I've never heard of that... Sounds like a major manufacturing defect on
the bearings to me, unless it did somehow have to do with the engine
assembly procedure.
My understanding is that the oil flowing between the bearing shell and
the rotating assembly forms a wedge of lubricant and prevents metal to
metal contact. If the bearing clearances are too tight, then your oil
pressure will be high but there won't be enough flow to maintain the
wedge at higher RPMs and you'll wipe the babbitt material off the shell
(and then the copper... Etc.). Higher RPM operation and higher load
operation requires a thicker oil film and therefore more crank to
bearing clearance, which in turn requires more oil pump output volume at
any given pressure.
Maybe the oil was being preferentially directed away from the main
pressure point (relative to crank rotation) on your engine and therefore
you needed (a) to radius the oil passages and (b) loosen the bearing to
crank clearances to increase the flow to the parts of the crank that
needed it most.
I seized the engine in my Pinto (when I was 17) due to the pickup tube
becoming detached from the oil pump, which destroyed the bearings and
required the crank to be turned 10 or 20 under to clean up. When I was
racing Toyotas, we used stock Clevite bearings on a stock polished
crank, and never had a bearing issue even with more than double the
stock output and sustained 7000+ RPM operation.
With the smallblock Ford, I think a critical thing related to the oil
pump operation, especially with high pressure/high output pumps is the
oil pump driveshaft and the distributor gear. Those parts have to
transfer the several horsepower required to run the oil pump and any
additional load you put on the oil pump means that the shaft and gear
get extra wear and tear.
Cheers,
Theo
> -----Original Message-----
> From: tigers-bounces@autox.team.net
> [mailto:tigers-bounces@autox.team.net] On Behalf Of Howard gentry
> Sent: January 14, 2010 5:45 AM
> To: Jerry & Maureen (Mo)
> Cc: tiger list
> Subject: Re: [Tigers] Tigers Digest, Vol 4, Issue 11 (oil pump)
>
> Hi,
> This is, indeed , a very interesting thread..When I was
> racing in the SCCA club races in the mid 60's, we had to
> really watch the pressure and volume going to the rod and
> main berings..The 1622ccMG series A engine in our Elva
> Courrier had problems with too much pressure..We experienced
> situations where the pressure would actually scour the bering
> material out of the bering shells..actually scoop out the
> babbit material or at least peel the outter layer of it off.
> We found tha careful radius work around the oil entry holes
> to the berings, along with the correct volume and pressure of
> oil, when at operating temps, would allow us to lubricate the
> engine without ripping the bering shells apart..Has anyone
> run into this problem?
> zym
>
> The Blues is the only music Original to the United States of America.
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