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Re: Timing / balance belt change - setting TDC
Posted: Tue Aug 09, 2022 7:41 pm
by Tom
Since #1 and #4 are at TDC at the same time, if you set the cam gear to the timing mark, then the valves will be closed enough on #1 and #4 to not make contact with their pistons. Otherwise, the piston would hit the valves on #4 every time #1 is at TDC on the compression stroke.
Re: Timing / balance belt change - setting TDC
Posted: Tue Aug 09, 2022 8:37 pm
by Darwin
I'd have to agree with Tom here. Crank position doesn't really matter except that pistons 1 and 4 are at the top. Since the cam gear is keyed, and can only be installed one way, lining up the notch sets both intake and exhaust valves at whatever their position is supposed to be for all cylinders, so that point is moot.
To the OP, there should also be a notch in the flywheel that lines up with a cutout in the bottom of the bellhousing. See photo below.
- flywheel1.JPG (136.43 KiB) Viewed 811 times
You can also do the old wooden dowel trick by removing a sparkplug, and placing a wooden dowel into the combustion chamber. Slowly move the crank back and forth, watching the dowel to see where TDC is. Considering it sounds like you only rotated it through two revolutions by hand, you'd have to be pretty strong to bend any valves, and I'd guess you'd stop after feeling the resistance as you tried to turn it. Valves are pretty stout.
Re: Timing / balance belt change - setting TDC
Posted: Sun Aug 14, 2022 5:21 pm
by Wicke944
Hey sorry for the late reply! I hope no one was at the edge of their seat waiting for my demise! Haha
I can report that what I believed to be TDC by using the cam marking and #1 plug out with a paper straw. Then confirm it with a very light scribe (but no “OT” onset Ed from above.
I can report that I DO NOT have the secondary tab as shown above when viewed from below. Trust me…. I spun my crank more than half a dozen times and watched from both up top and underneath with my car raised up on a lift.
I did this post belt removal as I had already turned it once (by hand, no socket on crank) with zero resistance (all plugs removed).
I reinstalled new belts (with all marks I had lined up and confirmed TDC with the #1 spark plug method.
Test fired with no issues. Runs great
I’d still like to pull everything off and test the belt tension those 3D printed tools at some point
The odd marking (on flywheel) I have that can be viewed from underneath beside the clutch inspection hole on the the side (I painted yellow), it lined up with a casting line May just be a coincidence, as I don’t believe it’s a TDC tell mark.
Thanks for all the help! Glad to be back on the road!
Re: Timing / balance belt change - setting TDC
Posted: Sun Aug 21, 2022 2:18 pm
by Race5103
First congratulations on getting your car back together without damage.
Tom: you were correct about the valves. I didn't pull the valve cover but came across a degree wheel forgotten and buried in my toolbox I had used years ago when building a Datsun engine. Although the degree is of course not specific to a car so shows a very wide range of valve timing it does show no open valves on #4 cylinder when #1 is a TDC on the firing stroke.
Lou
Re: Timing / balance belt change - setting TDC
Posted: Sun Aug 21, 2022 2:55 pm
by Tom
Race5103 wrote: Sun Aug 21, 2022 2:18 pm
First congratulations on getting your car back together without damage.
Tom: you were correct about the valves. I didn't pull the valve cover but came across a degree wheel forgotten and buried in my toolbox I had used years ago when building a Datsun engine. Although the degree is of course not specific to a car so shows a very wide range of valve timing it does show no open valves on #4 cylinder when #1 is a TDC on the firing stroke.
Lou
Thanks so much for circling back and confirming this for posterity's sake! A lot of people would not have done that, but it elevates the board a great deal to have people like yourself who are focused on getting tech info correct. If only all boards/groups were as lucky. I tip my cap to you.
Re: Timing / balance belt change - setting TDC
Posted: Tue Sep 27, 2022 8:56 pm
by boom10ful
Wicke944 wrote: Sun Aug 14, 2022 5:21 pm
Hey sorry for the late reply! I hope no one was at the edge of their seat waiting for my demise! Haha
I can report that what I believed to be TDC by using the cam marking and #1 plug out with a paper straw. Then confirm it with a very light scribe (but no “OT” onset Ed from above.
I can report that I DO NOT have the secondary tab as shown above when viewed from below. Trust me…. I spun my crank more than half a dozen times and watched from both up top and underneath with my car raised up on a lift.
I did this post belt removal as I had already turned it once (by hand, no socket on crank) with zero resistance (all plugs removed).
I reinstalled new belts (with all marks I had lined up and confirmed TDC with the #1 spark plug method.
Test fired with no issues. Runs great
I’d still like to pull everything off and test the belt tension those 3D printed tools at some point
The odd marking (on flywheel) I have that can be viewed from underneath beside the clutch inspection hole on the the side (I painted yellow), it lined up with a casting line May just be a coincidence, as I don’t believe it’s a TDC tell mark.
Thanks for all the help! Glad to be back on the road!
I also had the same issue when doing my own timing belt job. The OT markings and line were not on my flywheel and I suspect someone has been in there before. Had to use the bottom marking to line up the flywheel and the marks on the camshaft gear. Car runs great! Going to retension the belts in a few hundred miles with the Arrnworks tool and going to try out the new 3D printed tool from here.
