Page 129 - 2018 Racecar Engineering Engine Parts and Accessories Catalog

OEM REPLACEMENT BEARINGS

Oldsmobile V8
M77 Federal
Description P-Series Mogul
350-400-403-455
Main Bearings, 350/403 M77MS805P —
Main Bearings, 400/455 M77MS804P —
Rod Bearings, 350/403 M77CB684P —
Rod Bearings, 400/455 M77CB542P —
Cam Bearings, 350/403, 1978-80 M77SH1355S —
Cam Bearings, 400/455 And 350/403, 1968-76 M77SH1354S SEA1234M
Pontiac V8

M77 Federal
Description P-Series Mogul Durabond
326-350-389-400-421-428-455
Main Bearings, 326/350/389/400 M77MS483G SEA4040M —
Main Bearings, 421/428/455 M77MS667P SEA4221M —
Rod Bearings M77CB758P SEA1555CPA —
Cam Bearings M77SH292S SEA1220M DURP-4
TECH TIP

Leakdown Testing And Cylinder Sealing
Regardless whether it’s used as a method of preventative maintenance or for trouble shooting, leak testing is an effective means in determining the sealing
efficiency of the piston rings, valves and head gaskets. Contrary to a compression test, which measures how much pressure is generated inside a given cylinder
while cycling the starter, a leakdown test measures the amount of pressurized air that leaks out of a cylinder statically. Performed by engine builders and racers
for decades, leakdown testing can not only be used to provide insight of an engine’s condition, but it can also be used to help pinpoint a potential problem, deter-
mining whether the engine, for example, may have a bent valve, broken piston ring or blown head gasket.
Leakdown testers are relatively affordable, available from a variety of manufacturer’s including Longacre Racing (LON73010), Proform (PFM66839) and Total Seal
Piston Rings (TOT14MMLDT). A typical unit consists of a manifold that is fitted with inlet and outlet pressure gauges, air pressure regulator and a whip hose with
the necessary spark plug adapters. A balancer that is degreed in 90° increments or the installation of a timing tape will be required to perform the test. Available
from Mr. Gasket for a variety of popular engines, a timing tape may be applied to the outer ring of the balancer so that engine may be rotated by hand in precise,
90° increments.
To perform the test, the engine should first be started and warmed to normal operating temperature. Prior to beginning labor operations, a pair of mechanic’s
gloves, such as those available from Allstar Performance, would be recommended at this point to protect hands from hot engine components. After the engine
has been shut down, proceed by removing the #1 spark plug and rotating the engine by hand using a 1/2” drive breaker bar until the cylinder is at TDC. This may
be verified by removing the distributor cap and checking that the rotor is pointed at the #1 terminal.
Proceed by screwing the whip hose with the proper adapter into the spark plug hole and connecting it to the leakdown tester. Follow by connecting the leak-
down tester to a compressed air source capable of at least 100 PSI and adjusting the regulator so that the inlet gauge reads 100 PSI in order to simplify calcula-
tion of leakdown percentage. Finish by reading the outlet gauge to determine the amount of air that is leaking from the cylinder. With the inlet pressure set at
100 PSI and the outlet gauge reading 90 PSI, for example, cylinder leakage would be 10%.
With the unit still connected, listen for air leakage at the crankcase breathers, air intake and exhaust outlet. Air heard leaking from the breathers indicates
leakage going past the piston rings. Leaks at the air intake indicate an intake valve that is not seating properly, while air coming from the exhaust or header out-
let is evidence that an exhaust valve is leaking. Next, slowly remove the radiator cap as to relieve coolant pressure and examine the coolant for bubbles, which
would indicate the possibility of a head gasket leak. After the #1 cylinder has been checked and the results noted, replace the spark plug, remove the spark plug
from the next cylinder per the engine’s firing order, rotate the engine 90° and check the next cylinder. The goal should be that leakdown percentages are relatively
consistent, cylinder-to-cylinder. Proceed through the firing order, recording the results from each cylinder.
Once testing is completed, compare and review the results. Recording the results can come in handy when diagnosing a problem as neighboring cylinders with
high rates of leakage, for example, can signal the possibility of a head gasket that has blown between neighboring cylinders. Additionally, if a particular cylinder
has a significantly greater amount of leakage than the others, it may be wise to run the engine again for a bit and re-check the cylinder in question in order to
confirm the results. If a given cylinder offers the same results, it’s probably time to properly diagnose the problem before it gets worse.
Leakdown percentages should be consistent from cylinder-to-cylinder. When testing a variety of different engines, keep in mind that different piston ring pack-
ages will yield vastly different results. For example, an engine fitted with “Dykes” style rings that rely upon combustion forces for sealing may leak in excess of
20%, while traditional rings may result in roughly 8-12% and gapless rings may show as little as 1-3%, however, since the results are gained statically, it doesn’t
necessarily mean that one engine is sealed up better than another. Only true, “apples-to-apples” dyno testing can substantiate whether one ring package offers
improved sealing efficiency and more horsepower over another.
There are many reasons that may cause a cylinder to leak out of the norm, including a broken or damaged piston ring, bent or pitted valve, blown head gasket,
improperly adjusted valves or simply, top and second compression rings that have their end gaps lined up. Due to the simple fact that compression rings turn in
the ring lands during engine operation, they will occasionally line up and create a virtual leak path. When encountering a possible dilemma, it’s best to check the
basics before pulling the engine from the car, only to find out later that the problem was caused, for example, by valves that were out of adjustment.
Although viewed as archaic by some, leakdown testing remains as a viable, quick and cost effective method in determining an engine’s condition and combus-
tion sealing capability.
128 2018 ENGINE BUILDER CATALOG