The below is in response to a number of private enquiries about…
XK ENGINE MODIFICATIONS
A complete blueprint would be beneficial, not necessary, but helpful. The
factory tolerances were terrible even in the best of cases. Add to that the
wear over 50 or so years and there’s room for improvement.
First, make sure you have a good block. Magnaflux the bearing saddles. Check
for cracks in the bores etc. If all is well then you can start spending money.
I would make sure the block deck is parallel to the centerline of the crank
to start off.
You may need to align hone. Some people align hone, some align bore. Smokey
Yunick hones and that’s good enough for me. Once that dimension is achieved
you will be able to bore and hone the cylinders with accuracy.
Using a grinder, clean all the flashing marks off the block, both inside and
You can buy pistons “off the shelf” from any number of sources or have them
custom made. There is very little price difference but great flexibility as
to size and CR. Forged or cast, there are advantages to both. Forged are
stronger at high RPMs, cast’s are more dimensionally stable. Once you have
the pistons then it is time to bore and hone. When honing, use a crosshatch
pattern and make sure that your shop will bore/hone to each piston. Not the
standard 20 or whatever over across the board. If possible use a surface
plate. BHJ makes them, ask your shop.
Make sure all surfaces are flat, the oil pan, timing chain cover, etc., and
make sure there are no sharp edges anywhere on the block.
Have the rods resized, ensuring that the big and small end are within
tolerances. Rebush the small end as a matter of course and hone to fit the
Grind away all forgeing/casting marks on the crank and bring a good crank to
a good crank grinder that has a good crank grinder and have him grind the
journals if necessary. Radius the oil holes and chamfer the edges.
Have the shop order bearings, do not economize on the bearings.
Retap all the threaded holes using a “cleaning tap,” you don’t want to remove
metal if necessary. Chamfer the top of the holes, you don’t want the top
threads pulling up into the gaskets.
Paint outside of block after a cleaning that would embarrass most surgeons.
15 dollars worth of spray carb cleaner, some liquid Dawn dish soap, a bunch
of clean lint free rags, HOT water, and some compressed air will be the best
investment you can make for the longevity of the engine. Mask off all
machined surfaces before painting using body shop masking tape… the
solvent resistant kind.
Some people will paint the inside of the block with GE’s Glyptal to aid oil
flow down to the sump. You need a very clean block otherwise the paint may
flake off and…
Now the block is done. Cover it with a plastic trash bag and tie it. I put a
few moth balls in there to absorb moisture.
The above is a BRIEF synopsis of what to do. There is no way to translate
years of experience that your machinist and or engine builder may have into a
Later will talk about the head and misc. parts.
All this work may seem like overkill, and to some extent it is, but the need
to lessen a failure should be at the top of everyone’s list. It is no fun to
pull and redo an engine for want of saving a few dollars (Pounds, Franc’s,
The XK power plant is probably one of the most reliable engines made in
history. By careful assembly and workmanship behavior one can have an engine
that will outlast the owner in many cases. It DOES require “going the extra
mile” and to assume nothing. Make your shop PROVE to you what was done. They
have the mics and gages. Have them show you EVERY dimension and take notes.
Cost. Costs very. Big help Ron… but, boring and honing should be about
$30-40 a cylinder, align hone about $150. Crank grinding about $150. or so.
Surfacing the head surface on the block about $50.
All that grinding of casting flash… free, YOU can do it with a small
grinder and some abrasive rolls.
I would be willing to stand corrected on any and all of the above.
No ego involved, just the dissemination of correct information.
ANY QUESTIONS ?
Post them as others are probably interested in the answer also.