Bearing clearances?

[MN_luda]

assembling my 4.7 short block. Crankshaft mains and rods are about .0025. according to AERA spec sheet this is correct, does that sound acceptable?

[SilverXJ]

Yes, that is fine.

[Cheromaniac]

Yes, that is fine.

x2.
Clearances should be 0.0020-0.0025" so yours are just within spec.

[jason-alex]

what happens if your at .001?

[SilverXJ]

Thats quite tight. Its the very minimum of the stock spec. Not sure I would run it like that.

From the 2000 FSM:
Mains: 0.001" - 0.0025"; preferred: 0.0020"
rods: 0.001" - 0.003".; 0.0015" - 0.0020" preferred.

[Cheromaniac]

what happens if your at .001?

Should still be OK. With clearances that tight you could use a thinner grade of oil and still have a generous oil pressure.

[Retlaw01XJ]

what happens if your at .001?

Just be sure the crank is straight and journals are not out of round. There's not much room for error with that tight clearance.
What method are you using to measure? I would not rely on reading from plastigauge. Use mics and/or bore gauges.

[jason-alex]

I was just wondering I plastic gauged it when i had the oil pan off at 100k miles... was/am trying to figure out my oil pressure problem..... rod and main bearings where find so i am guessing spun cam bearing.

[sly-jeeper]

if you haven't already check the oil pump pick up tube for it's seal in the pump, the pick up tube to pan clearance, and that the casting on the block isn't holding the pump on an angle just se if it fits flush without gasket finger tighten bolts to check

[IH 392]

I was having oil pressure issues in my Jeep, I schit canned the OE aluminum pump and installed an iron MELLING pump and and new pickup tube and all was right!

[SilverXJ]

if you haven't already check the oil pump pick up tube for it's seal in the pump, the pick up tube to pan clearance, and that the casting on the block isn't holding the pump on an angle just se if it fits flush without gasket finger tighten bolts to check

See here: http://www.jeepstrokers.com/forum/viewt ... =34&t=2671

[sly-jeeper]

i just re read and realized you said 100K!...because of that my first educated guess would be the oil pump

[beiwulf]

I am reading a research article on bearing clearances and materials at the moment. A formula they mention for applying to crank/journal bearings.

0.001 x diameter to 0.0015 x diameter = tolerance to seek out for medium speed build engines.

These numbers seem consistent with thread and what SilverXJ is stating. Just a bump on thread. Love the information on this site and the experience being shared.


Brian

[beiwulf]

This for me seemed to express the importance of replacing bearings whenever you take it apart and reassemble. Atleast that is how I viewed it.

Free spread
Free spread is the term given to the excess dimension across the
bearing joints with the bearing in its free state, compared with
the housing diameter. This allows the bearing to be positively
located radially and should generate sufficient friction to hold
the shell in its housing even when inverted.
Following operation in an engine, bearings may show a loss
of free spread on removal for the following reasons:
(i) The lining of a steel-backed bearing, because of its higher
thermal expansion, can yield in compression at operating
temperature producing a residual tensile stress when cooled to
room temperature. This effect becomes greater with higher lining
to steel thickness ratio.
(ii) A high radial temperature gradient across the steel backing,
due to malfunction, can cause differential yield and therefore
additional free spread loss.
(iii) Relief of strains induced during fitting or by the manufacturing
and machining processes.
The forces which result in free spread loss after releasing the
bearing from its housing are of relatively small magnitude and
will not cause malfunction of the bearing whilst in operation.
Problems only arise upon reassembly, particularly if one half
has negative and the other positive free spread. The half with
the negative free spread may become trapped against the shaft
and lead to overheating or seizure. Therefore bearings with
negative free spread should not be refitted.

reference from the below link:
http://www.mae.ncsu.edu/eischen/courses ... Design.pdf