Jackshafts & Waterpumps

[Daryl Gatenby <Daryl.Gatenby@domain.elided>]

Thanks for the replies I have recieved on this subject thus far. The engine
rebuilder, his insurance company (the rebuilder has lodged a Public
Liability claim) and I are still determining the cause/s of the failure. I
would appreciate any further suggestions listers may have on the matter.
What follows is some background on the engine rebuild, a more detailed
account of the failure and some theories on the cause/s of the failure. 

The engine has done 5000k's since a full rebuild. The Waterpump fitted
during the rebuild was new. The Jackshaft, it has now been determined, was
the original item presumed to have done 140k. 

The failure first manifested itself as abnormal upward temperature guage
movement due to the Waterpump not being driven by the Jackshaft. Examination
of the Jackshaft showed that it had an extremely worn Waterpump drive gear.
The teeth on the gear were very sharp with blue heat marks at their tips.
The Waterpump gear sustained very similar damage and also had blue markings
on it. The Waterpump was free running and had the required cover clearance.
The Jackshaft sustained score marks on its bearing face at the timing cover
end. It also had some wear on the distributor drive gear. The wear was
consistent with the work the shaft had done pre-rebuild. The wear on the
Distributor drive gear on the Jackshaft did appear slightly uneven across
the length of each gear tooth.

Upon seeing the damage I consuted two leading New Zealand Stag authorities
seeking advice on what may have brought rise to it. Both have rebuilt many
Stag engines and both claimed to have seen similar failures (on more than
one occasion) to that as I described to them. Neither have, as yet viewed
the damaged parts. Their initial appraisal of the cause/s for the failure
were the same. 

Theory # 1
This theory is proposed by the "experts" as being the most likely. The
clearance between the Jackshaft bearing face (Timing Cover end) and the
block face was too great and culminated in the Waterpump gears recieving
insufficient oil. In their opinion there should be no more than 4 thou
clearance between the two surfaces in order that oil pass from the galleries
in the block to the oiling mechanism on the Jackshaft and then on to the
gears. This, they say would explain the failure of the gears which
undoubtedly have suffered from inadequate lubrication. 

Theory # 2
This theory involves the quality of the parts. This is the theory which
seems to be most intensely examined by the rebuilders' insurance company. It
suggests that the hardening on the Jackshaft and/or Waterpump gears is
substandard and has lead to premature failure of both gears. 

Theory # 3
This theory involves the incorrect meshing of the two gears. It has been
suggested by the rebuilder that the Waterpump gears may have been defective
from new and that the angle of the teeth may have been incorrect to allow
proper meshing leading to premature failure of both gears.

Theory # 4
This theory is similar to # 3 in that it involves the incorrect meshing of
the two gears leading to premature failure of both gears but as a result of
a new W/P being fitted to an old J/S.

Theory # 5
The drive directional score marks on the J/S bearing face give rise to this
theory. The theory is that inadequate clearance between the J/S and the
block allowed insufficient oil to travel to the oiling mechanism and on to
the gears resulting in their premature failure. I am not convinced that this
theory is even possible.

I believe it is a somewhat difficult situation to conclusively prove any of
the theories that involve either the hardness of the gear teeth or their
mesh angles as little is left of the gears. I have been told that testing
the hardness of the J/S's shaft will not necessarily provide a result that
is indicative of the hardness of the gear teeth. I suppose that it may be
similarly inconlusive to rely upon the hardness measurement of the
distributor end teeth to provide an indicative result. I now understand that
there are some crook W/P's made. I would be interested to know exactly what
was wrong with them, who made them and who distributed them. Is their fault
restricted to hardness of the spindle teeth or does it involve gear cut? 

In your speculative opinion what has caused the failure of this engine?

Regards

Daryl Gatenby
daryl.gatenby@domain.elided
Hamilton
New Zealand

73 MOD