[Vwdiesel] The Story of my Engine, its controversial headskim, and the offensive rebuild, {A bit long}
lbaird119 at aol.com
lbaird119 at aol.com
Wed May 15 22:20:28 PDT 2013
Can't say that I disagree with much of what you did at all. I had a shop bore and hone start using oil at 15K due to an incorrect hone. Had it torn down and supposedly honed only to repeat (with new compression and oil rings, TS second rings). FInally did it myself, the third time. Used my 3 stone hone.
You CAN get a decent cross hatch but it requires moving up and down rather quickly with a variable speed drill going fairly close to the slowest sustainable speed. I also lean closer to the 180 ring placement compared to the 1/3. Major exception is a horizontally opposed engine where they recommend about a third but only in the top half. I kept to the top half on those but used a wider spacing, closer to 180. Found out that the depth of the cross hatching is important for ring lubrication. Shop didn't have it deep enough (coarse enough) so the rings wore prematurely. Diesels tend to need more coarseness than gassers, which is where all the ultra fine grit honing ideology come in.
I'd say you did well.
Loren
-----Original Message-----
From: Mark Shepherd <mark at shepher.fsnet.co.uk>
To: vwdiesel <vwdiesel at vwfans.com>
Sent: Wed, May 15, 2013 2:07 pm
Subject: [Vwdiesel] The Story of my Engine, its controversial headskim, and the offensive rebuild, {A bit long}
HEAD-SKIM
ere’s my engine rebuild details:
ought engine in a 1985 Quantum wagon 6 years ago. Ran it and the car for nearly
year. Retimed engine to get me from 36mpg imp to 45-48imp.
ead gasket blew.
id my hand skim of head on plate glass, leaving on manifolds, cam, etc. I did
ot need to mess about with the precups, unlike the choice of many machinists
ue to the
oft/hard metal interface, and they all ‘machined’ along with the tips of the
xhaust manifold!
did it like this because I wanted to avoid any possible flexing and reflexing
f the head during the removal-skim-replacement process.
I admit now that I probably overdid the skimming, and probably used my
ounter-weight, of a bar of steel 24” x 4” x1/2”, end tucked under the cam a
ittle too late to
revent slightly more being machined off the head along the manifold side,
ompared with the injector side...
et, 5 years on no issues, other than the knocking that I’ve mentioned before
rom the valve faces being brought closer to the pistons, and indeed I suspect
atching up
ith the piston face both after TDC, and being caught by piston before TDC. This
ust be the initial reason that VW threw away the heads for all those years
ather
han skimming them...
did nothing else to the engine, other than to peer down the bores and notice
light wear.
ENGINE REBUILDt long
years on ( 3 years ago), I had a few starting issues, scattered over a couple
f months, and needing a jumpstart mid journey a couple of times. The Automobile
Association put it down to a weak starter motor, but they didn‘t have one[As it
urns out fortunate]. A complete strip down revealed half a cup of old engine
il, that must
ave accumulated over the years from leaking rocker covers. A few weeks respite,
efore the flat battery reoccurred.
I built an adaptor for a compression tester, and did some tests, as the engine
eemed to be turning over reasonably, as far as I could judge, compared with my
ther
uantum TD. I think the results were 190, 250, 250, and `290, or thereabouts.
hus I decided, that even if my lead filled injector body adaptor was reading
ow, the
ompression spread was out of spec, so a rebuild was necessary.
Ordered some rings from Autohause $22 per set of 4 pistons, Grant brand,
tandard size, and some shell bearings. Couldn’t justify the more expensive,
ssumed
hrome ones , as the whole car had only cost $45.Couldn’t contemplate oversized
ings and rebore oversized pistons etc.
Left block in the car. Sump off, pulled[pushed] pistons out of top of block, so
aybe top of bore not too bad... Piston crowns did indeed have both inlet and
xhaust
alve imprints. Exhaust most prominent and #1 and #4 the ‘worst’ #2 and #3 mere
host like shadows in the carbon. All imprints were concentric rings,
emonstrating
hat they were a product of 1000’s of hits of rotating valves.
All I did was to scrape the ridge from the circumference. Looked worse than it
as, as only a couple of thou deep when checked. No wrist bearings, big end
earings,
r crank bearings showed enough wear to be replaced, indeed most showed no wear
t all. Thus I did not make the mistake of replacing, and introducing lesser
atched parts.
RINGS:
out of 12 rings were stuck in Careful removal, revealed extent of their
ear... Top compression rings had gaps up to an astounding 160 thou, with
everal mm being
emoved from their radial thickness. Middle rings slightly less, and oil rings ,
round down almost to the wires. Apart from carbon infill, those hard ring
arriers perfect.
nly one piston showed any skirt scraping, and that was only to be expected with
he stuck rings. I felt new rings would fix this. Put a set of new rings into a
ore to
heck specs. Fine except for the top ring at the top was just inside the limit.
o way I’m going to spend money on rebore etc, and after all new rings had to be
n
mprovement, and apart from the final straw of rings sticking, these rings had
aken years to get to this stage..
. Now for the apparently contraversal treatment of the cylinder bores, which
plit the GTD forum down the middle, including the moderators...
THE HONE.
do have access to a spring tripod type stone hone, but I thought it a great
pportunity to experiment, after all what harm could it do?
ere was my reasoning:
he purpose of working on the bores of an engine is to create a trued up bore,
nd a matt finish. The matt finish is to provide a window to break-in the rings,
nd to get
hem to hug the bores with a minimal, yet essential mutual wear. The purpose of
he crosshatching is to allow lubrication of the compression rings
A rebore gives a nice mat finish,.
I have my doubts about the 'perfection' of a machined hone, as an addition to a
achined rebore, because it weakens the surface of the cylinders... Too much
nurling
eaves sharp edged mountains which level off further with break in, than mere
eglazing and relatively few crosshatches do, which start off with resilient
lateaus.
Machine work is a modern mass-production invention that produces 'satisfactory'
esults everytime. No books will tell you why you need 10000 crosshatchings,
ather
han 10, per stroke for lubrication. There seem to be plenty of people out there
ho do ‘perfect by the book’ hones, yet still get oil burn issues.
Remembering the old techniques of latheing up a piece of wood to fit the bore,
nd covering with emery, I took this idea and brought it into the present time
y using a
nug fitting plastic bottle and glueing onto it some 600 grade emery/glass
aper.
eaving the bottle cap on, and holding the neck of the bottle I determined that
could create pressure to the abrasive fairly evenly around the bore of the
ylinder as an
pproach to the official tool, and ensure that in addition to the deglazing, I
ould drop some strategically placed cross hatchings around the bore at the
agical 45
egrees, using a twist and thrust movement of my arms. Somewhat like the end of
karate punch. Changing hands to get some crossing...
Using a drill to spin the abrasive stones must surely result in much less than
5 deg hatching...
PISTON RINGs
hen setting the rings about the piston, many books say spread the gaps about
20 degrees around . Why? Why start an engine running with the rings at less
han
ptimum compression setting? I make that a third shorter route distance for the
scaping gasses. If the rings do rotate, before deciding on a place to rest ,
hen there is a
0% chance of compression getting worse. I always set the rings 180 deg apart,
o start out at the best possible compression, and hopefully settle quicker, and
efore
he official starting position...
easembled and drove it, and reached over 50mpg for the first time.
So what responses did I get? Varied. The power crazy Moderator said I couldn’t
ossibly achieve the results of a proper tool, and spending $500 on the work inc
ools
as the way to go. Others full of praise. or sided with the $500man. Not
onvincing me, he then pointed out that I did not cover the injection pump
utlets 8op. What if
ome grit got in there? Someone else said I could grenade the engine... Well a
it of grit in the line would either pass straight out or get crushed by the
igh carbon steel
ozzles, and besides just exactly how fast did he think my wrist moves, compared
ith a drill. What kind of an ‘anker does he think I am? I did have cloth down
elow
ores.
Further to their annoyance was because I also didn’t change the head gasket
although I had one) as gasket leak was not the issue, and amazingly the gasket
as a
erfect fit ;o) Also, because I never torque beyond the plastic point of the
ead bolts, they were also reused.
efinitely never change the tensioner pulley, unless showing signs of wear,
specially if it looks like an early one. As I never over-tension the timing
elt, the pump’s
earings don’t leak either.
inally I demonstrated and explained why reuse of heatshield is actually good
or the head....
UPDATE:
conomy constantly beats book values: of 42.1mpg URBAN and 57.6mpg
Constant90Kmh for the wagon
Urban 43; 47; 48, 44.5; Two trips 61.4; 59.5; These are the last 6 fuel readings
iming is set to 0.57mm Injectors were set to 130bar. Recently had a smoking
ssue on
tart-up. Only for a matter of seconds and only from overnight rest. Removed
njectors before using car, to catch problem and found one injector 3 or 4 bar
elow the
ther’s and one other spitting slightly. Fixed and reinstalled.
Mark
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