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Replacing crank seals a big job? ('91 KX250)

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My bike is old (so am I).

 

It has always seemed to run rich.  Way smokey when I got it (two years ago).  It had stock 160main and 58pilot.

 

I have continued to lean it down and am at 155main and 42pilot now.  Runs a ton better.  Not so gurggly on the low end.  Not as much smoke...but still some.

 

It has never ideled like my buddy's KTM200.  He starts his and lets it idle on the kick stand for a minute or more.

 

Some have pointed out:  It's an old bike and should have the crack seals repalced every 150 hours or so.  I personally have put way more than 150 hours on it over the past 24 months.  The PO probably didn't do it any time recently.

 

Is it good practice to replace crank seals on a scheduled maintnence program?  I put a new piston in it every winter so far....good practice.

 

The question is:  How involved is the crank seal replacement?   Have to take the whole motor out and split the cases and all that?  :(  Or, take both side covers off and can get to them there from each side=not much more difficult than a piston replacment? 

 

It's an old bike and probably needs them done.  But, maybe they are still good....how would I know?

 

CooHead

Edited by CooHead

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Yea...I was looking in the service book about it.

 

What are the chances they are still in good shape  and sealing properly?

Not much I'm guessing.  If they are wear items, they need replacement I'd guess.

 

The bike has was in good condition when I got it...even better condition now that I have had it.

But if seals do indeed wear, these should be worn I'd guess.

 

What are the tell tale signs of it needing crank-seals?

 

CooHead

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You should pressure test the motor to see if the seals are leaking. I think there is a thread on it in the Honda 2stroke forum. When you do the test sometime the power valve actuating rod seal will leak pressure,if it does try greasing that little seal to make it stop so you can check the main seals.

 

I have a case splitting thread up in the FAQ thread above if you want to check it out.

 

Ed

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Yea Clyde, I was hoping you would respond.

I did indeed see and read that thread in Honda form.

Guess I could and should do a proper leak down test.

 

Wouldn't be surprising that it does indeed need crank seals tho, yes?

 

I can try to track if it's loosing tranny oil BW.  Like note where the level is in the window and see if it drops after riding a bunch.  But don't know if that will be true to the crank seals as it often has a drop....or two of tranny oil under it after riding.  It comes from the vent tube.

 

Guess I could learn how to split the cases and replace them myself this winter.  Give me something to do.  I'm sure I'm capable and could get the proper tools needed.  Hence my question how big a job is it?

 

Coo

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It starts AOK.  Usually bump start it first time as my garage is on a hill....and I'm old.

Cranks easy and fires first kick from there on out.

 

Just did the silencer packing the other night.  It was indeed oily and saturated.  Doesn't spooge much, couple drops here and there because I didnt have any high temp silicone when I put the silencer back together.  Plug is often black.

 

I have it jetted much leaner than when I got it.  Much leaner than factory.  155main and 42pilot (factory was 160 & 55).  Still smokes good and doesn't idle well.

 

I'm assuming that crank seal lets tranny fluid into the equation.  If that were the case, would I get a hint of tranny burning smell in the smoke?  I thought I whiffed that recently.  NAPA didn't have ATF type-F, so I got their ATF (that said on the back it was good for type-F applications).  But today and yesterday (since I changed the tranny oil and moved the needle and changed the air screw), I've been conscious of what it needs, what its been doing.  Seemed to notice a different smell.....like burning tranny fluid.

 

Is that the case?  Could smell bad crank seals in the smoke?

 

Thanks guys
Coo

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Oh yea.  I texted the local race shop guy.  He only works on dirt bikes.  He said $300 for new seals to be put in. 

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Do crank seals leaking have most influence/detriment at low engine speed or hi?

My hi rpm rips straight away, NP.  Low rpm doesn't seem as strong.  Doesn't idle.

I know it's a 2stroke and it aint suppossed to tractor at low rpms and all....but, does crank seal leak show up more at low rpm or hi rpm?

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Do crank seals leaking have most influence/detriment at low engine speed or hi?

My hi rpm rips straight away, NP.  Low rpm doesn't seem as strong.  Doesn't idle.

I know it's a 2stroke and it aint suppossed to tractor at low rpms and all....but, does crank seal leak show up more at low rpm or hi rpm?

I don't think it makes that much difference, if they leak, they leak.

Oh yea.  I texted the local race shop guy.  He only works on dirt bikes.  He said $300 for new seals to be put in.

FWIW I do all my own wrenching, except cases. I pay a local guy 300 to split and put together, parts are extra but the labor is the same. Last time I had him do an engine for me I had him do mains and seals, makes sense to do the bearings while you're in there. I'm not saying you or I couldn't do it, but for me I'd rather spend that time on other things. Someday when I have more time than I do now I'll give it a shot. I trust the guy who I have do the work, and know he will stand behind it, so it's worth it for me to pay to have it done....but if you want to do it I'm sure you can...

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I just did new seals and bearings. It's not really that hard just have to tear the whole thing down.

I'd leak down test it like other have suggested and if it passes keep riding.

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