Hi list -
This post is somewhat long and contains novice questions related to
re-assembling the 1500 I am putting back into my '79 Midget. I
apologize in advance for the non-relevance this has to some list
members.
That said, as some of you know, I'm beginning to learn about cars and am
rebuilding the 1500 in my '79 Midget, putting on new headers, weber
carb, big(ger than I thought) exhaust, etc.
While I've learned much from many folks on the list and on the online
BBS I'm still a little foggy on how some of this stuff works.
This is how I understand it, partly because I bought a Piper cam and got
some information about it:
** WARNING: Basic engine questions ahead, please attempt to minimize
newbie flame responses, though I will take them with a
grain of salt. :)
The pistons drive the crankshaft, which through the timing chain drives
the camshaft.
[ Question: How do I properly align the cam and crankshafts
when re-assembling the block? I have been lead to believe
there are "timing marks" which must be aligned. The Piper
cam instructions go through a method involving a protractor
and finding TDC (I finally found out that means Top Dead
Centre) and rotating the enging through to find X degrees
ATDT (is this "After" Top Dead Center, IE, clockwise??)]
The camshaft pushes up on cam followers, or "tappets", which contain
pushrods sitting in them. The cam drives the pushrods up against the
rocker arm assembly, which through a pivoting motion opens the proper
intake or exhaust valve to the proper cylinder. As the camshaft turns,
valve springs atop the head push the pushrods back down so as to force
the cam followers to follow the curve of the cam lobes.
[ Question: I bought new tappets for my new camshaft as
was recommended. Can I use my old pushrods in any order
now, or do I have to get the pushrods machined in order
to use them again? ]
The shape of the cam lobes determine the rate at which the valves are
opened and closed and the time duration that each individual valve is
held open, right? I know that playing with the cam lobe shape is
supposed to "increase performance", but I'm not sure quite how. My
current guess is that the irregular shape of the cam lobe opens and
shuts the valves in such a way as to alter the stock movement of the
valves from a more or less equal opening and closing rate (a constant
valve acceleration) to making the valves travel faster during the middle
stages of opening and closing, a variable valve acceleration. Thinking
about it, the vacuum of the cylinder really won't be affected by this,
so it's going to suck in the same amount of air/gas as with a normal
cam, or so it seems... so why does changing the cam lobes increase
performance? At higher RPMs, does the cylinder sometimes fire before
the valves can shut? Is this where the lobe shape comes into play?
This I could understand and is the only reason I can think of to upgrade
to a new cam, for basically extending your power band up another few
ticks on the tach. Am I right?
Or does the irregular shape of the cam lobe in fact really allow
slightly more air/gas mixture to be taken into the cylinder?
Another question - using assembly lubricant is obviously important when
putting the new camshaft in. Can anyone recommend a brand and/or
supplier for this "cam lube"?
When I put the new cam in, as I understand it I'm supposed to clean off
the coating that Piper put on the cam to keep it from rusting, except
for the cam lobes themselves. Piper actually states, "DO NOT REMOVE
BLACK PHOSPHATE COATING FROM CAM LOBES" in step 4 of their instruction
sheet that they send along with it. With all that grinding of the
tappet against the cam lobe, wouldn't the coating eventually come off
anyway? If its so important to remove all dirt and coatings from metal
parts inside the engine, why am I supposed to leave the coating on the
cam lobes, which probably take the worst beating of metal-metal damage
on startup against the tappets?
When I put the new cam into the block, do I just kind of slide it into
the block, align it with the crank (there are timing marks or something
like that I assume), put the timing chain on, lube up the tappets and
pushrods and slide them down onto the cam and continue reassembly?
Finally, for those of you who made it through this book, one last
question - timing.
I bought a Mallory vacuum-advance distributor and have fitted the
DRIVING DOG (Who comes up with these names?) off the old Lucas to it
after bead blasting it and painting it to look shiny fresh. As I
understand it, this distributor with "vacuum advance" modifies the point
at which the plug fires in each cylinder according to the vacuum created
by the action of the cylinder drawing the air/gas mixture into the
chamber through the carberetor. I have a Weber DGV and see no little
convenient fitting to connect a vacuum line to - I bought the DGV
second-hand from a fellow online MG enthusiast and it didn't come with
an air cleaner assembly or gasket. I have a K&N assembly and filter on
its way to me now. Do I just connect a hose between the distrubor's
vacuum fitting and the air cleaner?
Often in race cars and computer games where you put together engines and
race them in simulations, you have to adjust the timing for optimal
engine performance. Is this with mechanical advance distributors? Is
this how you adjust timing? With the vacuum advance setup, do I
therefore not have to worry about adjusting timing with a timing strobe
gun and all that? Or do I? If I do, how exactly would this be
accomplished? I don't really see any way to adjust the timing once I
align the marks on the cam and crankshaft and put the timing chain on.
I wouldn't think that you would want to fool around with timing there,
just the timing of the firing of the plugs, which, it appears to me in
my particular setup, is controlled only by the vacuum-advance
distributor, which is itself controlled by the vacuum created by the
motion of the cylinders drawing air through the carberetor through the
air filter.
I lied - another question, regarding LEAKS. When I pulled my engine,
every part in the car was covered with at LEAST a half inch (to a full
inch in some places) of pure CRUD. Black, greasy filth. Underneath the
filth was nice metal, thankfully. I am assuming that this is the
"Waxoyl" that I've heard about in myths and legends and online
catalogs. At any rate, my transmission is COVERED with "crud", but it
looks to be mostly oily dirt as opposed to a thick greasy "waxy" kind of
stuff that covered most of the engine compartment. Is it okay to take
the transmission off the car (I guess you'd have to disconnect the
tranny mounts and pull it up out of the car through the engine
compartment), stick it in the parts cleaner (Safe-T-Kleen), wire brush
the whole thing down with solvent, dry everything off with compressed
air, and re-fill it with new gear oil? My only fear is by not "leaving
well enough alone" I'm apt to break something and be stuck with a really
great running engine and a shot transmission.
Then there's the issue of "natural" oil versus "synthetic". Since I
don't plan on having any major leaks I am considering putting synthetic
in. Lasts longer, better lubricating properties. If anyone has had any
disastrous synth oil experiences with the 1500, please let me know.
Yes, I am installing a 16-row oil cooler. I'm foregoing the oil
thermostat because I live in NY, and I have never driven the Midget on a
day where the coolant temp gauge wasn't reading halfway between C and H
within 4-5 minutes. I really don't think running the oil too cold is a
serious issue that warrants the purchase of an oil thermostat.
Whew! You made it to the end! *applause*!
I think if I could sort all these questions out, it would really help me
a lot in determining what it is exactly that I need to purchase in terms
of parts before I begin actually putting the engine back into the car.
Oh, what a day that will be! :)
One last question that will probably expose my naivity - I have been
told it's impossible to put a 5-speed into my Midget without serious
body modifications. What prohibits one from simply taking 4th gear out
of the stock tranny and throwing a larger gear in, effectively having
three gears and an overdrive in place of fourth. This is probably a
stupid question but it's one that I have been wondering about
nevertheless.
Many thanks to those who will read and have the patience to respond.
For those of you who are interested, I'm a 22-year old college student
(electrical engineering) about to graduate and this is a car that I plan
on driving and enjoying for many, many years to come.
eric
--
__.o,\____ Go, Lil' Racer! * Eric C. Mumford
/__ \ / _ ) 1979 MG Midget * mumford@rpi.edu
(+)`---(+) http://travolta.stu.rpi.edu
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