spills

iTrader: (9)

Ok, Ive searched for this and got a few vauge answers. I got a GMPP 8" balancer for my 383, comp cam and timing chain, and a summit adjustable timing pointer. My question to you gentlemen is this: According to the cam and crank gears, when should I set the balancer/pointer for TDC for the #1 piston? Should they be at 12 and 12, or dot to dot (cam at 6, crank at 12)? It seems that it should be 12 and 12 because dot to dot seems to be the top of the exhaust stroke, right before the intake stroke.

Some guy at my work said the only cams you install with the marks at 12 and 12 is old 427 (421?) Pontiac motors. But I just see this lining up dot to dot on the compression stroke. HELP!

Apeiron

The engine is at #1 TDC whenever the crank dot is at the top, regardless of where the cam dot is.

spills

iTrader: (9)

that makes sense. How about when #1 is TDC on the compression stroke? Just outta curiosity

F-BIRD'88

When the timing marks on the gears are aligned 6 and 12
the engine is at TDC fireing #6. you have to rotate the motor's crankshaft 1 complete turn from there so the timing marks are at 12 and 12. This position is TDC #1 fireing.

This not a good way to align and set the adjustable timing tab for the balancer. You should use a piston stop to find true TDC. Easiest with the heads off. But can be done with the heads on. Make sure the valves/ rockers on that cylinder (#1) are loosened off completely so the piston stop does not hit a valve during checking TDC. True TDC is exactly 1/2 way between the points where the piston stop stops crank rotation forward and backward.

vernw

iTrader: (2)

But what do you do when you buy a piston stop, thread it in all the way, and the piston never touches it? I bought one from Summit and can crank the motor over by hand all day and never touch the piston stop.....

Apeiron

The angle of the plugs in your heads could be too parallel to the deck, or you could have dished pistons. Unfortunately then you might just have to pull the head.

vernw

iTrader: (2)

Sure hope not. Is there a chance that the piston stop is too short?

Apeiron

Maybe, which one did you get? I have the Crane one I think.

vernw

iTrader: (2)

I got the "Tavia Piston Stop Tools Piston Stop, Top Dead Center Stop, Cylinder Heads On, Spark Plug Style, 14mm, Adjustable Depth, Kit" for $15.xx plus overnight shipping, received it on Friday so I could TRY to get it resolved over the weekend.

vernw

iTrader: (2)

OK, did the check over the weekend. Mid-point between the 2 marks (rotating one way until it hits the stop and make a mark, go other direction ans mark the point where it stops) ends up being 4*BTDC. Sounds to me like I'mrunning 4* less timing that I thought I was.....

F-BIRD'88

I make my own piston stop that works with smog heads ( horizontal parrallel plug placement.)
I knock the porceline out of a old spark plug. I get a 3/8" steel tube and weld it in the hole cockeyed so it points down toward the piston when screwed in. It works. Ya have to lossen off the valves for that cylinder so thye don;t contact the piston stop during checking.
For a dished piston the end of the rod has to be a little longer. may need to bend the end too.