My TR4 oil pressure is running quite close to what you describe
here. I have heard several times now how easy it is to replace these
bearings. Never having done it, I assume that means that the
engine does not have to be removed, and that one just gets at
the bearings via the removed oil pan.
It's easy - I did it a month or two after I bought my TR4A, when I had
essentially zero experience as a mechanic.
To do it right, you'll need to have the car off the road for a few days,
because you don't know what size bearings to order up front. Beware. I got
lucky; I ordered STD bearings and they were the right thing!
To do the job, you'll need a couple of jackstands and a new sump gasket. Whie
you're down there, you might consider swapping in a clearanced oil pump from
Ken Gillanders - cost is about $40 and well worth it.
Jack the car up in front, place the jackstands under the frame rails as wide
apart as possible. Drain the oil. Remove bolts from the pan. Notice that
several (probably four) are shorter and one is longer (that one holds the
clutch slave cylinder stay). Make sure to get them back in the right places
when reassembling. I painted the heads of the short ones green so I could tell
if I had one in my hand when I grabbed it out of the pile.
Anyway, take out all the bolts, save two on diagonal corners. Loosen those (or
take them out completely if you're feeling brave). The pan will almost
certainly not drop. Use a plastic headed mallet to tap (hard) the pan under the
sealing surface. You'll hear the sound change as it comes loose. Lower the pan
and remove it.
Take out the plugs, put the car in neutral. You'll want to be able to rotate
the engine easily. Pop off a set of rod bolts, drop the cap, push up the piston
to free the other bearing half. The back of the shell should be marked with the
size. Order new bearings.
(You may find some locktabs holding the rod bolts. I don't care for them - I
prefer to use a torque wrench and get the stress right. If I'm worried, I'll
use some blue loctite.)
When assembling, use a good assembly lube (moly based or Redline synthetic) on
the surface that contacts the crank. (Don't put anything on the back, you want
good contact for heat transfer.) Put the new bearings in (orientation matters,
there's a divot/tab that have to match up) and tighten the bolts hand tight.
Make sure the engine rotates easily. Torque up with a torque wrench in a couple
of steps, making sure the engine rotates each time. Repeat for the other three
sets.
Remove all the old gasket, put the new gasket on with some aviation permatex,
replace the pan using new spring washers on the bolts.
Probably three hours work the first time you do it, with a break in the middle
for getting the right bearings.
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