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Date:         Sun, 15 Jun 2003 11:13:14 -0700
Reply-To:     Damon Campbell <damoncampbellvw@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Damon Campbell <damoncampbellvw@YAHOO.COM>
Subject:      rod bearing clearance (again)
Content-Type: text/plain; charset=us-ascii

I'm glad i am rebuilding a second motor, and not the one out of the van, as i certainly am taking my time with this...

I have something i am a little confused by, now, regarding the big end rod bearing clearance. Bentley clearly specify a rod bearing clearance between .0254mm-.05mm (.001-.002in), with the crank's rod journal diameter between 54.983mm-54.996mm (corroborated by Haynes). The rod housing bore is called out to 57.8mm-57.818mm (2.2756-2.2763in).

My parts measure out to: rod housing bore = 57.8mm-57.81mm (all rods - measured with an inside snap guage and measured with digital calipers - both mitutoyo) crank rod journal diameters = 54.97mm (#4 = 54.98) Rod bearing measures out at 1.38mm thick (std. kolbenschmidt)

So: 57.8 - (54.97+1.38*2) = 0.07mm clearance. This also, fortunately, matches up to the measured rod bearing inside diameter of 55.04mm when mounted up. Plastiguage also confirms this (about .08, actually)

What i don't get is that the crank and rod bore are within spec, so a std. rod bearing should be what you want, right?

A +.010 (+.254mm) bearing measured at 1.51mm thick, which would add up to: 57.8 - (54.97+1.51*2) = .19mm interference.

Obviously, i am missing something. I *think* i know how to use a caliper (sarcasm), and it is reasonably accurate (.0005"/.01mm), and i am getting consistent measurements (and i've done them many times by now!).

Any help would be appreciated. Of course, it could be something bonehead like not realizing that the specified rod bearing clearance is the nominal gap all the way around, not justified to one side (ie. diameter difference, not radius, which would halve my results, magically making everything perfect?).

I'll just work on clearancing the rod/camshaft interference until i figure out why the rods don't seem right...

Thanks,

-Damon

===== '84 Westy (Sparky) '65 Kharma Ghia (Dharma)

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