Scott, its time to check your car's compression. Warm it up then pull
all plugs. Remove the distributor cap or just remove the rotor. Open
the throttle 100% and block it open. Spin the engine on the starter
for about 4-5 revolutions with a compression gauge held into each plug
hole in turn, and record the pressures. Gauge available at Harbor
Freight quite inexpensively. After making the 'dry' measurements, add
about 1 teaspoon of motor oil into each cylinder, through the plug
holes, and make the 'wet' measurements, again recording the pressures.
THEN, post the results here please.
-rick
PS: Remember, "Diagnose BEFORE surgery."
On Mon, Apr 29, 2013 at 12:20 PM, Scott Fisher <sfisher71@yahoo.com> wrote:
> So after nursing my new-to-me '51 TD home last Monday (swapping in a spark
> plug at the roadside, to replace the one on which the ceramic had snapped in
> two), I set about making a few discreet inquiries, as they say, into what was
> up with it.
>
> The dashpots were not quite dry, but certainly very low. Adding a
> little light oil (actually, ATF, which I understand to be the active
> ingredient in Marvel Mystery Oil) brought the level up above the brass dampers
> on the rods. I still suspected much of the trouble to be in the ignition, so I
> pulled the distributor cap.
>
> The cap had no cracking or tracing, but the
> carbon brush didn't retract very far when I tested its spring, suggesting it
> was quite worn. The rotor had the usual discoloration indicating it was
> well-used, but didn't seem abnormally so. The points gap seemed appropriate at
> 0.012" but my feeler gauges (which have spent many happy hours under the
> rocker arms of my Midget and MGBs) are a little large to fit into the TD's
> dizzy.
>
>
> I was a bit more concerned with the advance mechanism. The rotor
> WOULD turn when twisted, but there seemed to be some slop before the weights
> and springs engaged. (I've had a distributor wear so much that the pivot holes
> in the advance weights were oval, making for scattered timing at full
> advance.) I simply added some more light oil down the central shaft and
> returned the cap.
>
> The car ran significantly better after this, but still had
> some backfiring on acceleration about 3500 RPM. So when I went to the auto
> parts store to buy rags, a soft brush, and some other bits for the cleaning, I
> also ordered four spark plugs of the appropriate size (Champion L 10,
> available at the warehouse, shipped to my local shop the next day). I also
> bought a feeler gauge with smaller blades.
>
>
> On installing the new plugs,
> after gapping them to 0.022" as per the manual, I noticed that the #1 plug --
> the one which had broken at the roadside, and which I replaced with an old
> spare from the box the seller included -- was broken AGAIN, this time in my
> plug socket. VERY odd. I think this might be due to the condition of the plug
> wires, which are so old and stiff that they barely bend out of the way to get
> to the plugs. Could the vibration be transferred into the #1 plug (it being
> the longest wire) and weakening the porcelain?
>
>
> When I pulled the #4 plug
> lead, the wire separated from the clip that holds it to the plug. Damn. I
> shoved it back in as best I could and held it in place with some duct tape --
> only because I had the car's first official outing the next morning. I had
> already ordered the full tune-up gear from Moss, including new plug wires with
> the correct screw-on ends, new cap, new rotor, new plate in the distributor
> with points and soldered-in condensor, and just for fun, a new Lucas Sport
> coil. (Next year: bumblebee plug wires!)
>
> The car started as it always has,
> even with only three plugs: a gentle tug on the starter switch and the car
> roared to life. But even backing out of the driveway I could tell there was
> more throttle response. Motoring down the road, the car felt like an M.G.
> again, brisk acceleration and that wonderful straight-cut gear whine in first!
> The car pulled strongly past the 5000 mark on the chronometric tach, no
> backfiring apart from an incredible snap and burble from the well-worn
> exhaust. (It appears to have a single cherry-bomb glass pack in the straight
> tube.)
>
> More later, including the car's first public outing and a bit of
> "interior design" work...
>
> --Scott Fisher
> Tualatin, Oregon
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