A Christmas teaser for the technically minded. I've just bought myself some
problems to solve instead of taking the more expensive but conservative route.
The excuse is to save money for other projects but in truth I'm an optimist
and miser ! Story first, then ideas, then questions.
In the days before Phoenix made their excellent Austin 7 cranks people took a
lot of trouble to make the Reliant crank and rods fit an Austin 3 bearing
crankcase. The problem with this setup is that oil for big ends 1 and 4 has to
be pumped into the centre main, past 2 and 3, then back against the centrifugal
(centripital ?) force.
The particular setup I just bought was more successful than many but number 4
big end has gone. The prior owner had it on a race cam, ran it regularly to
7500rpm, mostly used Castrol Syntron but may have had GTX in it the day it
went pear shaped, and had the crankcase bolted to the chassis. Its been
sitting under his bench for a few years and came to me for small change as he
is never going to bother with it. He now runs splash fed phoenix cranks in his
racing engines.
Easy ways to improve the odds :
o Only bolt the crankcase at the rear. This stops the chassis twisting the
crankcase twisting the centre main out of line. Apparently Colin Chapman found
that engine was a great chassis brace with two bearing engines but the same
trick with three would knock the centre main out in short order. His solution
was flexible mountings and a frame over the engine.
o Add a small oil cooler and thermostat.
o Add a larger or secondary sump.
o Milder cam, lower rev limit.
o Block the pressure relief valve and add a remote one after the filter.
Perhaps something got in there and held it open. This is common practice on
nose-fed Austin 2 bearing engines. With that setup they have to be very
careful not to over pressure.
o Blue-print the oil pump. In particular reduce the end float.
More expensive solutions :
o bigger pump - one successful version of this setup runs 100psi to the crank
and a second 'low pressure' circuit for the other gubbins.
o better support for the center main, fit an undersize bearing, and line bore
to size.
o replace the front and rear mains with shell bearings and feed 1 and 4 from
the ends instead of the middle. By this stage I will have bought a phoenix
crank.
Questions :
o I've had a very strong recomendation for MOTUL synthetic oil. Anyone able
to tell me why it might be any better than other synthetics ?
o Do I really just need a heavier oil ? What is available ? I don't mind
losing some power and am happy to take care with the pressure relief
arrangments and warming up.
o What are the dangers from over pressure if I just block up the current
pressure relief device ?
o What are the benefits of a larger sump against an oil cooler ?
o What are the physics/chemisty of low oil pressure ?
Any comments, hints, tips or empathy welcome.
David
PS - Anyone know the origin of the phrase 'gone pear shaped' ?
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