OK group, lotsa lbc content here. I finished the cosmetic part of
restoring Kermit, my tree-frog green '60 Sprite, in Sept. 92. There were
a number of niggling mechanical things that I put off worrying about while
I reordered my life. This winter, I hope to do some fettling, and I could
use advice.
For the record, the engine is the original 948, rebuilt by a mechanic who
had misspent 20 yrs fixing and racing Sprites. He seemed to know what he
was doing, and had a wallfull of certificates of expertise (from Volvo,
but wotthehell) to prove it. He said it was done to approximately "Stage
IV" tune. He polished the head, relieved the areas around the valves,
ported it, etc. He cc'ed the head, and had it shaved to the highest
compression ratio consistent with unleaded pump gas. It has Janz racing
pistons, is bored .040 over, etc. I believe it is using a 1098 or 1275
cam, anyway one a bit hotter than stock. It is still using the stock
bugeye carbs. He rebuilt those, too, though I don't know how well. I
suspect carbs were what he was least good at. I do remember that he
replaced the shafts and reamed the carb bodies, but he did it by hand and
may not have made a good job of it. He's gone away, so I cannot ask him
for help.
When the engine was rebuilt, I was surprised by the cumulative cost of
parts. By the time we got to the valve train, I looking for at least
temporary relief from the wallet hemorrhage. My mechanic suggested I
could defer some cost by reusing the original rocker arms and shaft.
These could easily be replaced later. So the rocker arm/shaft assembly
was reinstalled as is; the assembly has at least 100K miles on it.
Questions:
1) The idle is all over the place. If I put a killer throttle return
spring on the car, idle is around 1400 rpm, but somewhat variable, but the
throttle is hard to push and I worry about wearing the carb shafts. With
a softer return spring, idle may be 2000-2200 rpm. It is hard to look way
cool at stop lights when your engine is idling at 2200 rpm. Pushing on
the linkage under the hood will return the idle to a more reasonable
level. Originally, the car was really running rough. I followed standard
cookbook adjustments, and ended up leaning out both carbs about as much as
I could. This improved running considerably, but did not cure my idle
problems. I do not think there is much friction in the throttle cable or
accellerator pedal--I have tried to make sure these operate freely; the
problem seems to be in the carbs or their linkage. Where should I start?
Is there some common cause of this problem?
2) At the time of the rebuild, I was interested in at least visual
authenticity, so wanted the original carbs. The mechanic said that I
could get a useful increase in performance whenever I was ready, if I
installed the next size larger SU carbs. I have a set of the larger
carbs. If the collective net wisdom (I like the concept of net
wisdom--you add up the good opinions and the bad ones, to get the net
wisdom--but I digress) is that the carbs were improperly rebuilt, and I
have to start over, I am tempted to have the larger set rebuilt for a
performance gain. The question is, would there really be a significant
gain? If I am not mistaken, the original carbs are 1-1/8 inch, and the
other set is 1-1/4 inch from a later Spridget.
3) My impression is that the oil pressure is low (or the gauge isn't
accurate). This despite almost all new parts and expert assembly of the
engine, a "high output" oil pump, etc. What should the pressure be? Last
Tuesday, with the weather cold enough to keep engine temperature just
about at the thermostate opening temp (180), I had about 62 psi registered
at 4000 rpm with the engine cold. It dropped off gradually to about 42
psi at 4000 with the engine fully warm (indicated 170 degrees).
2a) is this low, or not?
2b) could the worn rocker arm bushings/shaft have a significant impact
on the pressure, or would their effect be too small to detect? I do have
new shaft and nos rocker arms to install, and I will give it high priority
if it will improve the pressure.
3) Apropos installing the new rocker arms and shaft: I am working from
memory, which may be faulty, but I think I've read that the rocker arm
bushings should be reamed to fit the new rocker shaft. The NOS rocker
arms I bought seem to fit the shaft very nicely without reaming. What's
the story here--any reason I should not simply slide them on and button it
up?
4) When I install the rocker arms, I will necessarily undo some of the
head bolts and have to retorque them. We have been through a lot of
discussions of torque here, and I don't want to go through that again.
The question is this: given that I must take off some bolts and retorque
them, I feel I should retorque all of the head bolts. But what is
best--slightly loosen all head bolts, including those I didn't remove, and
then retorque them in the proper sequence? Or torque the head bolts I
removed, then loosen and retorque each head bolt in sequence?
In general, when one retorques a head, does he/she loosen one nut,
retorque it, loosen the next, retorque it, and so on, or does he/she
loosen all the nuts, then retorque them in the sequence prescribed by the
manual?
Awaiting your pearls of hard-earned wisdom, I am respectfully yours.
Ray Gibbons Dept. of Molecular Physiology & Biophysics
Univ. of Vermont College of Medicine, Burlington, VT
gibbons@northpole.med.uvm.edu (802) 656-8910
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