center crank seal

[gavinvader]

Hello again guys!!!   Im a revisiting old member.  Been awhile since i've been here but getting ready to tear into the old invader again!!  I had troubles with frying one of my pistons over and over.....like 3 times i think.  If i remember correctly, Jim donated to me another new piston to help soften my discouragement.  Well its been i think 6 years or so and am finally gonna get back at it.  I also have a new cdi box to put on it, Jim thought maybe that could be the problem.  My question is about the center crank seal.  I feel i should replace this while it is apart in case it may be the culprit also.  Where can i get a replacement and does the crank have to be pressed apart to change one?  Thanks in advance and good to be back.  Nothing sounds like a good kaw engine!!   oh yeah.......79 invader is my sled

[mswyka]

I have heard many things said about center seals but it is my firm belief that center seals can't blow out and never need to be replaced.  The end seals are rubber gland seals and actually wear on the crank.  The center seal is a wave interference seal that is made up of a series of rigid grooves that trap the compression wave and do not allow it to communicate from one cylinder to the other when in operation.  When not moving the center seal allows free communication between the two cylinders.  I have a photo or two here somewhere and will post if I can find it.  Ok, found the photos and hope they come through clearly.  You can see that the inside sleeve is smooth and then the outside part, that is the aluminum part with the rubber bands around it has the grooves in it. So they don't actually touch but have a couple of thousandths clearance between them.

[mswyka]

Well those are bad looking photos!  The secondary in the background is more in focus than the center seal.  If I can find it again I will take better photos.  But the long and the short of it is that you should not be fooled into an unnecessary, and expensive center seal replacement.

[gixxer6]

mswyka is correct.  It uses a Labyrinth seal.  This is a quick and interesting read:  http://en.wikipedia.org/wiki/Labyrinth_seal

Unless there is problems with the crank bearings causing the crank to contact the seal, they won't wear out or go bad.

[jimvw57]

I always thought the center seal worked off the oil pump, oil was injected into the labrynth and sealed the crankshaft. Since there is no actual 'seal' just a coating of oil, it should never wear out. (unless the oil pump fails or is disconnected) The oil is then fed to the bearings.

[mswyka]

Jim, it is actually not a labyrinth.  In a labyrinth the path is made longer because you have to go up and down, note the diagram on Wikipedia.  In the Kawasaki center seal it is more like a hallway with little side rooms that allow the compression wave to expand and re-compress.  There is actually very little oil that enters at this seal, and because it is wide open all the time, never enough to actually form a plug.  I would have to get into the mind of the engine designers, but I personally believe that the center injection of oil is more a function of providing lubrication for the bearings on the sleds that have the extra shields on the crank.  It is important to note here that the Intruder has the same seal but has no center oil injection and does not have the crank shields next to the counter weights.  I think I should take some more photos.

[jimvw57]

I think I have one of the two piece ones around somewhere, not sure where but I should probably take a look at it...  The manual does say injected oil goes to the bearings and doesn't say anything about the seal, although it shows a picture of the oil going through the seal..

Great! now you got me thinking again! I hate that!!!

[gixxer6]

Looking at your second picture, it appears to have grooves cut cross-axis of the crankshaft.  Which would provide a "tortuous path to help prevent leakage". 

It looks like a Labyrinth seal to me...But who knows!   

[kawhead]

the kaw motors that had center seal problems were in the old cats....if its bad on a newer sled you've got other issues.....3 pistons .....ouch!always the same side?  crank seals replaced? running an airbox?

[Invader440]

the kaw motors that had center seal problems were in the old cats....if its bad on a newer sled you've got other issues.....3 pistons .....ouch!always the same side?  crank seals replaced? running an airbox?

Yup, 71-73 Cat was the engines with the center seal problem that was replaced with the 2 piece unit.  If you do want to replace the O rings, Cat part number is 3001-437.

[gavinvader]

Thanks guys for stopping me worrying about the center seal.  I love how every one jumps in with some advice here .....its great!!  Forgot what a great group you guys are.  Kawhead ...yes it was always same side.  New crank seals and yes running an airbox.  That was why Jim thought CDI box could cause the issue.  Always had trouble getting the coolant sealed up to....might be a contributor to the problem.   Any suggestions on better seal for heads?

[gavinvader]

i found the post under help topics about sealing the heads so no need for replys...thanks

[kawhead]

a kaw piston that burns down lean will have a 4 corner score....if the exaust is 12 and intake is 6 o'clock, lean will be scored at 2,4,8 and 10.

[mswyka]

I don't know if this photo is any better than the other one, but there is a series of square grooves on the inside of the seal.  The mating part of the seal is just a smooth steel collar.