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crank tail pitting & scoring
https://www.ausmini.com/forums/viewtopic.php?f=5&t=89938		 Page 1 of 1
Author:  simon k [ Sun Jul 12, 2015 6:12 pm ]
Post subject:  crank tail pitting & scoring
I got these two large journal 1100S cranks cheap, the PO had them stored away for a long long time. The journals were covered in grease to look after them but the tails were a bit manky.

I sent them away for tanking and crack testing, no cracks, but the tails aren't flash

this one has pitting

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and this one has a big score in it

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DSC_0358 (Medium).JPG

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DSC_0357 (Medium).JPG


fatal?
Author:  drmini in aust [ Sun Jul 12, 2015 6:45 pm ]
Post subject:  Re: crank tail pitting & scoring
I don't think so.
My 1360's S crank laid in dirt under my boss's house for 14 years, is pitted like that on one side, it's now run in 5 of my blocks without a regrind. Polish it a bit with 220 wet & dry. Those pits just hold a bit more oil. :)

re the other one with the score mark on the taper, they never break there. I would deburr it with some 220 wet & dry, then lap it to the flywheel.
[edit] this one has some bits of flywheel metal friction welded to it, they need to be carefully (professionally, as in I'm a fitter not a butcher) dressed off with a file before using the wet & dry paper.
Author:  simon k [ Sun Jul 12, 2015 7:49 pm ]
Post subject:  Re: crank tail pitting & scoring
kewl, thanks Kev - that makes 3 std/std LJ cranks ripe for stroking, or de-stroking :D
Author:  carbon [ Tue Jul 14, 2015 4:14 am ]
Post subject:  Re: crank tail pitting & scoring
Simon,

+1 for drmini's comments.

If you have got access to a lathe this makes cleaning up the crank tails a lot easier. Even with a relatively small lathe such as Myford 7 you can grip the part where the pulley fits, and use a lathe centre at the other end to hold steady.

Either use fine emery as drmini suggest, or for any 'welded on' lumps on the taper I have used a file (single cut, very fine teeth) with care to clean up, but without removing anything from the main taper.

Using this you can start with a pretty grotty looking crank and end up with remarkably decent surface finish. If you are going for ultimate polish on journals and crank tail where the primary gear bushes run then Solvol Autosol is my abrasive of choice, takes a while but gives mirror finish.
Author:  drmini in aust [ Tue Jul 14, 2015 8:08 am ]
Post subject:  Re: crank tail pitting & scoring
Measure the diameters where the primary gear's bushes run. Original size was 1.500" dia on the straight bit, and 1.625" on the shoulder.
Don't take much metal off the diameter if you can help it, just make it smooth.
If the shoulder is worn down (happens sometimes) it can be cylindrically ground down to 1.500" and you then use a 998 primary gear instead.
This mod has been successful even on race motors.
Author:  simon k [ Tue Jul 14, 2015 12:05 pm ]
Post subject:  Re: crank tail pitting & scoring
thanks muchly Carbon, I have a little lathe, not sure if it has enough swing but I'll see. Good suggestion

I think (hope) the gunk on the tail you can see there is a heavy bit of rust, rather than a bit of flywheel. I'll carefully see if it'll clean up.

I was wondering about going down to a small bore primary gear - though the cranks BOTH came with their 1275 primary gears :shock: I got a surprise out of that when they showed up

thanks :)
Author:  simon k [ Mon Jul 20, 2015 2:35 pm ]
Post subject:  Re: crank tail pitting & scoring
both cranks cleaned up very nicely, thanks for the advice

all oiled and wrapped up now
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