Date: Sun, 15 Jun 2003 14:05:45 -0700
Reply-To: wilden1@JUNO.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1@JUNO.COM>
Subject: Re: rod bearing clearance (again)
Content-Type: text/plain; charset=us-ascii
Deciding a go or no go on the parts you are describing is more elemental
that.
#1) Case bore is of first priority.
#2) Toque the case up with the main bearings and crankshaft in it.
#3) The bearings should be oiled with about 40 wt oil.
#4) Give the crank (without the cam in the engine) a little spin from
either end and you should have about 5 to 7 revolutions. (no flywheel)
#5) Install a rod with the bearing, again with 40wt oil, torque the rod
properly. It should slowly drop from top of your case cylinder opening to
the bottom evidencing some minor resistance. It will drop in about 1-2
seconds if it's a fit. If you get a resounding clunk, its a no go.
You are absolutely right in taking the care to mic everything before hand
but unless you have newly reconditioned rods and a freshly ground crank
and those parts consistently have exactly the same readings from three
points 120 degrees offset then you are dealing with the unknown.
If this is a Wasser boxer engine I'd suggest that you start with align
boring the case. I'd have to quite Boston Bob on this but if you skip
this step then skip the rebuild.
I've rebuilt many Air Cooled VW engines and fortunately the parts came to
me at reasonable prices and I've had the parts resources at hand to be
very selective in which parts met my mic responses and my intuitive risk
taking procedures on parts selection.
Your first goal in completing the rebuild is sufficient oil pressure
right from the start.
Minor infractions in specifications can be offset by closer tolerances at
another parts junction but overall it's the main bearings and case
alignment that determine engine life.
Rods stretch, caps stretch and lubrication fluctuates.
Every bit of this discussion is totally irrelevant if you did not closely
examine the bearing wear when you disassembled the engine.
To put it in laymans terms ............... you still got what you started
with and if that wasn't good then have the crank turned, rods
reconditioned, case align bored, knock out the oil gallery plugs and rod
out the galleries, thread the galleries and install threaded plugs, use
only a new oil pump and double check the piston ring end clearance.
Stan Wilder
66 Westy _________ DFW Taxi Service
On Sun, 15 Jun 2003 11:13:14 -0700 Damon Campbell
<damoncampbellvw@YAHOO.COM> writes:
> 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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