View Full Version : Crank center seal?

03-21-2003, 05:53 PM
Rebuilding motor on 95' street RS in the US. As it is apart I want to replace the center crankshaft seal between the con rods. Aprilia dosn't show a part number for this seal. Anyone know how to get this part. Thanks

micah apriliaforum com
03-22-2003, 11:05 AM
The crank center is welded to the crank wheels along the center line....so replacing that seal is diffucult at the very least. If you do get yours apart without destroying the seal just take the seal to the local bearing house and they should be able to get it for you.

03-22-2003, 02:05 PM
When I had one of my cranks rebuilt I was told the centre seal is a labyrinth seal so it should still be OK. And it was. The crank was rebuilt because one of the outer seals was not sealing. Poor running at low revs[below 8000] and popping in the exhaust, spitting back through the carbs. Above 8000rpm it was still strong.

03-22-2003, 02:11 PM
Thats 8000 rpm not 800 rpm

03-24-2003, 11:37 AM
I have my crank on the workbench right now and have a question about the center seal which is supposed to be of the labyrinth design.

How is this seal supposed to work?
My seal spins on the shaft and it has 0.1 mm radial play to the shaft.
I thought that the inner ring of the seal was supposed to be connected to the crank somehow.
The outer part is obviously clamped by the crankhouse halves so it is stationary.

Is my seal defective or is it supposed to behave in this way?
Canīt see how the labyrinth thing would work if the inner ring isnīt connected to the crank.

How can I check for proper operation of the seal?:|

micah apriliaforum com
03-24-2003, 12:13 PM
I am not sure on this one either, even brand new cranks seem to have play in the center seal which I cannot imagine makes the best seal possible. I do not have experience with two cylinder two strokes other than the RS250 so I do not know if this is common practice or not.

03-24-2003, 01:44 PM
Deefred wrote: <blockquote><strong><em>Quote:</em></strong><hr>How can I check for proper operation of the seal?[/quote]

you're going to hate this answer... with the engine assembled, apply 3psi of pressure to one sealed cylinder and then listen for air to escape from the other cylinder.

i made block off plates to seal the exhaust and plugs for the carb ports. there should be no leaks anywhere. when you pump up one cylinder, there should not be sizeable leaks from the crank end, around the reed cage, from the cases, or out the other cylinder. NOTE: only use 3 psi. i use a leak down tester and have found that with the regulator set to something like 82% leak down, the pressure maintained on the outlet is 3 psi.

the last time i assembled a RS250 bottom end, i had to do it 3 times to get enough sealant on the center and end seals. the real sucky part is removing all the sealant from the previous attempt before reapplying more.

good luck,

03-24-2003, 02:35 PM
My thoughts on the possible make up of the centre seal would be like.A sleeve pressed on the the crank with an even number of viton-rubber-plastic? circular discs with an outer sleeve with odd number of discs facing inwards a bit like meshing two combs together.[as in hair] Hence labyrinth seal.With that sought of make up, the seal could have some movement. Well thats my 2pennies worth UK style.

03-24-2003, 03:43 PM
I know a friend who has a damaged crank, perhaps we can remove the seal from that one and see the design of it.

03-26-2003, 03:00 PM
Best answer so far can be found here,
<a href="http://autos.groups.yahoo.com/group/Apriliacup/message/3834" target="top">autos.groups.yahoo.com/group/Apriliacup/message/3834</a>