Engine Issues (302)

[FoMoCoBronCo]

I’ve got a 1971 bronco with a 302 and three on the tree. I was driving down the road yesterday in second gear and gave it a little bit too much gas. Engine made a thunk sound and died. (like it overly bogged down and something got overpressurized, not a metal on metal sound)
I can turn the engine by hand, but I can’t get it to start… It’s like there’s too much back pressure on the fly wheel to get it to turn over. Any ideas on where to start?

 

[Lawndart]

Timing chain?

 

[Timmy390]

Timing chain?

My first thought as well.

Pull a valve cover and see if the top end is moving when you turn the bottom end my hand. If the valves are not opening and closing you know where the issue is.

Tim

 

[Lawndart]

When mine did it, it just jumped a tooth or two.
https://classicbroncos.com/forums/threads/sudden-power-loss.275935/#post-2954221

 

[SteveL]

Does it crank but not start like no spark? If your oil pump dies it will snap the pin on the distributor gear so motor will not run.

 

[spap]

I had a distributer shaft break once,
doesn't explain why it wouldn’t turn over with the starter.
sorry bro that always sucks

 

[Broncobowsher]

My first thought as well.

Pull a valve cover and see if the top end is moving when you turn the bottom end my hand. If the valves are not opening and closing you know where the issue is.

Tim

Distributor cap is easier and can tell more.

What happened between the noise happening and coming to a stop? Being a stick shift the engine would be coupled to the wheels and should be spinning until you press the clutch. What happened during that time?

Have you checked the oil? Enough in it? Sparkles?

 

[Timmy390]

Distributor cap is easier and can tell more.

I do things the hard way sometimes....

Tim

 

[DirtDonk]

I was driving down the road yesterday in second gear and gave it a little bit too much gas.

Not really such a thing as too much gas! Well at least not usually.
But just how much do you figure you were giving it? Really putting on the load, or did you rev it up higher than normal?

Engine made a thunk sound and died.

Maybe the thunk you heard was some spitting out the carburetor, such as when it runs out of fuel?
Or maybe a timing chain breaking like the others were saying.
As said, easy enough to check by removing the distributor cap and turning the engine over by hand. If the rotor does not move, then something broke inside and you'll have to at least take the timing cover off to have a look.

(like it overly bogged down and something got overpressurized, not a metal on metal sound)

Overly bogging down is not great, since it's indicating a very large load on the engine, unless it's just lack of fuel or spark.
But nothing to "overpressurize" in this case. It's not a bad thought, but I don't see how it could happen to an engine.
But at least it did not sound like metal to metal. At this point anyway...

I can turn the engine by hand, but I can’t get it to start…

So you can turn the engine over by hand, which is great. But when you say it won't start, is the starter not cranking the engine? Or is it cranking but not firing?

It’s like there’s too much back pressure on the fly wheel to get it to turn over. Any ideas on where to start?

No way to have backpressure (from whatever) on the flywheel and still turn the engine over by hand.
Something in the transmission could be jamming it up, but releasing the clutch would release that pressure and you'd be able to turn the engine over. Similarly, if the damage was in the clutch, releasing it might not relieve the pressure against the flywheel. But the bottom line is that the flywheel is physically and securely connected to the engine, so anything jamming up the flywheel also jams up the engine.
Which leads back to the question of, are you using the term "turn over" to indicate cranking, or firing?

Just some more clarification for now. But definitely check to see if the distributor is turning. It's easy to do.

Paul

 

[FoMoCoBronCo]

Wow. Thanks to everyone for the replies. I am relatively new here and I am really appreciative of all the help.

OK, I pulled the distributor cap and turned the engine by hand. The rotor turns, but it feels more difficult to turn in some places than others.

The engine will turn over, but very slowly, as if there is something restraining it. When this happened, I definitely revved it higher than normal. My dad was in town and I wanted to give him a ride around town to show it off a little bit. I should have been in first gear, but stepped on it too much in second.

The engine cut off immediately after I heard the noise, and I depressed the clutch and put it into neutral and let it roll to a stop once I found an access road close by.

Gas tanks are full and I’ve been cranking and driving this thing at least every three or four days for two months now.

 

[matts460]

If the timing is off alot it can turn over very slow when cranking over with the starter. Gotta check timing. Pull #1 spark plug, roll it over by hand and pull valve cover get it all on top dead center and see were your at. Rotor will be pointing to #1 plug wire spot on cap too. If none of that makes sense we can step by step it... Also when turning by hand it will be hard to do in places as each piston comes up and makes pressure in cylinders when valves are closed.

 

[Broncobowsher]

Too much timing is an easy one to rule out. Leave the coil disconnected and hit the starter. Advance means nothing if there is no spark.