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Bearing clearances and Plastiguage

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Mail From: "Jerry C Shaw" <(email redacted)>

Have lower oil pressure for a rebuilt engine than I would like.

What main and connecting rod bearing clearances are normal?

Used micrometer on all reground crank surfaces giving 0.010 undersize with
mains @ 2.303" and crankpins @ 1.865" . Stupidly didn't check clearances
during installation assuming shells were 0.010 undersized as stated on the
box.

Also, one of the car mags says Plastigage is not accurate. See
carcraft.com/techfaq/116_0701_plastigage_vs_micrometer/index.html
Jerry
'74 TR6
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Mail From: "Vance Navarrette" <(email redacted)>

Jerry:

Oil pressure is sensitive to lots of things, including oil
viscosity and the spring pressure of the relief valve.

What type of oil are you running?

Plastigauge is accurate enough to get the job done, although
there are more accurate ways of getting things measured plastiguage is
cheap and easy. For the occasional driveway mechanic, it is definitely
the way to go. I have built several engines, and in every case,
plastigauge indicated that the crank journals were spot on. Could be
dumb luck, but it seems to work for me.

Vance



-----Original Message-----
From: (email redacted) [mailto:(email redacted)]
On Behalf Of Jerry C Shaw
Sent: Sunday, August 08, 2010 6:05 AM
To: (email redacted)
Subject: [6pack] Bearing clearances and Plastiguage


Have lower oil pressure for a rebuilt engine than I would like.

What main and connecting rod bearing clearances are normal?

Used micrometer on all reground crank surfaces giving 0.010 undersize
with
mains @ 2.303" and crankpins @ 1.865" . Stupidly didn't check
clearances
during installation assuming shells were 0.010 undersized as stated on
the
box.

Also, one of the car mags says Plastigage is not accurate. See
carcraft.com/techfaq/116_0701_plastigage_vs_micrometer/index.
html
Jerry
'74 TR6
_______________________________________________

(email redacted)
Donate: team.net/donate.html
Archive: team.net/archive
Forums: team.net/forums


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Mail From: "Robert M. Lang" <(email redacted)>

Hi,

I haven't had a chance to flush this thread out completely, but if you
haven't tried this yet, it will PROBABLY solve your low o.p.:

blueprint your oil pump.

The Bentley manual lists all the clearances in the oil pump. That's all
really kool and everything, but unless your motor has a gazillion miles on
it, the rotor clearances are _probably) okay and close to spec.

However, there is a fix that I've done a bunch of times that is easy and
pretty much automatically raises o.p pressure 10 psi everywhere. Drop the
pan and pull the oil pump. the bottom cover of the oil pump will likely
have scoring. On a flat surface with some emery cloth of very find wet or
dry (400 or 600 grit) and some OIL, polish the cover 'till all evidence of
scoring is gone. Clean the part three times with brake cleaner (make sure
there is no grit left on the surface (hopefully, for obvious reasons)).
Reassemble.

I did this a couple of years ago when my oil pressure idiot light kept
coming on at idle (motor hot). Oil pressure went from under 10 psi to
about 25 psi. If your oil pump rotors are knackered, you can buy new guts
for something like $30 from the various sources. You do not need a new
pump body unless the outer rotor clearance is way off - the inner rotor
tips to the rotating body clearances are most important, then the pump to
body clearance and the only one (in my experience) that matters is the
rotor to bottom clearance. Also note that if the rotor is too deep in the
pump body (scoring on the upper end of the body) you can reduce the
"height" of the pump body be polishing as described above, BUT you must
make sure the pump body is square as well as flat or you'll dish the
bottom cover and you'll be back to crappy oil pressure in due time.

Cost: $5, $10 if you screw up the oil pan gasket (or (shame of shames) you
glued it to the pan and block).

Time: 1 2 hours MAX. Most of that time will be trying to figure out how to
put the three pan bolts that are just above the frame rail. Leave 20
minutes to wash your hair of all the oil that drips on you while you
remove the pump. Hint: use cardboard to keep the drips off the floor and
let the motor drip for an hour or two before you pull the pump.

Seriously, this is an easy fix. If it doesn't work, then check your
bearing clearances. I'm amazed at how many motors have low oil pressure
and the only prob is the oil pump clearances.

regards,
rml
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