Thread: crank index issue with 780
08-05-2012, 04:10 PM #1
- Join Date
- Aug 2012
crank index issue with 780
i own a 96 Polaris 780. bought is brown up. pulled the heads and cylinder towards rear of ski is burnt. piston is fried. i checked crank index and it is off. My question is that is there any known permanent fix for this polaris issue? i dont want to have my crank re timed and waste 1000 bucks rebuilding this engine only to have the same thing happen.
I was told by a dealer that this happens by the ski coming out of the water reving up and coming back down into the water. i know that this is very hard to avoid while riding, so if there is no known good fix i am just going to scrap the whole project.
I have found a few re manufacturing company's who weld these cranks. is this a known good fix? thanks for your time...
08-05-2012, 05:00 PM #2
Welcome to the Hulk!
Some companies will weld the cranks after they are trued. This will prevent the problem but make it almost impossible to rebuild again.
08-05-2012, 10:19 PM #3
- Join Date
- Jun 2008
- Bullhead City AZ.
The Dealer is right about the rev’ing and jumping out of the water it also happens if you suck up a rope or something like that to stop the impeller suddenly. This does mainly cause the mid and or rear cylinder to come out of Index.
The only way to fix it is to rebuild the crank, sometime can be done without replacing the parts but its very hard and takes longer to do then rebuilding. When trying to save parts like rods or bearings the rebuilder must be very careful taking it apart and there is no Guarantee.
When I rebuild cranks we use a 24 inch chop saw and cut the rod pins and rods making the job much faster then trying to save and re-use parts.
On the welding part; Yes welding is very good but on all Polaris cranks the rod pins can only be welded, Not the centers like on a Kawasaki, Seadoo, Yamaha crank. The Polaris crank use a center Hub system and the only way to insure the crank won’t come out of index is to Pin the centers which is very pricy.
On the comment that a crank can’t be rebuilt again after its welded is Not True 25% of the cranks I rebuild are welded its very easy with the right tools to take care of that. I have a 80 ton press most crank go together with 3-5 tons and welding only helps the rod pin will not move as easy as a non-welded one. Once it's apart you can grind out the weld like chamfering a cylinder on a 45 degree then rebuild, true and then re-weld and once its cool again re-true the crank.
I use all custom made CNC machined rebuilding jigs to Index the crank right.
Anything can be done with the right tools and know how.
I hope I shed a little light on Crankshaft rebuilding
08-05-2012, 11:38 PM #4
- Join Date
- Jul 2007
- near Toronto, Canada
There are many Fuji engined Polaris watercraft reliably running around and sometimes jumping waves.
It does stress the driveline when the jet pump reconnects with the water, but releasing the throttle when the jet pump first catches air goes a long way towards keeping the engine happy.
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