Tom Wagner - Program Manager wrote:
> To All:
>
> Can someone tell me if the whole
> crank needs to be replaced when doing
> a replacement of the main bearings or
> is there a way to leave it in there.
>
> Also are the thrust washers a difficult
> job to replace them at the same time.
>
> If the crank does need to come out, any
> suggestions on how to remove the big nut on
> the end of the fan extension????
>
> Please reply directly to me as it takes
> me a couple of weeks to see the digest.
>
> Thanks
>
> Tom Wagner
> 67 MGB
> 72 TR 6
> Houston, TX.
> 713-964-7068
Hello Tom,
If the crank can be left in or not depends on what kind of a job you are looking
for... The best way to do the job is to remove the crank and have it ground to
the next available undersize at a machine shop and then install oversize bearing
shells. However, removing the crank in the car is quite a job - you must remove
the transmission, radiator, timing chain cover, etc. At that point, struggling
to do that with the engine in the car seems somewhat counter-productive. I
suggest you'd be better served to pull the entire engine and while you have it
out, to strip it entirely and do a proper rebuild. However, this can be very
pricey and time consuming to do correctly to better-than-new specs.
If you are simply looking to correct a low oil pressure condition and you don't
mind the fact that you'll have to do the job again in a few years, you can get
by
quite nicely with changing the bearings in the car. Before deciding, check the
end float on the crankshaft - less than, oh, about .020" and the TW's are worn,
but probably still in place in the block - if you get about 1/8" play or so,
then
the washers have already dropped and the block and crank may not be salvageable.
If the TW clearance indicates the washers are still in place, then go ahead and
pull the oil pan and bearing caps for a look. If the journals have some light
scoring that will be pretty normal for an engine with upwards of 50,000 on the
clock. Light scoring means you can feel a general wavy quality to the journal,
but you can't catch your nail on any specific grooves or scratches. If you do
have deep gouges/grooves or scratches, then you'll probably want to pull the
engine and have the crank ground. (If you have those kind of problems on the
bottom end, then you've probably also got a lot of wear in the top of the motor
too and you might want to consider rebuilding the entire engine.) Yes, the
light
scoring will accelerate the wear on the new bearings, but in most cases you
should be able to get upwards of 20,000 more miles out of your TR-6 before
you've
got oil pressure problems again.
Look on the back of the bearing shells for any markings such as '010', '020' or
'030' to indicate a previous oversize. If all you can find is a part number,
then you've probably got the original shells still in place. If you have the
ability to measure the journals, that's best to be sure you've got the right
size, but if not and you can't find any indications of an oversize you're
probably safe to order standard size replacements. (17 years working on engines
and I've never seen an oversize that wasn't marked so.) If you don't have the
ability to measure and the engine gets tight to turn over when you're putting
things back together, then stop and investigate further.
Loosen all the main cap bolts slightly, but only replace the main bearings two
at
a time so the full weight of the crank is still on the remaining two mains and
isn't resting on the front/rear oil seals possibly damaging them - resulting in
a
leak later on. To install the upper shells in the block webbing, fashion a
small
cotter pin into a 'T' shape (note that the 'leg' of the 'T' must be bent over at
an angle and not perpendicular to the top so that it fits flush into the crank).
Insert the modified cotter pin into the oiling hole in the journal and rotate
the
crank until the cotter comes into contact with the old upper shell. Continue
rotating and the shell will slide out the other side as the cotter rolls up and
around with the crank (look at one edge of the bearing for a tang that prevents
the shells from rotating - turn so that the cotter contacts the plain end and
the
end with the tang comes out first). Now place the new bearing up against the
crank with the cotter at the edge with the anti-rotation tang. Now spin the
crank again so that the cotter comes to rest up against the edge of the bearing
and continue turning as it pushes/spins the new bearing up into place in the
block. Install the shell in the bottom cap and snug up the cap (note that both
tang edges are always on the same side). Be sure to wipe the shells carefully
until they're clean before actually installing them - a slight amount of dirt
can
be a big problem when trapped under a bearing.
On the rear main, install new thrust washers before installing the cap. Note
that to get the proper end-float, you may need to mix and match between standard
and oversize sets (one standard washer in front, and one .005" oversize at the
rear for example) Carefully examine the rear cap on the flywheel side for
evidence that the crank has been contacting the cap. Damage here can reduce the
'ledge' that retains the TW's and make them more susceptible to 'dropping' in
the
future.
After all the shells are replaced, go back and torque all the cap bolts to spec.
Moving on to the rod bearings, undo the rod caps two at a time as access permits
on each throw of the crank turning the engine in-between each pair. Fully
replace the bearings and tighten the caps on the rods before moving on to the
next pair, otherwise you may not be able to reach the heads of the bolts if the
rod/piston is close to TDC. On the rods, you can swing the beam of the rod away
from the crank for clearance to insert the upper shell - you don't need the
cotter pin anymore.
Take down the oil pump and examine each of the blades of the rotor for
scratches/gouges - replace if it looks rough at the tips of the blades. Check
the endfloat of the rotor and housing.
When reinstalling the alum. block that seals the front of the oil pan, carefully
scrape away the old gasket from the front motor plate and be sure to put a good
bead of sealer along the edge to seal where the gasket had once been. Don't
push
the block in so hard as to squeeze all the sealer out of the gap. Upon
reinstalling the oil pan and filling with oil, remove the long hex plug on the
side of the block that contains the oil pressure relief valve. Fit a piece of
rubber hose into the hole and pour clean engine oil down the hose for about a
minute - reinstall the pressure relief valve, spring, and hex plug. This will
prime the oil pump providing quicker lubrication on the restart.
All told, your investment should be less than $150 (about $90 for an oil pump,
$20 for a set of rod bearings, $25 for a set of main bearings, $6 for thrust
washers, $5 for a pan gasket and a couple bucks for 5 quarts of oil) and a
Saturday spent under the car. No, it won't last as long as the bearings did the
first time, but it will breathe new life into your oiling system to give you
years of driving before you'll have to repeat the procedure or then decide to
rebuild the motor properly.
Good luck!
Brian Schlorff
Power British
610-270-0505
http://www.powerbritish.com/~britcars
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