Piston damage found....

While you're at it, Angelo, change your rod bolts and nuts. You have the std 'football-head' bolts which are prone to fail at higher rpms. Boss bolts have a pentagonal head and while Boss nuts look identical to what you undoubtably have, they are a grade stronger.
Detonation with stock cast pistons bends the ring 'lands' that support the rings, locking them in the pistons and allowing blow-by to mess things up. On high mileage engines, carbon residue builts up around the rings and also restricts ring movement. If you're lucky, a light honing of the block rather than a bore job will clean up any scratches. Honing the bores up to 0.004" oversized will still allow you to run std 4.000" bore forged pistons, since the stronger forged pistons can use more clearance than cast pistons and still seal, due to their higher expansion rate when at operating temp. Tell your engine guy that the common erosion at the very top of the bores does NOT need to be honed out or cut away with a ridge-reamer, since its above the areas the rings touch. Leaving that area alone reduces the amount of bore metal needing to be removed; valuable if the block is already bored to 0.030-oversized. Cylinder wall thickness is marginal in almost all 351-C blocks so the less cut away, the better. The only negative to not removing the ridge at the top of the bore- aside from it not looking pretty- is a very small increase in total combustion chamber volume.
I did this on my present block- in 1991- and it still runs perfectly and makes good power to this day.

Angelo

Since your motor is apart, now is the time to address the problems and improve the durability

The 351C 4V has 2 weaknesses.

(1) There was a problem with the quality control of the nitriding process of the production 4V valves. Like many valves the 4V valves are a two piece design, the stems are welded to the valve heads. Over the last 4 decades many 351C owners have experienced the misfortune of having one of their 4V valves drop its head while the motor is running, resulting in devastating damage to the motor. The valve head breaks off where it is welded to the stem. It has happened to completely stock motors, mildly modified motors and extensively modified motors too. The damage can occur while the motor is idling in the driveway, cruising on the road or wicked fully open (WFO). There is no way to predict if or when it will happen. The fact that a motor has run for 4 decades using the original valves is no guarantee it wont drop a valve tomorrow. If your 351C 4V is still equipped with the original Ford valves, it is a ticking time bomb.

(2) The production connecting rod nuts were the weakest link in the 351C reciprocating assembly. The threads will pull out of the nut when the motor is run hard and the result is major carnage. An easy upgrade is to simply replace the nuts with parts from ARP, #300-8371. The connecting rod bolt can be re-used. If you replace the bolts the big-ends of the rods will have to be re-sized. Leaving the bolts in place and replacing only the nuts will avoid having to have the rods re-sized. The nuts truly are the problem

Yes, replace the pistons with a set of Forged full round skirt flat top pistons. Possible manufacturers include (A) Arias #1210020 (B) BRC Performance #31404 (C) Ross #80556. You'll need new rings as well. I'd have to see, feel and measure the cylinders before I could tell you if a simple honing would clean the cylinders up for the new rings, or if the block needs to be bored. New pistons means you MUST remove the ridge at the top of the cylinders. If any of the rings ride higher in the cylinder than they did with the old pistons, they will break when they hit the ridges.

Replace the crankshaft main journal bearings and rod journal bearing with Clevite 77 bearings, use the uppers from two sets of main journal bearings so that your main journal bearings are fully grooved, 360 degrees. Replace the camshaft timing set with a new full roller billet timing set from Roll Master. The crankshaft rear main seal is a rope seal, replace it with a neoprene seal, this requires pulling a small pin from the seal groove in the rear main bearing cap and filling the pin hole with a dab of sealant. The harmonic dampener is over 35 years old, the rubber bonding the outer ring to the inner hub cannot be trusted, please have that dampener rebuilt or replaced. I would like to suggest the dampener from a 1977 - 1981 351M or 400 truck motor as a replacement.

Have the reciprocating assembly dynamically balanced before reassembly.

If your motor still has a breaker point ignition now is the time to upgrade to a breakerless system.

You should pull the lifters & cam & inspect them for worn lifter faces and worn camshaft lobe noses. Each lifter MUST go back into the bore it cam out of. If you re-use the cam, I suggest you install it 4 degrees advanced. The cam timing in the '72-'74 Cobra Jet motors was retarded 4 degrees. Advancing it 4 degrees brings it back to 1971 specs. The Roll Master timing set should have a multi-index crank sprocket which will allow you to do this. The camshaft should be "degreed" during installation (to insure accurate valve timing).

Is there anyway I can talk you into a high pressure oil pump spring, restrictors for the camshaft bearings and push-rods with 0.040" restrictors in the tips? Ideally your hot oil pressure should be at least 70 psi at 2000 rpm and above, 50 to 69 psi hot oil pressure at 2000 rpm and above is acceptable only on a temporary basis, I don't recommend running the motor hard if that's all the pressure you have. Don't run the motor at all with hot oil pressure less than 50 psi. The restricted push rods will control the amount of oil flowing to the valve train with hydraulic lifters. If you upgrade the oil pump spring you must start using a high pressure oil filter too, because on cold starts the oil pressure will be about 130 psi.

The pic below shows the carnage created by a dropped valve head.

-G

I can speak from experience about the valve problem. My valve head dropped at 140 mph and the resulting damage was similar but the head was also destroyed.

New one piece valves are cheap insurance.

Mark

About those rod nuts.

Inspect the picture below.

The first thought by most is this failure occurred because rod bolt #1 snapped in two!

However, observe there is less thread protruding beyond the end of the nuts of the busted rod (1 & 2) compared to the nuts of the good rod (3 & 4).

The threads in one or both nuts gave way, the bolts pulled out of the nuts, the loose cap hammered or sheared the bolt in half and a moment later this motor came to a stop. There is no evidence of a spun bearing, so it is safe to assume this happened very quickly and the nuts were the source of the failure.

-G

Thanks for the valuable information.... And carnage pictures.

I think I found this issue before any real damage could occur, guess being a bit OCD does pay off every now and then. I only opened the engine because it was out of the car for the other R&M issues.

This engine is already .30 over by previous owner. The bores look fine with the crosshatch still looking fresh, just a very little shows where the piston damage shows, looks like a light hone will work there, it is in the machine shop now waiting for me to decide what to do to it. It is getting all new bearings, already have new cam/lifters, etc on the shelf. Just have to decide what my wallets pain level is for the bottom end. I think it is screaming at me louder than the wife at this point since I started the back end rebuild project. I did not even consider the rod nuts, ordering today with the oil pump and second set of bearings for the upper halfs. As for the top ridge on the cylinders, there is none that I can feel at all.

How can I tell the difference between one piece and 2 piece valves? Can I tell by the retainers, magnet? The heads have already been done and are waiting all wrapped up on the shelf to go on. Since I have to take the inner spring off anyway for cam break-in, I can break down the heads now and recheck to make sure I have the one piece valves....boy I hope so...there goes the screaming wallet again.

Again thanks for the information!

Angelo

quote:

How can I tell the difference between one piece and 2 piece valves? Can I tell by the retainers, magnet?

Any stock multi-groove-retainer Cleveland valve- intake or exhaust- will be a suspect two-piece type. And as I said, the far-east people have found ways to weld stainless valve-heads onto stainless shafts, so magnets are no indicator. Go with a single-retainer-groove valve that is a name brand and says in plain english: "one piece ss valve".
There are people around who can break an anvil with a leather hammer, so such valves are not an absolute guarantee, but for most, they work fine.

The 4V intake valve has the oval Ford logo cast into the head.

Angelo,
with such localized scuffing damage on the piston skirts, I would check also for bent or twisted connecting rods.