To build or not to build

[mswyka]

We have a 78 340 L/C powerplant on the bench just about ready to be reassembled.  Inspecting the crank it would appear that there is some nominal pitting around the mag end of the shaft - right where the seal would ride. 

I have made the mistake before of building an engine with pits in the shaft only to  have the seal demolished in short order.  So the answer is that I cannot put the engine together this way. 

Now however, with that said, If i turn the seal around, the seal now rides on a clean part of the shaft.  Anyone have any insights as to whether the orientation of the seal makes any difference?

I will see if I can get a photo of the shaft.

[mswyka]

Here is a photo of the shaft.

[jimvw57]

change the crank. 340 and 440 use the same crank.

[Tory944]

  That's a good/interesting question.  Never seen this done, but I will be anxious to see the responses!

[gixxer6]

If it were my build, I would find a different crank.  That seal is too important...

[Interceptor398]

I agree with not using that crank.  If it were the last one around I would put it up in the lathe and polish it.

[mswyka]

We had pits on the crank for our 1980 440.  First assembly it destroyed the seal.  Second time around we turned the crank smooth.  Smaller diameter, but still enough for the crank seal to seal.  She has been running strong since 2005.

For now I think that i will use a 79 crank and crankcase for this build.  And since I can be a glutton for punishment, in the future I might just go ahead and build the 78 case and reverse the seal just to see how long it lasts.

[rminier]

  Interesting stuff....the crank seals have that tiny spring that encircles the I.D. part of the seal, that seals against the crankshaft. If you flip it around, won't this spring now be exposed to the elements (dust, dirt, moisture) rather than being continuously bathed by the 2 stroke oil passing thru the internal side of the motor? I'm sure it would work...for awhile....until the spring craps out.
  Since it's on the mag end, it's buried behind the recoil, the flywheel, the stator....you would never see the seal again until the next rebuild. On the PTO end you could at least pop the drive clutch once in awhile to check the seal and spring...and maybe squirt a little oil on the spring to keep it from rusting.
  I can't remember, without tearing into my Kawi, if it's seals have that spring on only the one side....I remember one motor I worked on long ago had 2 springs on the crank seal...both inside and out.
  It would be like searching for a needle in a haystack....but ya just know there is a crank seal out there that has the same O.D. as the Kawis....but has a millimeter or 2 smaller I.D.....that would be the berries....a machine shop could spin the pitted area on the crank down to the new dimension and you would be good to go.
  You would have to attach a note if you ever sold the sled.....some poor bugger would be on this site asking why he keeps seizing a piston after installing new (stock) crank seals!! 

[Lloyd (ljm)]

Hey Mark

  That is a bummer that a otherwise good crank has pitting like that.

 In my opinion your idea of turning the seal the other way would work for a sled that wasn't ridden much. Seals work better when installed the correct way. If they are backwards they will fail earlier.

 I would be tempted to find a shop with a large selection of seals. A wider or narrower seal with out the center rib would move the sealing surface off the pits on the shaft.  Would take some trial and error. But would make the crank usable.

[mswyka]

Lloyd:

Good thoughts.  I spoke with the engine shop that I have been using for the machining that we can't do at home.  He referred me to another crank shop but also suggested that I take a look at possibly using a Speedi-Sleeve.  At the end of the day I expect that I am going to go for the turn and polish, but the Speedi-Sleeve option looks very interesting.

[gixxer6]

I have a couple used cranks that are no good but have good shafts.  Maybe you could have a crank shop replace the shaft? 

[mswyka]

Tom, thanks for the offer and good thought.  We have a couple of good stub ends kicking around also.  When we go to the crank shop I will give them that option.