Main and Rod Bearing Replacement
on the Midget 1500 Engine
(engine in car)

Disclaimer:  This is a delicate job, requiring that you manage a number of simultaneous conflicts:  Delicate parts that must be fastened down with great force.  Absolute cleanliness when working in the assortment of grit and grime that prevails on the underbelly of a british car, and applying various lubricants and sealers that have a tendency to attreact and hold crud.  If you don't think you can manage this project, don't try it.  The only promise I make is that I have successfuly followed the procedure detailed here.

The Project:
Replace Main Bearings, Connecting Rod Bearings, and Crankshaft Thrust Washers on a MG Midget 1500 without removing the engine from the car.  (This may or may not be possible on a Triumph Spitfire 1500, the engine is the same, but I don't know if there are body/chassis clearance issues.)

Why do it:
The 1500 is notorious for thrashing it's "bottom end".  The bearings relating to the crankshaft may have a lifespan as short as 35,000 miles, while the rest of the engine remains in good shape.  The crankshaft thrust washers are particularly problematic, as the only retention they have is the rear main bearing cap, and when sufficiently worn, can drop right out into the sump, causing the throws of the crankshaft to start smacking into the edges of the "webs" inside the block.  Ugly and expensive noises follow immediately.

Symptoms that may require this job:
A knocking sound that is louder in the sump than in the cylinder head.
Oil pressure dropping below 20 lbs @ idle.

In addition to detailing the procedures for replacing the bearings, I also include some opinions on maximizing their life.

Tools Required:
1/2" socket, 1/4" drive
9/16" socket, 1/2" drive
11/16" socket, 1/2" drive
Long flat blade screwdriver  (You may also find a shorter one handy to have, particularly if you can't jack the car up very far.)
One 6-8" long 1/4" drive extension, one 3" long 1/4" drive extension. (used together totalling about 10 - 11")
1/4" drive ratchet
1/2" drive "breaker bar"
1/2" drive torque wrench
An assortment of dental picks (no joke here).

Supplies needed:
New Main Bearings (READ THE NOTE!)
New Rod Bearings (READ THE NOTE!)
New Thrust Washers (READ THE NOTE!)
Blue "Form-a-Gasket" Silicone sealer.
Assembly Lubricant (STP Oil Treatment works fine, possibly the only legitmate use for the stuff.)
Ready access to somewhere to wash your hands (you'll be doing this a lot, so the closer the bettter).
A large quantity of clean, lint-free, rags.

THIS IS THE NOTE!
 
 

Step Process Comments
1 Clean the engine thoroughly.  Pay particular attention the the underside of the engine, and the area (difficult to reach) behind the crankshaft pulley. A can of spray degreaser and a coin operated car wash pressure washer hose go a long way here, particularly for the bit behind the crankshaft pulley.
2 Clean the work area.  Sweep carefully or wash down the floor where you will be performing surgery. If you wash it, let it dry thoroughly, because you will be lying here for a while, and you will need to be meticulous and patient.  Nothing's harder than being meticulous and patient while lying on a cold wet floor.
3 Get the car up in the air, safely. Once again, you will be lying under here, so safety is an absolute must.  Get the car high up so you have room to work, but it MUST be stable.  This is paramount.  I cannot emphasize this enough.  If it falls, you are likely to die.
4 Drain the oil Since this is also going to be a full oil change, you will want to change the filter as well, but I wait for the end.
5 Remove the oil pan.  Inspect the bottom of the pan for metal bits. This will require the 1/2" - 1/4" drive socket, and all the extensions you have handy.  Work your way around the oil pan.  If you have some electric or pneumatic tool to speed this up, use it.  It will save you frustration.

You may find anything from small flakes of metal to a fine silvery slurry of metal particles and oil.  If you find them, it's an indication that you need to proceed.

6 Remove the spark plugs. You will need to turn the engine over by hand.  This will make it easier.
7 Rotate the engine until 2 pistons are just past TDC. This will give you your best shot at the rod bolts on those two pistons.
8 Unbolt rod cap.  Remove cap. Set bolts in a clean place. 9/16" socket and the breaker bar.  Only unbolt one at a time.  This will prevent you from inadvertantly swapping the rod caps.
9 Use a dental pick or small screwdriver to remove the bearing shell from the rod cap.  Pitch the shell, set the cap in a clean place. There is a "tang" on the bearing shell that fits into a notch on one end of the rod cap.  There is enough space between the back of the "tang" and the bottom of the notch to stick a small implement in there and flip the shell out.
10 Use a dental pick or small screwdriver to remove the bearing shell from the rod. Push the rod up to unseat the rod end from the crank journal.
11 Wipe any oil off of the rod cap, fit the new bearing shell, and luibricate the inner surface of the shell with assembly lube.  Set it in a clean place. Be generous with the assembly lube, but not sloppy.  Wash your hands before handling the new bearing shell if there is any trace of anything but clean oil on your hands.
12 Wipe the bearing seating surface of the rod dry, fit the new bearing shell, and luibricate the inner surface of the shell with assembly lube.  Pull it back down and seat it on the crank throw. You may find it helpful to thread one of the cap bolts in to give you a handle to pull down with.
13 Fit the rod cap to the rod. Note: The cap goes on with the "tang" on the bearing and the "notch" in the cap on the same side as the "tang" and "notch" in the rod.
14 Reinstall the bolts, and torque them up. 9/16" socket and torque wrench.  The torque setting depends on the type of rod bolt.  Phosphated take 46 ft/lbs.  Color-dyed take 50 ft/lbs.  I fyou don't know which is which, show them to someone who does.
15 Repeat steps 8 through 14 on the other rod.
16 Turn the engine 180 degrees, so that the other two pistons are just past TDC.
17 Repeat Steps 8 through 15 on the other two rods.
18 Remove the two bottom securing screws on the front endplate. This is a bit of a pain, but it can be done with a long flat-blade screwdriver.  Look under the front of the car, with your eye level just above the sway bar.  You should see the two screws either side of the crankshaft pulley and above the crossmember, at about the 4:00 and 7:00 positions relative to the crank pulley.  If you can't see them above the crossmember, your engine mounts may have collapsed.  The rubber perishes and lets the front of the engine settle.
19 Remove the bottom bolt from the timing cover. This will require the 1/2" - 1/4" drive socket, all the extensions, and some patience.  The bolt is under the crankshaft pulley at around the 6:00 position.  You will have to sneak the socket and extensions around a bit.
20 Wash up and take a break for a few. Your frustration level will be high, and your hands will probably me messy from road grit that stuck to the front of the engine.
21 Remove the sealing block from under the front Main bearing mount. Two screws, one on either end of the sealing block, sitting in round recesses (which may be obscured by gasket compound).  Once those are out, you should be able to pull the block out.  (If not, did you skip step 19?  THose two screws and the bolt also engage the sealing block.)  Do not use excessive force.  The sealing block is aluminum, and if you mangle it, you'll have the devil's own time getting it back in.  There are wood (yes, wood) blocks sealing the ends of the block.
22 Clean up the sealing block and set it in a clean place.
23 Loosen all 3 main bearing caps, but do not remove them. 11/32" socket and breaker bar.  Back them out about 1/4".  Grab the bearing caps and wiggle until they're loose and sitting on the bolt heads.
24 Remove one main bearing cap. Unsrew the bolts all the way.  The main cap will come with it.  (I work front to back, and the thrust bearings are at the back.  Note the comment on Step 30.)
25 Use a dental pick or small screwdriver to remove the bearing shell from the main cap.  Pitch the shell, set the cap in a clean place. There is a "tang" on the bearing shell that fits into a notch on one end of the main cap.  There is enough space between the back of the "tang" and the bottom of the notch to stick a small implement in there and flip the shell out.
26 Remove the other bearing shell from the seat. This is tricky, and is why all the caps are loose.  You will need the play.  Like the rod bearings, the main bearings have a "tang" and "notch".  Push the bearing on the side opposite the side with the notch until the bearing starts sliding around the crankshaft.  Pull it the rest of the way with a dental pick a little at a time.  It will tend to cling to the journal becasue of suction with the oil clinging to the surface.
27 Wipe any oil off of the main cap, fit the new bearing shell, and lubricate the inner surface of the shell with assembly lube.  Set it in a clean place. Be generous with the assembly lube, but not sloppy.  Wash your hands before handling the new bearing shell if there is any trace of anything but clean oil on your hands.
28 Lubricate the inner surface of a bearing shell and slip it around the crankshaf journal until it seats. Set the bearing on the bottom of the crank journal, with the "tang" away from the notch.  Rotate the bearing around the crank throw until the tang seats in the notch and the ends are flush.
29 Refit the main cap loosely. Like the rod caps, the notches in the main caps go on the same side as the notches in the bearing mounts in the block.  Thread the bolts in , but not even finger tight. Leave 1/4" play because you've got more bearings to do.
30 Repeat steps 24 through 29 for the other main bearings. HOWEVER: On the rear main bearing, follow steps 31 through 34 to fit new thrust bearings before refitting the cap.
31 Apply assembly lube to the new thrust washers. The assembly lube goes on the side of the thrust bearig that has the notches across the face.
32 Look at the rear main bearing seat.  You should see the ends of the thrust bearings outside the main bearing. Hard to describe.  Look at the end of a new thrust bearing.
33 Slip the new thrust bearing under the crankshaft and rotate it around into position.  It will push the old one out.  Repeat for the other one. The notches in the faces of the thrust bearings face the rear for the rear bearing, and the front for the front bearing.
34 Once the thrust bearings are in place, return to Step 29 for the rear main bearing.
35 Tighten all Main Bearing Cap bolts to 65 ft/lbs.
36 Reinstall Sealing Block Liberally smear the sealing surfaces with silicone sealer.  You can try to re-use the wood blocks if they're not mangled.  If they are mangled (or are missing), fill the gap with silicone sealer.  Reinstall the screws.
37 Reinstall the front plate screws and bottom timing cover bolt. Being double-jointed helps here.
38 Clean out the oil pan, paying attention to the sealing surface of the pan. I tend to leave the cleanout of the pan for last so that any "forensic" evidence is undisturbed.  I like to connect what I see in the old bearings with what I see in the pan.
39 Liberally coat the sealing surface of the oil pan with silicone sealer.
40 Reinstall the oil pan This will require the 1/2" - 1/4" drive socket, and all the extensions you have handy.  Work your way around the oil pan.  If you have some electric or pneumatic tool to speed this up, use it.  It will save you frustration, BUT, these bolts don't need a lot of force.  Just "snug and a tug" will do.  I go around twice.
41 Reinstall the drain plug, and refill the oil. Now is the time to change the filter.  Why wait until now? Because the filter holds a reservoir of oil, a tingy bit of which will trickle back into the pump, which will help it stay primed.
42 Disconnect the primary leads from the coil, and spin the engine over on the starter until you see oil pressure on the gauge. No more than 30 second bursts, let's not overheat the starter.
43 Reinstall plugs, reconnect the coil.  Fire it up and inspect for leaks.  Listen for bad noises,  Generally drive easy for a little bit.

HOW TO PROLONG THE LIFE OF THE BEARINGS:
The following is stricly opinion, but it seems to follow from common sense.
 
1) NEVER USE CHEAP OIL.   It may be fine initially, but it will break down before the 3,000 mile change interval, particularly if you drive hard.  I use Castrol GTX most of the time, but I sometimes go to a synthetic on a new engine (after break-in).

2)

NEVER USE CHEAP OIL FILTERS.
Most oil filters have two deadly flaws:
(a)  They don't filter as well as they shoud.  Grit in the oil kills bearings.
(b)  They have inadequate anti-drainback valves.  This allows the oil in the filter to drain back into the sump while the engine is off, which means no oil pressure for the first few seconds of the next start while the oil filter re-fills.
I use Purolator PureOne filters.  Other people like other filters, and there are a couple of sites on the Web that review oil filters.  Check them out.
3) FIT AN OIL COOLER.  An expert on these engines disagrees with me.  However, Triumph offered oil coolers as a dealer option to these engines.  It was "highly recommended" for hard driving.  I drive hard.  If you do, think about fitting an oil cooler.  Might not be a bad idea even if you don't.