Well, after the 3-cylinder fiasco two weeks ago the MGA with an Attitude is
on the rampage again, and I have some curiosities to report about the
engine failure.
Important stuff first. Less than 3500 miles back (this spring) I had
installed Crane tubular pushrods along with the new cam and tappets.
Tappets and pushrods were the later model 18V engine parts. These (Crane)
pushrods are formed from tubing with the bottom end formed into the small
ball (with coaxial hole), and the top end socket is made of a separate
piece that is pressed into the tubing. On 6 of the 8 pushrods the top end
fitting had come loose to the point the it can be rotated with light finger
force, and most of them could be pulled out with finger force, and a couple
of them were loose enough to fall out if the part was inverted. In fact I
found one of these end pieces in the oil pan, and I therefore have high
suspicion that this may have been the cause of the engine failure. Go figure.
Now the condition of the other parts. The #2 intake valve had hit the
piston and bent the valve head in the process of punching a large ragged
piece out of the center of the piston top. The top end (stem) of that
valve was broken just below the cotters. Having a badly bent stem that
valve subsequently ejected the valve guide out the top of the head. The
mating pushrod was badly bent and missing the top end fitting (previously
mentioned). The exhaust valve on the same cylinder was only slightly bent,
probably as a result of hitting a bit of broken metal from the piston, and
that mating pushrod was slightly bent but still functional (marginally).
And there was a mild dent in the side of the valve cover (from the inside
outwards), just enough to chip the paint off the outside, in the vacinity
of the output end of the #2 intake rocker arm, probably from whacking the
spring cap aside after the valve stem broke. The hardened valve seat
inserts were dinged up a bit, but not beyond repair.
You may now recall the patchwork that got the car home (200+ miles) without
a tow. After sealing the gaping hole left by the missing valve guide with
plumber's epoxy putty and pinning the bent intake valve up with a large
hairpin, it was more than a little tough to start the engine before driving
it home. In 20-20 retrospect it is now more clear. This car has a vented
crankcase with a draft tube on the front tappet cover and a vent hose from
the front air cleaner to the valve cover. With the open intake valve and
the large hole in the piston it was drawing considerable air through the
crankcase into the intake manifold without benefit of fuel to mix with it.
This clearly explains the hard starting, bad running at low speed,
continued fouling of #1 spark plug, and the 4 quarts of oil used in the
last 130 mile trip. Ah, water over the dam.
That all sounds pretty bad, huh? Well, if I had a good used mating piston
and some pushrods lying around I could have had it back on the road within
24 hours. In fact I did have some pistons and pushrods, just not of that
particular type, so I had to actually spend some money on this fix. You
can imagine how painful that had to be for ME, of all people. (I'm so
tight I squeak when I walk). I bought a full set of 18V type pushrods from
Moss (original one piece solid type), cheap enough. But since they don't
sell single pistons I had to buy a full set of those (bummer), not so
cheap, and now I do have a few good used pistons to keep for spares. After
that everything else I needed was close at hand.
Much of the rest is again Grapes of Wrath repairs. The cylinders honed out
okay, so no other machining required there. First item in the head to
attend to was the errant valve guide, which was somewhat beat up on both
ends but otherwise fairly young and not much worn. For this I ran a drill
bit through the bore, Gibbonized both ends to debur the piece, and tapped
it back into place in the head. Then out of the brown and slightly greezy
boxes I pulled one slightly used stellite exhaust valve and one good used
intake valve, and one slightly used umbrella seal with a good teflon inner
collar.
To touch up the slightly dinged valve seats I place a couple of bits of
sticky backed sandpaper on the edges of the valves, drop them down the
guides with a bit of oil, and give then a healthy spin with a power drill.
The exhaust seat cleaned up easily with very little material removed. The
intake seat took a bit more persistence and lost more material, leaving a
wider than desired landing surface. Not a big problem for a steady hand,
as I haul out the Gibbonizer again with a small spherical stone and proceed
to take a smidge off of the inside edge of the land to narrow it up a bit
(don't try this after even one beer). Thereafter just a minute of hand
lapping on each valve set them together properly, and the rest of the game
was just normal cleaning and reassembly.
Additionally off the shelf came a head gasket, oil pan gasket, and a couple
of valve cover grommets, a manifold gasket, and the exhaust seal ring.
These parts (about $28) will now need to be reordered to replenish
inventory (unless I find some cheap on sale or at a flee market). The
dense cork valve cover and tappet cover gaskets were reused, as were the
carb throat paper gaskets and the full charge of coolant. And there was
5-1/2 quarts of oil and a new oil filter, but it was time for an oil change
anyway. I will of course do that again after just one day of driving
(considerable mileage in this case), as well as cleaning off my magnetic
oil drain plug. You may now make mental notes of parts that were not
replaced, and of the cleanup proceedure necessary after honing the
cylinders (with block lying on its side) without removing the crankshaft.
One additional note about oil priming. During this repair operation the
engine was completely drained of oil with the oil pan and oil pump removed
and the innards being washed out with solvent. The oil pump may have
retained not much oil after lying on its side on the bench for 3 days, but
was probably at least still wet internally. While the engine was still on
the engine stand after reassembly I topped it up with oil and proceeded to
rotate the innards with the MGA hand crank. After fewer than 20 turns of
the crank (10 turns of the oil pump) oil came pouring out of the port at
the right rear corner of the block. After installation in the vehicle I
pre-filled and installed the oil filter, connected the oil cooler lines and
cranked it with the starter. After only 15 seconds of cranking without
spark plugs it had oil pressure reading on the gauge. No doubt about it
having a good oil pump.
And now the next interresing note. Today (Sunday) I expect to have about
125 miles on the freshly honed cylinders with new pistons and rings when
the car ventures out onto the track for its next autocross date.
Speculation anyone? YEEHAA!!!
Barney Gaylord
1958 MGA with an Attitude
http://www.ntsource.com/~barneymg
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