Ok,
1. have you measured the height of other springs and checked spring
tension with a scale or somesuch to see if somewhere along the line
someone bought a spring from Ace hardware that will fit but has
different specs? different wire thickness or spring rate?
2. Can you measure the diameter of the hole in the block? Insert a
drillbit or something to compare size at the thimble and at the pan
side?
Lester
..
On Jun 23, 2006, at 8:18 AM, Wm. Severin Thompson wrote:
> Youse Guys,
>
>
>
> So, I snatched the 120 lb on starter cranking oil pressure motor out
> yesterday.
>
>
>
> Paul A had solved his identical issue on a customer's car by
> replacing the
> pressure relief thimble with a ball bearing, and a shorter spring.
>
>
>
> I can't go that route, as this motor will be seeing extreme duty,
> and 8000
> rpm in a race application. I need to cure it, not treat the symptom.
>
>
>
> FYI, this is a newly built motor, from a collection of parts I had.
> I have
> no history on the block, but it was hot tanked (in new fresh
> solution),
> honed, line bored, and assembled.
>
>
>
> First thing I've checked (without dismantling the motor (that will
> happen
> next week) is the passageway from the relief valve to the pan. I
> took a very
> thick, wide wire tie, and had it make just enough bend to catch the
> 2nd
> (inner) hole, and confirm there's no blockage all the way into the
> pan.
>
>
>
> A relief spring shortened 3/8ths of an inch had not lowered
> pressure. A
> different plunger/thimble changed nothing.
>
>
>
> So, I got out the dial caliper, and measured the distance from the
> machined
> outer edge where the cover cap & washer seat, to the inside of the
> thimble
> "in place" on several blocks. (What I'd really like to measure is the
> distance from the seat of the thimble in the block, to that 2nd
> inner hole.
> the one closest to the thimble, but haven't figured out how to do
> that yet.
>
>
>
> So, 5 blocks (2 1275s, and 3 948s) returned interesting measurements.
>
>
>
> 1, a 1275 1.558"
>
> 2. a 1275 1.804"
>
> 3. a 948 1.870" (the Bishop motor)
>
> 4. a 948 1.832" (the one giving 120lb + on starter crank)
>
> 5. a 948 1.840" (my regular race motor, that was always
> on the
> low side of acceptable oil pressure)
>
>
>
> So, I suppose what's really critical here is the measurement from
> the seat
> inside to the hole, because it's that relationship of distance that
> would or
> wouldn't allow the relief valve thimble to be pushed outward enough
> to allow
> oil to drain into the pan, relieving excess pressure.
>
>
>
> FYI, oil is traveling through the block (enough to blow out an oil
> cooler,
> and an oil filter gasket).
>
>
>
> Also, the pump was used for one race in my last motor, the one with
> the low
> side of acceptable pressure, so I can't imagine it is the issue.
>
>
>
> This motor was line bored, has new main, rod, and cam bearings, spins
> freely. Bearings on the rods & mains were plastigauged. Most have
> suggested
> the issue cannot be tight bearing clearances, as they would not
> cause these
> extreme pressures. and that the issue must be in the relief valve
> area.
>
>
>
> So, all you collective geniuses, any words of wisdom before I break
> this
> motor back down on the bench?
>
>
>
> WST
>
>
>
>
>
> Wm. Severin Thompson
>
>
>
> wsthompson@thicko.com
>
> www.thicko.com <http://www.thicko.com/>
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