Crank Play and Splitting the Crankcase


4 replies to this topic
  • Eggbert

Posted March 21, 2010 - 05:43 AM

#1

My KTM 85SX is getting very difficult to start and smokes a lot. I do believe the crank seals are shot...the right side sucking air keeping the mixture too lean to start and the clutch side leaking oil which is causing the smoke. So I decided to change them.

I didn't get too far as I realize I need one of those 27 x 1 LHT flywheel pullers. That's next on the list. However a new problem (maybe) has arisen so I thought I'd post here to ...er......"get attention"... and hopefully some advice....LOL.

It seems I can feel (more like hear, not feel) a bit of play in the flywheel. Mostly in and out, but some up and down as well. I will have to check it with my dial indicator as the play is very small.

Doing a Search, I found a spec....0.001" for up and down movement. I'll have to dig out my dial indicator and check it.

The question is, how hard are the cases to get apart? I've done small Honda engines before (Z50 and CT70) and it ws quite easy, but I see KTM sells a crankcase splitting tool...is it likely I would need it?

Once I get the crank out (presumeably with bearings attached), I'l probably take it somewhere to have the bearings removed and new ones pressed on. I have a small 4 ton press, but not sure about fixtures thin enough to fit under the old bearings.

I have about 4 or 5 hours on the bike since I did the top end. There wasn't any rod play and rod side clearances met specs (although I can't remember where i found the specs anymore), so Im hoping the crank assembly can be re-used.

Any thoughts from those of you who are familiar with this work...i.e. splitting the cases and changing crank bearings?

Thank-you.

ps: On the original problem on difficult starting: Cleaned carb, checked reeds, checked rubber intake for rips, new sparkplug, compression about 154 psi with engine cold....still very diffiuclt to start. I got it going yesterday, but the revs wouldn't come down when I turned the choke off, so there's an airleak somewhere.

  • Eggbert

Posted March 21, 2010 - 02:37 PM

#2

I just got back from measuring my crank bearing endplay...on the flywheel.

For freeplay (up and down, side-to-side), I got just under 0.002"

For endplay (in and out), I got 0.006"

Not sure what to make of that. Bearings arn't new, bike wasn't warmed up, so bearings would be a little looser than normal, plus it's a tad cold outside in March...maybe snow tomorrow.

Overall, I suspect it's normal wear, but the bearings should be replaced soon. Or should it be "now"?

A Search of this forum found 0.001" for up and down.

A general spec foound in the link below says 0.004 to 0.006" max for up and down.

http://www.wikihow.c...ling-the-Engine

Any thoughts on what acceptable clearances are?

  • sbest

Posted March 21, 2010 - 03:28 PM

#3

Hey fellow Nova Scotian, some nice day the past few, eh? Where are you at?

The dial indicator is a great way to check plain bearing clearances but it has an odd way of magnifying them. On the crank of a car engine it seems to add a thou, I don't really know why. On a bike crank, it measures the clearance of both bearings combined. As you load the crank hard to one side it tightens up that clearance on that bearing and the opposite clearance on the back bearing. These bearings are high speed "C3" high clearance bearings.

On a roller bearing a visual (or vibration) examination is the best way to determine wear. Get a jeweler's loupe out and look for flaking or roughness. Spin it looking for noise. A good bearing goes "whirrrrrrrrr", and bad one goes "rrrahh". No kidding! Even spinning the crank you can feel the roughness of a bad bearing.

The rod big end is a tricky business. It usually fails from peening at Top Dead Center. You have to put the crank at TDC and feel carefully for roughness and vertical play. Takes an experienced touch, hard to feel it. If you think you feel a rough spot, you probably did and need the crank redone.

About the seals. They do go hard with time and lack of use but they can be revived. Get a bottle of engine or transmission "seal restore" and dump it onto the outside (magneto) seal, inside the engine, and into the transmission oil. Leave the bike on one side, then the other for a few days. Flush it out of the engine and magneto and try it. Often worked for me on bikes and snowmobiles but not a permanent fix, it can save you major engine surgery for a while.

Carb cleaner (careful, it is flammable) sprayed on the seal will tell you if it is sucking air. If the idle changes when sprayed, there is a problem.

Cold weather can make for high idle and hard starting if the pilot jet was lean.
Try a richer pilot or raising the float level and see if it helps.

Oh, and you do not need special tools to split the case, other than a left hand thread flywheel puller. Be careful, the clutch side crank nut is left hand too.
A little oven heat will drop out all the bearings. The roller seat is hard to get off the crank but it can be marked and split. Put it back on heated with a driver.

Edited by sbest, March 21, 2010 - 04:42 PM.


  • Eggbert

Posted March 21, 2010 - 05:46 PM

#4

Hey....thanks for all the info. I"ve been suspicious of bearing freeplay as instead of wearing down, the races usually flake or the balls or rollers chip, so I think my bearings are more "broken-in" than worn out. No rough spots are funny noises.

I'm not familiar with Seal Restore....sort of sounds as useless as belt dressing, but as you say, could be good for a temporary fix.

Good tip on the case splitting. Saves me from some tool expenses, although I may get some specialty stuff sometime if I start doing a lot of overhauls. Flywheel puller is certainly cheap enough and a "have to have it now" device.

Cleaned the plug today and it still wouldn't start....until I realized I left the plug wire disconnected...then it fired right up. Seemed to work better than it did last fall for some reason. Maybe the weather...isn't it incredible for this time of year?

I'm near Bridgewater, on the South Shore. I find it too far to make the New Brunswick MX races, although I may got to 1 or 2 this year. Port Clyde is 1st NS race I think, and it's the closest to me.

Thanks again for your reply.

  • sbest

Posted March 22, 2010 - 05:01 PM

#5

Well, I have had good luck with the seal restorer stuff and 2 stroke seals. My old DT200 is still working fine several years after we gave it the "goo", as well as some old sleds we fixed up with it.




 
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