Hmmm, 1977 302 ford, just thought of something, I've been thru this several times, and once with a 302... A compression test or a vacuum gauge will either verify it or rule it out:

Timing chain has jumped. Very possible, especially if the cam sprocket is nylon. But I've seen double roller setups jump too, the chain will stretch to the point they start wearing the steel teeth down, letting the chain jump...

If the chain has jumped one-tooth, cylinder pressure will be WAY down, so the burn will be very weak. The engine can seem to run fine, but throttle response will be slower. And in a boat, trying to turn that prop with no power, getting to, or past 2500 rpm would be a trick.

If it's jumped, a compression check would reveal very low, but consistent cylinder pressures. A vacuum gauge connected directly to manifold vacuum should read 15 to 20" of vacuum at idle, if timing has jumped, vacuum will be down to the 7 to 11" range...

At least it's a cheap fix, at Auto Zone the last timing gear set I bought from them, including both sprockets and a new chain, was less than $15.

Anyway, compression check or a vacuum gauge check is in order...

I found my father's old vacuum gauge that he gave me many years ago...it also says "fuel pressure" on the gauge....this is back from the days of the old mechanical fuel pumps. This will come in handy now.

Worth a check...and the timing chain isn't that hard to replace...as getting to the front of the motor is easy.
I remember reading about nylon gears in Ford V-8's once...so this would make sense.

Well....

Dusted off the vacuum gauge....

10" at idle.

Looks like I am going to check the timing chain.

I have a garage, a set of tools and a Selloc manual...so it shouldn't be that big of a deal...the front of the engine is easy to access.

It's real easy, the only special tool you'll need is a puller for the harmonic balancer.

Be sure to buy a new oil seal for the timing cover when you pick up the new gasket--and new timing set if needed!

If it is the timing chain and the nylon is broken off some of the gears you will need to pull the oil pan and clean all the nylon pieces out of the pick-up screen,(ask me how I know).

Of course that may mean pulling the motor to be able to access the pan. At that point you have to weigh the cost of reduced oil flow against pulling the motor. Personally, if I were to pull the motor I would go ahead and rebuild it but boat motors are usually easier to pull so maybe not.

I can tell you that on the two motors I personally had this happen to the oil pressure was very low and the screens were completely plugged with nylon peices.

Oil pressure is normal...at least the gauge indicates that...
Should have the cover off soon too look at the timing chain.

If I have to pull the motor...I am going to have to go to Harbor Freight and buy one of those electric hoists and hook it the the rafters in the garage..only way I can think of doing it...

I concur with Prober, the problem with the nylon pieces is they'll float around in the oil. But you may not have to pull the engine to get the pieces out. You may have enough room to get a small wet-dry vac hose down into the pan from in front...

Well...

I do know the motor was rebuilt over 10 years ago...

I opened up the timing case and the sprockets are steel...the chain seemed tight, with a little slop in it...

I put the ballance bolt back int the crakshaft and rotated it to TDC... (lined two dots up on the timing sprockets)

Pulled the distributor cap and noticed that the rotor did not line with cylinder number one on the cap...

Grabbed the plastic rotor and was able to rotate it cylinder 1, but the distritor shaft did not move.

I grabbed the original rotor...it had very little slop and was closer, but not on cylinder 1 (think this is because I adjusted the timing last with the NEW rotor).

I think this may explain why the engine was running fine for several hours, then all of a sudden the problem started at 3,000 RPM...then went down to 2500 RPM.

If the rotor moves, it would throw off the timing, right?

Half tempted to go to Autozone, grab a gasket set, slap it back together with, install the old rotor and go run it...

What do you guys think?

If the gears are steel and the dots line up, a 'little slop' is fine, and your cam timing should be fine. I'd go ahead and button up the front.

As for the rotor, it could be the one is cracked, and is "floating". AND, regardless if it's broken or not, if it's not pointed at or near the correct tower on the cap, it's possible that your spark is jumping to one of the towers next to it, lighting off the wrong spark plug--if this is the case it could firing your cylinders either really late, or really early. This could be the case if your distributor or the gears that drive it are installed a tooth off one way or the other.

Determine which way your distributor turns. At TDC the rotor tip should point AT or slightly past the correct tower for the #1 plug. The reason for slightly past is because as ignition timing advances and fires earlier, the rotor tip position will 'work its way backward'. If you find the tip is "behind" the correct tower, then as timing advances the rotor tip will work its way closer to the 'previous' tower. If it gets close enough, then the spark could jump to the previous tower, firing the plug that should've already fired, very late timing...It will run but have hardly any power...

I'm still concerned with your 10" of idle vacuum. However, if your cam has a profile with a lot of overlap, then 10" isn't so bad. Still, it might indicate a gasket leak...



Hope that all makes sense!

Now that you have discovered the bad rotor and since you timed it with the bad rotor, I would time it with the old rotor and see where you are. At this point it can't hurt, all you are out is a timing cover gasket.

Well...

Timed it with the old rotor...12 degrees BTDC...

I adjusted it to 10 BTDC...she pulls 12" of vacuum...

Considering that Boise, ID is at about 3,000 ft elevation...this may not be that bad as the Seloc manual says that the engine vacuum should be between 15 and 20" at sea level...

Time to take her to Lucky Peak Resevoir, about 15 minutes away from my house...and test her out. I hope this works...keeping my finger crossed

Just got back from the resevoir...

Had the same problem....then checked the timing after about 1/2 hour on the water...it showed 10 degrees ATDC (I KNOW I had set it 10 degrees BTDC). So I set the timing back to 10 BTDC...and it ran a lot better. I don't know why it moved as the distributor bolt was locked down.

The timing does advance...at 2K RPM it is about 30 degrees BTDC.

It runs rough when I bring it down to idle now...but runs a lot better at top end...still can't get it over 2500 RPM as the throttle cable does not push the throttle all the way open on the new carb...

Going to throw the old carb back on and see how it runs.

I think it is time to pull the distributor and see if the shaft is broken. That would explain your wandering timing.