ENGINE
MAIN BEARINGS: What again I hear you groan? A small point, quite often with the super-blend, the inner
race, especially on the timing side, comes loose on the crankshaft; this does not seem to be detrimental
in any way, so do not worry about it. The next time things are apart down there a blob of Retainer Loctite
is recommended. Clean both surfaces with Carbon tetrachloride or similar (Evostick Cleaner) degreasant
(not petrol, it leaves a faint oily film) and use Loctite-601 green Retainer fit, this is some four times
stronger than the 641 yellow Bearing fit. Bearing fit 641 is for use up to four thou. gaps, 601 for use up to
six thou gaps. While the ultimate is Studlock 270, stronger than 601 but it needs a minimum gap of two
thou. and will fill up to 10 thou. This pulled the hooks off of Les Emery's bearing puller. Tee Hee!
J.H. Surely R does not matter if the inner race on the timing side is a free fit on the shaft as it is secured
endwise by the oil pump driving worm when this is properly tightened.>>
Yes, but carrying out modifications to slacken timing gear (as per page 4 last para), and having bearing
inner loose has caused odd faults when the oil pump worm nut has loosened, odd ticking noises and
even an apparently seized engine when the timing gear came loose and jammed on the oil pump. All up
tight as original would be preferable here. Al Oz.
TIMING CHAIN TENSIONER: Do not overtighten chain as this can rip up the rubber surface of the
tensioner, the metal underneath is not hardened ! ! ! CAMSHAFTS: Have still been known to be of an
inferior hardness, check followers or replace them when replacing camshaft.
REV. COUNTER DRIVE: Leaking! Possibly changing to a 750 unit can cure it. A 750cc housing with an
850cc drive spindle gives 'O' ring seal. EXHAUST VALVES: It's not unknown for these to get bent, one
cure suggested is to fit racing NIMONIC 80A, once available from Gus Kuhn. This can also be caused by
keeping oil level up to maximum level-the oil is then sucked through the air filters and cokes valve stems
up causing exhaust valves especially to stick in the guides.
PUSHRODS: On Combat engines or any engine which has had a significant amount machined off the
head (my 750 racer had over fin off) the pushrods must be shortened by the same amount and both ends
of the rod may need attention, otherwise, you could find the end cap contacts the radius on the reduced
diameter of the rod. On the head make sure the head gasket does not protrude into the pushrod tunnel,
or the pushrods will wear away. Some Mark III models have a casting 'Flash' which protrudes into the
pushrod tunnel, causes rubbing of push-rods, and ultimately failure of the camshaft. When the head is
removed it is well worth clearing out the push-rod tunnels with a large round file, this only takes five
minutes since the alloy is easy to remove, and should restore sensible camshaft life.
PRIMARY CHAIN CASE: A rattle -in here at low revs, especially after the bike has been standing for
some time, maybe on its side stand, is usually due to the Primary Chain hydraulic tensioner not having
enough range to cope with a partially worn Primary Chain, so it thrashes around and hits the case. The
only cure is a new chain even though it may have only done 20,000 miles or so. On Les Emery's racer
they use "much stronger" tensioner springs to cure this problem.
J.H. I never heard that the hydraulic tensioner 'did not have enough range'? It loses its 'prime' if left
standing and will often re-prime itself when the machine is next run. If not, remove outer half of case and
squirt some more oil in collecting trough and push piston up and down by hand. We did this with new
bikes after standing for long periods and it always worked, >>
CLUTCH SLIP: A part from the "cures" already noted, this can be corrected by machining away the centre
1/4in from the phosphor bronze surface of the plates, (both sides) so giving greater pressure on the
remaining surface and
34
Summary of Contents for 850 Mk 1 1974
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