Home » Public Forums » GMCnet » [GMCnet] Dumb Timing Confusion
| [GMCnet] Dumb Timing Confusion [message #75471] |
Tue, 02 March 2010 22:41  |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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I know this will sound like the dumbest question to come down the pike in a
long time, but I've go to ask it:
I've always thought I understood the 4-stroke cycle, timing, TDC, BTDC,
ATDC, and all the rest of that weird stuff pretty well. So, my current
state must undoubtedly be CRS, or some other old man slipped cog.
Today we located #1 cylinder TDC, using a probe into #1 cylinder as it came
up on compression stroke. A dial indicator on the probe indicated 0.000"
until the crank was turned in either direction.
I fabricated and installed a new pointer to reach the '89 Mercury Marquis
double serpentine crankshaft pulley, then filed a notch in the pulley to
mark TDC. Carefully measuring the diameter of the pulley, I calculated the
circumference and divided that by 60 to tell me the distance from the TDC
mark to the 6* BTDC mark I wanted to make for initial timing of my computer
controlled distributor and EFI.
That's when the confusion set it: Which way should I measure to 6* BTDC
from TDC? Let me explain how I've reasoned the answer and why I'm confused:
The engine rotates clockwise (CW) when viewed from the rear (driver's seat)
(Right???). So BTDC marks should be located CW from TDC, meaning the BTDC
mark will reach the timing pointer before the TDC mark -- right? Well, that
pretty well satisfied me until I looked at the timing pointer on the Olds,
and that which formerly fit the Cad, and THOSE BTDC marks are CW -- the TDC
mark does not reach them until AFTER TDC. OMYGOSH! I KNOW the OEM timing
indicators are correct, but I'll be darned if I can, today, reconcile what I
see with what I think I know.
Y'All please help me see the error of my ways. I'll gladly join TSUA
(Timing Screw Ups Anonymous) if necessary!
Ken H.
Americus, GA
'76 X-Birchaven
www.gmcwipersetc.com
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] Dumb Timing Confusion [message #75475 is a reply to message #75471] |
Tue, 02 March 2010 23:27  |
Craig Lechowicz
Messages: 541
Registered: October 2006
Location: Waterford, MI
Karma: 0
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Senior Member |
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Ken wrote:
>Which way should I measure to 6* BTDC from TDC?
Ken,
If I read through your description correctly (and I agree this is a confusing topic) I think you are mixing up the difference between the stationary pointer on the Olds, vs. trying to make a mark on the moving damper on the Cadillac. If you think in terms of the notch on the damper spinning clockwise, (Olds setup) it will get to a 6 degree mark on the timing tab BEFORE or counterclockwise from the 0 mark on the timing tab. It sounds like on the Cadillac you are using a fixed pointer, and then marking a 6 degree mark on the turning damper. If that 6 degree mark wants to be Before top dead center it has to be further clockwise from the 0 notch on the damper, so it gets to the fixed pointer before the notch does. Not sure that made it any clearer, but think in terms of the crankshaft being slightly counterclockwise of tdc (piston still traveling up) the damper 0 mark is "before" or CCW from the 0 mark on the tab. So, you either mark the damper one way, or the tab the other. Clear as mud, I think, but hope I helped.
Craig Lechowicz
'77 Kingsley, Waterford, MI
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| Re: [GMCnet] Dumb Timing Confusion [message #75477 is a reply to message #75471] |
Tue, 02 March 2010 23:36 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Ken,
I'm not sure if I understand what you've written below so lets start over.
I'm standing in front of the Caddy so the crank pulley rotates counter
clockwise (when the engine is running).
The pointer was attached to the front of the engine block.
The engine has number 1 piston at TDC.
The pointer was attached to the front of the engine and a notch was filed
into '89 Mercury Marquis double serpentine crankshaft pulley that aligned
with the tip of the pointer.
The BTDC mark should be filed into the '89 Mercury Marquis double serpentine
crankshaft pulley to the LEFT (counter clockwise) by 6° of the TDC mark.
That way as the engine rotates clockwise the BTDC mark will arrive at the
pointer before the TDC mark.
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Ken Henderson
Sent: Wednesday, 3 March 2010 3:42 PM
To: gmclist
Subject: [GMCnet] Dumb Timing Confusion
I know this will sound like the dumbest question to come down the pike in a
long time, but I've go to ask it:
I've always thought I understood the 4-stroke cycle, timing, TDC, BTDC,
ATDC, and all the rest of that weird stuff pretty well. So, my current
state must undoubtedly be CRS, or some other old man slipped cog.
Today we located #1 cylinder TDC, using a probe into #1 cylinder as it came
up on compression stroke. A dial indicator on the probe indicated 0.000"
until the crank was turned in either direction.
I fabricated and installed a new pointer to reach the '89 Mercury Marquis
double serpentine crankshaft pulley, then filed a notch in the pulley to
mark TDC. Carefully measuring the diameter of the pulley, I calculated the
circumference and divided that by 60 to tell me the distance from the TDC
mark to the 6* BTDC mark I wanted to make for initial timing of my computer
controlled distributor and EFI.
That's when the confusion set it: Which way should I measure to 6* BTDC
from TDC? Let me explain how I've reasoned the answer and why I'm confused:
The engine rotates clockwise (CW) when viewed from the rear (driver's seat)
(Right???). So BTDC marks should be located CW from TDC, meaning the BTDC
mark will reach the timing pointer before the TDC mark -- right? Well, that
pretty well satisfied me until I looked at the timing pointer on the Olds,
and that which formerly fit the Cad, and THOSE BTDC marks are CW -- the TDC
mark does not reach them until AFTER TDC. OMYGOSH! I KNOW the OEM timing
indicators are correct, but I'll be darned if I can, today, reconcile what I
see with what I think I know.
Y'All please help me see the error of my ways. I'll gladly join TSUA
(Timing Screw Ups Anonymous) if necessary!
Ken H.
Americus, GA
'76 X-Birchaven
www.gmcwipersetc.com
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Dumb Timing Confusion [message #75480 is a reply to message #75477] |
Wed, 03 March 2010 00:11 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Ken,
I just re-read the previous message I sent in and it confused me so let me
try again.
I'm standing in front of the Caddy so the crank pulley rotates counter
clockwise when the engine is running.
With the number 1 piston set at TDC compression a pointer was attached to
the front of the engine and a notch was filed into the crankshaft pulley
that aligned with the tip of the pointer.
The BTDC mark should be filed into the crankshaft pulley to the LEFT of
(counter clockwise) the TDC mark by 6°.
That way as the engine rotates counter clockwise (standing in front of the
engine) the BTDC mark will arrive at the pointer 6° before the TDC mark.
There, that makes more sense!
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Ken Henderson
Sent: Wednesday, 3 March 2010 3:42 PM
To: gmclist
Subject: [GMCnet] Dumb Timing Confusion
I know this will sound like the dumbest question to come down the pike in a
long time, but I've go to ask it:
I've always thought I understood the 4-stroke cycle, timing, TDC, BTDC,
ATDC, and all the rest of that weird stuff pretty well. So, my current
state must undoubtedly be CRS, or some other old man slipped cog.
Today we located #1 cylinder TDC, using a probe into #1 cylinder as it came
up on compression stroke. A dial indicator on the probe indicated 0.000"
until the crank was turned in either direction.
I fabricated and installed a new pointer to reach the '89 Mercury Marquis
double serpentine crankshaft pulley, then filed a notch in the pulley to
mark TDC. Carefully measuring the diameter of the pulley, I calculated the
circumference and divided that by 60 to tell me the distance from the TDC
mark to the 6* BTDC mark I wanted to make for initial timing of my computer
controlled distributor and EFI.
That's when the confusion set it: Which way should I measure to 6* BTDC
from TDC? Let me explain how I've reasoned the answer and why I'm confused:
The engine rotates clockwise (CW) when viewed from the rear (driver's seat)
(Right???). So BTDC marks should be located CW from TDC, meaning the BTDC
mark will reach the timing pointer before the TDC mark -- right? Well, that
pretty well satisfied me until I looked at the timing pointer on the Olds,
and that which formerly fit the Cad, and THOSE BTDC marks are CW -- the TDC
mark does not reach them until AFTER TDC. OMYGOSH! I KNOW the OEM timing
indicators are correct, but I'll be darned if I can, today, reconcile what I
see with what I think I know.
Y'All please help me see the error of my ways. I'll gladly join TSUA
(Timing Screw Ups Anonymous) if necessary!
Ken H.
Americus, GA
'76 X-Birchaven
www.gmcwipersetc.com
_______________________________________________
GMCnet mailing list
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http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Dumb Timing Confusion [message #75481 is a reply to message #75480] |
Wed, 03 March 2010 00:33 |
idrob
Messages: 645
Registered: January 2005
Location: Central Idaho
Karma: 0
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Senior Member |
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| Robert Mueller wrote on Tue, 02 March 2010 22:11 |
Ken,
I just re-read the previous message I sent in and it confused me so let me
try again.
I'm standing in front of the Caddy so the crank pulley rotates counter
clockwise when the engine is running.
With the number 1 piston set at TDC compression a pointer was attached to
the front of the engine and a notch was filed into the crankshaft pulley
that aligned with the tip of the pointer.
The BTDC mark should be filed into the crankshaft pulley to the LEFT of
(counter clockwise) the TDC mark by 6°.
That way as the engine rotates counter clockwise (standing in front of the
engine) the BTDC mark will arrive at the pointer 6° before the TDC mark.
There, that makes more sense!
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
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Rob: I am not good at these engine things, but this second explanation made sense to me, that Is I could visualize what you said, and it seems like it is correct. So, good job!
Rob Allen
former owner of '76 x-PB
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| Re: [GMCnet] Dumb Timing Confusion [message #75482 is a reply to message #75471] |
Wed, 03 March 2010 00:41 |
George Beckman
Messages: 1085
Registered: October 2008
Location: Colfax, CA
Karma: 11
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Senior Member |
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| Ken Henderson wrote on Tue, 02 March 2010 20:41 |
I know this will sound like the dumbest question to come down the pike in a
long time, but I've go to ask it:
Let me explain how I've reasoned the answer and why I'm confused:
The engine rotates clockwise (CW) when viewed from the rear (driver's seat)
(Right???).
Ken H.
|
Ken,
I may be having a bit of a senior moment here, too. What I am about to say is something I learned from cranking a 1923 Fordson tractor. When you face an engine, the engine turns clockwise. And the Fordson is not unique. Car engines all do. When you sit behind the engine, as in the seat, it is going counter clockwise. Don't look at the fan on a serpentine belted engine as it goes the other way. Tell me I haven't gone completely crazy??
'74 Eleganza, SE, Howell + EBL
Best Wishes,
George
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| Re: [GMCnet] Dumb Timing Confusion [message #75486 is a reply to message #75482] |
Wed, 03 March 2010 02:08 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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You guys really have me confused. I understand what happens and why. I decided to give up reading before I become confused.
Stand in front of the engine and picture a clock with 12 noon being TDC. Now mark on the clock face a position that will be 6 minutes before 12 noon or 6 degrees before TDC. That is the point Ken is trying to mark on the clock face.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Dumb Timing Confusion [message #75492 is a reply to message #75471] |
Wed, 03 March 2010 05:55 |
g.winger
Messages: 792
Registered: February 2008
Location: Warrenton,Missouri
Karma: 0
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Senior Member |
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Ken and Rob M,,, the rotation on the cadillac is CLOCKwise when viewed from the front. Counterclockwise if your in the bathroom. If you mark the Harmonic(cads dont have one)ballencer/pully for BEFORE TDC mark it CLOCKwise when viewed from the front. This will be BEFORE TDC,,,,it will get to a stationary mark on the block FIRST before the "0" or TDC mark,,,hope this helps,,,PL
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| Re: [GMCnet] Dumb Timing Confusion [message #75493 is a reply to message #75492] |
Wed, 03 March 2010 06:32 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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MAN!, Do I ever feel better! At least half of you are just as confused as I
am! :-)
I'm about to leave for a doctor's appointment, so I don't have time to go to
the shop and re-re-re-check the fan operation to be SURE of the engine
rotation. Still sitting in the driver's seat, CCW rotation is the only
explanation for the way I'm seeing things, as described by Paul. But I
checked that fan (normal operation; my serpentine does NOT reverse its
rotation) several times and I CAN tell which way a propeller should turn!
That tells me engine rotation is CW from the rear.
More when the hand surgeon has LOOKED at me.
Thanks for brightening my day.
Ken H.
On Wed, Mar 3, 2010 at 6:55 AM, Paul Leavitt <leavittpaul@yahoo.com> wrote:
>
>
> Ken and Rob M,,, the rotation on the cadillac is CLOCKwise when viewed from
> the front. Counterclockwise if your in the bathroom. If you mark the
> Harmonic(cads dont have one)ballencer/pully for BEFORE TDC mark it
> CLOCKwise when viewed from the front. This will be BEFORE TDC,,,,it will get
> to a stationary mark on the block FIRST before the "0" or TDC mark,,,hope
> this helps,,,PL
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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List Information and Subscription Options:
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| Re: [GMCnet] Dumb Timing Confusion [message #75495 is a reply to message #75492] |
Wed, 03 March 2010 06:58 |
Steven Ferguson
Messages: 3447
Registered: May 2006
Karma: 0
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Senior Member |
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Thank you Paul.
Finally, we have the engine turning in the right direction. With the
engine at TDC, #1 firing (not #6), the key on the crank will be
somewhere around the 2:00 position.
Ken, in the absence of timing marks, you can buy a timing tape based
on the dia of the balancer. Drop the distributor in at 6 deg BEFORE
TDC with the rotor exactly at the #1 post on the cap. This is where
you want the engine to fire, fine tune from there.
On Wed, Mar 3, 2010 at 4:55 AM, Paul Leavitt <leavittpaul@yahoo.com> wrote:
>
>
> Ken and Rob M,,, the rotation on the cadillac is CLOCKwise when viewed from the front. Counterclockwise if your in the bathroom. If you mark the Harmonic(cads dont have one)ballencer/pully for BEFORE TDC mark it CLOCKwise when viewed from the front. This will be BEFORE TDC,,,,it will get to a stationary mark on the block FIRST before the "0" or TDC mark,,,hope this helps,,,PL
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
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>
--
Steve Ferguson
'76 EII
Sierra Vista, AZ
Urethane bushing source
www.bdub.net/ferguson/
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| Re: [GMCnet] Dumb Timing Confusion [message #75496 is a reply to message #75471] |
Wed, 03 March 2010 07:10 |
Gary Casey
Messages: 448
Registered: September 2009
Karma: 0
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Senior Member |
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I agree with all those things everyone said, but a fine point: The "accepted practice" method of determining TDC is to set up a dial indicator and turn the crank until the indicator reads some convenient distance from TDC - say .100. Put a temporary mark on the crank and then turn it the other way to get the same reading. Put another temporary mark on the crank. Measure the distance between the marks and put the final TDC mark halfway between. I usually don't have a dial indicator around so I put a bolt or whatever into the spark plug hole and move the crank until the piston just touches. Then turn it the other way until it touches. Not hard enough to poke a hole in the piston, of course :-).
Gary
I've always thought I understood the 4-stroke cycle, timing, TDC, BTDC,
ATDC, and all the rest of that weird stuff pretty well. So, my current
state must undoubtedly be CRS, or some other old man slipped cog.
Today we located #1 cylinder TDC, using a probe into #1 cylinder as it came
up on compression stroke. A dial indicator on the probe indicated 0.000"
until the crank was turned in either direction.
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| Re: [GMCnet] Dumb Timing Confusion [message #75499 is a reply to message #75493] |
Wed, 03 March 2010 08:06 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Hey Henderson,
What are you laughing at you're the guy that confused us all! ;-)
Well me at least!
Bloody pilots!
Regards,
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Ken Henderson
Sent: Wednesday, 3 March 2010 11:32 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Dumb Timing Confusion
MAN!, Do I ever feel better! At least half of you are just as confused as I
am! :-)
I'm about to leave for a doctor's appointment, so I don't have time to go to
the shop and re-re-re-check the fan operation to be SURE of the engine
rotation. Still sitting in the driver's seat, CCW rotation is the only
explanation for the way I'm seeing things, as described by Paul. But I
checked that fan (normal operation; my serpentine does NOT reverse its
rotation) several times and I CAN tell which way a propeller should turn!
That tells me engine rotation is CW from the rear.
More when the hand surgeon has LOOKED at me.
Thanks for brightening my day.
Ken H.
On Wed, Mar 3, 2010 at 6:55 AM, Paul Leavitt <leavittpaul@yahoo.com> wrote:
>
>
> Ken and Rob M,,, the rotation on the cadillac is CLOCKwise when viewed
from
> the front. Counterclockwise if your in the bathroom. If you mark the
> Harmonic(cads dont have one)ballencer/pully for BEFORE TDC mark it
> CLOCKwise when viewed from the front. This will be BEFORE TDC,,,,it will
get
> to a stationary mark on the block FIRST before the "0" or TDC mark,,,hope
> this helps,,,PL
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Dumb Timing Confusion [message #75500 is a reply to message #75495] |
Wed, 03 March 2010 08:06 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Hey,
Don't get on MY case! My Caddy 500 is sitting in a crate in Humble, TX
disassembled!
As an ex USAF Mechanic AND retired Hamilton Standard PROPELLER Rep I should
have known better than to believe what a pilot said about the way something
works! ;-)
I just looked at the pictures that were in the ad for the Caddy 500 I bought
off eBay and sure enough I can tell from the fan (propeller) that it turns
CLOCKWISE!
Rob Mueller
Sydney, Australia
AUS '75 Avion-The Blue Streak TZE365V100428
USA '75 Avion-Double Trouble TZE365V100426
-----Original Message-----
From: gmclist-bounces@temp.gmcnet.org
[mailto:gmclist-bounces@temp.gmcnet.org] On Behalf Of Steven Ferguson
Sent: Wednesday, 3 March 2010 11:59 PM
To: gmclist@temp.gmcnet.org
Subject: Re: [GMCnet] Dumb Timing Confusion
Thank you Paul.
Finally, we have the engine turning in the right direction. With the
engine at TDC, #1 firing (not #6), the key on the crank will be
somewhere around the 2:00 position.
Ken, in the absence of timing marks, you can buy a timing tape based
on the dia of the balancer. Drop the distributor in at 6 deg BEFORE
TDC with the rotor exactly at the #1 post on the cap. This is where
you want the engine to fire, fine tune from there.
On Wed, Mar 3, 2010 at 4:55 AM, Paul Leavitt <leavittpaul@yahoo.com> wrote:
>
>
> Ken and Rob M,,, the rotation on the cadillac is CLOCKwise when viewed
from the front. Counterclockwise if your in the bathroom. If you mark the
Harmonic(cads dont have one)ballencer/pully for BEFORE TDC mark it
CLOCKwise when viewed from the front. This will be BEFORE TDC,,,,it will get
to a stationary mark on the block FIRST before the "0" or TDC mark,,,hope
this helps,,,PL
> _______________________________________________
> GMCnet mailing list
> List Information and Subscription Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Steve Ferguson
'76 EII
Sierra Vista, AZ
Urethane bushing source
www.bdub.net/ferguson/
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
_______________________________________________
GMCnet mailing list
List Information and Subscription Options:
http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Dumb Timing Confusion [message #75501 is a reply to message #75471] |
Wed, 03 March 2010 08:16 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| Ken Henderson wrote on Tue, 02 March 2010 23:41 |
I know this will sound like the dumbest question to come down the pike in a long time, but I've go to ask it:
I've always thought I understood the 4-stroke cycle, timing, TDC, BTDC, ATDC, and all the rest of that weird stuff pretty well. So, my current state must undoubtedly be CRS, or some other old man slipped cog.
Today we located #1 cylinder TDC, using a probe into #1 cylinder as it came up on compression stroke. A dial indicator on the probe indicated 0.000" until the crank was turned in either direction.
I fabricated and installed a new pointer to reach the '89 Mercury Marquis double serpentine crankshaft pulley, then filed a notch in the pulley to mark TDC. Carefully measuring the diameter of the pulley, I calculated the circumference and divided that by 60 to tell me the distance from the TDC mark to the 6* BTDC mark I wanted to make for initial timing of my computer controlled distributor and EFI.
That's when the confusion set it: Which way should I measure to 6* BTDC from TDC? Let me explain how I've reasoned the answer and why I'm confused:
The engine rotates clockwise (CW) when viewed from the rear (driver's seat) (Right???). So BTDC marks should be located CW from TDC, meaning the BTDC mark will reach the timing pointer before the TDC mark -- right? Well, that pretty well satisfied me until I looked at the timing pointer on the Olds, and that which formerly fit the Cad, and THOSE BTDC marks are CW -- the TDC mark does not reach them until AFTER TDC. OMYGOSH! I KNOW the OEM timing indicators are correct, but I'll be darned if I can, today, reconcile what I see with what I think I know.
Y'All please help me see the error of my ways. I'll gladly join TSUA (Timing Screw Ups Anonymous) if necessary!
Ken H.
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Ken,
You are in all likelihood the first person to ever have this confusion (on GMCnet, about a Cadillac, Today).
Look in the GMC (or Cadillac if you have) books. In the GMC books it is the ignition section figure 10. It is a picture of a damper and a timing scale. Now to the thinking part. If that scale was on the Cad, then the TDC mark on the damper would be LEFT of the ZERO mark at 6*BTC (facing the front of the engine). SO, your scale or timing mark on the damper should be RIGHT of ZERO to achieve the same thing.
Please read Gary Casey's advice on actually locating TDC. You may have it right, you can also be 3* off pretty easily. The only thing Gary does not emphasize is that you must bring the piston UP to the reference point from both sides to eliminate the backlash in the piston/connecting rod assembly.
Also, if your mark ends up where it is separated from the crankshaft by the rubber element in the damper, do your self a favor and paint or punch mark the hub and damper before the engine is installed. That way, the day you find the timing way off and the engine runs really badly when you set it to the mark, you can look at the front of the damper see that it has slipped. (I would like you to think that nobody you know ever spent several days trying to isolate this issue.)
Good Luck at the doctor.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Dumb Timing Confusion [message #75510 is a reply to message #75496] |
Wed, 03 March 2010 10:02 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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| Gary Casey wrote on Wed, 03 March 2010 07:10 |
I agree with all those things everyone said, but a fine point: The "accepted practice" method of determining TDC is to set up a dial indicator and turn the crank until the indicator reads some convenient distance from TDC - say .100. Put a temporary mark on the crank and then turn it the other way to get the same reading. Put another temporary mark on the crank. Measure the distance between the marks and put the final TDC mark halfway between. I usually don't have a dial indicator around so I put a bolt or whatever into the spark plug hole and move the crank until the piston just touches. Then turn it the other way until it touches. Not hard enough to poke a hole in the piston, of course  .
Gary
I've always thought I understood the 4-stroke cycle, timing, TDC, BTDC,
ATDC, and all the rest of that weird stuff pretty well. So, my current
state must undoubtedly be CRS, or some other old man slipped cog.
Today we located #1 cylinder TDC, using a probe into #1 cylinder as it came
up on compression stroke. A dial indicator on the probe indicated 0.000"
until the crank was turned in either direction.
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I always use VERY LOW air pressure applied through a spark plug hole on #1 cylinder. Then I feel TDC with a breaker bar attached to the bolt in the center of the crank. I do it this way because it is how I learned to do it years ago on airplane engines only the breaker bar is substituted with the propeller.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Dumb Timing Confusion [message #75550 is a reply to message #75512] |
Wed, 03 March 2010 16:14 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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OK, I'm ready to award the prize:
Paul gets it, even though he's certainly not the only one to come up with
the correct answer(s). He wins because he was first to come up with the
clear, concise, correct answer: "... the rotation on the cadillac is
CLOCKwise when viewed from the front. Counterclockwise if your in the
bathroom..."
I can now admit that I started this whole thing with the bassackwards
proposition that the engine turns CW from the driver's perspective.
Only when I went by the shop on the way to the doctor, after my last note
this morning, did I realize that the known reverse- rotation fan I took off
of my serpentine equipped 455 had blades twisted the same direction as the
one I just bought at the junkyard. I chose another reverse-rotation fan
when I bought it!!! :-(( That's where my dumbfoundedness and confusion
began.
With no hard, locked-in-concrete, remembrance as to which way engines run,
that "propeller" bollixed my thinking all up. I was ready to put the 6*
BTDC in the right place -- based on that wrong assumption. Now that I know
"CCW", I know to put the mark to the RIGHT of the TDC mark as I look at the
front top of the pulley.
As for harmonic damper slippage, I don't have to worry about that since the
Cadillac didn't come with one, nor does the '89 Mercury Marquis pulley pair
I'm using include one -- it's adapted with a centering ring to the Cad's
removable crankshaft hub.
Nor am I going to worry about any marks other than TDC and 6* BTDC, since
I'll be using a Computer Controlled Distributor in conjunction with the EFI.
I intend to standardize on that *6 BTDC for initial timing -- the computer
will take over immediately after the engine starts and control the advance
to suit itself regardless of that setting.
More about TDC in another message.
Thanks to all of you for your input -- especially proving that I can confuse
at least some of you as well as myself. :-)
Bet I don't soon forget again that engines like to run CCW! (At least until
after I've had a nap.)
Ken H.
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| Re: [GMCnet] Dumb Timing Confusion [message #75553 is a reply to message #75512] |
Wed, 03 March 2010 16:43 |
GMCWiperMan
Messages: 1248
Registered: December 2007
Karma: 1
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Senior Member |
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Paul,
Thank you very much for the offer. We already degreed the crank with an 18"
wheel. But since I didn't have the crank pulley, the front plate, nor the
then-nonexistent pointer at the engine shop, we didn't mark TDC.
At home, with the assembled engine, including the pulley and its new
pointer, I made the other stupid mistake for yesterday: Not really giving
much thought to the geometry/trigonometry of the piston movement, I decided
to locate TDC with the dial indicator.
Since I don't have long extension for the dial indicator's plunger, I made
one by removing the ceramic from a spark plug body and drilling it to fit a
plunger. Unfortunately, that 's where I got too smart for my own good: I
used a piece of 20+ year old plexiglas rod from my workbench drawer. My
rationale was the plastic wouldn't mar any of the freshly machined surfaces.
I put a snug-fitting O-ring around the top of the plunger to be sure it
couldn't slide through the spark plug body into the cylinder.
With the piston already near TDC, I installed the spark plug body and
dropped the plunger in place, then positioned the dial indicator and zeroed
the indicator. When my helper turned the crank "just a smidgen", the
plunger dropped to the O-ring stop!!! OH, OH! What's going on?
What happened was that the piston was NOT close enough to TDC, so the
plexiglas plunger was pushed to one side and broke!
OH....MY....GOSH!!! NOW what do I do???
Well, what I did, after wasting probably an hour with flashlights, sticky
tape on wire feelers, scratching my bald head raw, kicking my butt a few
more times, and generally wallowing in self-pity and loathing, was remount
the engine on the engine stand and turn it upside down. With the spark plug
hole aimed straight down, nothing fell out, but I was able to keep the loose
rod mostly in sight. When I displaced it with my probes, a squirt of
compressed air into the plug hole would bounce the piece around enough to
eventually bring it back into sight. Finally, the rod landed with one end
over the plug hole and I was able to grasp it with forceps well enough to
extract it end-on through the hole. We matched the two pieces from the
cylinder with the piece from the outside and determine that we had all the
original rod.
I then inserted a bolt for the plunger and determined TDC. I don't believe
we're more than 1* off, But I will now follow the "approved procedure" of
rotating both ways to a fixed stop and marking 1/2 way between them -- if
only to verify what I've already got. I'll just make the stop from the
spark plug I've already modified, so I won't need yours, Paul.
Thanks again.
Hope everyone had a good laugh from the single stooge (didn't even have two,
'cause John Nicholls was an innocent bystander watching my antics). :-)
Tomorrow I expect to permanently install all the accessories and raise the
drive train into its compartment -- with or without the arrival of my son to
help. Y'All may REALLY get some good laughs from that exercise.
Ken H.
Americus, GA
'76 X-Birchaven
www.gmcwipersetc.com
On Wed, Mar 3, 2010 at 11:15 AM, Paul Leavitt <leavittpaul@yahoo.com> wrote:
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> Ken, if you want I can send you my 11" degree wheel(largest I could make on
> my lathe) crank bolt and spacer along with a piston stop made out of a spark
> plug. Could be there on Friday I guess.PL
> _______________________________________________
>
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