At 08:50 PM 6/7/02 -0500, Carter Tuggle wrote:
>.... 79 midget. Last week I started hearing a faint knock when I gave it
>gas. Today it got louder. So I went straight to the Mg guru.. He says by
>listening it sounds like I have blown a rod.
If it's still running, you have a worn rod bearing, and possibly some
damage to the crankshaft rod bearing journal, but probably still no problem
with the rod itself (unless the knocking noise was REALLY LOUD and always
persistent, even at idle).
>.... First he says that he will Drop the oil pan to look at it.
Good call.
>If it is a rod he will have to pull the engine to fix.
Maybe not. If you notice a little tapping noise on accelleration, and you
stop and check it right away, chances are that only the white metal in the
bearing shell is worn and you can get away with just installing a new set
of bearing shells and nothing else. But you won't know until you pull the
pan and remove the rod ends for inspection. The bearing journal on the
crankshaft should have a near-mirror finish and be perfectly smooth to the
touch when you run your finger across it from front to back. If it is
perfectly smooth, then it is likely also still round and the correct
diameter, not worn. Still a good idea to measure it with a micrometer to
be sure. If that be the case, then all it needs is new bearing shells.
On the other hand, if the crankshaft bearing journal has any roughness at
all that you can feel with your finger tip, then it needs to be
reground. For that you do need to remove the engine from the car to R&R
the crankshaft for rework.
> If this is true, I would be a fool not to go ahead and replace the
> clutch. Right?
Join the fool's brigade? I do not replace a clutch that was new less than
10,000 miles earlier. But if it has more than 30K on it, or is of unknown
history, or has noticeable wear on the parts, then by all means change the
disk and/or the release bearing and almost always the spigot bushing in the
crankshaft and the pivot bushing and bolt in the release arm. If the
pressure plate (diaphram type) has unknown history, it's a judgement call,
but I'd chuck it and put in a new one. They tend to lose the thin metal
eyelet that holds the heavy steel thrust ring in the center of the
diaphram. That part should be fairly snug with little or no motion in the
middle of the diaphram. If it rattles about a bit, toss it.
>Is there anything else I should do while I have the engine out?
Good time to check/inspect all of the peripheral parts as they are
R&R'd. Check all rubber hoses (water and fuel and emissions parts), engine
mounts, belts, water pump bearing, condition of radiator, and any
electrical connectors. Assuming the engine is disassembled enough to R&R
the crankshaft, you will be replacing virtually all of the lower engine
gasket set and front and rear crankshaft seals, and most likely all of the
crankshaft bearings (mains, rods, and thrust washers). Also plan on a new
timing chain tensioner and maybe a new timing chain (cheap).
If it was running okay and not using too much oil before this, I would not
get carried away with anything in the cylinders or cylinder head, and not
even remove the head. On the other hand, it would be a good time to do a
cam shaft inspection while it's open. Worn cam lobes are always
irritating, and as I recall those engines are notoroius for wearing the cam
journals in the engine block (as well as the crankshaft thrust washer).
> What I'm thinking is after he pulls the engine I will go get the body,
> bring it home & clean up & paint the engine bay. Anybody else out there
> who have been through this, I would appreciate your insights into what
> you did or what you wish you would have done.
A reasonable plan. Just don't get carried away with a bad case of the
might-as-well's and end up doing a full restoration just because you had a
rod knock.
Barney Gaylord
1958 MGA with an attitude (and lots of rod bearing changes in past years)
http://www.ntsource.com/.~barneymg
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