The Stovebolt Site Forums The Shop Area Engine Shop GMC 228 engine timing

I have been discussing this on the oldgmctrucks discussion boards, but something is going wrong and I can't get on today. I really need to figure this out and get on with my project today, though. I have been having some trouble finding TDC and timing the gears since I got it back from the engine shop. I guess I'll start from the top:
I am assuming the crankshaft rotation is clockwise, because after observing the valve and piston action after cranking it several times, this is all that makes sense.
http://good-times.webshots.com/photo/2884918280100058208tGaoMY .
Here is where I started. I got the crank and cam back from the engine shop and the crankshaft gear had a new white mark painted on it. I assumed this was the timing mark and lined it up with the punched "O" mark on the cam gear.
http://good-times.webshots.com/photo/2349212370100058208tjPPeU .
This was not at #1 TDC however. So I cranked the engine until #1 was at TDC and this is what the timing gears looked like:
http://good-times.webshots.com/photo/2985075090100058208sdFggn .
I made a mark there on the cam. It was just a pencil mark and only temporary.
I then watched the valve action more carefully and determined something was definitely not lined up right because on the way up to TDC, the intake valve for #1 was barely closing. This would definitely not work because it is supposed to be open when the piston is on the way down to suck in the fuel/air mixture.
I then changed timing marks on the front. After sanding the face of the crank gear, I found another punched "O" mark, and lined this up with the same mark on the cam gear.
http://good-times.webshots.com/photo/2046990060100058208IbuDrh .
This, however, was lined up at #6 TDC.
I watched it more carefully and determined that this was definitely #6 TDC, but the valves and pistons worked together for the whole rotation though 1-5-3-6-2-4.
I was sure that when the timing marks lined up, it was #6 TDC, because one revolution before that, #6 was intaking:
http://good-times.webshots.com/photo/2068461200100058208RpdvRZ .
I then cranked through it some more and after 6 went past TDC and should have fired, if the engine was hooked up, #1 started to go down and intake. I should note too, that when 6 was compressing and reaching TDC, 1 was exhausting.
http://good-times.webshots.com/photo/2803178130100058208dHsQmi .
I then cranked the engine some more and found TDC for #1.
http://good-times.webshots.com/photo/2706930230100058208kBHLPo .
Here is what the timing gears looked like at #1 TDC: (The cam gear was 180 degrees from the punch mark)
http://good-times.webshots.com/photo/2024266140100058208FafaSc .
My question is this:
Does it matter if #1 is not at TDC when the timing marks align, as long as everything functions the way it should? Why would #1 TDC be 180 degrees from the cam timing mark? Could the shop have put the cam gear on backwards? Should the engine be at #1 TDC with the marks lined up? Everything works properly now, the timing marks just line up at #6 TDC. I am pretty frazzled by now and I just want to figure this thing out. Thanks for reading this long post.

justin squire,

You have confused yourself. Simply line the two factory timing marks on the cam gear and the crank gear up and you are done. Don't worry about piston or valve position, only about having the timing marks aligned on both gears.

You should buy a manual for your engine.


Stuart

So you're saying it doesn't matter where TDC is? just as long as the marks line up. That makes sense. As long as the shafts are aligned right, the valves and pistons will work correctly together. I just need to be able to find TDC to time the distributor to it right? Thanks.

justin squire,

That is a different operation than the one you are doing right now, and will be done later. Does the GMC use the peephole and ball on flywheel like the Chevrolet does?

Stuart

Yes, I believe that is how the manual says to do it, but I have been told by folks on the oldgmctrucks forums that all you have to do is find TDC, then you can time the distributor. Section 12 in the chevy service manual gives an easy way to time the distributor to the engine if you are at #1 TDC. I can't use the flywheel mark yet because the engine is on the stand and there is no way to attach it. I am hoping to get the distributor timed or at least pretty close, so all I have to do is fine tune when it is on the truck.

justin squire,

Installing the distributor and timing the engine after it is in the truck is VERY simple...don't let it freak you out. Keep at it and keep us posted.

Stuart