TDC piston stop won't stop piston

[FOMOCO_1546]

Hi, I believe my damper pulling might have shifted. Right now I'm running 19 degrees intial timing and 34 centrifugal timing. The engine is a 1974 302 with possibly a mild cam and Pertronix in the distributor.vacuum seems low at 15 inches. Engine runs very well but I'm trying to find top dead center. My question is when I screwed a piston stop in #1 it won't stop the piston. You guys have any suggestions. Thanks

 

[DirtDonk]

Is it in all the way? Is it a bit sloppy do you think? Seems like if it's not pushing far enough in, and/or the tip is allowed to flex one way or the other, the piston could just push it out of the way.

Otherwise, I've only used them a few times and they worked as expected. Been many years though, so might be something else I'm not thinking of.
What brand/model is the stop?
What style cylinder head? Stock original, or something else?

Paul

 

[centex77]

Only three reasons it won’t stop. It’s not in far enough, you didn’t rotate the engine far enough, the piston is missing.

 

[FOMOCO_1546]

It's a Crane Cams piston stop and I have stock heads with 14mm spark plugs. When I turn the center part of the piston stop in almost to the fullest extent, it hits something. Would that be the cylinder wall?

 

[FOMOCO_1546]

As you can see hear, piston stop is in very far and stops turning in. I back it off just a very little. I can rotate the engine forever. And yes, I'm turning the engine by hand not with the starter. Thanks

 

[hammer189]

Try something like a straw to find approx. TDC. Then try the stop when u know your close.

 

[Boss Hugg]

again, with the stop in all the way, are you able to turn the engine 360 degrees?

 

[DirtDonk]

And while you said it's in almost all the way, can you still turn it in farther?
Maybe take it out and see how far it will actually screw into the fitting before it falls out the other side. Be even better if it's got some sort of stop, but if it doesn't this is a good argument for taking it out before experimenting with it going in all the way.

Once you can judge how far in it extends before any chance it will fall out, put it back in.
Or leave it at it's full extension, literally as far as it will go without falling through (maybe it's just a socket and can't fall all the way in), bring the piston up visually by looking into the spark plug hole (or using the straw/stick method mentioned) and then screw the stop tool back into the plug hole to see if it will still go in all the way.

If it still goes in after all that, the stop is too short for your application.
Which seems weird and not possible. But I've learned long ago to not be too surprised at stuff like this. Maybe they make two styles and this is the one for compact center plug high-compression engines with almost no clearance at the top of the piston.

Good luck.

Paul

 

[FOMOCO_1546]

Ok guys, I feel pretty much like an idiot. I went with the straw method I verified that I was on the compression stroke. As I stated I would screw it in and it was hitting something and stop, it wasn't. It was the threads on the stop. I turned it in with a screw driver and then it kept going in.
I turned clockwise until it hit the stop at 3 degrees btdc and then counterclockwise 360 until it stopped at 2 degrees atdc. So all this and I'm a whole 1/2 degree off.
I'm running 19 degrees intial timing to make 34 degrees centrifugal timing. Does that even make sense? Vacuum at idle reads 15 which indicates late timing. Thanks for all of your help.

 

[rmk57]

The vacuum line is plugged off when your checking the timing right?

 

[FOMOCO_1546]

Vacuum is plugged. I ran 10-12 degrees initial timing since I owned this bronco. It felt like when pulling out on hills that I was in 2nd gear. I always thought that was carburation because when it was hot out it was worse. I bumped the initial timing to 16btdc and that gave me 26 centrifugal timing. It felt like I dropped a new engine in it. I then talked to a guy that races Ford's and told me to set it to 34 degrees centrifugal and close the hood. Im not sure if it runs better or not. I just thought something was off. No pinging on hills, and no slow starting.

 

[Broncobowsher]

Sounds like your distributor has one of Fords finest (wack job) emissions style advance curve. You are trying to get a good non-emissions total advance at the cost of overly advanced initial timing.

How does it idle with only 10-12° advance and the idle speed adjusted back up?

Now that you got good experience turning the crank back and forth by hand, take the cap off the distributor and do it again. How much backlash is there between the distributor and the crank? You might just be suffering from bad cam timing due to stretched timing chain. The factory timing gear is a nylon coated gear, to be quieter. Nylon didn't age well inside an engine. The teeth fall off and the chain rides on the base cast gear with a lot of extra slop in it. In nearly 30 years I have only seen one Ford V8 that came apart with the nylon intact, it was shocking.

 

[FOMOCO_1546]

After changing the intial timing to 19btdc I had to lower my idle speed. Going to check distributor in the morning. Thanks

 

[Rustytruck]

If you have 1974 ford 302 you have Fords finest piece of junk 302. if factory stock it has the higher deck and deepest piston dish. then ford went and retarded the cam 4 degrees. this drops vacuum pretty low. They retarded the the springs in the distributor too to have sluggish advance. Turn the engine to top dead center by hand. pop the cap and look at the rotor and turn the engine backwards until the rotor just moves. Check the timing marks again and see if the timing moves more than 15 degrees. That is checking the timing chain slack, after 15 degrees you will see performance loss and you should start thinking about replacing the chain assembly especially if you ever need to do a water pump.

 

[Skiddy]

Ok guys, I feel pretty much like an idiot.

whew there for a second I thought you were going to say the piston is missing

 

[FOMOCO_1546]

Thanks Rustytruck, just did the distributor test and when turning engine backwards from tdc rotor started to move between 3-4 degrees. When I redid my 73 bronco I bought a 74 with a bad frame. I bought it for the perfect hood, and power steering set-up. The guy told me he just had to have $300.00 for it because they had just rebuilt the engine. I drove it home and it ran great. I pulled the engine and dismantled it pulling the distributor out without verifying where they set it. I backed the timing off today to 16 initial giving me 30 centrifugal. Runs great, but it also ran great at 19 initial and 34 centrifugal.