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Topic: Distributor/timing mark off?

in Forum: C3 Engines

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Distributor/timing mark off? (1/9)
6/29/05 7:56pm

YellowLT1
Former Member
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Louisville, KY - USA

Vette(s):
1971 LT1 Convertible PS PB 43K miles

Joined: 11/11/2003
Posts: 97

Car is not running good. Pull plugs and try to find TDC so I can check valve lash but....

When distributor is pointing at #1 plug wire - 7 O'clock position looking down from the top, timing mark on balance wheel is about an inch from the 0 mark on the timing tab, or conversly if I put timing mark on 0 degrees, distributor points about 3/4 inch past #1 plug position on the compression stroke.

Does the distributor have to point exactly at the #1 spark plug wire or is 3/4 inch past "close enough"?

If this is not right, how do I tell whether the balance wheel is off or the distributor is not installed correctly? If this is not right I assume it would be difficult to set the ignition timing correctly.

Thanks
Neil (Stock 71 LT-1 w TI)

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Distributor/timing mark off? (2/9)
6/29/05 8:57pm

Adams' Apple

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Duncanville, TX - USA

Vette(s):
#1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas

Joined: 11/8/2003
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The rotor on the dist. should normally be a little before the terminal on the cap. This is where the 'advance' comes into play. If the rotor is directly on the # 1 plug, at TDC, you have "0" deg. advance. Most engines run best with some advance in the timming, usually 8-12 deg. BTDC(before top dead center)
The best way to locate true TDC is to remove the # 1 plug, and put a small rod, or screwdriver in the hole. Then turn the engine over by hand until you feel it touch, and then when you feel it (the piston) stop moving up, mark the balancer at the "0" spot on the timming tab. Then turn the engine by hand back the opposite direction until you feel the piston again, and mark the balancer again when the piston no longer moves up. Then measure the distance between the two marks on the balancer, and mark the balancer at half of that measurement. This will be TDC. If the mark you made is not where the factory groove is on the balancer, then the outer ring of the balancer has shifted, or possibly you have the wrong "pointer/tab" on the engine.
If you just want to adjust the valves, just watch them. Turn the engine over by hand, and when the rocker arm on the # 1 exhaust just starts to open, adjust the intake valve. Then turn the engine until the intake valve just starts to close, and adjust the exhaust valve. Then just repeat on each cylinder until you're done. Then go get a cold one!

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Distributor/timing mark off? (3/9)
6/29/05 9:22pm

anips
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sonoma, CA - USA

Vette(s):
72 LT-1 AC coupe,69 l-36 coupe

Joined: 8/9/2002
Posts: 784

Sounds about right to me, if your rotor is pointing dead on to #1 and the mark om the dampner is about 1"above the 0 or TDC that would give you about 10-12 BTDC initial timing which is about right, when you move the mark to 0 and the rotor is 3/4" past #1 going clockwise its geting ready to fire #8.

Distributor/timing mark off? (4/9)
6/30/05 6:56am

YellowLT1
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Louisville, KY - USA

Vette(s):
1971 LT1 Convertible PS PB 43K miles

Joined: 11/11/2003
Posts: 97

I just read how to determine true TDC using a 14mm bolt in the #1 spark plug hole and I dont get it. How long a bolt? You turn the crankshaft by hand clockwise until the piston contacts the bolt end, mark the balncer, then stop and turn counterclockwise until piston contacts bolt end again. I thought if you go counterclockwise the piston will be moving AWAY from the bolt end. How far do you have to turn the crank backwards 360 or 180? This seems like a lot to go thru every time you want to set the valves or find TDC for some reason. I tried putting a rod in the #1 plug hole and turning the crank until the rod got to top of travel but the rod keeps getting jammed by the piston in the hole. Also I have no idea why this #@% computer is typing in italics.

Thanks
Neil

Distributor/timing mark off? (5/9)
6/30/05 9:25am

Pumps
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Virginia City, NV - USA

Vette(s):
1979 Coupe, white in color

Joined: 1/19/2005
Posts: 314

The method is used, because of piston dwell. When the piston is at TDC, the crank still has to go "over center" while the piston is still at it's high point. The idea is to stop the piston in BOTH directions of travel at the same point in the bore, and same crackshaft position in each direction. Sounds difficult, but not. True TDC is half way between the marks. Best to take all the plugs out, so your not fighting compression when you turn the engine. You do turn it in the normal direction of rotation (by hand ) till you touch the piston stop, and then turn it backward untill you hit the piston stop again. Remember to mark both points on the balancer, then half way between them is true TDC. They do make special tools for finding TDC, it looks like a nut with plug threads on it and a smaller bolt in the middle. I've never used a 14MM bolt, but don't see why it wouldn't work either. Just go SLOW!

Distributor/timing mark off? (6/9)
6/30/05 2:26pm

anips
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sonoma, CA - USA

Vette(s):
72 LT-1 AC coupe,69 l-36 coupe

Joined: 8/9/2002
Posts: 784

they also make a little whistle that screws into the spark plug hole ,when it quits sounding your at TDC, your not building a piano, engine wear, manufacturing, tolerances,timing tab position, etc,make things a little difficult, if the dampner outer ring has slipped it slips either in or out or spun on the inner hub, because of the angle of the spark plug hole in relation to the piston travel its imposible to set up a dial indicator, its all a guessing game, the only way to find true top dead center is with a dial indicator, the head off and a degree wheel bolted to the dampner, may I suggest that you use a remote start switch, hold your finger over #1, when you see the mark come over the top do the rest by hand, when you approach TDC it will get harder to turn by hand,soon as you go past TDC it will get easy again, then go back, its a feel thing, when you "feel" you close to center of the stroke look at the tab, if you are + or - a degree or two from O I'd say the dampner is OK.

Distributor/timing mark off? (7/9)
6/30/05 4:13pm

anips
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sonoma, CA - USA

Vette(s):
72 LT-1 AC coupe,69 l-36 coupe

Joined: 8/9/2002
Posts: 784

OK, I went out and dug up my degree wheel out of the tool box, haven't used it in years, heres what it say on the wheel,

    Find TDC by one of three way, positive stop, dial indicator, posi stop through the spark plug hole with heads installed,

    I won't go into the first two

    bolt a pointer to the block heavey enough to hold a permanent position. ( in your case the timing tab will be the pointer, O will be the tip of the pointer)

    the method used with the heads installed is accomplished by welding or brazing a rigid rod onto the bottom of a spark plug so when tightened into the hole it will extend into the cylinder approx. 1/2" ( in your case a 14mm bolt that extends 1/2" into the cylinder will do)

Rotate engine clockwise find the highest point of piston travel and tighten the degree wheel with TDC mark in line with the pointer ( in your case make a mark on the dampner) Rotate engine CC wise until piston touches stop, check reading on degree wheel. (in your case case make another mark on dampner) TDC is halfway between the two stop readings.

    There you have it, pretty much what everbody's has been saying.

   Well maybe not everybody.

Distributor/timing mark off? (8/9)
6/30/05 7:21pm

YellowLT1
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Louisville, KY - USA

Vette(s):
1971 LT1 Convertible PS PB 43K miles

Joined: 11/11/2003
Posts: 97

OK finally got it all done. Todays projects included resetting all intake and exhaust valves cold to .026 exhaust and .021 intake. I read about these "cold" settings in the Oct. 04 issue of Corvette Enthusiast and I must say it works GREAT. Much easier than setting them hot and the car runs better too. Hardest part of the job was finding TDC and marking the balancer at 90 degree intervals. Marked the balancer with a paint pen for future reference.

Changed all spark plugs, set timing advance to 12 degrees at idle 32 degrees all in by 2500 rpm. Then rechecked float levels (rear float was way high), reset mixture screws and idle screw to 800 rpm and went for a test drive. Took it to 6000 rpm on the onramp and ran smooth as silk. Took me most of the day but time well spent and hopefully wont have to mess with it the rest of the season.

Thanks for all the help
Neil

Distributor/timing mark off? (9/9)
6/30/05 7:27pm

jackmoore
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Joined: 7/12/2004
Posts: 38

I use a soda straw in the spark plug hole. It's a lot softer and easier to move. If u break it off, big deal, it will pass through the head. rotate the motor until it stops coming up, rotate it a little past, see the straw go down, roatate it up, see it come up. Get it right in the middle of the point it stops rising and the point is starts dropping, that is TDC. The balancer should have been set correctly when the motor was built. It sounds like somebody missed stabbing the distributor when they put it in. Write if u need directions for pulling and restabbing the distributor correctlly. that or get out your Hays.

jackmoore38533.8135532407

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