The Top 5 Ford 351 Cleveland Engine Issues. The 351 Cleveland engine is a small-block 5.8L V8 developed by Ford from 1969 to 1974. The engine belongs to Ford’s “335” engine family, which consists of 90-degree overhead valve V8 engines. Despite the fact that the 335 engine family was produced until 1982, the 351C was only built until 1974. The 351C engine was designed to be a high-performance engine. By 1974, emissions concerns were growing, and the era of high-performance muscle vehicles was coming to an end, which reduced interest in the 351C and eventually led to its demise.
The 351C is known as the Cleveland because it was manufactured in Brook Park, Ohio, a Cleveland suburb. While being from distinct engine families, the 351 Cleveland and 351 Windsor share many commonalities. The 351 Cleveland shared many commonalities, such as the same 351 cubic inch displacement, bore spacing, and cylinder head bolt pattern, but it also had several changes.
The 351C features a two-inch longer block, making it a heavier engine. The water pump housing was integrated into the block, as opposed to being at the front of the block in the 351W. It also has a dry intake manifold rather than a wet one like the Windsor, as well as smaller spark plugs and an 8-bolt rocker cover rather than a 6-bolt one.
With production capacity constraints at the Windsor facility, Ford moved the 351 engines to the Cleveland plant. Nonetheless, Ford opted to make several enhancements and changes to the Cleveland plant’s engines, such as freer flowing heads.
351 Cleveland Engine Variations
There were various performance-oriented engines made out of the original 351 Cleveland engine. The majority of these engine types were designed for high-performance purposes, whereas the H-code engine was designed primarily for low-performance base model cars. While they all use the 351 Cleveland engine, the combustion chambers, compressions, tappets, and camshaft duration and lifts are all different.
The 351 M-code should not be confused with the 351M engine. Ford introduced the Ford 400 in 1969, a pushrod V8 based on the 351 Cleveland with a 4.0in bore and stroke and 402 cubic inches of displacement, making it a 6.6L engine. In 1975, Ford de-stroked this 400 engine while reducing the crankshaft stroke to create a 5.8L, 351 cubic inch engine. This engine, known as the 351M, is distinct from the 351C “M-code” engine.
Issues with the Ford 351 Cleveland Engine
Typical Ford 351 Cleveland issues include:
- Head Cracks
- Valve Guides that have become worn
- Weakness in the block and thin cylinder walls
- Overheating and Thermostat Failure
- Failure of a bearing due to a lack of oil
Throughout this essay, we will look in depth at the 351 Cleveland engine difficulties listed above. It is, however, necessary to emphasize that this is a 50-year-old engine. Given their age, these engines will almost definitely require some further TLC. Well, let’s get started with the 351 Cleveland difficulties, followed by opinions on overall dependability.
1. Cleveland Broken Head Issues
The cylinder heads were one of the most noticeable differences between the 351C and the 351W. The cylinder head came in two varieties. Ports and valves on 351Cs with two-barrel carburetors were larger. The ports and canted valves on 351Cs with four-barrel carburetors were significantly larger. These models moved much more air than the 351W heads. This is why, for performance applications, many enthusiasts combine the 351W block with the 351C head, resulting in the 351 Clevor.
Despite their high performance, the 351C heads were prone to shattering. Yet, their actual problem is overheating. The most prevalent cause of broken heads in the 351C engine is overheating. While thermostat failure is a typical source of overheating, other common causes include faulty radiators and radiator caps, faulty water pumps, and coolant leaks.
Cracks in 351 Cleveland cylinder heads are most common across the exhaust seat and in the lifter valley. While cracks are more common in bored engines producing considerable levels of power, they are still a regular problem in stock engines.
Metal expands when heated and compresses when cooled. There is a certain temperature range that the heads can sustain. When the heat range is surpassed, the metal in the heads creates small cracks, which worsen due to internal engine pressure and more heat, resulting in major performance concerns.
Signs of 351C Cracked Head
Among the symptoms of 351 Cleveland fractured head problems are:
- Leaks in the cooling system
- Overheating of the engine
- Misfires in the cylinders
- Inadequate acceleration and performance
- Idling in a rough manner
Unfortunately, the only way to replace a cracked head is to replace the heads. Nowadays, most heads are constructed of aluminum, which has a higher heat tolerance. Owners typically upgrade to performance aluminum heads like the Edelbrock RPM Performance Heads.
2. Worn Valve Guides 351C
Each valve has its own valve guide within the cylinder head. Valve guides work in tandem with valve springs to ensure that the valve makes good contact with the valve seat. The guides are metal cylindrical bits pressed into the cylinder head. Within the valve guide, the valves then travel up and down. Aside from providing appropriate seat contact, the guides help keep gases out of the crankcase and oil out of the combustion chamber during intake strokes.
Because the valve stem is continuously in contact with the valve guides they are prone to wearing down. Oil starvation is a typical problem with 351 Clevelands, causing the valve guides to receive insufficient oil and so wear out faster than they should. If the guides are sufficiently worn, the valves might get off-track and close at an angle against the seat, finally resulting in broken valves.
While worn valve guides can be machined and fixed, it takes considerable skill to do so. Machinists typically utilize the reaming procedure to expand the valve guide bore and add thicker valve guides. When compared to purchasing completely new heads, reaming can be a less expensive alternative to repair worn out valve guides.
Signs of a Worn Valve Guide
Among the symptoms of 351 Cleveland valve guide difficulties are:
Exhaust fumes produce smoke (caused by oil leaking into combustion chamber)
- Excessive use of oil
- Misfires in the cylinders
- Inadequate performance
- Inadequate acceleration
The most obvious indication is smoke emanating from the exhaust. This is especially common when the engine is cold. While the engine is turned off, oil will leak into the combustion chamber and be consumed shortly after it is started. The most of the smoke will go as the engine heats up. The second best indicator is excessive oil usage along with exhaust smoke.
3) Cylinder Walls That Are Too Thin
The 351 Clevor is a name given by enthusiasts when a 351W block is combined with 351C heads. Because 351C blocks are weaker and have less power potential, 351W blocks are favored.
Despite its larger and heavier block, the 351C had exceptionally thin cylinder walls. The performance potential is limited due to the thinness of the walls. Overboring or attempting to push too much power on a standard block can cause cylinder walls to break.
With stock 351C engines, cracked blocks are not a concern. But, given the number of individuals who modify these engines, I wanted to highlight the block’s power limitations.
Cleveland Maximum Overbore 351
Ford Overbore Recommendation: 0.030′′ maximum overbore
Maximum overbore recommended by the performance community is 0.040′′.
Maximum Overbore: 0.060″ overbore (not recommended)
Due to the thin cylinder walls, Ford has publicly suggested a maximum overbore of 0.030′′. The aftermarket community generally recommends a 0.040′′ overbore, while bores up to 0.060′′ have been reported. I want to be clear that we do not recommend 0.060′′ and would rather stick to the commonly accepted maximum of 0.040′′.
You should have the cylinder sonic tested if you are concerned about over-boring or block strength. The depth of the cylinder walls is measured via sonic testing. With a 351 Cleveland, the minimum reliable cylinder wall thickness is 0.12′′. This level is regarded as trustworthy by the performance world, however anything thinner than that is likely to fail in high horsepower applications.
4) Failed 351C Thermostat & Overheating
The cooling system thermostat is in charge of monitoring engine temperatures and managing coolant flow. The thermostat connects the engine to the radiator. When the engine is cold, the thermostat is closed, recirculating coolant through the engine and preventing it from entering the radiator, allowing the engine to heat up faster. When the engine warms up, the thermostat opens, allowing coolant to flow into the radiator and cool before returning to the engine.
The thermostat on the 351C is one-of-a-kind. Rather than passing coolant through the intake manifold, the 351C directs coolant from the head to the block. After that, coolant flows into the chamber beneath the thermostat. A restrictor plate, also known as a “bypass orifice plate,” is positioned beneath the 351C thermostat. Coolant runs through this restrictor plate and into the water pump for recirculation when the thermostat is closed.
When the engine warms up, the restrictor plate closes, allowing the majority of the coolant to flow into the radiator to cool before being recirculated. If the restrictor bypass plate is missing, water will continue to flow directly to the water pump rather than the radiator, resulting in chronic overheating.
The thermostat is special in that it is in charge of closing the bypass valve when the thermostat is in the open position. If you install a normal thermostat on these engines, the bypass valve will not be blocked, leading to overheating. Furthermore, even with the right thermostat installed, removing the restrictor plate will cause your engine to overheat.
Signs of Cleveland Thermostat Failure 351
The following are some indicators of thermostat failure on the Ford 351 Cleveland:
- Overheating of the engine
- Leaks of coolant near the thermostat housing
- Sudden temperature rises (thermostat stuck closed)
- Alternatives for 351C Thermostat Replacement
The most crucial step is to replace the thermostat with the correct 351C thermostat. A regular Ford thermostat will not suffice. When changing the thermostat, do not remove the restrictor plate. Several individuals remove the restrictor plate because it appears to obstruct coolant flow. It is supposed to, and removing it will result in overheating.
5) 351 Cleveland Main Bearing Failure & Oil Starvation
With the 351C engine, Ford engineers prioritized cost savings. The oiling system was one area where they determined they could save money. While the 351W and Windsor families of engines had three major oil galleries, the 351C only had two. The design of the oiling system directed oil first to the cam bearings instead of the main bearings. While this would not normally be an issue with low-performance H-code variants, high-performance 351C models were designed for power and high RPMs. These high-performance applications experienced the most oil hunger, resulting in insufficient oil flow to the mains and possible bearing failure.
To make matters worse, the lifter bores had too much clearance, allowing oil to flow from the bores. This exacerbated the problem of oil scarcity by reducing oil flow to the mains.
While oil starvation in the 351C normally occurs at high RPMs, it is a constraint worth noting for those intending to run high power applications. Nevertheless, oiling system adjustments can let the 351C to run consistently at high RPMs. For anyone looking to go more into engine lubrication, here is a wonderful article on 351C engine oiling.
Signs of Main Bearing Failure
Keep an eye out for the following symptoms, which may signal a main bearing failure:
Engine / rod knock noises
Oil pressure is low.
Oiled metal shavings
Cleveland Reliability 351
Heat and power are the 351 Cleveland’s Achilles’ heels. While a standard 351C is a solid engine, it becomes more problematic when more power is added. Without adjustments, the narrow cylinder walls generate possible dependability difficulties and block cracks with overboring, and the oiling system is insufficient. Also, these vehicles’ cooling systems are insufficient for large power and will need to be modified for performance purposes. Having said that, with the right modifications, these engines may be quite reliable even in high horsepower applications.
Stock made of bone the 351 Cleveland is a strong engine that should be free of fractured heads, blocks, main bearings, internals, and so on.
Overall, the 351C is a dependable engine, but it will require considerable modifications and additional funds to be dependable in high horsepower applications.