I posted this message to the engine forum and got a couple
of nice replies, but wondered if any readers in this group
might have experience or opinion related to this problem.
I own an XK 120 that came from the estate of its deceased
original owner in Buffalo, NY. Its ‘‘rebuilt’’ engine
evidently sat on a stand for a decade or three with the head
and pan off. On tearing it down for proper rebuild, I made
an interesting discovery. This matching number block has
been bored to take 3.8 Liter pistons. The standard AE 9:1
pistons and rings in it appear brand new, but there is a
ridge at the top of all the cylinders, and from my initial
hasty measurements, it looks like the block would require
.020 overboring. No evidence that there have been liners
placed. I believe the engine to have been run hard (Anyone
familiar with John Mills of Mills Engineering who might have
raced it in the 50s and early 60s?) The crank rod journals
are cross drilled and chamfered, intake valves are oversize
(1 3/4’’), and I think some porting of the head may have been
done. A custom, billet aluminum manifold for an XK head
drilled to accept 4 - yes, 4 carburettors , came with the
car and does appear to have been used - don’t know whether
on this engine.
I have a couple of
expert opinions that I should sleeve it back to standard 3.8
and use the pistons I have, but am a bit nervous about being
close to the water jackets and studs. Does anyone have
personal experience with this modification? I have to
admit, I like the idea of added performance and it would
save me the cost of a piston set, but don’t want to take a
big risk with the original block, not to mention the expense
and effort of the rebuild if it fails. Thanks–
Ron Smith '53 120 FHC
Olympia, WA, United States
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In reply to a message from Ron Smith sent Sun 6 Feb 2005:
Hi Ron its been done before, sleeve the block and bore it to
standard 3.8 deck the top, and you are in business. you did say the
hep’s are standard? and when you do get it togeather get deves
rings.–
The original message included these comments:
an interesting discovery. This matching number block has
been bored to take 3.8 Liter pistons. The standard AE 9:1
pistons and rings in it appear brand new, but there is a
ridge at the top of all the cylinders, and from my initial
hasty measurements, it looks like the block would require
.020 overboring. No evidence that there have been liners
placed. I believe the engine to have been run hard (Anyone
In reply to a message from pajtas sent Mon 7 Feb 2005:
Ron,
Just to add a few numbers to my earlier communication in the XK
engine section. From the Jag service manual:
‘‘Standard 3.4L bore = 83.00mm
Max oversize .030 gives bore dia 83.76 mm - resleeving back to 83
mm recommended after 030.
Bore size for fitting 3.4L liners 86.16 to 86.13mm’’
But
Standard 3.8L bore 87.00mm
Bore size for 3.8L liners 90.16 to 90.13mm
So you’re going from 83mm to 90 mm bore if you’re installing 3.8L
liners in a 3.4L block - and remember, on top of the bore diameter,
there’s a spigot machined into the top deck to take the register on
the top of the liners (which stops them slipping down the bores)
Also,other feedback - I’ve just this minute received an email from
Alex Zonoff, the previous owner of my 3.4L XK120. In it he
says ‘‘My father overbored a 3.4 block to 3.8 and had disasterous
results. The block cracked and wasn’t worth salvaging at the time
(late 60’s)’’.
Obviously some 3.4L blocks have enough metal in them and are OK
overbored to 3.8L or 3.8L+ for sleeving - and some are not.
Best regards
Shane–
The original message included these comments:
Hi Ron its been done before, sleeve the block and bore it to
standard 3.8 deck the top, and you are in business. you did say the
In reply to a message from SWA1 sent Mon 7 Feb 2005:
Shane,
That is very interesting information. Thanks again.
Obviously, this block had enough strength to withstand the
initial overbore, as it ran long enough (probably without
air cleaners) to wear a ridge into the cylinders, but
further boring to accept 3.8 liners sounds risky to me, at
least without sono testing. However, your numbers also make
me wonder if the bores are already too large to accept 3.4
standard liners - 87mm(+wear) vs 86.16mm to 86.13mm for 3.4
liners. perhaps there are thicker liners available. I need
to do more careful measurments of my block and talk with
local machinists about this. If the bores are too large, I
may be stuck. I’ll let you know what happens.–
The original message included these comments:
Bore size for fitting 3.4L liners 86.16 to 86.13mm’’
But
Standard 3.8L bore 87.00mm
Bore size for 3.8L liners 90.16 to 90.13mm
So you’re going from 83mm to 90 mm bore if you’re installing 3.8L
liners in a 3.4L block - and remember, on top of the bore diameter,
Hello Ron Smith:
What Shane points out is correct …
I may add additional info.>>Reboring is normally recommended when the bore
wear exceeds .006" …Reboring beyond the limit of .030" is not reccomended &
when the bores will not clean-out at .030" ,liners & standard pistons shoild
be fitted
Liners,standard pistons & the following pistons are available::+.005,
+010", +.015",
+.020"& + .030"
Bore size for fitting liners>>>>>>>>3.392" to 3.391"
Outside dia. of liner #.3945 to 3.3955"
Interference fit>>.0025" to .0045"
Overall lth; of liner when fitted>>>6.31/32"
As per the jaguar 120 shop manual
Bill Terry at Terry’s Jaguar Parts in Illinios has raced Jags seriously for
decades. He has a GREAT deal of experience with XK’s of unusually large
displacement.
In reply to a message from Gwen Tilton and Mike Spoelker sent Tue 8 Feb 2005:
As a matter of fact, I already talked to Bill Terry. He
said sleeve it back to standard 3.8 and build it, but sonic
test it first to make sure the walls are thick enough.
Jerry Oliver and I paid a visit to Alan Gerard of Palladin
Auto in Belleview today, who said the same or option to bore
20 thou over 3.8 if sonic shows enough wall. The most
experienced machinists in our area are at Autosport in
Seattle, and I’ll have them look at it next week. They’ve
evidently done a number of similar engines. Alan was
telling us about several successfully hot rodded 3.4s from
decades past with similar modifications, one reported to
have gone 145mph! I really don’t like fast so much, but I
do like quick. If it works out, this will be a 9;1
compression 3.8 internally with heavier XJ6 rods, oversized
valves, and a pair of HD8s mated to a T5. We’ll see.
Evidently, there are sleeves available to put it back to 3.4
if need be. Thanks to Mike and all for advise.–
The original message included these comments:
Bill Terry at Terry’s Jaguar Parts in Illinios has raced Jags seriously for
decades. He has a GREAT deal of experience with XK’s of unusually large
displacement.
Regards,
Mike Spoelker
Louisville