|February 2000 Tech Feature||www.virtualindian.org|
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Inspection steps require some specialized instruments and techniques. My favorite is magnafluxing rods on my armature growler. But first we ought to gather some basics, like feeler gauges; perhaps the new pins that you know you are going to need anyway for plug gauges; lapping compound or prussian blue for checking tapers; A 1" micrometer seems prudent (or buy 100 lots of rollers in every size, and just go by the label); and truing of the shafts and wheels pretty much dictates at least one dial indicator. From Enco, that's about $60 worth, not counting your new shafts.
For rod straightening and alignment, I've got a trick old AAMCO gauge stand that I added a magnetic dial indicator to, but one of the Listers better offer an alternative method for those without access to such an instrument. Perhaps GreatGranpa's granite headstone and an accurate V-block big enough to span the rodhead? But then how do you gauge twist? I would not wait to do it assembled in the cases; too much chance of skewing the wheels, marring the races, etc. The female rod is difficult enough to straighten out in fixture: the race webs will distort enough to bind the prefitted rollers if one does not secure the rod beam separate from the webbing when you 'discipline' the rod to straight. Actually straightening is a Machining step even though no metal is cut. (A lever is a machine, isn't it?)
Gauging wristpin fit is 'Feelable'. Some of you might dictate a looser fit anyway, since I'm not afraid to set them up as tight as .0008". I'd say that .0005" is about as tight as can be easily assembled, but most of you are going to be at the mercy of your reamer anyway.
Gauging crank roller
fit is a different matter. If you feel there is 'meat' enough left to resize
the races, beware that the male rod race is usually stretched oval length
wise with the rod, often a full .001" yet still show factory grind. The
stretch is in the web also. I have a customer's machine in service where
I pressed the race out, rotated it 90 degrees and re-installed before hone-fitting.
It squeezed quite round!
The feeler gauges
are for the sideplays, and that's about the crux of it for crankshaft repair
inspection with bare minimum instrumentation. The main race fits are gaugeable
similar to the rod races: As small as you can keep them and still have
the oversize rollers fit in and roll smooth.
From: Theo Gibb <firstname.lastname@example.org>
From: "Cotten" <Liberty@npoint.net>
The rod is placed
over the mandrel and tightened to the point of snug, but still swingable:
no sideplay at the top. A wristpin is inserted into the bushing for gauging
against the U-block with feelergauges, or just by inspecting for daylight
opposite the side that touches. The side face indicates 'twist'; the top
of the block determines 'bend'. The rod is removed, flipped over, and re-gauged
to note if, for certain, the high side of the wristpin switches also.
Note also that I have sped up the 'bend' gauging process with a magnetically mounted indicator. This not only reads a differential between sides of the wristpin, but often quantifies the differences between rods in a pair (as if we could do anything about it). "Twist' on a rod is different in that flipping the rod still leaves the daylight on the same side. This is the harder plane to straighten, and should be accomplished first, as it often changes the 'bend'.
This apparatus is similar in use to the Sunnen unit.
I am certain that many of you have rebuilt many a motor without doing more than looking down the rod like a pool cue. (I had a partner once who had never observed a rod straightened, or even gauged, during his entire six year-plus tenure at Lakeshore H-D, THE most prestigious H-D shop on the planet; They just sell crappy import rods if the bend is apparent. Considering the price of aftermarket Indian replacements, most of you will want to gauge your originals.
The point must be made here that unless you mill-bore your wristpin bushings like a Moto-Guzzi, the alignment between bushings an rod races are subject to the additive errors of presswork, reaming and honing, natural rod "set" or stress from use, and concievably even shotpeening or stress relieving treatments may splay the delicate parallelism of the bores. I straighten all rods "'cause they aren't". The methods of doing so are a treatise in themselves.
This vintage Aamco rod alignment gauge has been altered for motorcycles by reducing the toes on the expanding mandrel through the crankbore of the rod, as well as adding the magnetic indicator.
|To Part 4: Preparation||