My son's new 1971 F100 has a 302. I believe everything is stock. The odometer says 103k on it, but not sure if that's accurate or not. The truck likely sat for at least the last 2 years w/o being run.

We tested compression once and got all low, but even(ish) numbers across the board -- but we did it wrong and didn't warm up the engine first, or test with WOT. We had a battery charger on the battery and all spark plugs removed. All cylinders were about 80psi. It took about 5-7 compression strokes to get the PSI this high. It didn't jump up to 80 right away.

The next test, we let it idle for about 5 minutes first, then retested with WOT this time. The numbers weren't much better. We had readings from 90-100 PSI on all cylinders. It still took about 5-7 compression strokes to get the PSI this high. It didn't jump to 90-100 right away.

We didn't try putting any oil in the cylinders and re-test since they are close to the same PSI. My son already returned the 'rented' compression tester from Advance Auto. It was a screw-in type tester.

It runs with a stumble, but not a consistently timed misfire from a single cylinder. But we don't know of the condition of the fuel or the carburetor cleanliness or adjustment. We haven't replaced points/cap/rotor or spark plugs yet. He will be putting a Rock Auto order in soon so we can replace those ignition parts after that and see if there's an improvement. It does need a lot of work.

Are there any other tests for the engine? Or, did we perform them wrong?

 

It may have receded exhaust valve seats. They didn't do hardened seats until 72, and unleaded gas will cause damage. One way to check is to pull a valve cover, rotate the engine around until an exhaust valve is closed, and see if you can spin the pushrod. If it's tight, then the valve is hanging very slightly open.

 

Would this simply take a valve clearance adjustment to correct? Or, something more major done with the exhaust valve seats (replacement)?

 

I like it up to full operating temp for doing "wellness" testing like compression. I actually prefer leak down testing to see where it's leaking. After the ignition tune up, might try running a tank of gas through it with a cleaner like sea foam (after it's fully inspected for safe driving) and see if stumbling improves. Sea foam in the gas would held clean goop from the carb...definitely helps neglected lawn mowers.

Besides older valve seats needing leaded gasoline (or lead substitute), flat tappet motors need high zinc oil to better lubricate the cam.

Vacuum gauge while the motor is idling/running can also give clues to health of the motor. Should be 20ish and steady at idle for a stock cam. You can google how to use/interpret vacuum gauge results. You'll want a vac gauge to fine tune the carb's idle anyway.

 

We ordered parts last night. They'll come next week. I'll check the exhaust pushrods for spinability after we get the parts below installed. Great idea on checking vacuum. I always forget about checking vacuum.
We plan on draining all the gas out of the tank and starting over with fresh gas. The oil and filter have already been changed.

Parts ordered:
dist. cap, points, plugs, rotor, condenser, wires, coil
fuel filter
brake master cylinder, all 4 brake hoses
thermostat and gasket, radiator cap
oil pan gaskets
valve cover gaskets
shocks
Something else I'm forgetting.

Then, my son ordered some 'upgrades' - some of which may actually help it run better (carburetor)...and some frivolous parts....
Holley 600 and gasket
Edelbrock intake manifold and gaskets
valve covers and gaskets
other items I'm not sure of

The goal is to get it running well and dependable, then drive it to see what it needs for parts in that area.

 

It would be a good time to check the backlash in the timing chain. Since you have a pan gasket coming it would be a good time to replace the timing chain set. Performance upgrades are not any good with a sloppy timing chain.
An off idle slight miss can be caused by a worn out distributor.

 

Looks like a good start. Even if you later on find the engine needs work, all the stuff you're getting can be re-used (except the gaskets).

Nice thing about 302's is that there is tons and tons of aftermarket support.

 

In the end with that low of compression, I'd wait to install the intake manifold as you'll just have to pull the heads an get the them worked over an exh. seats installed later.

Just face the facts that no additives will bring back the compression enough to make it run much better. Sorry to say since all cylinders our all so close in having the same psi numbers.

Note sea foam will cause the engine to put out a lot of exh. smoke that may get you a fix it ticket if your out driving it around town. An counting the people who live close to you as some may call the fire dept. thinking your house is on fire if they don't see the truck exh. smoking. Just sayin!

Doing the intake swap now will only mean doing it all over when having to do the heads later. Doing it once saves time & money in the long run with out disappointments of repeated work.

Orich

 

Thanks for the suggestions. I'll check them all.

I was thinking that either we need to replace the carb or rebuild the stock carb at a minimum. My track record rebuilding carburetors is not good - which is why I was OK with him getting a new one... I'll have to contemplate on that some more.

Regarding smoke - my son had an RX-7 a couple years ago. It had a bad rotor. If it's the apex seal that sometimes gets stuck, you can sometimes free it up by running the engine with ATF or water ingested. We did that and filled the entire neighborhood with white smoke. It was crazy.

 

I should have been more clear on using sea foam. No need to run it directly through the carb and make smoke. Just dump a can into the fresh fuel and drive it until nearly empty.

 

Welcome to FTE and the Bumpside Kingdom.
Congrats on the father/Son project. Good Job. 2X on the seafoam. But I think you need to get all the old gas out of it before anything else. Siphon it out. Not that new gas would be a wonder drug but at least it will burn correctly. And it has been known that old gas can freeze intake valves open. And when Mr. piston meets Mr. valve it ain't pretty. You see, when the intake valve is open and the piston is drawing air/fuel in the cylinder, part of that valve's valve stem is exposed. The old gas gets on the stem. Then when the valve closes that old gas goes up in the valve guide. Old gas does not lubricate like new gas does. If enough old gas builds up in the valve guide this can cause the valve to hang open. The pushrod and rocker arm is forcing the valve open but only the valve spring closes it.

 

80 PSI is real low, but I don't know what a serviceable set of rings/engine would read when a compression test is done incorrectly, as you noted the throttle needs to be blocked open to perform a good test. Plus it's been sitting a good while. Rings may be sludged up a little too. I like Marvels in both the fuel and oil according to directions to free stuck or sticky rings and lifters &c from gum and varnish. See what the compression bumps up to after running it in for a while and a few highway test flights. Then run a cylinder compression test "by the book". Also check manifold vacuum with a mechanic's vacuum gauge at factory idle RPM. Make sure ignition timing is set correctly. A steady 18" to 20" on the gauge and clean plugs means it will run OK I'd expect.

 

We were putting parts in that we ordered from Rock Auto. It appears we may have a different engine than the 302 that the VIN says it came with.

Is this a 351? Is there some way to tell?

The Distributor cap was way different. It doesn't have points either. The son went to Napa, who gave him the same distributor for a 302 (same as the one he got from Rock Auto). They found the correct cap at Napa, and the guy said it fit 400, 360 (or was it 390) and others.

The spark plugs weren't the same. It had the smaller socket type plugs in the engine. The plugs we got from Rock Auto are the larger size socket plugs.

We were also trying to check the slack in the timing chain with the 'rotate the engine and watch the timing marks as the rotor moves in each direction' method. I can't find any timing marks on this engine.

 

I measured the top of the intake manifold (not the deck, however you measure that) - on the engine. It's 10.5" from head to head on the top side.

The top side of the intake he bought from Summit is only 9". So, I'm suspecting that his truck may have had a 351 swapped into it. Or, could it even be something else? It has a 2-barrel carb.

The distributor has an electronic/magnetic/whatever type points setup instead of real points that you have to gap.

The engine is really dirty/greasy and I don't see any numbers on it, but don't really know where to look either.

 

The dizzy is the Duraspark ll setup that's what the little square metal box is in the left inner fender wall where a aux battery would be mounted.

Orich