Modification of the Cleveland motor's lubrication system tends to be a source of confusion for owners. Since there are several members in various stages of planning for a motor rebuild, I thought providing some clear guidelines might be helpful at this time. So as I promised last week, here's my thoughts on the 351C lubrication system.
The 351C has a problem with under-lubricated rod bearings. This leads to bearing damage. Bearing damage leads to the hot oil pressure running below spec. Another "related" problem is excess oil supplied to the valve train.
Most "formulas" for modifying the 351C lubrication system involve changes which (1) boost hot oil pressure, (2) route more oil to the rod bearings, and (3) limit oil flowing to the valve train.
To maximize the lubrication of the rod bearings low viscosity motor oil rated 10W30, 10W40, or 15W40 should be used. But, (1) to cope with the factory machine tolerances, (2) to promote a persistent oil wedge at the rod bearings, and (3) to avoid any problems arising from the use of fully grooved main bearings, oil viscosity lower than 10W30 is not recommended.
An oil pump cannot provide an uninterrupted supply of oil to the engine unless its suction is constantly submerged in a bath of non-aerated oil. An inadequately designed oil pan can exacerbate the engine's lubrication problems. A high-capacity oil pan with baffles, hinged doors, a windage tray, and a scraper enables the lubrication system to better cope with the high G-Force capabilities (braking, cornering, acceleration) of the Pantera's chassis. Such an oil pan should have been standard equipment for the Pantera.
The manner in which the main oil passages intersect the tappet bores creates large ports in the sides of the tappet bores. Few people comprehend just how severely these large ports impact the Cleveland's lubrication system. They disrupt the flow of oil to the crankshaft, they create extreme leakage at the tappets, they create tappet incompatibility issues, and they give rise to excessive valve train lubrication.
"Thin-wall" bushings can be installed in the tappet bores to close-off the large ports and replace them with small orifices. The bushings must be "thin-wall" otherwise they will protrude too far into the oil passages and restrict oil flow.
Tappet bore bushings became “the fix” for the 351C lubrication system in 1973, that was the year Dyno Don Nicholson and other Pro Stock drag racers began installing tappet bore bushings in their 351C drag racing engines. The bushings quickly became standard in NASCAR engines too.
Another solution, a main bearing lubrication manifold sold by Hank the Crank, received some "mention" in Hot Rod magazine and Pat Ganahl's book titled Ford Performance. It was introduced because the manifold's designer believed the tappet bore bushings would restrict the flow of oil through the main oil passages. However, the effectiveness of the manifold was inconsistent. The designer, believing the inconsistent results stemmed from improper installation, redesigned the manifold several times. It eventually fell out of favor with most of the teams which had used it. Thus the tappet bore bushings became the racer's de rigueur solution for the Cleveland lubrication system.
Ford introduced a kit for installing tappet bore bushings about 1974; a year or more after the February 6, 1973 Corporate Ford decree which ended the corporation’s involvement in racing and the sale of performance parts. Ford stopped publishing the OHO Parts Newsletter in the spring of 1973, therefore the existence of Ford’s bushing kit was never publicized. It was sold "under the table" via a semi-secret racing parts network.
Nobody can deny that the rod bearings come out of the Cleveland looking very bad. This includes the bearings of lightly used street engines. Installing tappet bore bushings resolves the root cause of the problems. They (1) boost hot oil pressure, (2) route more oil to the rod bearings, and (3) limit oil flowing to the valve train. ALL Cleveland engines in any application can use them.
Extensive wear and damage to the rod bearings of a street engine does not usually result in engine failure, just low oil pressure. As a consequence some folks are oblivious to the extent of bearing wear in their car's engine. Tappet bore bushings are considered overkill for street engines, even though all the other "tricks" people employ don't improve rod bearing wear very much. The hesitation to use tappet bore bushings for street applications was (past tense) due to the expense of installing them … or the lack of familiarity with installing them (fear).
There's a fellow named Denny Wydendorf, a machinist and Super Stock drag racer, who began selling a well thought out and comprehensive bushing installation kit a few years ago; for a reasonable price. Denny's do-it-yourself installation kit makes tappet bore bushings easy to install at home, and affordable for even the most modest of engine projects. There's no longer any reason to not install bushings in the tappet bores.
The benefits of installing 16 tappet bore bushings include:
• Hot oil pressure at 2000 rpm shall be within spec (50 to 70 psi).
• Minimizes the amount of oil loss due to leakage at all 16 tappet bores.
• Maximizes the amount of oil supplied to the main bearings.
• Prioritizes the lubrication of the main bearings.
• Isolates the oil passages from tappet motion (cavitation).
• Prevents the random collapse of left-hand hydraulic tappets.
• Resolves tappet compatibility issues on both sides of the engine.
• Prevents an excessive amount of oil flowing to any part of the valve train.
• Equalizes the amount of oil metered to all 16 rocker arm/valve/valve spring assemblies.
New bearings should be heavy duty bearings (Clevite tri-metal or similar). Heavy duty rod bearings are not damaged as badly by under-lubrication as standard babbitt style bearings are. They will also stand-up better to less than perfect journal surfaces.
The main bearings should be fully grooved. Fully grooved main bearings were once standard equipment in heavy duty bearing sets; they more than double the amount of oil supplied to the connecting rod bearings. The 351C has NEVER suffered any problems stemming from the use of fully grooved main bearings, only benefits. Considering the Cleveland's problems with under-lubrication of the rod bearings, fully grooved main bearings should be considered essential.
Here's the summary of my 351C lubrication system recommendations:
• Utilize 10W30, 10W40, or 15W40 synthetic motor oil
• Install a wet sump racing oil pan
• Install 16 tappet bore bushings (with 0.062-inch orifices)
• Chamfer the oil holes at the crankshaft journals.
• Install heavy-duty, fully grooved main bearings; Clevite # MS1010HG or # MS1010VG. If fully grooved bearings (G suffix) aren’t available, improvise by using the upper shells from two sets of standard Clevite # MS1010 main bearings.
• Install heavy-duty rod bearings; Clevite # CB927.
• Set the bearing clearances and rod side clearances to promote lubrication:
a. Main bearing clearance = 0.0025 inch to 0.0030 inch
b. Connecting rod bearing clearance = 0.0025 inch to 0.0030 inch
c. Connecting rod side clearance = 0.018 inch to 0.022 inch
Those clearance specs are from the 1972 OHO Parts Manual. They are endurance racing specs recommended in Ford literature by Ford engineers and they have proven over the last 3 decades to work just as well for street engines.
Moroso sells a restrictor kit for the Cleveland lubrication system. It contains 4 small restrictors for cam bearings 2 - 5, and a larger restrictor for the left hand oil passage. The larger restrictor has led to the random collapse of hydraulic tappets on the left-hand side of the engine. DO NOT install the larger restrictor in the oil passage supplying the left-hand bank of tappets. It's only needed when merely 8 tappet bore bushings are installed (in the right hand tappet bores), and it is only viable with solid tappets. It's not needed at all when bushings are installed in all 16 tappet bores.
For racing applications the 4 small Moroso restrictors for cam bearings 2 - 5 are beneficial.
The # 1 cam bearing lubrication is supplied by a vertical oil passage which branches directly off the main oil passage where the main passage is routed across the front of the block. In the 1970s “authorities” claimed the # 1 cam bearing oil passage did not need restricting, yet experience indicates the # 1 cam bearing oil passage impacts the lubrication system more than people realize; it was probably the first oil passage that should have been restricted. To restrict this oil passage a 5th small restrictor (requiring a second Moroso restrictor kit) must be installed between the main oil passage and the cam bearing bore. If it’s not done properly however, if it’s not installed deep enough, oil to the # 1 main bearing will be restricted instead.
To install the restrictor properly enlarge the first 1¾ inches of the oil passage between the # 1 main bearing saddle and the # 1 cam bearing bore with a 5/16 inch drill; the oil passage is drilled out until the main oil passage routed across the front of the block is “crossed”. This creates clearance for a 5/16 inch tap, making it possible to thread the oil passage deeper within the block, above the main oil passage. Thread the smaller diameter portion of the oil passage, above the portion of the passage that has been enlarged, with a 5/16" tap. This requires a long tap with a reduced shank to do this. After a thorough cleaning screw the 5th small restrictor into the threaded passage.
A remote oil cooler will be needed any time high loads (high speeds) and continuous high rpm are encountered. If the engine needs an oil cooler then the gearbox oil will also need to be circulated through a remote cooler via an electric oil pump. The engine may also need an Accusump or a dry sump lubrication system.
Engine Durability Suggestions
Going beyond the topic of lubrication, racing (continuous high rpm) also calls for an internally balanced crankshaft, longer chromoly rods, forged round skirt pistons, and spin balancing the crank (aka dynamic balancing). It is also advisable to have the cylinders "indexed" to the crankshaft axis during the boring process if the chromoly rods shall employ floating pins … which they usually do. Limit the revs at 7000 to 7200 rpm.
Here's the details for all of that:
Indexing the boring machine to the crankshaft's axis during the boring process insures the cylinders are perpendicular to the axis of the crankshaft. There are three benefits to this: (1) A piston trying to stroke up and down in a cylinder that is canted to the front or rear must operate in a “wedged” manner that causes floating wrist pins to hammer out their locks. (2) A piston trying to stroke up and down in a cylinder that is canted to the front or rear, operating in a “wedged” manner, also puts an abnormal load on the cylinder wall. A piston will operate in a cocked manner if a cylinder is canted to the left or right which also puts an abnormal load on the cylinder wall. This abnormal cylinder wall loading contributes to cylinder wall cracking, therefore indexing the boring machine to the crankshaft's axis helps to alleviate cracking of the production block's thin cylinder walls. (3) It also reduces frictional losses which allows more horsepower to reach the back tires!
An internally balanced crankshaft shall require a neutral balanced (no counter weights) crankshaft damper and flywheel. BHJ Dynamics damper # FO-IB351C-7 has a steel hub and steel ring, it is SFI approved, it is Fully Bonded, it weighs 9 pounds, and it is neutral balanced. ATI damper # 918920 is another choice for a neutral balanced steel crankshaft damper. Yella Terra offers a light weight steel flywheel drilled for long-style clutches, # YT9902N, it weighs 26.4 pounds, and it is also neutral balanced.
The chromoly long rods can be 351W rods (5.956 inches length) for a stock crank or 6 inch Chevy rods for an aftermarket crank. They should have doweled big ends and 7/16 inch chromoly fasteners.
Ross Racing Pistons sells forged round skirt pistons for the 351C. Ross pistons can be custom ordered to suit your engine's compression height, wrist pin diameter, and bore diameter. They are also available with an optional anti-friction coating for the piston skirts.
# 80556 is a forged flat top piston (3 cc dome volume) designed for a 3.500 inches stroke crankshaft and 5.78 inch 351C rods (0.912 inch wrist pin) which comes standard with a 1.668 inches compression height. The piston weighs 537 grams (the stock piston weighs 616 grams). It is machined for 4.030 inch bores off the shelf.
# 80566 is a forged flat top piston (3 cc dome volume) designed for a 3.500 inches stroke crankshaft and 6 inch Chevy rods (0.927 inch wrist pin) which comes standard with a 1.446 inches compression height. The piston weighs 497 grams (the stock piston weighs 616 grams). It is also machined for 4.030 inch bores off the shelf.
6.00 inch long Chevy connecting rods were once considered de rigueur when preparing a 351C for racing. The rod length to stroke length ratio with Chevy rods was 1.71:1 and the wrist pin remained 0.087 inch above the lower edge of the bore at BDC. To use 6 inch Chevy rods with the stock crank required machining the crankshaft’s rod journals for wider connecting rod big ends (0.940 inch) and smaller diameter (2.0995 inches) journals (CB826 bearings). It was (and still is) standard for aftermarket 351C cranks to be machined for Chevy rods. Custom Cleveland pistons, like the Ross # 80566 piston, are required which are machined for larger 0.927 inch Chevy wrist pins and lowered 1.43 inches compression height. Add 0.020 inch to the compression height if the block shall be “zero decked”.
All this crank journal machining can be avoided by using aftermarket 351W rods with the stock crank. The 351W rod at 5.956 inches length would have a rod length to stroke length ratio of 1.70:1 and the wrist pin would remain 0.050 inch above the lower edge of the bore at BDC. 351W rods have the same big-end width (0.831 inch) and wrist pin diameter (0.9122 inch) as 351C rods. The 351W rod uses a thicker rod bearing (Clevite # CB831) but the bearing fits a rod journal of the same diameter and width as the 351C. This custom application shall require custom Cleveland pistons with 1.474 inches compression height. If the block shall be “zero decked” add 0.020 inch to the compression height of the pistons.