Hi guys, I’m kind a new here so bit of a learning going on. Please be patient.
I’m building 351cleveland to my ’71xr7 and have bit of an issue with timing:
I have new cam, heads, waterpump… When I put new cam in I checked that those dots in chain and sprocket were right. No. 1 is also compression stroke and I marked that TDC on balancer. I just started turning engine bit over 180degrees and started wondering how to find TDC again for sparks? That engine is hard to turn backwords. All it wants to do is loosening the bolt. I actually found a way to turn the engine backwords, but it takes two man to do it and I’m not fit or calm enough for that.
So the question was: how do I find tdc again after I loose it?
P.s. That instruction where you turn the engine first 180deg then 270deg. That dont work. Not for my cam anyway. There were valves that was supposed to be closed, but were not with that 180deg turning.
You don’t mention what state of assembly your engine is at. That would be helpful.
Assuming it is fully assembled, I would rotate the additional 180 degrees until you are at the mark you put on earlier. Now you should be at the top of the exhaust stroke. Turn another 360 degrees you should now be at the top of the compression stroke.
If you have lost track of which crank rotation you are on, I would take off the distributor cap and see where the rotor points when you are at your mark.
If the distributor isn’t in, I would either take out all the spark plugs except number 1. You should be able to feel the compression when you are in the compression stroke.
Or you could take off the valve cover and see when you are at the mark whether the valves are closed (compression) or open (exhaust overlapping with intake).
Welcome to the challenge and satisfaction of making something 50 years old run better than any 50-year-old ought to.
The “finger trick” PonyMan recommends works well for determining which of the two passes of TDC is the compression stroke - that is, the one to use as basis for timing.
Remove #1 spark plug, stick a finger in, and have a friend hand crank the engine by the balancer bolt, and as you get to the correct compression stroke of the piston up, the air will practically push your finger out. That’s the TDC to leave it at while seating the distributor - the TDC that is squeezed by the piston cresting with both valves closed.
You can do a crazy man’s version of this, ignition OFF, by bumping the starter at the solenoid on the front passenger fender well with a screwdriver. This is for if you lack the combination of sockets to get at the crank snout bolt.
Remember the distributor rotor will have two TDCs - one false, one real - as far as referencing the spark plug wire routing.
I hope I didn’t miss the point of your question…
R.B.
If you don’t have hands to do this, a compression gauge works too.
Thank you guys for help. I think I got it right after serious thinking and reading.
Engine was already assembled. I took valve cover of and looked at the rocker arms of the 1. cylinder. When those were closed I turned hose into the spark plug hole. Then my friend turned the engine while I felt with my thumb is it sucking or pushin air out. It was much easier to feel it from that hose than straight from spark plug hole. While it was very close we confirmed that it really is tdc and not the bdc by sticking bended rod in there. When we were sure of that, we did the final adjustment. Another secure thing was mark on the balancer that I did draw to it while building the engine (I was not sure that it was right). Having all of these pointers showing same I think it must be good now.
P.s. If I ever need to do it again pressure cauge is my recommendation for the job!
I like these brainstorming threads.
A lot of good ideas here.
I’m glad you found them helpful
Feel free to ask about Oil, Brake Fluid, Brakes, or Electrical too. The members on this site are pretty good about differentiating fact from opinion and avoiding the “Holy Wars” those topics usually result in.
