390 Crankshaft timing assistance. (Help!)

[derbydrifter]

Hey guys, in the case of things having got mistakenly turned a little with the timing chain was off, (!!!!) I need some help understanding how to set up the crankshaft timing on my 390 engine again. My manual simply says make sure the marker dots on the crankshaft and camshaft sprockets are ligned up - with engine in the car, larger cam sprocket dot pointing downwards, smaller crank dot pointing up - but what about which stroke number one piston is top dead centering on at the time? What about the risk of being 180 degrees out here?

Should those two dots line up like that while piston number one is at TDC, valves closed, on the power stroke?

Appreciate anyones time here.
Kurt

[STDog]

The crank doesn't have a stroke. The camshaft makes that distinction.

Just line the dots up per the manual.

Most likely that will put #1 at TDC on the exhaust stroke, so you'll need to rotate the crank one full turn before setting the distributor in.
Check the shop manual, as it should say.

Or look at the valves and see if both are closed on #1, or if both are open a little.
If both are open closed then you're on the compression stroke and can set the distributor in.
If not, rotate the crank once.

[derbydrifter]

Okay, I'm starting to get it. Thanks. 'Just line up them dots.' My original workshop manual though, other than describing how to set the ignition timing, really doesn't help much.

Shouldn't the valves be closed on the compression stroke?

[STDog]

Shouldn't the valves be closed on the compression stroke?

Yeah. Too much going on when I posted that 


I've not seen one of those manuals. I do know the '70 manual mentions rotating the crank after installing the timing set.

[derbydrifter]

Ah! now it makes complete sense. And then the rest's all down to fine tuning.

I'll double check my manual for information, I may just be missing it. Mind you, it's so old I'd better check the pages, there may be some of those missing.

Happy New Year STDog, and to all who run and subscribe to the forum!

[STDog]

I'll double check my manual for information, I may just be missing it. Mind you, it's so old I'd better check the pages, there may be some of those missing.

Here's the engine section from the 1970 shop manual. The timing install is on page 20-21 (6-106 and 107), particularly the last item on page 20 that continues to the top of page 21.
http://cadillacmisfits.com/gallery2/main.php/d/2498-1/cad_manual_2.pdf

[derbydrifter]

The timing install is on page 20-21 (6-106 and 107), particularly the last item on page 20 that continues to the top of page 21.

Thanks STDOG, that explains things niclely. I see on your 472 when the dots are lined up cylinder four is in the firing position, and a 180 degree turn of the crank would put it on number one cylinder. For my 390 this may be the same, I don't know. Nowhere in my manual does it mention anything about it! If anyone has that information I'd sure appreciate it, but failing that, with this data I can get the job done. 

Kurt. . .

[STDog]

I see on your 472 when the dots are lined up cylinder four is in the firing position, and a 180 degree turn of the crank would put it on number one cylinder.

360^o turn of the crank. (180^o at the cam/distributor. The manual isn't real clear there).

#4 and #1 are both up at the same time. Not sure which 390 you have (it changed in '63) but it's similar.
Look at the 5th cylinder in the firing order. It'll be up with #1 and depending on the cam one will be compression and one will be exhaust.

Again, look at the valves to be sure, or just find the compression stroke with alternate means (finger in the spark plug hole) and use the timing marker/pulleys for TDC.

[derbydrifter]

 Oops, my apologies, I meant 360 degree turn, not 180. Thanks again for all your help. I'm all info'd up, good to go and looking forward to getting into the workshop on Friday. Shame I won't be able to start the engine up straight away though, I still have the water pump off waiting for a rebuild kit to arrive. Never mind, needed doing.

Kurt . . .