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General Category >> Rubber Side Down! >> Crankshaft Blues
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Message started by DragBikeMike on 12/02/19 at 00:19:28

Title: Crankshaft Blues
Post by DragBikeMike on 12/02/19 at 00:19:28

So I'm reassembling the engine and I notice this.  Anyone seen anything like this before?  The right crank throw is black & blue around the gudgeon pin.  If something was burnin up it would be the rod, not the crank throw, right?  Does the factory use some sort of induction heater to build up the crank?  Do they weld the gudgeon on the right side to lock it in place?

Title: Re: Crankshaft Blues
Post by DragBikeMike on 12/02/19 at 00:20:09

Here is another angle.

Title: Re: Crankshaft Blues
Post by DragBikeMike on 12/02/19 at 00:20:46

And one more shot.

Title: Re: Crankshaft Blues
Post by DragBikeMike on 12/02/19 at 00:24:45

I have never seen anything like this.  If any of you know what this is I'd appreciate anything you can tell me about it.  It turns free, no evidence of rubbing, rod thrust washers look fine, no discoloration on the rod or the left hand crank throw.

Help!   :-?

Title: Re: Crankshaft Blues
Post by srinath on 12/02/19 at 04:15:37

That's not from running. If it was, the motor would be a mess of melted metal. That's a weld heat signature.
Is the pin welded in this bike ? I've opened a few of these, I don't remember. I think its OK though.
Cool.
Srinath.

Title: Re: Crankshaft Blues
Post by Armen on 12/02/19 at 05:16:48

Any chance someone tried to heat up the outboard crank bearing to get it off? I've never seed a crank pin welded from the factory.
Realistically, how many folks would have pulled apart the crank and rebuilt it?
Crazy.

Title: Re: Crankshaft Blues
Post by zevenenergie on 12/02/19 at 05:41:17

It can,t be rubbing. The blue spot is to small for that. It must be a weld.
Or maybe they induction heat before the put the pin in at the factory and some one wasn,t paying atention.

Title: Re: Crankshaft Blues
Post by srinath on 12/02/19 at 09:22:39

Is it welded to the gear to its right ? I am pretty certain I have seen this before, only thing is, I don't remember on which bike. I did weld my XS650 into a 277 crank, that definitely had weld burns in every part of that crank.
Cool.
Srinath.

Title: Re: Crankshaft Blues
Post by srinath on 12/02/19 at 09:24:47

Look in a manual with pics. They do these disassembly etc etc and put pics in the manual. Clymer or Haynes is better than factory. Factory tends to do a lot of drawings, Haynes in fact says they pull the bike apart in their preface don't they ?
Cool.
Srinath.

Title: Re: Crankshaft Blues
Post by Dave on 12/02/19 at 12:53:13

It is normal I believe......the right side of the crank is a weird color and the other is not.  Your color pattern looks a bit different than the cranks I currently have open - but I don't see how the running engine could color the crank in the manner that yours is colored and still keep the needle bearing or thrust washers intact.

And if your crank got so hot that it blued while running.....I would suspect you would have cooked the oil that came in contact with the hot surface and you would see traces of burned oil sticking to the crank.

(NOTE:  The dark side is the right side.......regardless of how the photos got flipped around while posting).


Title: Re: Crankshaft Blues
Post by Dave on 12/02/19 at 13:19:48

1 more

Title: Re: Crankshaft Blues
Post by Dave on 12/02/19 at 13:20:26

1 nother more

Title: Re: Crankshaft Blues
Post by Ruttly on 12/02/19 at 14:19:29

Possible that that crank halves are different colors for assembly so workers don't put 2 of the same halves together. As far as the blue most likely heated on assembly and maybe reheated for alignment. Spins OK !

RUN IT !

Title: Re: Crankshaft Blues
Post by DragBikeMike on 12/02/19 at 22:17:14

Thanks very much for the comments & advice.  I appreciate the pictures Dave.  Since I did the initial post, I was able to find several photos of cranks (mostly eBay).  All these things seem to be black on the right and steel-grey/silver on the left.  That's pretty strange.  But I have yet to find any with the black & blue coloration indicative of major localized heating.

I'm not overly concerned since I see no way that the heating could be the result of operation.  It has to be related to manufacturing.  This is a 2016 model that I bought used when it was one-year old.  It had about 1050 miles on it and there is virtually no evidence that it had ever been disassembled.  I'm pretty confident it came from the factory with these black & blue marks.  

I beat it up real good.  If it hasn't failed yet I don't think the black & blue coloration is a problem.  It is very interesting though.  Almost seems like the OEM made some sort of change to their manufacturing process.  Probably figured out a more expedient way to build up the crank, or they welded the pin.

Anybody ever heard of an LS twisting the gudgeon?

Title: Re: Crankshaft Blues
Post by Armen on 12/03/19 at 05:07:38

FWIW, 'gudgeon pin' refers to wha the Yanks call a 'wrist pin'. The pin that holds the piston to the rod, not the rod to the crank.

Title: Re: Crankshaft Blues
Post by Dave on 12/03/19 at 11:15:43

I have never heard of anyone breaking or wearing out a crank on a Savage.

Title: Re: Crankshaft Blues
Post by justin_o_guy2 on 12/03/19 at 16:10:41

I don't have sufficient experience inside engines to put a foot down and make a stand, but my first thought was
That's a welding heat mark.

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