Oldsmobile 455 Engine Rebuild

The “rebuilt” engine purchased for project Dangerboat ultimately would fail within its first year. This page details the rebuild process for the engine, hopefully the right way this time. The engine only had 600 installed miles in the car. This pushed me to consider an LS swap, but to keep the feel of an authentic classic, an Olds 455 engine rebuild instead of an LS was the way to go, but with some upgrades.

Last year a full frame-off restoration of the car was completed, referenced here: Cutlass Restoration Timelapse Video, which is when the rebuilt engine was purchased and installed.

Table of Contents

Summary of Issues

Scope of the Rebuild and Parts List

Rebuild Procedures and Specs

Rebuild Notes

Rebuild Pictures

Timelapse Video

Summary of Issues

Investigating the various problems with the engine are described HERE (Diagnosing an Engine Tick) and includes photos of disassembly and inspection.

Summary:

• • • Excessive metal in the oil even after 600 miles and 3 oil changes.
    • Bearing surface scoring, likely due to metal contamination in the oil or dirty assembly.
    • Brown sludge in coolant passages and lower block. Likely rust from 20 years of sitting with full jackets. This was not communicated at time of sale.
    • While the engine was purchased in 2017 as a newly “rebuilt” engine, the main bearings were dated from 1997.
    • Bent pushrod on cylinder number 3. Possibly others.
    • Broken cam bearing
    • Broken flexplate tooth
    • Oil in combustion chambers.
    • 1/16″ piston rings, while the pistons called for 3/32″ top and second compression rings. Oil rings were correct. This would have caused excessive side clearance on the rings and the issue above.
    • More than expected carbon buildup on pistons after only 600 miles.
    • 0.007″ piston to wall clearance. The piston’s and Oldsmobile’s spec is 0.003. They were double the spec!
    • Piston to deck clearance of 0.015. This isn’t necessarily bad, but stock is 0.025.

Scope of the Rebuild and Parts List

The primary purpose of this rebuild was to correct issues, and achieve reliability and longevity. Where possible, improvements were made, but this was not the primary motivation.

The previous builder had already installed the following upgrades, which were kept:

• • • Oldsmobile “C” heads
    • 1969 block with forged nodular iron crankshaft
    • Decked block 0.015″ (higher compression and better quench)
    • Flattop Mondello (Eagle) 0.060″ over pistons with 14.5 cc valve reliefs
    • Mondello (Probably Harland Sharp) aluminum cnc machined roller tip rocker arms, 1.6 ratio.
    • Aluminum Edelbrock performer RPM intake manifold.
    • Mondello 7 qt oil pan.
    • Upgraded and oversized 2.072″/1.625″ stainless valves.
    • MSD Billet Ready to Run distributor
    • Mondello oil restrictors

The following upgrades were added, as described below:

• • • Plugged exhaust gas crossover with molten/cast aluminum using a home-made charcoal forge.
    • Mildly polished intake and exhaust runners in the cylinder head.
    • Mildly polished combustion chambers and Shaping.
    • Internally balanced rotating assembly, allowing neutral balance flexplate and harmonic balancer replacements.
    • Hydraulic roller camshaft

The following parts were replaced or repaired.

• • • All bearings (mains, rods)
    • New piston rings (moly electroplated, nodular iron top compression ring)
    • New solid one-piece hardened pushrods
    • All new gaskets and seals everywhere
    • Valves lapped
    • SFI rated Flexplate replaced (neutral balance)
    • Harmonic balancer replaced (neutral balance)
    • Powermax Starter solenoid rebuilt
    • Block Machine Work:
    • Cylinders sleeved to be within factory spec piston to wall clearance (0.003″)
    • Block decked the minimum necessary to be flat after sleeving.
    • Check line bore of mains and cam
    • Heads planed on head surface, intake surface and exhaust surface 0.001″

Parts List

CLE-CB542P20 ROD BEARING
CLE-MS804P20 MAIN BEARING SET
EDL-7284 OLDS INTAKE GASKETS
FEL-8171PT1 HEAD GASKET
HOK-10846HKR GASKET OLDS
LIL-21100 LARGE VALVE LAPPER
MLE-4185MS PERFORMANCE RINGS
PTX-80037 VALVE GRIND COMPOUND
PTX-80697 101MA COPPER GASKET SPRAY
SLP-SPG1 PLASTIGAGE
SME-90A4120 ADJ. RING COMPRESS 4.120-4.220
SUM-941234 RTV SILICONE BLACK 8 OZ
SUM-G1418 CARB GASKET HOLLEY 4BBL OPEN
HRS-91464 ROLLER LIFTER SET
LUN-302 BREAK-IN OIL SINGLE QUART
MAH-JV618 REAR MAIN SEAL SET
SLP-SPG1 PLASTIGAGE
WMR-W89220 CAM BEARING INSTALL TOOL
TFS-21408850 8/850 PUSHRODS
Milodon 17000 Milodon Magnetic Drain Plug
901-CR0190-60 4.185 5/64 5/64 3/16 8CYL
901-CR0190-60 Total Seal piston rings. 4.185 5/64 5/64 3/16
375-CS8171-2 CONVERSION SET OLDS
20420711 Lunati CAM, OLDS 68+UP V8 RF-V272HR12 Voodoo Roller
228-1845513 PRW FLEXPLATE PQ XTREME DUTY

Parts Total = $1,575

Machine work = $1,585 (Half of this cost was sleeving the cylinders. 25% was internally balancing the rotating assembly)

Grand total = $3,160 plus my time and misc parts and sealers.

Cost could have been reduced by using a flat tappet cam vs roller (-$300), maintaining external balance vs internal (-$500), not having to sleeve the cylinders (-$700), using cheaper piston rings (-$50) for an approximate possible cost reduction of $1,550. However, doing things cheaply or incorrectly is what caused this fiasco to begin with, and it really depends on the condition of your block and heads.

Rebuild Procedures and Specs

Procedures

At-home gasket surface planing procedure can be found HERE

Cylinder head exhaust gas crossover plugging procedure can be found HERE

General Rules of Thumb for Engine Builds

• • • 0.001″ of main or rod bearing clearance for each inch of journal thickness. This would be 0.003″ clearance for an olds main bearing clearance, and 0.0025″ clearance for rod bearings.
    • 0.004″ of ring gap per inch of cylinder bore diameter for a factory motor. This equals 0.0165″ ring end gap for an OEM Olds 455. The goal is to have as little end gap as possible, without allowing the ring ends to touch during high heat, or high RPM conditions. NOS, forced induction, and higher combustion temperatures (high compression, detonation) result in the need for more end gap, at the expense of cylinder sealing, emissions, horsepower, and oil consumption. Some sources say the second ring should have more gap than the top compression ring, however others say that because the top ring will expand more from heat, the second ring gap can be the same as the top at room temperature.
    • Hydraulic lifter preload between 0.020″ and 0.060″, or 1/4″ to 3/4″ turn on adjustable rocker arms. This is specific to the lifter and rocker arm manufacturer.
    • If you can’t fit a feeler gauge somewhere for some reason, a sheet of copy paper is roughly 0.004″ thickness. Measuring the cam button thrust clearance with the timing cover installed is one example.

Oldsmobile 455 OEM Specs

Actual as-built/measured specs:

Generally, the tighter end of the OEM spec ranges were used. This engine was built for reliability, streetability, efficiency, and compatibility with fuel injection with an excellent power band. It was not built as a high RPM drag car that’s useless at low rpm, or for NOS.

Piston Ring Install Instructions Used

Cam bearing clearances

Measured with Digital Micrometers

Main Bearing clearances

Rod Bearing Clearances

Hydraulic Lifter preload on the Mondello/Harland Sharp roller rocker arms = 1/2 turn on adjustment nut per Harland Sharp.

Crankshaft endplay was tight. Probably 0.001-0.002″.

Piston ring end gap for the top and second compression rings was set to 0.014″ on all cylinders. Gaps were oriented per instructions attached above. If NOS or high RPM’s are going to be used, the gaps will need to be widened. For street use, this will work well and provide good sealing and longevity.