Crank seals?

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Mnmonster
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Crank seals?

Post by Mnmonster »

Dekon wrote:Looking at your pictures, it appears that one case half was changed. From what I understand, the two cases are matched at the factory so you do not have a step like that. I bet that is what is happening at the rear of the cylinder under the reed block; there is a step in the case also.
I would agree, however, this thing still had the stock piston in it...I highly doubt the case had ever been pulled apart...but I guess you never know.

There is a sight difference on the intake side as well, but not nearly as bad...and interestingly it is higher on the opposite side than the front.
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Tedh98
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Crank seals?

Post by Tedh98 »

Mnmonster wrote:I would agree, however, this thing still had the stock piston in it...I highly doubt the case had ever been pulled apart...but I guess you never know.
Here is a scenario you can't rule out. The stock piston fell apart and did a good bit of damage. A shop or the PO split the cases to clean-up the piston pieces and installed another OEM piston. As far as the difference in the height, they either replaced the damaged case half with a replacement or when they put the two halves together, they didn't use one or both of the alignment dowels/pins.
Mnmonster
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Crank seals?

Post by Mnmonster »

Tedh98 wrote:
Mnmonster wrote:I would agree, however, this thing still had the stock piston in it...I highly doubt the case had ever been pulled apart...but I guess you never know.
Here is a scenario you can't rule out. The stock piston fell apart and did a good bit of damage. A shop or the PO split the cases to clean-up the piston pieces and installed another OEM piston. As far as the difference in the height, they either replaced the damaged case half with a replacement or when they put the two halves together, they didn't use one or both of the alignment dowels/pins.
Yup, a dealer would have probably used an oem piston. No way to know, and no point in trying to figure it out I guess. Just have to try to find a solution.

I ordered an OEM gasket from Rocky Mountain. We will see if it seals it up any better. What are your thoughts on using a bit of gasket sealer in those areas? Or is dry the way to go?
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Tedh98
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Crank seals?

Post by Tedh98 »

Mnmonster wrote: What are your thoughts on using a bit of gasket sealer in those areas? Or is dry the way to go?
My first thought would be yamabond or the equivalent since that is what is used to seal the cases. But I'm not sure how well it will work being in contact with a gasket and spanning a "large" gap like that. What I mean is that type of sealant is used on metal to metal with much tighter tolerances. Someone else may have another product that would work better.

I think I saw in another one of your posts that you have a 1997. If that bottom end has never been split, those seals and crank bearings are 19 years old and the seals can't have too much life left in them.

Throwing this out there - take this opportunity to split the cases and properly fix the misalignment. At the same time install new crank seals and bearings. Then you can ride with confidence and not have to worry if a band-aid fix is still holding. But it is easy for me to spend someone else's time and money. . . .
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Re: Crank seals?

Post by Mnmonster »

I know the "right" thing to do is tear down and completely rebuild and machine the cases flat. However that is a lot of time, money, and work to put into a 20 year old dirt bike, even if I do like the dang thing. I am at the point where I just want to RIDE this summer and I am getting sick of finding something new that needs to be fixed every time I take it out. I may feel differently this winter when I have the time to put into it, but right now I'm sick of it. If I can get this thing sealed up to ride for the rest of the year, I would be happy with that. Maybe I'll fix it the "right" way this winter... or maybe I will just invest in a newer bike that I won't have to keep fixing failing parts on.
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Tedh98
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Re: Crank seals?

Post by Tedh98 »

I completely understand what you are saying. Once you get it all fixed up I think you will be very happy with it. It doesn't get much more bulletproof than a KDX.
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Re: Crank seals?

Post by Dekon »

I did exactly what you are saying. I rebuilt mine from the ground up but did not touch the engine. Rode it for the season and noticed it was using up a little transmission oil. It that point I knew the crank seals were going. Winter came, popped the engine out and rebuilt that. New seals, all new bearings and bushing inside the cases, had the crank rebuilt, spent some money doing it, was it worth it? Absolutely. Have not had more fun on a bike ever.
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Crank seals?

Post by pumpguy »

Take a look at the cases down near the bottom where the serial number would be stamped. If the stampings are there, then most likely that case half is original. If that flat boss is blank with no stampings, then it's a replacement.

Mine had a similar problem before I got it. No stampings where the serial number should be. On mine, both case halves were replaced as a matched set.

It doesn't look like the mis-matching on the deck faces is a whole lot; maybe just a couple thousandths? Using a straight edge and feeler gauges, you should be able to get some idea what the difference is.

IIWM, I would see if I could make a slightly thicker base gasket from softer material. This along with Yamabond or similar sealant should get you going for this season.

Good luck.
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