305 HEI ignition advance problems
Ken Alford
I'm a newbie to to this group... after a
http://groups.google.com/advanced_group_search?dq=&num=25&hl=en&lr=&group=alt.trucks.chevy
search, I still need more info.
I did some work on a friend's '81 stock 1/2 ton today.
It's got a 305 w/ 2 bbl and automatic and the odometer hasn't turned
over yet.
At idle, I pulled plug wires off their individual plugs and one at a
time.
I hooked my tach. and watched it and my vacuum gauge as I pulled and
replaced each one.
One had no RPM drop when I pulled the plugs themselves, that one was
fouled....
I did a compression check and all 8 holes read 185-200 most of them 190.
the fouled cylinder had good compression. I discovered
the smog had ben arbitrarily removed (there are no smog checks here in
Hawaii)
and and the lines randomly capped.
Unfortunately, one was left open to the inside of the air cleaner...
the inside was pretty gummed up. I remedied the missing plugs and
replaced all the caps.
The timing degree scale thingy was missing and im guessing the timing
was set by ear.
After replacing it w/ the a chrome one from Mr. Gasket the thing read
way advanced,
off the scale. So I brought it back down to 12 Btdc.
I did a little test run and the thing overheated and died at a stop, and
wouldn't start.
I dialed in more advance and found out i had left the radiator cap
loose.
I did a 39 cent tune up (oakie or portagee tune up for the non PC crowd)
on the carb.
and set the timing back where it was.
My question is how much initial advance should I run,
and how much total advance should I expect @ what RPM?
I guess I'd read it with my advance light with the vacuum plugged and
then do the vacuum,
But how?
Is anyone still awake out there?
Bye
Ken
Ken Alford
a chevy friend just told me that a 305 has a 7deg. offset crank balancer key way.
that would explain the lack of proper degree tab
and off initial advance reading.
i still need specs for total and vac advance though..
aloha
ken
D&D Dyok
Greasemonkey
engine as you probably have now, and one that got welded to the middle of
the timing chain cover. Odds are you probably have the ladder. Unless you
have a adjustable distributor like a MSD then you can't adjust the total
timing. Just set the initial timing at about 7 or so. Continue to advance
it till you get pinging under load, then back it off a couple of degrees
till the pinging under load stops and the engine is still startable. This
is the easiest way to set these without specs.
Grease
"Ken Alford" <labmi...@earthlink.net> wrote in message
news:3CFBAF32...@earthlink.net...
Houblues
chrome tab from Mr. Gasket is specific for your year and vehicle type.
Chevy had at least three different tab locations, using different front
covers, tabs and balancers. On a vehicle as old as this one, any of these
may have been changed out, so you will probably have to find Top Dead Center
on the engine, then find a combination of tab and balancer that shows zero
at that point. Doing anything else before you get this straightened out is
purely a waste of your time.
"Ken Alford" <labmi...@earthlink.net> wrote in message
news:3CFAE8A8...@earthlink.net...
BOYJUKI
Dean Dardwin
The correct timing for any engine where the timing is not computer controlled is established as follows:
1) Hook your vacuum gauge up to manifold vacuum.
2) Remove and plug any vacuum advance.
3) Start the engine and let it warm.
4) Loosen the distributor hold-down bolt just enough to let you turn the distributor.
5) Check the vacuum reading.
6) Turn the distributor a tiny amount in the retard direction until the vacuum falls a bit (the engine speed will also decrease).
7) Turn the distributor in the advance direction very slowly. The vacuum reading will go up as will the engine speed.
8) Keep going until you notice the vacuum reading start to become unsteady.
9) Back off the timing just a bit until the vacuum reading remains steady.
10) Tighten the hold down bolt carefully so as not to move the distributor.
11) Reattach any vacuum advance line.
12) Scribe a matchmark on the distributor base and block so you can reestablish timing in the future.
This is an old tuner's trick and is the only way that always works. I have seen factory timing tabs 40deg. off. I have seen rebuilt engines with the timing tabs installed on the wrong side of the engine! As you have found, timing tabs are useless.
Dean
Ken Alford
Dean Dardwin wrote:
Mahalo (thank you) Dean.
this vacuum gauge procedure is the way to go, seems to me.
with your permission i'd like to include it with the following
other vacuum gauge trivia ( need to fix my web site:
http://home.earthlink.net/~labmission/ )
from an old post of mine on http://www.type2.com/archive/
an old VW site... (flame shields up!!!)
This is a compilation of about five or so old instruction sheets and
repair manuals.
There is a section in Tom Wilson's How to rebuild VW air cooled engine
that use the vacuum gauge.
(This book rates right up there with the idiot book, how to hot rod vw
engines by B. Fisher, Service Repair Manuals by Bentley, etc.)
I've tried, by using Wilson's specs and other vw repair books to avoid
American V8 bias and adjust the readings to reflect that of a volks.
These readings are analogous to medical lab tests such as,
titers for viral infections or ESR testing.
The results are going to vary from individual to individual
and will tell if a patient is getting sicker or how the body is
performing relative to itself and changes in it's environment.
Ergo, like head temps in air cooled engines the readings are not
definitive but very helpful in trouble shooting.
Please forgive the cryptic nature of the rest of these notes,
but I've typed enough as it is.
Thanks for staying with me so far.
Here Goes!
General formula:
Atmospheric Pressure - Pressure inside intake manifold = Gauge reading
in " Hg
adjustments for elevation:
Zero to 2000 feet above sea level is Okay; if >2k then 1"/1k' elevation
increase
attach gauge down stream of throttle plate
ENGINE FAULT / SYMPTOMS AND GAUGE READINGS:
Normal Engine: 18"-22"Hg, 6-4 cly. engines lower (again V8 bias)
valve overlap needle causes needle fluctuations; constrictor valves are
placed in the gauge hose barb (.015" on mine) or pinch hose until
fluctuations go away.
Sticky Valves: rapid intermittent drop (each time the valve is suppose
to
close)
-spray penetrating oil on stem or in intake tract to see if
valve
unsticks and reading returns to normal
-pull plug wire, no RPM change?
Ignition Miss: see sticky valves
Weak or Broken Valve Spring: fluctuates rapidly between 10"-20" Hg at
2,000 RPM;
weak springs, "Hg goes up as RPM goes up,
Broken springs; rapid fluctuations every time valve attempts to
close
(even at idle)
Worn Valve Guides: Lower than normal reading with fast fluctuations of
"3
Hg on each side of reading with engine idling, pointer steadies out as
RPM increases
Readings at idle 14"-19" Hg
Leaking valve: point will drop 1"-7" Hg at *regular*intervals, burnt
valve; regular drop of aprox. 5" Hg (think- tight valve clearance?)
Intake manifold leaks:3"-9" Hg Below normal; change leak, spray carb
cleaner at
suspected leak, if RPM increases, it's a leak.
Late Valve Timing: 8"-15" Hg at idle
Late Ignition Timing (or uniformly close valve clearance): 14"-17"
Steady
Poor Compression, piston ring defects: open throttle, increase to 2k RPM
close quickly, should jump 2"-5" Hg or more if rings good,
drops almost zero if bad
Blown Cylinder Head Seal: Drops 10" Hg each time cylinder fires at all
RPMs
Spark Plug Gaps Set Too Close: floating between 19"- 16" Hg
Incorrect Idle Air - Fuel Mixture; floating between 13" -17" Hg
(slowly)
or slowly down to a lower reading, adjust to highest value.
Restricted Exhaust System: Incase to 2k RPM, close throttle quickly
-normal; drop to 2" Hg then back to 25" Hg quickly (normally
quick)
-choked exhaust;
not more than 5" Hg greater (compared to 25")than normal
"Hg and
seems to stop momentarily in it's return to a normal
reading =
partial restriction
Slow drop to zero "Hg = choked exhaust
Choke Test: (Ignition off, no throttle) turn starter, gauge should
increases to 18"-21" Hg,
if low, check for manifold leaks, throttle failing to close
fully
Fuel Pump Test: Run engine on carb float bowl gas, put gauge in tank
side of fuel pump
- should go up to 10" Hg
Gas Line test; same test, put gauge at petcock (reserve)end of gas line
Ken Alford
this is a good link
i'll digest it later...
i still need to know what total advance to expect at what RPM
i.e..
30 deg all in at 2500 RPM + vacuum can advance...
know what i meen vern?
D&D Dyok wrote:
> this helped me out
> somehttp://http://www.randomunity.com/superrod/tech_tips/distribtr_curves/distribut.html I
Ken Alford
Houblues wrote:
> Your first problem is that you have no idea what the timing is, unless that
> chrome tab from Mr. Gasket is specific for your year and vehicle type.
> Chevy had at least three different tab locations, using different front
> covers, tabs and balancers.
yeah yer right
from what i hear the balancer is generic the crank keyway is 7 dergees off and
the timing tab is directly on the top of the chain case but i have yet to verify
it...
> On a vehicle as old as this one, any of these
> may have been changed out, so you will probably have to find Top Dead Center
> on the engine, then find a combination of tab and balancer that shows zero
> at that point.
i've purposed to do that next time i work on it
Houblues
>
> yeah yer right
> from what i hear the balancer is generic the crank keyway is 7 dergees off
and
> the timing tab is directly on the top of the chain case but i have yet to
verify
> it...
>
I was skeptical about the difference in keyway position, but my David Vizard
(who usually has his facts straight) book on rebuilding the SBC does say
that around 1970 the keyway slot moved by around 8-9 degrees. In this case
the tabs changed, but the balancer apparently stayed the same.
But balancers definitely are not generic. Even outside of the timing mark
location, there are two diameters and two thicknesses that I know of. And
on the mark location, since the difference between top and side mounted tabs
is probably on the order of 25-40 degrees, the balancers would have to be
similarly different, unless the keyway location in the crank accounts for
the difference, which I have not heard of.
Dean Dardwin
Absolutely! It's yours to use as you see fit.
Dean