Unfortunately, boring requires oversized pistons – which are not
available for the Jag V12. The only legitimate method of correction
is to replace the liners. If someone’s mechanic claims he can fix it
with some boring or honing, one wonders what he plans.
Perhaps knurling of the pistons? (IMHO, a rather funky procedure, this
involves pressing some grooves into the skirt of the piston, which
apparently forces some metal outwards and consequently, increases the width
of the piston).
The parts book only lists one ring set, but there may be something
available on the aftermarket in +.001" or +.002".
Do I think any of this is a good idea? No.
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
2
Unfortunately, boring requires oversized pistons – which are not
available for the Jag V12.
Perhaps knurling of the pistons?
I can’t see how that would work too well, since the piston is
supposed to be gliding on a film of oil up and down in the cylinder.
A knurled surface can’t be good for oil films. IOW, you might meet
the SPEC for piston clearance, but you won’t meet the INTENT.
A better idea might be to find a way to plate the pistons. The
trick, obviously, is to provide a plating of a controlled and uniform
thickness that won’t peel off at 6500 rpm.
Alternatively, maybe you can plate the LINERS to get them back to
spec diameter (or smaller) so you can use the original size pistons.
Maybe remove liners from engine, grind out to uniform diameter,
plate, regrind to spec diameter, reinstall.
The parts book only lists one ring set, but there may be something
available on the aftermarket in +.001" or +.002".
I’ll bet there ain’t. Of course, if you fit the thing with Total
Seal rings, the actual fit may not be too critical.
Do I think any of this is a good idea? No.
Me either. Better to bite the bullet for new pistons and liners.
– Kirbert | Palm’s Postulate:
| If anything is to be accomplished,
| some rules must be broken.
| – Kirby Palm, 1979From: peter.cohen@unisys.com
Here’s an observation. The XK8 engine has the liners plated onto the
aluminium block. A few thou thick. So you get excellent thermal
contact. I have no idea what the technology is, but it seems both
impressive and scary; I wouldn’t want to inherit one of these babies in
15 years when the plating is starting to wear thin as a result of
under-maintenance
Unfortunately, boring requires oversized pistons – which are not
available for the Jag V12.
Perhaps knurling of the pistons?
I can’t see how that would work too well, since the piston is
supposed to be gliding on a film of oil up and down in the cylinder.
A knurled surface can’t be good for oil films. IOW, you might meet
the SPEC for piston clearance, but you won’t meet the INTENT.
A better idea might be to find a way to plate the pistons. The
trick, obviously, is to provide a plating of a controlled and uniform
thickness that won’t peel off at 6500 rpm.
Alternatively, maybe you can plate the LINERS to get them back to
spec diameter (or smaller) so you can use the original size pistons.
Maybe remove liners from engine, grind out to uniform diameter,
plate, regrind to spec diameter, reinstall.
The parts book only lists one ring set, but there may be something
available on the aftermarket in +.001" or +.002".
I’ll bet there ain’t. Of course, if you fit the thing with Total
Seal rings, the actual fit may not be too critical.
Do I think any of this is a good idea? No.
Me either. Better to bite the bullet for new pistons and liners.
– Kirbert | Palm’s Postulate:
| If anything is to be accomplished,
| some rules must be broken.
| – Kirby Palm, 1979
Unfortunately, boring requires oversized pistons – which are not
available for the Jag V12.
Perhaps knurling of the pistons?
I can’t see how that would work too well, since the piston is
supposed to be gliding on a film of oil up and down in the cylinder.
A knurled surface can’t be good for oil films. IOW, you might meet
the SPEC for piston clearance, but you won’t meet the INTENT.
A better idea might be to find a way to plate the pistons. The
trick, obviously, is to provide a plating of a controlled and uniform
thickness that won’t peel off at 6500 rpm.
Yeah thats it. Gold plated pistons… then we will be saving some REAL
money
Jag liners are expensive… If they need replacing Deal with it.
Rebuilding a engine is not my idea of something that is so fun I had to
do it twice.
My $0.02–
Mark Stoner Telemetry Electronics Engineer
email: mstoner@psl.nmsu.edu http://pslhost.wsmr.nasa.gov/
Ph: (505) 679-9745 Fax: (505) 679-9753
Research Rockets / Physical Science Laboratory / NMSU
Box 30002 Las Cruces, NM 88003 / N200 LC-35 White Sands Missile Range
Kirbert
(Author of the Book, former owner of an '83 XJ-S H.E.)
5
At 02:28 PM 11/17/98 -0500, you wrote:
A knurled surface can’t be good for oil films.
Well, thats just what you create with the “glaze breaker” when you turn it
on and run it up and down the bore. The smoothe boor is not good. It has
to be knurled to hold the oil.
I don’t think so. The smooth surface would work better for piston
sliding. The reason for “breaking the glaze” is to help the new
piston rings seat.
– Kirbert | Palm’s Postulate:
| If anything is to be accomplished,
| some rules must be broken.
| – Kirby Palm, 1979From: Jim Isbell jisbelljr@mail.utexas.edu
