More about improving your A10.
To complete this part of the modification a tube is inserted from the oil pump
outlet to the locating dowel hole below the main bearing housing. Also from
this dowel hole an oil way is drilled to the pressure relief housing and a
stainless steel tube pressed into place and sealed to stop it moving. The holes
in the outer face of the crankcase are sealed by tapping a thread into the hole
and screwing in a piece of alloy rod which is cut off and peened over. It is
almost impossible to tell the engine has been modified afterwards. The locating
dowel in the inner timing cover is replaced by a hollow dowel and is sealed
with an 'O' ring either side. The crankcases and timing cases are then
assembled and a special jig with a boring tool is passed through the assembly
to cut a hole in the casting which was Lumiwelded into the outer timing side
cover. The cutting of this hole is critical as it accommodates the oil seal
which fits over the quill in the end of the crank. Two cuts are made, one
smaller than the diameter of the oil seal. This is slightly larger than the
quill which passes through it. This is to protect the oilseal from very high
oil pressure which might occur in the fraction of a second before the pressure
relief valve trips on a cold engine. This is unlikely however as the oilseal is
rated at 150PSI. Isn't it nice to know that on a BSA engine precautions have to
be taken in case of too much oil pressure. The oil pressure relief valve is
also tested and adjusted before it can be fitted. The crank timing side journal
is turned down to 1.375" incidentally, the same as the drive side, to
accept the new roller timing side bearing race. My crank was checked for wear on
the big ends which where okay. It had only done a couple of thousand miles
since the last rebuild. The crank was cleaned and a pair of hexagonal sludge
trap plugs fitted. I didn't want to revert to a chisel and drill or any other
method to remove them ever again. The next step is to drill the crank on the
timing side to accept the quill which is pressed in, then machined true. The
last part of the conversion is to make a spacer to fit between the timing
pinion (which has its rear face ground flat) and the timing side bearing. The
intermediate timing gear also has an angle ground on its rear edge to clear the
timing side bearing. Before the parts are returned to the owner everything is
cleaned to remove any traces of metal debris left over from the machining
process. My engine was absolutely spotless when I returned to pick it up 8
weeks after dropping it off. The time the engine is with SRM varies so contact
them first for an estimate of how long it will take. |
Assembly
The assembly of the engine which I did myself, was straightforward, just
requiring new big end shells and piston rings. I always buy the next size of
rings up, i.e. my bore is plus 20 so I buy plus 30 rings as I have found that
some rings have gaps as big as 20 thou. I gap mine to 8 thou by filing the ends
and checking the gap with feeler gauges, after pushing the ring down the barrel
with an upturned piston. The crankshaft was assembled into the cases and the
barrels fitted. The thing that surprised me most when the crank was fitted in
the cases and the barrels were on, was that the resistance with the two roller
bearings was so low, it is possible to grip the drive side of the crank by hand
and with a snap of the wrist, turn the crank by two revolutions. When fitting
the oil pump, I discard the studs and instead, use three Allen screws. This
makes it easier to fit and allows more scope to position it against the worm
drive. It also means that the worm drive can be fitted to the crank while it is
out of the cases, otherwise, with studs fitted, if the pump needs to be removed
at any time, the primary side has to be stripped down to allow the crank to be
locked, so that the worm drive can be removed with the oil pump. Always check
the holes in the oil pump gasket line up and are not too small. While the crank
cases were apart I made a dynamo strap from stainless steel which I fitted with
two stainless dowels. Removing the old dowels involved cutting them in half and
filing flats on them so I could fit a small spanner on them because they were
rusted in solid. Not a job I could have done with the engine in the frame.
Still on the timing side, I have fitted a dynamo belt drive which has cut down
the noise in the engine considerably, it is available from a BSAOC Member on
(UK) 01325 318899 and uses an off the shelf belt. At the other side of the
crank I have made another modification. The normal method of securing the drive
sprocket cush drive is to tighten the special nut with a 'C' spanner then put a
split pin through the hole in the crank to stop it spinning off. Judging by the
number of primary case outer covers I have seen with gouges in them, this does
not work. However the primary cover on my bike is undamaged because I lock the
nut with a brake plate retaining nut from the front wheel of a late A10 which
has the same thread form. This is secured with thread lock. The other advantage
of this is that you can use a socket and wrench to tighten it which gives more
purchase and a better chance of tightening than a 'C' spanner. |