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/>
[demime 1.01d removed an attachment of type image/jpeg which had a name of
image001.jpg]
/// unsubscribe/change address requests to majordomo@autox.team.net or try
/// http://www.team.net/mailman/listinfo
/// Archives at http://www.team.net/archive/team-thicko
|