seal. If all the bearing are still good, I would just try and repair it. IF they makes noise or are rough, it is easier to rebuilt the whole thing while the engine is open.
04-15-2009, 09:42 PM #5
04-16-2009, 05:25 PM #6
A good shop can re-center that gear.. but how is your RV gear (last pic) looks pretty chewed up. Insect BOTH brass gears well, and folds, marring, chips or debris, and you will be asking for mercy once it blows again.
04-16-2009, 08:18 PM #7
ok, i got another one for you guys. this is the crank out of my 800rfi. the brass RV gear is stripped out. has a nice little flat spot in it. after i got all of the needle pins from the failed wrist pin out, the crank turned freely without the top case on it. i guess the needle barriering failed and the pins fell into the crank fubar-ing it up. so how do i get that striped gear out and replaced? where can i find a new one?
04-16-2009, 08:31 PM #8
Really easy to swap out that brass gear. You'll have to make a makeshift puller though.
You can either get an OEM gear or a WSM one (www.atlanticjetsports.com). I just sold a good used shaft/gear assembly on ebay for only 10 dollars, so if you are not in a rush you can surf ebay.
To remove the shaft:
1- Remove internal snap ring (you'll need good snap ring pliers)
2- Find a large socket that has an inner diameter larger than the shaft seal.
4- Find a long full threaded M6 bolt and some washers and nuts.
5- You'll need to pass the bolt through the socket and thread the bolt into the end of the shaft.
6- Tighten one of the nuts and washers against the socket so the bolt starts to pull the shaft out
7- Once it is out, you can remove the bearing seal and gear.
04-16-2009, 10:48 PM #9
When reinstalling try putting the cases in the oven on low and the shaft assembly in the freezer. This makes pressing the rebuilt shaft in so much easier.
04-17-2009, 11:29 AM #10
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