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one of 3 853R's
This is one of 3
748-853R conversions completed from 0ct to Feb 2010. It’s a lovely bike
and has only covered 1400 miles but the owner insisted for smoothness
and outright power without compromising reliability. I recommended
a full engine blueprint re-building the motor from the bottom up which I
always suggest to my customers. People who insist on bolting big
bore kits to an unknown or stock block usually ask for trouble.
With the engine in
bits the main bearings were changed, the crank and transmission was
re-shimmed. Re-shimming the crank is important. The cranks usually
come with too much preload as standard. Reducing 0.10 from the crank
preload enables the crank to spin with little noticeable drag.
Some bikes have really tight cranks which gives poor starting (starter
struggles to turn as crank too tight) and can cause premature main
bearing failure.
The crank/flywheel
assembly was rebalanced with a Kamna evo flywheel, journal surfaces
polished and refitted with the correct oil clearance. This is found
using plasti-gauge combined with using the correct grade shells.
Shells come in different sizes red, blue, yellow etc. Too tight a
clearance and the journal overheats causing scoring and too loose means
the engine will need to be overhauled sooner than later. A crank
blueprint includes honing the rods and deburring. This helps the sizing
process and also eliminates any possible burrs one the conrods that
can quash the shells out of shape when torqueing. Crank oil ways are
also keyholed as the factory's radius on some cranks are substandard.
Many builders omit these important steps and slap in basic sized shells.
.
I sent the primary
gears back to the customer who decided to lighten all the gears in his
machine shop. I must say the job looks pretty cool. The engine has now
lost a little weight, will spin up and accelerate from point A-B
faster.
The cylinders were
bored out and re-plated to 94mm with a pair of quality pistol pistons
making 853cc's. I don’t use anything else as the design fits the chamber
and valve reliefs perfectly.
Next up the cylinder
heads given the CJS ultimate treatment. One thing I noticed was
how bad these heads were (all 748r are bad) but this took first prize.
The port floors were ripped out on the exhaust ports of one head. I
know what shape an exhaust port is supposed to be in stock and modified
form but this took the p*ss. We had 2 choices, either buy another
head or re-work the strange port and make the untouched head the same. Whether this was a good or bad move I don’t know but the exhaust flow
has not been affected at all by its strange shape. This strange shape
has been found on some of the early corse bikes and still exists in some
early 996sps bikes and they all seem to go well. If the problem was in
the intake ports I would be very worried about performance.
Colsibro valve guides
come with every head I make for reliability reasons. They are
tighter meaning I can size the valve to the guide using different
reamers of selected sizes and a fine hone to finish the clearances. I
gave up on installing new sloppy fitting Ducati OE guides 4 years ago.
They are loose, wear quickly and cause valve walking with high lift cams
ruining my superb performance seat work. My seat machine is like a
portable serdi (seat and guide machine) with multi angle tips. The seat finish is amazing and
very concentric which give superior valve sealing. Valve jobs can make
or break a port job. Too many times I have seen heads that were ported elsewhere with no improvement. Some of the better ones had good
ports but poor valve jobs (stock angles blended together) resulting in
poor low and mid lift flows. Correcting releases the flow and power. It
takes 3x8 hour days to make a pair of heads here and the price does not
reflect the amount of effort they see. Enough ranting and back to
the project in hand.
The intake ports were
properly sculptured along with the chamber and modified, polished stock
valves. Flow testing revealed a substantial gain followed which
was a little more than my usual numbers. I ran the test quite a
few times making sure it wasn’t an error. It wasn't, so I spent an hour
meticulously measuring all the port and chamber dimensions until I found
where the gain came from. The ports velocity is also very high
meaning the midrange is going to be very strong. Too many misconceptions
out there about porting (peaky, unusable) - total rubbish I say if the
job is done correctly.
All the valve
clearances were set to the tighter spec of shimming. The old or tighter
spec of shimming gives less worn rockers, less broken half rings and
smoother running as the valves seal so much better and also give
extended service intervals. This shimming spec is now becoming common
also being used by my friend Tom at Hypertrick.
Finally the cams were
degree'd, squish set using different thickness base gaskets and the
engine was assembled. It looks nice and I'm in anticipation the
dyno results of all three of these identical 853r builds.
