Re: Honing cylinder liners - good or bad??

["Daegrigg (Don)" <daegrigg@domain.elided>]

John,

Thank you very much for your thoughts on honing.  It is timely for me since
I am in the middle of an engine rebuild for my '86 spider.  Some additional
questions if you will.

The engine has 110K on the original pistons and rings and was not burning or
using oil excessively before the teardown so everything is standard.  I
checked the gap on the new Deves rings  and It is .016 inches which is right
at the lower end of the range Deves recommends for my piston size.  There is
very little ridge that I can detect.

Now the questions,  I have a typical DYI hone that is used with the electric
drill.  I have read about different  grades of honing stones (course, fine ,
etc.) but they seem to apply to professional shop type hones.    For my DYI
effort ( I use to race/rebuild Giulietta's years ago) how do I know how much
honing is enough; do I need to use a "honing oil"?; is this the same as a
light maching oil or such; should I hone with the cylinders in the car or
remove?

Thanks for your thoughts.

Don


----- Original Message -----
From: "John Fielding" <johnf@domain.elided>
To: "alfa-digest" <alfa-digest@domain.elided>
Sent: Tuesday, July 23, 2002 3:07 AM
Subject: RE: Honing cylinder liners - good or bad??


> Hi Folks,
>
> All this talk of honing cylinder liners so you can fit new rings onto a
possibly worn
> piston has me a bit jittery.
>
> Honing is a process used by original manufacturers and cylinder block
restorers to remove
> the final tiny amount of metal to bring the cylinder to final size and
completely round,
> with a fine criss-cross series of surface scratches which retain oil and
allow the rings
> to bed in satisfactorily.  For those who aren't aware, when reboring a
cylinder, to say
> 30thou (mil) oversize, the boring machine will remove sufficient metal to
allow honing to
> final size, normally a cut of 26 thou (mil).  In many cases this will be
about 4thou
> (mils) left to hone off.  The important thing to understand is that the
boring operation
> makes the cylinder truly round, perpendicular to the block face and
removes any taper.
> In a worn cylinder the bore will  be least worn at the top (because the
top ring cannot
> reach this far up the bore) and the cylinder will be oval due to the wear
which occurs on
> the thrust side of the bore from the piston, ie the worn bore will be both
oval and
> tapered along its length.
>
> Honing a liner or block is normally done with an automatic honing machine,
it
> can be done by hand with a drill and a suitable set of honing stones but
it requires a
> definite skill only learnt through many years of practice, and one can
presume a number of
> poorly honed cylinders!.  To be able to "feel" the slight tightness as the
honing stones
> are run up and down the bore, because the bore is slightly tapered and
oval, is something
> I haven't mastered yet!
>
> The bottom line is this:  If the liner has minimal wear and hence no
perceptible ridge at
> the top of the bore, better yet you can actually see with a naked eye the
original honing
> marks on the liner all the way down and around the bore, then the liner is
probably usable
> without honing.  To start honing a liner without at least measuring the
bore ovality and
> taper is totally stupid.  How on earth can you tell how much metal and
from where in the
> bore needs to be removed to bring it back into true roundness and free
from taper??
>
> Free-hand honing will not normally remove a taper or ovality without a
conscious effort on
> the operator to do so as the hone will naturally follow the average bore
diametre and
> taper, and he needs to know where in the bore the problem areas are to
address this
> problem.  IMHO honing a liner in situ is not a correct method.  The liner
will rock in the
> block even though it appears to be solidly mounted in the ali bottom of
the block.  The
> best solution is to remove the liners and have a competent machine shop
perform the task
> on an automatic honing machine were the stone pressure and taper can be
acurately measured
> and controlled.  I had this done on the Alfetta motor built for racing,
here an extra bore
> clearance was needed to suit the pistons and rings being used.
>
> Fitting new rings onto an old piston is also a bit of  a Russian roulette
game.  If the
> ring grooves are within spec all well and good.  But the continual up &
down movement of
> the piston causes the top & bottom of the ring grooves to wear, the rings
are much harder
> than the ali piston and the point may come where the ring groove is no
longer small enough
> to control the compression rings correctly, thus causing the rings to cock
lengthways in
> the bore and excessive friction and wear result.  Without accurately
measuring the ring
> groove wear you cannot assume the piston is able to accept new rings.  One
can in certain
> instances buy over size thickness rings to counter this problem but they
are difficult to
> locate in many cases.  And before these can be fitted the ring grooves
need to be machined
> to create the correct clearance, not a cheap solution.
>
> As far as knurling pistons is concerned, well this is a cheap and dirty
fix.  Consider
> that in a few hundred kilometers the high spots caused by the knurling
will have been worn
> away and the tiny pieces of ali will descend into the oil pan causing
untold havoc to the
> the rest of the bearing surfaces!  The piston will now have more clearance
than before the
> knurling took place, not a very wise decision in my book!  In any case
pistons are not
> made to be round, they are machined with either a barrrel-shaped exterior
or an oval
> section depending on the manufacturer.  Knurling will tend to make the
piston round and
> this upsets the fine
> clearances desired, hence the heavy wear on the thrust side of the piston
when the motor
> is first run.
>
> just my 2cents worth.
>
> John
> Durban
> South Africa
> Alfetta 1.8L turbo
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