1972 Ford F-100



October, 20, 2012 AT 8:36 AM

Hello good evening. I was wondering if anyone could help me please, I recently finished rebuilding my first engine, im a student. I rebuilt a ford 351 new pistons, new rings, new main, cam and rod bearings. The engine was working great the seconds I had it on without water. As I was adding water, water started to leak from the temperature sensor on the intake, the water went directly towards the distributor hole which im sure alot of water got inside the engine and some water drained inside the hole of the timming cover where the oildipstick goes. I drained the oil when I saw that and changed the oil for new but now the engine is hard to crank, and when it turns on I can hear sometimes a hard knocking on the block, what should I do? Is it because the bearings got wet? Am I going to have to open the engine again Id apreciate so much if you could help me please thank you

2 Answers



October, 20, 2012 AT 8:52 AM

Water in the oil didn't cause damage that fast. Antifreeze is what will melt the soft outer layer of the bearings but that takes time too. More than likely the hard cranking is due to advanced ignition timing coupled with better sealing of the piston rings now that you've run it little.

Did you use plenty of assembly lube on the bearings when you put it together? Some people put them together dry. More wear takes place that way in the first few seconds than in the next 50,000 miles. Did you prime the oil pump before stuffing in the distributor? What about oil pressure? Monitor that with a mechanical pressure gauge. Also, did you keep the engine speed up for the first 15 - 20 minutes for proper break-in of the cam lobes? The higher speed insures sufficient oil splashes onto them. Once the lobes and lifters are seated, that's not so critical.

Before you remove the oil pan, take a look at the vibration damper to see if the bond between the hub and outer ring has let go. Check if the hub is cracked too. That will cause a banging noise. When the noise occurs, momentarily ground a spark plug wire, one cylinder at a time. If the noise stops, suspect that rod bearing. The crankshaft can cause a pretty noticeable knock too if the belts are too tight. They pull the snout up, then when the two front cylinders fire, the rods push the snout down and make the noise.

How long have you run the engine so far?



October, 20, 2012 AT 9:02 AM

Let me add that you can see how well it cranks with the ignition system disabled and the throttle blade wide open so it doesn't draw in fuel. (I'm assuming you're running a carburetor). If it cranks faster, the timing is advanced.

Ford has had more than their share of battery cable problems too. Measuring current flow isn't always accurate. A better method is to measure "voltage drops". Check out this page on how to do that:


You can start right at the starter to see if you need to check other places. You must find a minimum of 9.6 volts during cranking. If it's low, do the individual tests to find the poor connection. One common one is the strands of wire are corroded away and hidden under the insulation right next to where it bolts to the starter.

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